Allergy - Mechanisms

Section A

Allergy - mechanisms

* What is allergy * B cells * The discovery of IgE * Immunoglobulin E and other antibodies in allergy * Allergens: structure and function; mechanisms of * Role of superantigens in allergic diseases allergenicity; allergens and cross-reactivity; house dust * Cytokines in allergy mite allergens; pet allergens; tree pollen allergens; grass * Cell migration and chemokines pollen allergens; weed pollen allergens; food allergens; * Complement-mediated regulation of the allergic response venom allergens; emerging allergens; pollen allergens and * Lipid mediators of hypersensitivity and inflammation geographical factors * Lipid mediators in resolution of allergic inflammation * The underlying mechanisms in allergy * Allergy and the epithelial barriers * Innate immune response in allergy * Epithelial proteases and allergic diseases * Dendritic cells * Mechanisms of immune regulation in allergy * Natural killer cells and natural killer-T cells * Neuro-immune regulation of allergic inflammation * Innate lymphoid cells * United airways and immune regulation * Mast cells * Genetics of allergy * Basophils * Epigenetics of allergy * Eosinophils * Endotypes of allergic diseases * T cells * Animal models of allergic disease Global atlas oF allergy

1 WHAT IS ALLERGY

Johannes Ring Technische Universität München München, Germany

The term “Allergy” was born on July 24, 1906 in the Münchener Key messages Medizinische Wochenschrift as “specifically altered reactivity of • The term “Allergy” was first coined on July 24, 1906 as the organism”. Today, we define al- “specifically altered reactivity of the organism lergy as immunological hypersen- • Today, we define allergy as an immunologically-mediated and sitivity that can lead to a variety allergen-specific hypersensitivity of different diseases via different • Allergies can be seen in almost every organ, most commonly in pathomechanisms and thus differ- the skin and the mucous membranes ent approaches in diagnosis, ther- • Allergology is the science regarding allergic diseases and their apy and prevention can be taken. differential diagnoses and mechanisms (Table 1). Several misconceptions can be delineated (Table 2).

Allergology is the science regard-

- Allergy from genetics to mechanisms ing allergic diseases and their differential diagnoses and mechanisms. It requires clinical experience in allergic diseases, basic un-

S ection A derstanding of the immune system in physiology and pathology and finally extensive knowledge of environmental factors in eliciting or modulating allergic reactions. Allergy is not a disease itself, but a mechanism leading to disease. In clinical practice, allergy manifests in form of various different conditions such as anaphylaxis, urticaria, angioedema, allergic rhinoconjunctivitis, allergic asthma, serum sickness, allergic vasculitis, Figure 1 The word “allergy” first appeared on July 24, 1906 in the Münchener Medizinische Wochenschrift in an essay written by Clemens von Pirquet, a hypersensitivity pneumonitis, at- pediatrician from Vienna. (Reproduced with permission from Ring J: Allergy in opic dermatitis (eczema), contact Practice. Springer Berlin, Heidelberg, New York, 2005.) dermatitis and granulomatous

2 What is allergy Global atlas oF allergy

TABLE 1 Definitions of terms frequently used in allergy TABLE 2 Sensitivity Normal response to a stimulus The most common misconceptions of allergy Hypersensitivity Abnormally strong response to a stimulus Sensitation Development of increased sensitivity after repeated • natural reaction contact • a symptom or sign (e.g. rhinitis) Allergy Immunologically mediated hypersensitivity leading to • incompatibility of toxic/irritant disease substances (e.g. tobacco smoke) Anaphylaxis severe, life-threatening, generalized or systemic • psychological aversion hypersensitivity reaction • incurable

Enviroment-induced disease

Toxicity Hypersensitivity S ection A of a substance of the individuum - Allergy from genetics to mechanisms non- immune immune mediated

Irritation, Psycho- Intoxication, Idio- Intolerance neurogenic Allergy chronic syncrasy reaction damage

Figure 2 Classification of environmentally related health these disorders. Reproduced( with permission from Ring J: Allergy in Practice. Springer Berlin, Heidelberg, New York, 2005.) reactions, as well as the colorful patients may out grow their al- allergy for global use: Report of the spectrum of food- or drug – in- lergic disease spontaneously. We nomenclature committee of the duced hypersensitivity reactions. should study these patients in- World Allergy Organization. J Al- 2004; 113: 832- Allergies can be seen in almost tensively, who spontaneously lose lergy Clin Immunol 836. every organ. Most commonly, their allergy. Many allergic diseas- 3. Ring J. Allergy in Practice. Berlin: however, it is the skin and the mu- es have a chronic course, but there Springer, 2005. cous membranes that are involved are ways to cure. Allergic diseases 4. Adkinson NF, Bochner BS, Burks can be influenced by psychological since they represent the frontier AW, Busse WW, Holgate ST, Le- between the individual organism processes in a positive or in a neg- manske LF, O’Hehir RE. Middleton’s and its environment. ative way. Allergy Principles and Practice. 8th edition. Philadelphia: Elsevier Allergy often starts in the first Key References 2014. three months of life but very 1. Bergmann KC, Ring J. History of Al- 5. Ring J, Akdis C, Behrendt H, Lauen- rarely at birth, although there is a lergy. Basel:Karger, 2014 – in press. er RP, Schäppi G, Akdis M et al. strong genetic background. Aller- 2. Johansson SGO, Bieber C, Dahl R, Davos declaration: allergy as a glob- gy in some cases does not persist Friedmann PS, Lanier BQ, Lockey al problem. Allergy 2012;67:141- over life-time; it starts and some RF et al. Revised nomenclature for 143.

What is allergy 3 Global atlas oF allergy

2 The discovery of IgE

S.G.O. Johansson Karolinska Institute Stockholm, Sweden

Allergic asthma and rhinitis were already recognized in the 19th Key messages century, but the mechanisms be- hind the diseases were not under- • In 1921, Prausnitz and Küstner demonstrated passive stood. In 1919 Ramirez noticed sensitization of the skin, since then referred to as the PK-test that blood transfusion could trans- • In the 1960’s K. and T. Ishizaka published several articles fer allergic asthma and passively describing an antiserum that could block the PK-test indicating sensitize the recipient. In 1921, that it reacted with regain Prausnitz and Küstner demon- • In 1965 S.G.O. Johansson in Uppsala detected in the serum of a strated passive sensitization of myeloma patient an M-component that could not be identified as the skin, since then referred to as any of the 4 known immunoglobulin classes the PK-test. • The discovery of IgE and the understanding of the IgE-mediated inflammation, allergic asthma and rhino-conjunctivitis, food The search for reagin, the factor allergy and eczema has had a significant impact on diagnosis and in plasma causing the positive PK- treatment of allergy test, was unsuccessful for about - Allergy from genetics to mechanisms 45 years and some rather confus- ing proposals were published, e.g. identifying reagin as IgA. In the 1960’s K. and T. Ishizaka published S ection A several articles describing an antiserum that could block the PK- test indicating that it reacted with reagin. They referred to this antiserum as anti-γE. Not surprisingly considering the very low serum concentration of IgE, they did not succeed in isolating their γE. In 1965 S.G.O. Johansson in Uppsala detected in the serum of a myeloma patient an M-component that could not be identified as any of the 4 known immunoglobulin classes. Working with H. Bennich, the unique immunological and physicochemical characteristics

4 The discovery of IgE Global atlas oF allergy S ection A - Allergy from genetics to mechanisms Figure 1 From left L. Wide, H. Bennich and S.G.O. Johansson presenting RAST in 1974. of the new immunoglobulin, pro- port on the fifth immunoglobulin Key References visionally labelled IgND after the class, IgE. 1. Ramirez MA. Horse asthma fol- initials of the patient, were docu- lowing blood transfusion. JAMA The discovery of IgE has had a mented and published. Very small 1919;73:984. significant impact on the diagno- amounts of IgND did, in dose-re- 2. Prausnitz C, Küstner H. “Studien sis and management of allergic sponse, block the PK-test and the über die Ueberempfindlichkeit”, disease, enabling clinicians to dif- active structure was located in the Zentralbl Bakteriol 1921;86:160– ferentiate between IgE-mediated 169. Fc-fragment. A sensitive radio-im- allergic diseases and other hyper- muno assay was developed for 3. Ishizaka K, Ishizaka T. Identifica- sensitivity reactions, and to man- IgND. Extremely low serum con- tion of γE-antibodies as a carri- age allergic diseases according er of reaginic activity. J Immunol centrations, in the order of a few to their underlying mechanisms. 1967;99:1187. nanograms per ml, were found in Tests became available that al- 4. Johansson SGO, Bennich H. Im- healthy individuals but, interest- lowed a more simple and reliable munological studies of an atypical ingly, 10-100 fold higher levels diagnosis covering a very broad (myeloma) immunoglobulin. Immu- were found in allergic individuals. spectrum of allergens. The char- nology 1967;13:381-394. Purified IgND was sent to the acterization and standardization 5. Stanworth DR, Humphrey JH, Ben- Ishizakas in 1967 and was found of allergen preparations for clini- nich H, Johansson SGO. Specific to react with their anti-γE. In Feb- cal diagnosis and allergen specific inhibition of the Praunitz-Küstner reaction by an atypical human my- ruary 1968 the WHO Internation- immunotherapy, ASIT, improved eloma protein. Lancet 1967;2:330- al Reference Centre in Lausanne, although there is still much to do 332. where studies on IgND had been in this area. An injectable mon- 6. Bennich H, Ishizaka K, Johans- performed for some months, in- oclonal anti-IgE is now available son SGO, Rowe DS, Stanworth vited the two groups to a meeting that eliminates IgE and has an im- DR, Terry WD. Immunoglobulin to review comparative laboratory portant role in the management E, a new class of human immuno- studies of IgND and γE, resulting of severe allergic asthma, severe globulins. Bull World Health Organ in the publication of the official re- food allergy and chronic urticaria. 1968;38:151-152.

The discovery of IgE 5 Global atlas oF allergy

Allergens – structure 3a and function

Ronald van Ree Academic Medical Center Amsterdam, The Netherlands

Patients with type I allergy make IgE antibodies against some, but Key messages not against all environmental or dietary proteins they are exposed • A protein capable of instructing the immune system to start to. In fact, most allergens belong producing IgE antibodies is called a primary sensitizer to a rather limited number of pro- • Pro-allergenic properties of a protein cannot be separated from tein families. the individual being exposed or from the context of exposure • Several structural and functional properties have been identified Can we identify common struc- that contribute to allergenicity tural or functional properties of • There is not a single common denominator for allergenicity proteins that turn them into allergens? Before answering this question, it is important to clearly define what an allergen is. An ab- potential endogenous pro-aller- immune system. Many known al- solute prerequisite for a molecule genic properties of a protein can- lergens are indeed lipid binding to be designated an allergen is for not be seen in isolation from the proteins (e.g. Bet v 1 and homo- - Allergy from genetics to mechanisms it to bind specific IgE antibodies. individual being exposed and from logues, house dust mite group 2 Not every protein fulfilling that the context of exposure, which allergens, lipocalins of pets, plant requirement is however also ca- includes timing and dose of expo- lipid transfer proteins), and some pable of instructing the immune sure, and the presence of co-fac- are glycoproteins (e.g. peanut Ara S ection A h 1 and grass pollen Phl p 1). Their system to start producing these tors that may act as pro-allergenic lipid ligands and conjugated gly- IgE antibodies, i.e. of being a pri- or anti-allergenic adjuvants (Fig- cans have been shown to interact mary sensitizer (Figure 1). Clear ure 2). with pathogen recognition recep- examples of allergens not able to With that in mind, are there com- tors such as Toll-like receptors and do so are those in fruits, nuts and mon endogenous structural or C-type lectins on antigen-present- vegetables that are cross-reactive functional properties that deter- ing cells, thereby skewing the im- with the major birch pollen Bet v mine allergenicity? Glycosylation mune systems towards Th2-type 1. Their allergenicity is dependant per se has often been mentioned responses and IgE production on their structural (and functional) as marker for allergenicity, but (Figure 3). In addition, protease similarity to their “parent” mole- convincing evidence for such a activity such as of the cysteine cule Bet v 1, the primary sensitizer. general claim cannot be found. protease Der p 1 has been shown The more intriguing question is Some properties of proteins, in- to drive Th2 inflammation. It is however, what determines wheth- cluding specific types of glycosyla- important to note that all these in- er a protein is capable of being the tion and binding of lipids, seem to nate Th2-skewing properties may primary sensitizer. The answer to determine their role as allergens also turn other proteins without this question is complex, because via interaction with the innate these pro-allergenic properties

6 Allergens – structure and function Global atlas oF allergy

PROTEIN PROTEIN = IgE ALLERGEN

PROTEIN PROTEIN = ALLERGEN PROTEIN + SENSITIZER IgE S ection A

C PROTEIN 1 = PROTEIN 1 PROTEIN 1 ALLERGEN - Allergy from genetics to mechanisms + SENSITIZER homologous cross-reactive IgE PROTEIN 2 = PROTEIN 2 PROTEIN 2 CROSS-REACTIV ALLERGEN

Figure 1 Panel A illustrates the minimum requirements for a molecule to be designated as an allergen: it binds IgE antibodies Panel B and C depict the two identities an allergen can have: it can itself act as primary sensitizer (orange in panel B and C), or it cannot and binds IgE only based on cross-reactivity with the primary sensitizer (blue in panel C). into allergens during simultane- KEY REFERENCES gens and pollen. Ann N Y Acad Sci ous exposure. 1. Chapman MD, Pomés A, Breitened- 2002;964:47-68. er H, Ferreira F. Nomenclature and 3. Thomas WR. Innate affairs of aller- In summary, several structural and structural biology of allergens. J Al- gens. Clin Exp Allergy 2013;43:152- functional properties have been lergy Clin Immunol 2007;119:414- 163. identified that contribute to aller- 420. 4. Chapman MD, Wünschmann S, genicity, but it is safe to say that 2. Vieths S, Scheurer S, Ballmer-We- Pomés A. Proteases as Th2 ad- there is not a single common de- ber B. Current understanding juvants. Curr Allergy Asthma Rep nominator for allergenicity. of cross-reactivity of food aller- 2007;7:363-367.

Allergens – structure and function 7 Global atlas oF allergy

BIRTH protein with protein without genetic endogenous allergenic endogenous allergenic predisposition properties properties

DOSE DOSE low low

OR risk & protective OR context: factors factors high context: high risk & protective

COMPLEX INTERPLAY ALLERGY OR TOLERANCE

ELDERLY AGE

Figure 2 Sensitization is a complex interplay of the individual exposed (inherited risk of becoming allergic), the timing of exposure (earlier in life the immune system is more susceptible to sensitization but also to induction of tolerance), the dose (high early life exposure may skew towards tolerance), the context of exposure (environmental exposures such as pollution, microbes, parasites, diet, lifestyle) and endogenous properties of the protein. - Allergy from genetics to mechanisms

S ection A LIPID PRR Th-cell GLYCAN DC Th2 ALLERGEN

PAR PROTEASE

B-cell

IgE

Figure 3 Allergens can interact via various mechanisms with dendritic cells skewing them towards a DC2 phenotype, which in turn skews adaptive immunity towards Th2 and IgE production.

8 Allergens – structure and function Global atlas oF allergy

Mechanisms of 3b allergenicity of allergens

Heimo Breiteneder Medical University of Vienna Vienna, Austria

Allergens interact with various parts of the innate immune sys- Key messages

tem which plays a fundamental S ection A role in shaping adaptive immune • The innate immune system plays a fundamental role in shaping responses (Figure 1). The innate the response to potentially allergenic proteins immune system comprises sever- • Allergic sensitization, a multifactorial process, is influenced by a al cell types that express pattern protein’s biological and molecular features and by the interaction - Allergy from genetics to mechanisms recognition receptors (PRRs). pathway/s with the immune system PRRs recognize pathogen- or • Proteins interact with Toll-like-, C-type lectin-, NOD-like-, and damage-associated molecular protease-activated receptors (present on epithelial cells and patterns (PAMPs, DAMPs) which dendritic cells) or with surfactant proteins (present in soluble frequently accompany allergens. form) to manifest their allergenicity • Lipids (directly bound by allergens, present in the allergen Membrane-associated, source, or originating from microbial contaminations) modulate cytoplasmic and soluble the immune response of predisposed individuals by interacting PRRs with the innate immune system Toll-like receptors (TLR) are a conserved family of PRRs. The allergens Der p 2 (house-dust mite), SIGN; Ara h 1, Der p 1 and 2, Fel d and Ambrosia artemisiifolia pollen Fel d 1 (cat), and Can f 6 (dog) 1, Can f 1 and Bla g 2 (cockroach) extracts. with the mannose receptor. Pro- bind lipopolysaccharide (LPS) and Surfactant associated proteins tease-activated receptors (PARs) interact with TLR4, shifting the (SP), found in the alveoli of the signal in response to extracelluar LPS-response curve to a Th2-in- lungs, bind inhaled glycosylat- proteases. Allergens of house dust ducing range. Bacterial contami- ed allergens via a carbohydrate mite (Der p 1, -3, -9) and mold (Pen nations present on pollen, shown recognition domain. Der p 1 and c 13) activate PAR-2 and induce IL- for ryegrass and Parietaria, are Der f 1 degrade SP-A resulting in 25 and thymic stromal lymphopoi- responsible for triggering TLR2, increased degranulation of mast etin (TSLP). TLR4 and TLR9 signaling. C-type cells and basophils triggered by lectin receptors contain carbohy- NOD-like receptors (NLRs) sense these allergens. drate recognition domains that cytoplasmic PAMPs and DAMPs. bind glycosylated allergens and Some NLRs are core components Cells of the innate immune trigger pathways that determine of inflammasomes, protein com- system T-cell polarization. Ara h 1 (pea- plexes involved in generating the Epithelial cells function as phys- nut), Der p 1 (house dust mite) pro-inflammatory cytokines IL- ical barrier whose tight junction and Can f 1 (dog) interact with 1β and IL-18. Inflammasomes are proteins are degraded by proteas- the C-type lectin receptor DC- triggered by Der p 1, Api m 4 (bee), es including Der p 1 and Act d 1

Mechanisms of allergenicity of allergens 9 Global atlas oF allergy

Der p 2 Bacterial contaminations Ara h 1 Ara h 1 Der p 1, -3, - 9 Lipids from of pollen: Brazil nut Fel d 1 Der p 1, -2 Der p 1 Pen c 13 LPS LTA Sphingomyelin Can f 6 Bla g 2 Can f 1 Der p 1 from cow‘s milk CpG-DNA + Fel d 1, Can f 1 Api m 1 Lipids from LPS A. artemisiifolia pollen pollen

N-terminus

C-terminus TLR4-MD2 TLR2-TLR1/6 Mannose DC-SIGN PAR-2 CD1d receptor

Endosome

Inflammasome TLR9 complex

Figure 1 Simplified model of innate immune mechanisms activated by allergens. Examples are given for interactions of allergens with Toll-like receptors (TLRs) via binding by the allergen or co-delivery of bacterial compounds (LPS: lipopolysaccharide. LTA: lipoteichoic acid); with C-type lectin receptors via carbohydrate moieties present on allergens; with protease-activated receptor (PAR) 2 via the allergens’ proteolytical activity; and with inflammasome complexes

- Allergy from genetics to mechanisms (2-4). In addition, the presentation of lipids from the allergen source by CD1d to invariant natural killer T cells, which enhances sensitization or in some cases even drives it, is shown.

(kiwi). Following allergen contact, certain lipids and potentially aller- in human keratinocytes. Allergy S ection A epithelial cells produce TSLP, IL- genic proteins determine the out- 2012;67:1400-1407. 25 and IL-33 and instruct dendrit- come of the sensitization process. 4. Varga A, Budai MM, Milesz S, ic cells to induce Th2 responses. Bácsi A, Tőzsér J, Benkő S. Rag- Dendritic cells bridge innate and KEY REFERENCES weed pollen extract intensifies adaptive immunity and polarize 1. Thomas WR. Innate affairs of aller- lipopolysaccharide-induced prim- the T helper cell response (5). Po- gens. Clin Exp Allergy 2013;43:152- ing of NLRP3 inflammasome in human macrophages. larization towards a Th2 response 163. Immunology 2013;138:392-401. in dendritic cell-T cell co-cultures 2. Dai X, Sayama K, Tohyama M, Shi- has been shown for Bet v 1 (birch rakata Y, Hanakawa Y, Tokumaru S 5. Hammad H, Lambrecht BN. Den- dritic cells and airway epithelial cells pollen) and Pru p 3 (peach) when et al. Mite allergen is a danger signal for the skin via activation of inflam- at the interface between innate and cells were derived from allergic masome in keratinocytes. J Allergy adaptive immune responses. Allergy donors. Invariant natural killer T Clin Immunol 2011;127:806-814. 2011;66:579-587. cells (iNKTs) recognize lipids pre- 3. Dombrowski Y, Peric M, Koglin 6. Brennan PJ, Brigl M, Brenner MB. sented by CD1d (6). They secrete S, Kaymakanov N, Schmezer Invariant natural killer T cells: an IL-4, -5 and -13 when presented V, Reinholz M et al. Honey bee innate activation scheme linked to lipids from Brazil nut or sphingo- (Apis mellifera) venom induces diverse effector functions. Nat Rev myelin from milk. Co-delivery of AIM2 inflammasome activation Immunol 2013;13:101-17.

10 Mechanisms of allergenicity of allergens Global atlas oF allergy

Allergens and cross- 3c reactivity

Barbara Bohle Medical University of Vienna Vienna, Austria

Allergens belong to a relatively low number of different protein fami- Key messages

lies according to intrinsic features, S ection A e.g. similar amino acid sequenc- • Members of the same protein family may share IgE and T cell es and/or 3-dimensional folding. epitopes, which can cause allergic reactions by cross-reactivity Members of the same protein fami- • Shared IgE epitopes between inhalant allergens and food ly may share IgE and T cell epitopes, allergens can induce an immediate IgE-mediated reaction - Allergy from genetics to mechanisms which by cross-reactivity can cause confined to the oral cavity, known as the oral allergy syndrome allergic reactions. In this context, • Cross-reactivity at the T cell level represents one of the birch pollen-related food allergy mechanisms of worsening of atopic eczema in birch-pollen has been well studied. This special allergic patients form of food allergy affects more • Immunological cross-reactivity is explored as a possible cure than 70% of birch pollen-allergic for allergy, by inducing cross-reactive regulatory T cells and/or patients and is one of the most fre- cross-reactive blocking IgG4 antibodies quent food allergies in adults. Bet v 1, the single major birch pol- recognized by Bet v 1 - specific IgE depends on amino acid sequence len allergen belongs to the patho- antibodies (Figure 1A). Although homologies. After uptake by anti- genesis-related protein family 10 not all IgE-epitopes are shared, gen-presenting cells, allergens are and homologous molecules are Bet v 1 - related food allergens degraded into short linear pep- present in various foods, e.g. Mal d contain sufficient epitopes to tides, which are then loaded onto 1 in apple, Pru av 1 in cherry, Gly m achieve cross-linkage of IgE bound MHC class II molecules to be pre- 4 in soy and Ara h 8 in peanut. Al- to the surface of mast cells and sented to T cells (Figure 1B). Pro- though these proteins derive from basophils. In most cases, this in- teins with homologous amino acid plant species non-related to birch duces the oral allergy syndrome, sequences are processed in analog trees, their primary and tertiary an immediate IgE-mediated re- fashion resulting in similar pep- structures are highly homologous action confined to the oral cavity. tides. These activate cross-reac- with Bet v 1. Destruction of the 3-dimensional tive T cells to proliferate and pro- protein structure, e.g. by gastroin- duce cytokines. Clinically, T cell Bet v 1 contains mainly confor- testinal degradation or heat pro- activation by Bet v 1-related food mational IgE-epitopes, as destruc- cessing, reduces IgE cross-reac- allergens may result in a worsen- tion of its 3-dimensional structure tivity, which explains why cooked ing of atopic eczema in birch pol- leads to a dramatic reduction of foods containing Bet v 1-related len-allergic patients. its IgE-binding capacity. Due to proteins usually are tolerated by similar protein folding, Bet v 1 - The analysis of the immune mech- birch pollen-allergic patients. homologs contain surface patch- anisms underlying birch pollen-re- es forming epitopes that may be Cross-reactivity at the T cell level lated food allergy has markedly

Allergens and cross-reactivity 11 Global atlas oF allergy

A Bet v1

Pru av 1

B Bet v1 Mald1 NNCC

TLLRAVESYLLAHSDAYN GLFKLI ESYLKDHPDAYN

IL-4 IL-5 IL-13

Figure 1 A. Homologous conformational epitopes cause IgE cross-reactivity. A putative IgE epitope defined on Bet v - Allergy from genetics to mechanisms 1 and Pru av 1, the Bet v 1-homolog in cherry is shown in green (3). Protein models (pdb 1BV1 and 1E09, respectively) are displayed using Polyview3D. B. Homologous linear epitopes cause T cell cross-reactivity. Proteins with similar amino acid sequences (indicated as red and green lines) are processed in a similar manner by antigen-presenting cells leading to the generation of linear peptides. The highly cross-reactive C-terminal immunodominant T cell epitope of Bet v 1 and

S ection A the homolog peptide of Mal d 1 are shown (4). Identical amino acid residues are highlighted in bold, similar residues are underlined. T cell activation by either epitope induces proliferation and cytokine production.

contributed to our understanding Mari A, Breiteneder H. Allergens naboyina SC, Valenta R, Keller W. how immunological cross-reac- are distributed into few protein Prediction of IgE-binding epitopes tivity can induce allergy. Birch families and possess a restricted by means of allergen surface com- pollen-related food allergy is now number of biochemical functions. J parison and correlation to cross-re- Allergy Clin Immunol 2008;121:847- activity. currently investigated as a disease J Allergy Clin Immunol 852. 2011;128:872-879. model to elucidate whether immu- 2. Bohle B, Zwolfer B, Heratizadeh A, 4. Jahn-Schmid B, Radakovics A, nological cross-reactivity can cure Jahn-Schmid B, Antonia YD, Alter Luttkopf D, Scheurer S, Vieths S, allergy, e.g. by cross-reactive reg- M et al. Cooking birch pollen-relat- Ebner C et al. Bet v 1142-156 is the ulatory T cells and/or cross-reac- ed food: divergent consequences dominant T-cell epitope of the ma- tive blocking IgG4 antibodies. for IgE- and T cell-mediated reac- jor birch pollen allergen and impor- tivity in vitro and in vivo. J Allergy tant for cross-reactivity with Bet v KEY REFERENCES Clin Immunol 2006;118:242-249. 1-related food allergens. J Allergy 1. Radauer C, Bublin M, Wagner S, 3. Dall’Antonia F, Gieras A, Deva- Clin Immunol 2005;116:213-219.

12 Allergens and cross-reactivity Global atlas oF allergy

House dust mite 3d allergens

Wayne R. Thomas University of Western Australia Perth, Australia

House dust mites are the most ubiquitous source of indoor al- Key messages

lergens inducing allergies, highly S ection A associated with asthma. They are • Many house dust mite proteins elicit IgE antibody synthesis, but of paramount importance in all for most the titres are low but the few regions of the world, • The group 1,2 and probably the newly recognized group 23 where they do not survive due to allergens are the major allergens for Dermatophagoides species - Allergy from genetics to mechanisms aridness, extreme cold or high al- • As found for D. pteronyssinus, the group 4, 5, 7 and 21 allergens titude. are quantitatively the next most important, or mid-tier, allergens • Blomia tropicalis is an important source of allergens in some IgE binding studies have found tropical and subtropical regions with the major specificities Blo that while a wide range of mite t 5 and Blo t 21 proteins can elicit antibodies most • Mite proteases other than the group 1 allergens induce only low induce low or sporadically de- levels of sensitisation and very few allergens from other sources tectable titres (Table 1). Taking D. are cysteine proteases pteronyssinus as the exemplar, only 3 allergens bind IgE from most people at high titre, Der p 1&2 and the amino-acid sequence of tropo- studies conducted in urban tem- the recently recognized Der p 23. myosin group 10 makes them a po- perate regions. The allergens Der p 4, 5, 7 and 21 tential source of cross reactivity The main species that cause al- each elicit IgE antibodies in 30- with allergens from a wide range lergic sensitisation are D. ptero- 50% of mite-allergic subjects and of species. In most regions of the nyssinus and D. farinae. The most collectively, and sometimes indi- world, however, they only induce vidually, induce titres of a magni- abundant, D. pteronyssinus (Figure IgE in about 10% of mite-allergic 1), is essentially the only species tude considered important for the subjects. There are possible ex- induction of disease. The group found in Australasia and the Unit- ceptions mentioned in uncorrobo- ed Kingdom and mixed species 1&2 allergens can be readily de- rated reports from Zimbabwe and are found elsewhere except for tected in dust and proprietary D. Japan showing high titre binding, -rich regions of central and house dust mite extracts made farinae suggesting regional importance. In northern Korea, northern Italy from mites cultured in optimized another example of a regional ef- and high-latitude areas of east- allergen-producing conditions. fect, aboriginals in northern Aus- ern USA, where mites are found The distribution of other allergens tralia do not have IgE to Der p 1, 2 in low abundance. The allergens in the environment is largely un- or 10, but instead have high titres from these species cross react known and frequently cannot be to the amylase, Der p 4. The profile extensively so species-specificity detected in proprietary extracts. of allergens responsible for sensi- cannot be determined by skin test. The evolutionary conservation of tisation, thus might vary from the The possibility that the biochemi-

House dust mite allergens 13 Global atlas oF allergy

Figure 1 Stereomicroscopic view of Dermatophagoides pteronyssinus on fabric cover. Scale: mites are 0.3 mm long. Attribution: Gilles San Martin from Namur, Belgium (By Gilles San Martin from Namur, Belgium (House dust mites Uploaded by Jacopo Werther) [CC-BY- SA-2.0], via Wikimedia Commons.)

TABLE 1 KEY REFERENCES Known important house dust mite allergens 1. Thomas WR. House dust allergy Species Allergen Biochemical Category and immunotherapy. Hum Vaccin Immunother 2012;8:1469-1478. D. pteronyssinus Der p 1 cysteine protease Major Der p 2 ML Lipid binding Major 2. Thomas WR, Hales BJ, Smith WA. House dust mite allergens in asth- Der p 23 peritrophin Major ma and allergy. Trends Mol Med Der p 4 amylase Mid tier 2010;16:321-328. Der p 5 unknown Mid tier 3. Weghofer M, Grote M, Resch Y, Der p 7 LPS/BPI family Mid tier Casset A, Kneidinger M, Kopec J et - Allergy from genetics to mechanisms Der p 21 Der p 5-related Mid tier al. Identification of Der p 23, a peri- D. farinae Der f 1 cysteine protease Major trophin-like protein, as a new major Dermatophagoides pteronyssinus Der f 2 ML Lipid binding Major allergen associated with the peri- S ection A Other not investigated not investigated trophic matrix of mite fecal pellets. B. tropicalis Blo t 5 unknown Major J Immunol 2013;190:3059-3067. Blo t 21 Blo t 5-related Major 4. Thomas WR. Geography of house Blo t 7 LPS/BPI family Mid tier dust mite allergens. Asian Pac J Al- lergy Immunol 2010;28:211-224. The table lists allergens shown to have IgE-binding titres expected to make significant contributions to the total anti-house dust mite titres. 5. Casset A, Mari A, Purohit A, Resch LPS/BPI: lipopolysaccharide binding/bacterial permeability increasing protein Y, Weghofer M, Ferrara R, et al. Varying allergen composition and cal functions of the allergens might glycyphagoide mite found with D. content affects the in vivo aller- help promote their allergenicity pteronyssinus in some tropical and genic activity of commercial Der- has been mooted especially the subtropical environments pro- matophagoides pteronyssinus cysteine protease activity of Der extracts. Int Arch Allergy Immunol vides another source of allergens p 1, the lipopolysaccharide bind- 2012;159:253-262. where Blo t 5 and Blo t 21 are the ing activity of Der p 2 and the chi- 6. Thomas WR. Innate affairs of al- tin-binding of Der p 23, but this re- most important allergens and Blo t lergens. Clin Exp Allergy 2013;43: mains unproven. Blomia tropicalis a 2 is a minor specificity. 152-163.

14 House dust mite allergens Global atlas oF allergy

3e Pet allergens

Hans Grönlund Karolinska Institutet Stockholm, Sweden

Pets of mammalian origin are common in society and kept for social, Key messages

recreational or occupational rea- S ection A sons. In the United States alone • Exposure to pet allergens is ubiquitous in every-day life the number of dog and cat own- • 10-15% of the population in affluent areas show pet allergen ers is estimated to be 77.5 and specific IgE

93.6 million, respectively. Pets are • Allergy to pets is among the most common cause of asthma - Allergy from genetics to mechanisms among the most common causes and polysensitisation to several pets a risk factor for severe of allergy: scattered information problematic asthma suggests to 10-15% of the popu- • Allergen-specific immunotherapy for cat is efficacious, while lation in affluent countries. Sen- extracts from dog and horse needs improvement sitization is thought to depend on seeding of airborne particles from the pelt, saliva or urine. Upon in- to many identified components, dog and horse is more complex. Fel halation and mucosal uptake these Table 1, however there are many d 1 is a secretoglobin glycoprotein particles induce IgE antibodies more to be identified. Allergy to composed of 10-20% carbohy- pets is a risk factor for symptoms drates, which has been suggested of asthma, rhinoconjunctivitis and to increase allergenicity via man- eczema and in some areas is con- nose receptor uptake. Yet another sidered the most common cause of mechanism by which Fel d 1 exerts childhood asthma. its allergenicity is via signaling through the innate Toll-like recep- To date eight cat (Felis domesti- tors 4 and 2. cus), six dog (Canis familiaris), four horse (Equus caballus) and addi- Polysensitization between pets tional allergens from less common is extensive and a risk factor for sources have been identified, Ta- severe asthma. The most prom- ble 1. The major allergens in cat, inent group of cross-reactive al- dog and horse extracts are Fel d lergens is the lipocalin family, in- 1, Can f 1 and Equ c 1, with serum cluding e.g. cat Fel d 4, horse Equ IgE-reactivity in allergic patients c 1, dog Can f 6 and rat Rat n 1. Figure 1 Traditionally allergens of about 95, 50 and 75%, respec- A second cross-reactive cluster from pets are extracted from the hair. tively. However their proportions are serum albumins, responsible There is a growing awareness that other sources, such as saliva (Can f may vary between different ge- for the pork-cat syndrome, a rare 2) or urine (Can f 5) may contribute ographic regions. The serum IgE phenomenon that can lead to se- critically to the IgE profile of in dog profile in cat allergy is dominated vere reactions. IgE to the galac- allergic patients. by Fel d 1, whereas the profile in tose- α1,3- galactose carbohydrate

Pet allergens 15 Global atlas oF allergy

TABLE 1 moiety, present in ticks bites, helminths and mammals, but Current list of characterized allergens from pets (www.allergen.org) not humans, has convincingly Animal Allergen Protein Source MW Sensitized been shown to induce severe Family (kDa) (%) reactions after treatment with certain biopharmaceuticals Cat Fel d 1 Secretoglobin Saliva 30-38 80-95 and furthermore was linked to Dander, Sera, red meat food allergy. Fel d 2 Albumin 68 20-35 Urine The accuracy of pet allergy Fel d 3 Cystatin Dander 11 10 diagnostics and success of immunotherapy depends largely Fel d 4 Lipocalin Saliva 20 63 on the quality of the allergen source and the allergy profile Fel d 5 IgA Saliva, Serum 28, 64 38 of the patient. Thus, specific Fel d 6 IgM Saliva, Serum 28, 94 immunotherapy of patients with IgE sensitization to cat Fel d 7 Lipocalin Saliva 18 38 has proven efficacious, while specific immunotherapy of Fel d 8 Latherin Saliva 24 19 dog and horse allergy are not Dog Can f 1 Lipocalin Saliva, Dander 22-25 45-55 equally established.

Can f 2 Lipocalin Saliva, Dander 22-27 20-30 KEY REFERENCES 1. Portnoy J, Kennedy K, Sub- Dander, Sali- Can f 3 Albumin 69 15-35 lett J, Phipatanakul W, Mat- va, Serum sui E, Barnes C et al. Envi- ronmental assessment and Can f 4 Lipocalin Saliva, Dander 18 15-30 exposure control: a practice Can f 5 Kallikrein Urine 28 70 parameter--furry animals. Ann Allergy Asthma Immunol Can f 6 Lipocalin Dander 27, 29 38 2012;108:223.e1-15. 2. Brunekreef B1, Von Muti- Equ c 1 Lipocalin Dander, Saliva 22 76

- Allergy from genetics to mechanisms us E, Wong G, Odhiambo J, García-Marcos L, Foliaki S; Equ c 2§ Lipocalin Dander 16 50 ISAAC Phase Three Study Group. Exposure to cats Dander, Meat, Horse Equ c 3 Albumin 65 18 and dogs, and symptoms of S ection A Sera asthma, rhinoconjunctivitis, Equ c 4 Latherin Dander, Saliva 17-19 and eczema. Epidemiology 2012;23:742-750. Equ c 5 Latherin Dander 17 3. Nilsson OB, van Hage M, Grönlund H. Mammalian-de- Cav p 1§ Lipocalin Dander, Urine 20 70-87 rived respiratory allergens - Guinea- Implications for diagnosis and Cav p 2 Lipocalin Dander, Tears 17-19 55-65 pig therapy of individuals aller- Cav p 3 Lipocalin Saliva 18-19 54 gic to furry animals. Methods 2014;66:86-95. Ory c 1§ Lipocalin Dander, Saliva 17-18 4. Zuberbier T, Bachert C, Bousquet PJ, Passalacqua G, Rabbit Ory c 2§ Lipocalin Dander, Saliva 21 Walter Canonica G, Merk H et al. GA² LEN/EAACI pock- Ory c 3 Secretoglobin Dander, Saliva 18-19 77 et guide for allergen-specific immunotherapy for allergic Rat Rat n 1 Lipocalin Urine 17-21 66 rhinitis and asthma. Allergy 2010;65:1525-1530.

16 Pet allergens Global atlas oF allergy

A B

Figure 2 A) Saliva (n=14) from different dogs and breeds show variable allergen expression by IgE immunoblot using a pool of dog allergic patients. Molecular marker, left lane (Reproduced with permission from Polovic N, Wadén K, Binnmyr J, et al. Dog saliva – an important source of dog allergens. Allergy, 2013;68:585-92, with permission from Willey Blackwell.). B) Variability in protein content of dog dander extracts commercially available for skin prick test. Left hand lane in-house extract control, right hand side molecular markers (Reproduced with permission from Curin M, Reininger R, Swoboda I, et

al. Skin prick test extracts for dog allergy diagnosis show considerable variations regarding the content of major and minor dog S ection A allergens. Int Arch Allergy Immunol 2011;154:258–263; with permission from Karger Publishers.) - Allergy from genetics to mechanisms

rFel d1

(kUA/L) 1000

100

0.35

0.35 1 10 100 1000

Cat dander extract (kUA/L)

Figure 3 As opposed to dog and horse dander, one allergen, Fel d 1 (y-axis), is dominating in cat dander extracts (x-axis) as illustrated by IgE correlation analysis of 100 cat sensitized subjects using ImmunoCAP system (Reproduced with permission from Grönlund H, Adédoyin J, Reininger R et al. Higher immunoglobulin E antibody levels to recombinant Fel d 1 in cat- allergic children with asthma compared with rhinoconjunctivitis. Clin Exp Allergy. 2008 ;38:1275-81, with permission from Willey Blackwell.)

Pet allergens 17 Global atlas oF allergy

Tree pollen 3f allergens

Fatima Ferreira Gabriele Gadermaier Michael Wallner University of Salzburg Salzburg, Austria

GEOGRAPHICAL DISTRIBUTION AND CLINICAL Key messages RELEVANCE Trees belonging to the Fagales, • The most clinically relevant sources of tree pollen allergens are Oleaceae, and Cupressaceae com- found among Fagales, Oleaceae, and Cupressaceae plants, which prise the clinically most relevant are widely distributed worldwide sources of allergenic pollen in • Bet v 1-like proteins, Ole e 1- like proteins, and pectate lyases/ many regions around the world. polygalacturonases represent the major pollen allergens of This approach to the classification Fagales, Oleaceae, and Cupressaceae, respectively of allergenic trees according to • Bet v 1-like allergens are responsible for allergic cross-reactions their phylogeny provides useful among Fagales pollen and various fruits and vegetables, a clinical guidance both for their geograph- condition referred to as oral allergy syndrome ical distribution and typical flow- • Ole e 1-like allergens and pectate lyases/polygalacturonases are ering seasons (Figure 1). Thus, Fa- responsible for extensive IgE cross-reactivity between Oleaceae gales trees are widely distributed and Cupressaceae plants, respectively

- Allergy from genetics to mechanisms within the temperate climate zone of the Northern hemisphere and predominantly flower in spring. elicited by the Bet v 1-like aller- OLEACEAE POLLEN ALLERGENS Oleaceae trees grow in the Medi- gens, which belong to the family Ole e 1-like glycoproteins repre- S ection A terranean areas as well as in oth- 10 of plant pathogenesis-related sent the major allergen of aller- er parts of the temperate climate proteins. Besides cross-reactiv- genic Oleaceae trees, including zone. Their flowering season vary ity between Fagales trees, Bet v olive, ash, and privet (Table 1). It according to regions, ranging from 1 sensitization often leads to al- has been shown that exposure to early January to June. Cupres- lergic reactions to various fruits high loads of olive pollen can lead saceae plants are widely distrib- and vegetables due to homolo- to increased sensitization rates uted in parts of Europe, Asia and to minor allergens (lipid-transfer gous proteins found in certain Northern America, with pollina- proteins, 1,3-beta-glucanase) and plant families, including Rosaceae, tion periods occurring between correlates with more severe aller- Apiacea, and Fabaceae (Figure January and April, depending on gic symptoms, including asthma. the region. Figure 2 shows sensiti- 3). Furthermore, pan-allergens zation rates to representative tree belonging to the families of calci- CUPRESSACEAE POLLEN pollen allergen sources in four- um-binding proteins and profilin ALLERGENS teen European countries. contribute to the extensive food The major pollen allergens from and pollen cross-reactive patterns Cupressaceae trees (e.g. cypress, FAGALES POLLEN ALLERGENS observed among Fagales-sensi- mountain cedar, Japanese cedar) Fagales pollen allergies are mainly tized patients. belong to the family of pectate

18 Tree pollen allergens Global atlas oF allergy

Betula ssp Quercus ssp

Olea ssp Fraxinus ssp S ection A - Allergy from genetics to mechanisms

Cryptomeria ssp Juniperus ssp

Figure 1 Word maps showing the distribution of trees causing respiratory allergic reactions. Representative members of the Fagales family (Betula and Quercus), the Oleaceae family (Olea and Fraxinus), and the Cupressaceae family (Cryptomeria and Juniperus) are depicted in the maps as density of registered data (increasing density from yellow to orange) within the Global Biodiversity Information Facility (www.gbif.org), a free and open access data infrastructure funded by governments.

Tree pollen allergens 19 Global atlas oF allergy

Figure 2 Sensitization (colored) and clinically relevant sensitization rates (striped) to tree pollen allergens from the GA2LEN skin test study II. Patients (n=3034) referred to allergy clinics in 14 European countries were diagnosed using skin prick test extracts of birch, olive and cypress. In Northern and central European countries, a high prevalence to birch pollen was observed while reactivity to cypress was generally low. Sensitization to olive was most abundant in Switzerland and Greece suggesting an involvement of cross- reactive ash-tree pollen. The majority of sensitized patients (66%-75%) displayed clinical symptoms to the allergen elicitor. (Reproduced with permission from Burbach GJ, Heinzerling LM, Edenharter G, et al. GA(2)LEN skin test study II: clinical relevance of inhalant allergen sensitizations in Europe.Allergy 2009,64:1507-1515, with permission from Willey Blackwell.) - Allergy from genetics to mechanisms S ection A

lyases and polygalacturonases. Oleaceae, and Cupressaceae be- few protein families and show Natural purified Cupressaceae long to distinct families of pro- distinct patterns of species dis- allergens display extensive IgE teins, and thus represent ideal tribution. J Allergy Clin Immunol cross-reactivity, which is partly tools for molecule-based diagno- 2006;117:141–147. due to the presence of cross-reac- sis and therapy of tree pollen al- 3. Villalba M, Rodriguez R, Batane- tive carbohydrate determinants. lergies. ro E. The spectrum of olive pollen In addition, the overlap of flower- allergens. From structures to di- ing period with winter flu seasons KEY REFERENCES agnosis and treatment. Methods complicates the clinical diagnosis 1. Mothes N, Valenta R. Biology of 2013;66:44-54. of Cupressacea pollen allergies. tree pollen allergens. Curr Allergy Asthma Rep 2004;4:384-390. 4. Charpin D, Calleja M, Lahoz C, Pi- CONCLUSION 2. Radauer C, Breiteneder H. Pol- chot C, Waisel Y. Allergy to cypress The major allergens of Fagales, len allergens are restricted to pollen. Allergy 2005;60:293-301.

20 Tree pollen allergens Global atlas oF allergy

Tree pollen allergens Cross-reactive allergens Oleaceae Fagales pollen Cupressaceae pollen Pollen Fruits Vegetables Other allergens pollen allergens allergens Major allergens

Alder (Aln g 1) Gold kiwi (Act c 8) Celery (Api Hazelnut (Cor Birch (Bet v 1) Kiwi (Act d 8) g 1) a 1) Hornbeam (Car Kiwi (Act d 11) Carrot (Dau Soy (Gly m 4) b 1) Peanut (Ara h 8) c 1) Mung bean (Vig Chestnut (Cas Strawberry (Fra a 1) Tomato r 1) s 1) Apple (Mal d 1) (Sola l 4) Hazel (Cor a 1) Apricot (Pru ar 1) Beech (Fag s 1) Sweet cherry (Pru av 1) Hophornbeam Peach (Pru p 1) Bet v 1-associated (Ost c 1) Pear (Pyr c 1) oral allergy syndrome Bet v 1-related proteins Oak (Que a 1) Red raspberry (Rub i 1)

Ash (Fra e 1) Sweet beet (Beta v 1) Privet (Lig v 1) Pigweed (Che a 1) Lilac (Syr v 1) Privet (Lig v 1) Rye grass (Lol p 11) Timothy grass (Phl p 11) proteins English plantain (Pla l 1) S ection A Ole e 1-related Russian thistle (Sal k 5)

Japanese cypress (Cha o 1) Ragweed (Amb a 1) Japanese cedar (Cry j 1) Mugwort (Art v 6) Cypress (Cup a 1) Common cypress (Cup s 1) - Allergy from genetics to mechanisms Mountain cedar (Jun a 1)

Pectate lyases Pectate Eastern red cedar (Jun v 1) Japanese cypress (Cha o 2) Japanese cedar (Cry j 2)

Mountain cedar (Jun a 2) English plane tree (Pla a 2) Poly- English plane tree (Pla a 2) galacturonases

Minor allergens Birch (Bet v 2) Olive (Ole e 2) Ragweed (Amb a 8) Kiwi (Act d 9) Celery (Api Hazelnut (Cor Redroot pigweed (Ama r 2) Pineapple (Ana c 1) g 4) a 2) Mugwort (Art v 4) Peanut (Ara h 5) Bell pepper Saffron crocus Sweet beet (Beta v 2) Sweet orange (Cit s 2) (Cap a 2) (Cro s 2) Turnip (Bra r 5) Melon (Cuc m 2) Carro (Dau Soy (Gly m 3) Pigweed (Che a 2) Strawberry (Fra a 4) c 4) Latex (Hev b 8) Bermuda grass (Cyn d 12) Litchi (Lit c 1) Tomato Barley (Hor v 12) Sunflower (Hel a 2) Apple (Mal d 4) (Sola l 1) Rice (Ory s 12)

Profilins Annual mercury (Mer a 1) Banana (Mus a 1) Almond (Pru Wall pellitory (Par j 3) Sweet cherry (Pru av 4) du 4) Timothy grass (Phl p 12) Peach (Pru p 4) Yellow mustard Date palm (Pho d 2) Pear (Pyr c 4) (Sin a 4) Russian thistle (Sal k 4) Wheat (Tri a 12) Maize (Zea m 12)

Alder (Aln g 4) Olive (Ole e 3) Prickly juniper (Jun o 4) Ragweed (Amb a 9) Birch (Bet v 3) Olive (Ole e 8) Ragweed (Amb a 10) Birch (Bet v 4) Lilac (Syr v 3) Mugwort (Art v 5) Pigweeed (Che a 3) Bermuda grass (Cyn d 7) Polcalcins Wall pellitory (Par j 4) Timothy grass (Phl p 7) Birch (Bet v 6) Olive (Ole e 4) Common cypress (Cup s 3) Hazel (Cor a 6) Olive (Ole e 5) Mountain cedar (Jun a 3) Figure 3 Major and minor allergens identified in pollen from Birch (Bet v 7) Olive (Ole e 6) Eastern red cedar (Jun v 3) Fagales, Oleaceae, and Cupressaceae trees. Cross-reactive Olive (Ole e 7) Prickly juniper (Jun a 4) allergens identified in other allergen sources are shown in the Olive (Ole e 9) allergens left panel. IgE cross-reactivity between Bet v 1-like proteins Other minor Olive (Ole e 10) Olive (Ole e 11) found in pollen, fruits, and vegetables can cause a clinical condition referred to as Oral Allergy Syndrome.

Tree pollen allergens 21 Global atlas oF allergy

Grass Pollen 3g Allergens

Jörg Kleine-Tebbe Janet Davies Allergy & Asthma Center Westend The University of Queensland Berlin, Germany Brisbane, Australia

Botanical relationship Grasses are ubiquitous plants in Key messages most parts of the world. The grass family (Poaceae) includes >600 • Pollens from diverse grass plants are main contributors to genera and >11,000 recognized seasonal inhalant allergies worldwide species with a wide distribution. • Grass group 1 and 5 allergens represent highly cross-reactive Over 95% of allergy-relevant and potent major allergens, group 5 present only in temperate grass species belong to three sub- climate grasses (Pooideae) families; Pooideae, Chloridoideae • Depending on climate and region, global sensitization rates to and Panicoideae (Figure 1 and 2). grass pollen vary between 1% to 30% of the general population • Strong evidence supports specific immunotherapy with grass Global distribution pollen extracts Depending on climate and geography, grass pollens represent major consist of major (>50% sensitiza- been adopted by the European contributors of airborne allergens tion rate, SR) and minor allergens Medicines Agency (EMA).

- Allergy from genetics to mechanisms during spring as well as summer. (<50% SR). Due to their abun- They grow on all continents and dance and potency, grass group Clinical allergy based on represent 25% to 35% of the 1 and 5 allergens are considered sensitizations earth´s vegetation. Pooideae dom- immunodominant major Pooideae Sensitizations to grass pollen al- S ection A inate temperate climate zones; pollen allergens (Figure 4). While lergens, indicated by grass pollen Chlorodoideae cover the North group 5 allergens are restricted allergen (extract) positive skin American, African and Australian to the Pooideae subfamily, group test or specific IgE, reflect regional continents and Panicoideae grow 1 allergens are present through- plant distribution and pollen ex- in tropical and subtropical envi- out the subfamilies of Poaceae. In posure. Population based sensiti- ronments of Asia, Australia, Africa contrast, pan-allergens profilin zation rates are mainly available and South America (Figure 3). (group 12) and polcalcin (group 7) for Europe and the US and vary contribute to ubiquitous cross-re- considerably between and within Allergens of grass pollen activity between grass, tree and countries (Figure 5). Grass pollen Grass pollen allergens are grouped weed pollen in 10 – 15% of grass allergy is a global problem (Figure according to their protein struc- pollen sensitized subjects. Present 5c). At least half of grass pollen ture and function (Table 1). They concepts of homologous allergen allergen sensitized subjects will are named according to the offi- groups, are based on similar bio- suffer from symptoms of allergic cial nomenclature (www.allergen. chemical composition, homology rhinoconjunctivitis and/or bron- org), i.e.: Phl p 1 = grass group 1 al- and immune cross-reactivity re- chial asthma, particularly during lergen from Phleum pratense (tim- flecting in most cases their close the warm seasons in moderate cli- othy grass). Ten designated groups taxonomic relationship and have mate regions.

22 Grass pollen allergens Global atlas oF allergy

a b

c S ection A Figure 1 Pictures of different grass species and their pollen : a - Timothy grass (Phleum pratense), subfamily Pooideae; b-Bermuda grass (Cynodon dactylon), subfamily Chloridoideae; c - Bahia grass (Paspalum notatum), subfamily Panicoideae.

Family Subfamily Tribe Genus Common name (US) - Allergy from genetics to mechanisms

Poaceae Bambusoideae Oryzeae Oryza (Rice)

Arundinoideae Arundineae Phragmites (Common reed)

Chloridoideae Chlorideae Cynodon (Bermuda grass)

Paniceae Paspalum (Bahia grass) Panicoideae Sorghum (Johnson grass) Andropogoneae Zea (Corn, maize)

Dactylis (Orchard grass) Festuca (Meadow fescue) Poeae Lolium (Perennial rye) Poa (Kentucky bluegrass)

Anthoxanthum (Sweet vernal grass) Avena (Cultivated oat) Aveneae Pooideae Holcus (Velvet grass) Phleum (Timothy grass)

Bromeae Bromus (Smooth brome grass)

Hordeum (Barley) Triticeae Secale (Cultivated rye) Triticum (Wheat)

Figure 2 Taxonomy of grasses (important subfamilies within colored boxes). Overlapping circles (colored lines) indicate partial cross-reactivity between neighboring subfamilies (modified from (2), (4) and (10)).

Grass pollen allergens 23 Global atlas oF allergy

In: Lockey RF, Ledford DK, ed- itors. Allergens and Allergen Immunotherapy. 4th Edition ed: Informa Healthcare, New York; 2008. p. 107-126. 2. Andersson K, Lidholm J. Charac- teristics and immunobiology of grass pollen allergens. Int Arch Al- lergy Immunol 2003;130:87-107. 3. Hrabina M, Peltre G, van Ree R, a Moingeon P. Grass pollen allergens. Clin Exp Allergy Rev 2008;8:7-11. 4. Gangl K, Niederberger V, Va- lenta R. Multiple grass mixes as opposed to single grasses for allergen immunotherapy in allergic rhinitis. Clin Exp Allergy 2013;43:1202-1216. 5. Lorenz AR, Lüttkopf D, May S, Scheurer S, Vieths S. The principle of homologous groups in reg- b ulatory affairs of allergen products--a proposal. Int Arch Allergy Immunol 2009;148:1-17. 6. European Medicines Agen- cy (EMA). Guideline on allergen products:production and quality issues. (EMEA/CHMP/ BWP/304831/2007) 2009. 7. Newson RB, van Ree R, Forsberg B, Janson C, Lotvall J, Dahlen SE c et al. Geographical variation in the prevalence of sensitization to - Allergy from genetics to mechanisms common aeroallergens in adults: the GA2LEN survey. Figure 3 Global distribution of selected grass species (10): a- Timothy grass Allergy 2014;69:643-651. (Phleum pratense), subfamily Pooideae; b-Bermuda grass (Cynodon dactylon), subfamily Chloridoideae; c-Bahia grass (Paspalum notatum), subfamily Panicoideae. 8. Salo PM, Arbes SJ Jr, Jaramillo R, S ection A Calatroni A, Weir CH, Sever ML, Diagnosis and treatment gual home use of droplets or tab- et. al Prevalence of allergic sen- Positive skin prick tests and ele- lets with monopreparations of one sitization in the United States: vated specific serum IgE to grass grass species, but also grass mixes Results from the National Health pollen preparations indicate al- (mainly Pooideae), with or without and Nutrition Examination Sur- lergic sensitizations, being clini- vey (NHANES) 2005-2006. J Al- adjuvants. 2014 (in press). cally relevant only in case of cor- lergy Clin Immunol responding symptoms. Measuring Acknowledgement: We kindly 9. Davies JM. Grass pollen allergens globally; the contribution of IgE to major allergens (i.e. Phl p 1 acknowledge Andreas Nandy subtropical grasses to burden of and 5) increases analytical spec- (Allergopharma, Reinbek, Germa- allergic respiratory diseases. Clin ny), Jonas Lidholm and Kerstin Wall ificity for temperate grass pol- Exp Allergy 2014;44:790-801. len allergy, particularly in case of (ThermoFisher, Uppsala, Sweden) 10. Simon BK, Clayton WD, Harman sensitizations to cross-reactive for additional information and KT, Vorontsova M, Brake I, Healy pollen-panallergens. Specific im- helpful suggestions. D and Alfonso Y. 2011. Grass- munotherapy is most successfully World, http://grassworld.mys- applied for at least three years by Key References pecies.info/ (Accessed April 25, subcutaneous injections or sublin- 1. Esch RE. Grass pollen allergens. 2014).

24 Grass pollen allergens Global atlas oF allergy

TABLE 1 Grass pollen allergen groups Allergen Biochemical Molecular- Member in IgE Features group function weight [kDa] Phleum pratense reactivity Glycoprotein, major grass pollen allergen, >90% 1 β-expansin 27 - 35 Phl p 1 produced by every grass species 85-99% highly homologous to group 3 and 35 - 50% 2 Unknown 11 Phl p 2 C-terminal portion of group 1 allergens 40-60 % highly homologous to group 2 and 35 - 70% 3 Unknown 11 - 14 Phl p 3 C-terminal portion of group 1 allergens 57-67 % Glycoprotein, Berberine bridge enzyme Oxidoreduc- 50 - 75% 4 50 - 60 Phl p 4 family member, plant pathogen response tase 45 - 88% system found in Pooideae grass species, associated 65 - 85% 5 Unknown 27 - 35 Phl p 5 with submicronic cytoplasmic starch 50 - 88 % particles homologous to internal group 5 sequences, 60 - 70% 6 Unknown 12 - 13 Phl p 6 only in Anthoxanthum odoratum, Phleum

45 - 70% S ection A pratense and Poa pratensis Polcalcin, Ca++- Panallergen, dimer assembly in grass 5 - 35% 7 8 - 12 Phl p 7 binding protein pollen, broad pollen-related crossreactivity 2 - 12% Glycoprotein, similar structure to pollen

Ole e 1-related - Allergy from genetics to mechanisms 11 16 - 20 Phl p 11 allergens from olive tree pollen (Ole e 1) 18 - 56% protein and lamb´s quarter (Che a 1) Panallergen, highly conserved, broad pollen 10 - 40% 12 Profilin 13 - 14 Phl p 12 and plant food-related crossreactivity 9 - 32% Polygalacturo- Glycoprotein, susceptible to protease 30 - 40% 13 45 - 60 Phl p 13 nase degradation 36 - 56 % Modified from (1). Due to their taxonomic and biochemical relationship, many grasses contain similar allergens grouped according to shared amino acid sequences. Specific allergens from timothy grass (Phleum pratense, see middle column) are given as examples of the listed grass allergen groups.

Prevalence

Group 1 Figure 4 Involvement of Group High grass pollen allergens in patient 4 Group 5 sensitization (3). Group 2/3 50% Group Group 13 11

Low Group 12 Group Group 7 10

Low 40% High Potency (mean IgE level)

Grass pollen allergens 25 Global atlas oF allergy

14.5 17 25

21 20 22

23.5 b 17 22 29.5 22.5 10 10 24.5 28.5 21.5 11

24 15.5 18 12.5

c a

Saudi Arabia Taiwan (AR, 419) 61%  AR (54) ▼ 10%, Southern USA  2.1% - Allergy from genetics to mechanisms ▲ 57% AR (429) Thailand (AR, 100) ▼21%, ▲16% India 17% 12.5%, (AR/A, 48) S ection A 52% (GPA, 133)

Malaysia (A, 100) 20.5%, SPT test: ▲6.5% ▼Johnson GP ▲Bahia Australia (GPA, 48) Bermuda GP Zimbabwe ▼77%  (number tested) 50.4% AR (341) ▲81%  Subject group: d 84% A, asthma AR, allergic rhinitis, GPA, grass pollen allergic

Figure 5 Sensitization rates to grass pollen (Pooideae) in Europe (a: modified from (7)), to Ryegrass (b) and Bermuda grass (c ) in the US (b and c: modified from (8)) and to Johnson, Bahia and Bermuda grass pollen elsewhere (d: limited information, modified from (9)).

26 Grass pollen allergens Global atlas oF allergy

Weed pollen 3h allergens

Richard W. Weber National Jewish Medical & Research Center Denver, USA

Weeds can be defined as un- wanted plants; as such, they may Key messages

be very variable in form. While S ection A many are herbaceous, some have • The major weeds families inducing allergic rhinitis are the greater or lesser woody stocks, Amaranthaceae, the Asteraceae and the Urticaceae for example the sagebrushes, Ar- • Cross-reactivity between family members is frequent temisia tridentata and A. frigida. • In most temperate regions the weeds pollen season is August - Allergy from genetics to mechanisms Some are prostrate and hug the and September, but climate change can be associated with a ground, while others, such as giant lengthening of the pollination period ragweed, Ambrosia trifida, may be over 3 meters high. Herbaceous varieties may be annuals or per- in arid floristic zones. Redroot can natives, but most of them have ennials. Weeds found in numerous pigweed (A. retroflexus) is a ubiq- been introduced into Europe, and botanical families can be inducers uitous cosmopolitan weed, found have rapidly expanded across the of allergic rhinitis and asthma, but throughout temperate regions of Balkans, Ukraine, and into Poland. a few families stand out with the the globe. Allergenic cross-reac- In most temperate regions the pol- majority of aeroallergen sources. tivity is very strong amongst the len season is August and Septem- Atriplex weeds, and likewise be- ber. Cross-allergenicity is strong Amaranthaceae contains the pig- tween the Amaranthus species ex- amongst the major ragweed spe- weeds ( ), saltbush- Amaranthus amined; cross-reactivity between cies. Other important members of es (Atriplex), and tumbleweeds other chenopod weeds is present Asteraceae are in the genus Arte- (Salsola, Kochia, Bassia) as well as but more variable. misia, the sages. There are about a other chenopod weeds ( Cheno- dozen species found in the United ). The latter three groups Asteraceae (previously known as podium States. The most prevalent in east- were earlier placed in a separate Compositae) is the largest family ern U.S. and Europe is mugwort family, Chenopodiaceae. More of flowering plants (Angiosper- (A. vulgaris). Fringed sagebrush (A. recent systematics has, however, mae), and contains several noto- frigida) is a common groundcover redefined this group as a subfam- rious inducers of pollinosis. The in the Siberian steppes. Cross-re- ily of Amaranthaceae. The major genus Ambrosia contains all the activity is very strong between Ar- tumbleweeds of the North Amer- ragweeds, including several re- temisia species. ican Great Plains are Russian classified from the discarded ge- thistle (Salsola kali) and burning nus Franseria. The four major rag- Urticaceae includes two members bush (Kochia scoparia): both are weed (Artemisia) species are giant of significance: pellitory Parietar( - introduced plants. Other species (A. trifida) (Figure 1), short (A. aria) (figure 3) and nettleUrtica ( ). of Salsola and Bassia are common temisiifolia) (Figure 2), western (A. Pellitory is a major seasonal aer- throughout the Middle East. The psilostachya), and false (A. acanthi- oallergen of the Mediterranean Atriplex saltbushes are common carpa). These are all North Ameri- Basin. Climate change is associat-

Weed pollen allergens 27 Global atlas oF allergy

a c Figure 1 a - Giant sagebrush (Artemisia); b - short ragweed; c- pellitory (Parietaria).

- Allergy from genetics to mechanisms ed with a lengthening of its pollen 3. Smith M, Cecchi L, Skjøth CA, Ledoux RA, Westley CR, Weber season to about ten months. Karrer G, Šikoparija B. Common RW. Mugwort and sage (Artemi- ragweed: a threat to environmen- sia) pollen cross-reactivity: ELISA KEY REFERENCES tal health in Europe. Environ Int inhibition and immunoblot evalu- S ection A 1. Judd WS, Campbell CS, Kellogg 2013;61:115-126. ation. Ann Allergy Asthma Immunol EA, Stevens PF. Plant Systematics: 4. Leiferman KM, Gleich GJ, Jones RT. 1997;79:340-346. A Phylogenetic Approach. Sun- The cross-reactivity of IgE antibod- 6. Ariano R, Canonica GW, Passa- derland, MA, Sinauer Associates, ies with pollen allergens. II. Analy- lacqua G. Possible role of climate 1999:240-7. ses of various species of ragweed changes in variations in pollen 2. Weber RW. Cross-reactivity of and other fall weed pollens. J Aller- seasons and allergic sensitizations 1976;58:140-148. during 27 years. plant and animal allergens. Clin Rev gy Clin Immunol Ann Allergy Asthma 2010;104:215-222. Allergy Immunol 2001;21:153-202. 5. Katial RK, Lin FL, Stafford WW, Immunol

28 Weed pollen allergens Global atlas oF allergy

3i Food allergens

Barbara Ballmer-Weber University Hospital Zürich Zürich, Switzerland

Depending on the route of sensitization, immediate-type food Key messages

hypersensitivities are either a S ection A result of reactivity to food aller- • Differences in sensitization to food allergens across different gens through the gastrointesti- geographic regions have been particularly observed for plant nal tract (class I allergens) or the food allergens result of secondary sensitization • 65% of plant food allergens are part of four protein families/ - Allergy from genetics to mechanisms to cross-reactive food allergens superfamilies: the prolamin, cupin, Bet v 1 and profilin family mainly due to primary sensitiza- • In Europe, the prevalence of IgE to foods significantly correlates tion to homologous pollen aller- with the prevalence of sensitization to birch-pollen-associated gens via the respiratory tract (class allergens Bet v 1 and Bet v 2 II allergens, Figure 1). Class I aller- • Food allergic patients from Mediterranean countries show a gens are often resistant to heat, higher sensitization rate to profilin and non-specific lipid transfer degradation and digestion. Class II proteins compared to Central, Western or Eastern Europe allergens are mainly labile and easily degradable. According to these characteristics the clinical mani- More than 65% of plant food al- 6.6% (Iceland) to 23.6% (Switzer- festation is influenced by the type lergens are members of just four land) and was significantly corre- of allergens to which an individual protein families/superfamilies: lated with the prevalence of sensi- is sensitized. The class I allergens the prolamin, cupin, Bet v 1 and tization to birch-pollen-associated have a higher potential to induce profilin family (Table 1). Animal allergens Bet v 1 and Bet v 2 (pro- severe reactions compared to the derived food allergens mainly be- filin), whereas IgE sensitization to easily degradable class II food al- long to three protein families: the non-pollen-related plant allergens lergens, which induce often symp- tropomyosins, parvalbumins and were more evenly distributed. toms restricted to the oral cavity. caseins. These results confirmed the find- Due to such reasons, great efforts At school age, adolescence and ings from studies evaluating the have been made in the last few adulthood cross-reactive food al- sensitisation pattern to food aller- years to identify and characterize lergy is dominating. According to gens across Europe. Sensitization individual food allergen molecules new epidemiologic data sensitiza- rates to the Bet v 1 homologous in the most prevalent allergenic tion to the respective food aller- proteins in apple (Mal d 1), kiwi foods (http://www.allergen.org/; gens is heavily dependent on the (Act d 8), carrot (Dau c 1) or ha- http://www.allergome.org/; http:// exposure and sensitization to in- zelnut (Cor a 1) were significantly www.meduniwien.ac.at/allergens/ halant allergens. In a recent study higher in countries with high birch allfam/) and to compare sensiti- including adult participants from pollen exposure such the Neth- zation patterns between different eight European centres the preva- erlands, Austria, Northern Italy, geographic regions. lence of IgE to foods ranged from Switzerland and Denmark com-

Food allergens 29 Global atlas oF allergy

Figure 1 Homology between the major birch pollen allergen Bet v 1 and homologous food protein. High structural

- Allergy from genetics to mechanisms homology between the major birch pollen allergen Bet v 1 (top) and homologous food protein (here as an example the cherry allergen Pru av 1, bottom) explains the phenomenon of cross-sensitization between birch pollen and plant foods and the high prevalence of sensitization to foods in birch pollen exposed regions of Europe. S ection A TABLE 1 Most important protein families for plant food allergies

Protein Thaumatin-like Prolamin Cupin Profilin Bet v 1 family protein

Biochemical 7S-globulin 11S-globulin 2S albumin nsLTP structure vicilin legumin

pathogen storage plant storage storage actin pathogen function resistance protein defense protein protein binding resistance PR-5 PR-10

Rosaceae Rosaceae cherry, apple, peanut, soy, fruits, peanut, soy, fruits, peach, tomato, examples of tree nuts, peanut, soy, all plant nuts, pea, lentil, nuts, orange, grape, foods sesame, nuts foods seeds, nuts, sesame legumes, kiwi, bell mustard vegetables vegetables pepper

30 Food allergens Global atlas oF allergy

70 Northern Europe

60 Central/Western Europe

Eastern Europe 50 Southern Europe

30 % of kiwi allergics (n=311) 20

10 S ection A 0 Act d 1 Act d 5 Act d 8 Act d 9 Act d 10

Figure 2 Sensitization pattern to kiwi allergens. Sensitization pattern to kiwi allergens Act d 1 (Actinidin), Act d 5 (Kiwellin), Act d 8 (Bet v 1 homologous protein), Act d 9 (Profilin) and Act d 10 (non-specific LTP) in four European regions - Allergy from genetics to mechanisms (northern: Iceland; central/western: France, northern Italy, Switzerland, The Netherlands, United Kingdom; eastern: Bulgaria, Poland, Czech Republic, Lithuania, southern: Spain, Greece). Patients from Iceland were mainly sensitized to Act d 1 (32%), those from western/central and eastern Europe to Act d 8 (58% and 44%, respectively), and those from southern Europe to Act d 9 (profilin, 31%) and Act d 10 (non-specific LTP, 22%) (Le et al., J Allergy Clin Immunol 2013). pared to that observed in Medi- Differences in the sensitization 3. Le TM, Bublin M, Breiteneder H, terranean countries such as Spain pattern were also demonstrated Fernández-Rivas M, Asero R, Ball- or Greece (Figure 2: sensitization for children with peanut allergy mer-Weber BK, et al. Kiwifruit pattern to kiwifruit allergens from three different geographic allergy across Europe: clinical manifestation and IgE recognition across Europe). Spanish and Greek regions. Spanish patients were patterns to kiwifruit allergens. J Al- patients, however, showed a high- mainly sensitised to non-specific LTP (Ara h 9), Swedish patients to lergy Clin Immunol 2013;131:164- er sensitization rate to profilin and the Bet v 1 homologous allergen 171. non-specific Lipid transfer protein Ara h 8 and US patients to the 4. Ballmer-Weber BK, Skamstrup (LTP). A similar association of sen- storage proteins in peanut Ara h 1, Hansen K, Sastre J, Andersson K, sitisation to pollen from the Betu- Ara h 2 and Ara h 3. Bätscher I, Ostling J et al. Com- laceae family, particular alder, and ponent-resolved in vitro diagno- the development of fruit allergy KEY REFERENCES sis of carrot allergy in three different regions of Europe. was observed in Japan. Sensitiza- 1. Breiteneder H, Mills EN. Molecular Allergy 2012;67:758-766. tion to food LTP is highly prevalent properties of food allergens. J Aller- in Mediterranean countries and gy Clin Immunol 2005;115:14-23. 5. Vereda A, van Hage M, Ahlstedt S, Ibañez MD, Cuesta-Herranz J, van associated with a higher rate of 2. Burney PG, Potts J, Kummeling I, Odijk J et al. Peanut allergy: Clini- systemic reactions. Also in China Mills EN, Clausen M, Dubakiene R, et al. The prevalence and distribu- cal and immunologic differences sensitization to peach LTP, Pru p 3, tion of food sensitization in Euro- among patients from 3 different was associated with a high rate of pean adults. Allergy 2014;69:365- geographic regions. J Allergy Clin systemic reactions. 371. Immunol 2011;127:603-607.

Food allergens 31 Global atlas oF allergy

3j Venom allergens

Franziska Ruëff Ludwig-Maximilian University Munich, Germany

Insects For allergic sting reactions, main- Key messages ly social Aculeatae are important elicitors. Social insects have de- • 12 molecular allergens of honey bee venom, and five of Vespula veloped a division of labour with venom are known and have been sequenced sterile females forming a work- • Use of molecular allergens has improved testing of venom- ing class. Female workers have a specific IgE antibodies stinger by which venom is injected • Further research on the clinical role of individual molecular during a sting into the skin. Within insect venom allergens is needed the Aculeatae, Vespidae (vespids), • Allergen components of the venoms should be available for Apidae (bees), and Formidaceae routine testing (ants) are social insects (Figures 1 and 2). Vespidae are divided into the subfamilies Polistinae and Ves- eliciting an allergic reaction. Mi- pinae. The latter contains three nor allergens may also induce sIgE, however, this occurs in a small

- Allergy from genetics to mechanisms genera: Vespula, Dolichovespula and Vespa. percentage of venom allergic patients. Insect venoms Phospholipase A2, hyaluronidase, S ection A Insect venoms contain a complex and acid phosphatase are the ma- mixture of toxic proteins and pep- jor bee venom allergens. Major tides, of which some may induce allergens of Vespula venom are IgE-mediated sensitisation. Today, Phospholipase A1, Hyaluronidase, a 12 molecular allergens of hon- and Antigen 5. Some allergens of ey bee venom, and 5 of Vespula Vespula and bee venom share mi- venom are known and have been nor to moderate sequence iden- sequenced (Table 1). For some of tity and show a corresponding these allergens, isoforms have cross-reactivity. However, the been detected. closer is the taxonomic relation- Major allergens are characterized ship of insects the greater is the by the fact that there is corre- overlap of biochemical structures sponding specific IgE-antibodies of molecular venom allergens. b (sIgE) in the blood of the majority Honey bee venom allergens show of allergic patients. Major aller- more cross-reactivity with bumble gens are probably more important bee allergens compared to aller- Figure 1 a - Apidae (bee); b- than minor allergens in terms of gens of the venoms from Vespula Vespidae (vespids).

32 Venom allergens Global atlas oF allergy

TABLE 1 Testing sIgE to single venom allergens is of major importance for Most important protein families for plant food allergies improving sensitivity and specific- Molecular weight Percent of Allergen Name / Function ity of in-vitro diagnostics. Using (KDa) dry weight recombinant allergens improved Honey bee venom allergens the value of assays testing sIgE to the whole venom. Api m 1 Phospholipase A2* 16 12 Api m 2 Hyaluronidase* 39 2 Another problem for the diagnosis of insect venom allergy is the dou- Api m 3 Acid phosphatase 43 1-2 ble positivity although presuma- Api m 4 Melittin* 3 50 bly the patient only suffers from Api m 5 Dipeptidylpeptidase IV 100 <1 one allergy. Double positivity may Api m 6 8 1-2 be due to true double allergy, to Api m 7 CUB serine protease 39 ? cross reactivity between allergen compounds of honey bee and Ves- Api m 8 Carboxylesterase 70 ? pula venoms, and to sensitization Api m 9 Serine carboxypeptidase 60 ? to widespread cross-reactive car- S ection A Icarapin variant 2, carbohydrate determinants (CCD), Api m 10 50- <1 bohydrate-rich protein which are present in many aller- 50 (deglycosylated gen sources from plants and ani- Api m 11 Major royal jelly protein ? form) mals. The latter, however, usually - Allergy from genetics to mechanisms Api m 12 Vitellogenin 200 ? do not act as allergens. Allergen compounds, which are free from Vespula venom allergens CCD improve the specificity of in Ves v 1 Phospholipase A1* 34 6-14 vitro testing. Ves v 2 Hyaluronidase* 28 1-3 Ves v 3 Dipeptidylpeptidase IV 100 ? KEY REFERENCES 1. Eberlein B, Krischan L, Darsow U, Ves v 5 Antigen 5* 23 5-10 Ollert M, Ring J. Double positivity Ves v 6 Vitellogenin 200 ? to bee and wasp venom: improved diagnostic procedure by recombi- (IUIS Allergen Nomenclature Sub-Committee. www.allergen.org). Major allergens are nant allergen-based IgE testing and indicated by an asterix (*) basophil activation test including species. Venom allergens from ey bee venom (Api m 1) and two of data about cross-reactive carbo- Polistinae or Dolichovespula are Vespula venom (Ves v 1 and 5) are hydrate determinants. J Allergy Clin more related to Vespula venoms. available for routine diagnostics. Immunol 2012;130:155-161. It is assumed that in the near fu- 2. Vos B, Köhler J, Müller S, Stretz E, In-vitro diagnostics of ture more molecular compounds Ruëff F, Jakob T. Spiking venom venom sensitization will be available to identify venom with rVes v 5 improves sensitivity Demonstration of venom-specific sIgE. of IgE detection in patients with sensitization is essential for diag- allergy to Vespula venom. J Aller- nosing an insect venom allergy and In contrast to certain food al- gy Clin Immunol 2013;131:1225- is also a prerequisite to select the lergies, where the sensitization 1227. proper venom for immunothera- patterns were found to be associ- 3. Seismann H, Blank S, Braren I, py. To identify venom-specific IgE ated with mild or severe allergic Greunke K, Cifuentes L, Grunwald in human blood, insect venoms reactions and can be used for risk T, et al. Dissecting cross-reactivi- are in use since the seventies. In assessment, for venom allergy, ty in hymenoptera venom allergy the late eighties, purified allergens the clinical relevance of a certain by circumvention of alpha-1,3- were produced. Today, one recom- pattern of venom sIgE remains un- core fucosylation. Mol Immunol binant allergen component of hon- clear. 2010;47:799-808.

Venom allergens 33 Global atlas oF allergy

Emerging 3k allergens

Karin Hoffmann-Sommergruber Medical University of Vienna Vienna, Austria

In the recent past, great efforts have been undertaken to charac- Key messages terise allergens. This in turn has revolutionized in vitro diagnosis, • Only a minority of known proteins exert an allergenic activity by determining the range of cross • Allergen panels contribute to improve in vitro diagnosis of allergy reactivities and establishing aller- • While some allergens rather induce mild symptoms, others are gen panels. Of special interest is known to be linked with severe symptoms (marker allergens) the identification of marker aller- • Depending on environmental exposure and dietary habits IgE gens: allergens that tend to induce recognition patterns may vary in different patients groups rather severe symptoms versus allergens that rather account for mild symptoms. allergens from mites and cock- sensitization event. This highlights roaches. that alternative exposures have It is only a minority of proteins to be considered if new and unex- that exert allergenic activity. To Parvalbumins share an EF-hand pected cases of allergies occur. date allergens can be assigned to domain binding Ca2+ and thus are

- Allergy from genetics to mechanisms 2% of all known protein families. involved in signaling pathways or Plant-derived food According to allergen databases, Ca2+ transport. These major food the dominating protein families allergens were identified from allergens among animal-derived food aller- fish and amphibians, but not from The non-specific lipid transfer S ection A gens are tropomyosins, parvalbu- higher vertebrates. proteins (LTP) and the 2S albumins mins and caseins. Similarly, pro- belong to the prolamin superfam- Caseins are a major heterogenous lamins, cupins and PR10 proteins ily. Both types of proteins display protein fraction in mammalian are the 3 most important plant a rigid tertiary structure and are milk displaying a random-coiled resistant to enzymatic and ther- protein families (Table 1). 2+ structure. They function as Ca mal treatment. Non-specific-LTPs binders and allergenic caseins and Animal-derived food are involved in plant defense, and are highly cross-reactive among allergens are relevant allergens in various mammalian species. Tropomyosins are highly con- fruits, nuts and pollens. 2S albu- served eukaryotic proteins with a So far sensitization to carbohy- mins are seed storage proteins typical coiled-coil structure that drates has been regarded as of and together with the proteins are necessary for regulating mus- low clinical importance in allergic from the cupin superfamily they cle contraction. So far, allergenic diseases. However, recently, aller- represent important allergens in tropomyosins have been identi- gic reactions to alpha-gal epitopes seeds and nuts, usually evoking fied from e-vertebrates, highly were observed in meat allergy. severe symptoms in patients. The cross-reactive among crustaceans Previous administration of mono- PR10 proteins, involved in plant and mollusks, as well as inhalant clonal antibody doses induced the defense, are present in pollen as

34 Emerging allergens Global atlas oF allergy

TABLE 1 well as in plant food, usually evoking mild oral symptoms. Eventual- Overview of 3 most important plant and animal food allergen protein ly, they can induce severe symp- families toms as in soy allergy. Protein su- Protein Biological Molecular Allergens Structure perfamily family function mass (kDa) known from In conclusion, a number of allergens are now available for compo- Animal food allergens nent-resolved in vitro diagnosis. Analysis of their physicochemical features, especially their 3D struc- Muscle Crustaceans, Tropomyosin 36-38 ture contributes to our under- contraction molluscs standing of protein stability, range PDB: 1C1G of cross reactivity and changes in allergenicity during thermal or enzymatic treatment. Ca2+ Fish, Parvalbumin 12 binding amphibians KEY REFERENCES 1. Radauer C, Bublin M, Wagner S, PDB:1B8R Mari A, Breiteneder H. Allergens Ca2+ Mammalian are distributed into few protein S ection A Casein 20-30 Not available binding milk families and possess a restricted number of biochemical functions. J Plant food allergens Allergy Clin Immunol 2008:121:847-

852. - Allergy from genetics to mechanisms 2. Hoffmann-Sommergruber K, Mills Prolamin 2S Seed Peanut, tree 15-17 ENC. Food allergen protein families superfamily Albumin storage nuts, seeds and their structural characteristics and application in component-re- PDB: 1PNB solved diagnosis: new data from the EuroPrevall project. Anal Bio- anal Chem 2009:395:25-35. Plant ns-LTP 7-9 Plant food 3. Ballmer-Weber B, Hoffmann-Som- defense mergruber K. Molecular diagnosis of fruit and vegetable allergy. PDB: 2B5S Curr Opin Allergy Clin Immunol 2011:3:229-235. 4. Alessandri S, Sancho A, Vieths S, Cupin 7/8S Seed Legumes, 150-190 Mills CE, Wal JM, Shewry PR, Rig- superfamily globulin storage nuts, seeds by N, Hoffmann-Sommergruber K. High-throughput NMR assessment PDB: 3SMH of the tertiary structure of food allergens. PLos One 2012:7:e39785.

11S Seed Peanut, tree 60 globulin storage nuts, seeds

PDB:3FZ3

Plant PR10 17 Plant food defense

PDB: 2BKO (ns-LTP – non-specific Lipid transfer protein; PR10 – pathogenesis related protein family 10; structures retrieved from pdb)

Emerging allergens 35 Global atlas oF allergy

Pollen allergens and 3l geographical factors

Jeroen Buters Technische Universität München and Helmholtzzentrum Munich, Germany

Allergies to pollen are the most frequent type 1 allergies, surpass- Key messages ing the prevalence of allergies to house dust mite. Their prevalence • Pollen exposure varies between geographical regions have been increasing since dec- • The same amount of olive pollen releases 12-fold variable ades and an end is not in sight. amounts of Ole e 1, 10-fold differences in Bet v 1 is documented for birch pollen, while Phl p 5 from grass pollen can show even Pollen is a natural product and higher variations shows a large geographical and • Pollen allergen release potency is not geographically fixed and climatic variability. Indeed, natural changes between years variability is so large that a simple • Pollen allergen release potency is determined in the week before prediction of pollen load depend- pollination by two simultaneous competing ripening processes: ing on the year long experience is anther development and individual pollen ripening not possible. This has led to the implementation of pollen monitoring networks. Climate change is reported to conditions at source, which var- - Allergy from genetics to mechanisms influence pollen season for the ies with the geographical location. Geographic factors and starting date and for the intensi- The amount of allergen released pollen exposure ty for early blooming species. The per pollen is variable between Few pollen monitoring networks S ection A natural yearly variability in pollen years, locations and even days. In exist worldwide (Figure 1). In addi- exposure is large, making the ef- a EU-wide project (www.hialine. tion, rotorod samplers are used in fect of climate change difficult to eu) the allergen release potency USA, while Hirst-type pollen traps predict. An elongation of the birch for olive, birch and grass pollen are frequent in Europe making pollen season was reported only was analyzed with standardized quantitative comparison between in a few random places. Pollen methods. Across Europe, pollen continents challenging. exposure is mostly dependent on potency varied 12-fold for olive However, similar results emerge: short-term local weather, making pollen, 10-fold for birch pollen pollen exposure varies substan- on the spot monitoring an essen- and even more for grass pollen. tially. For Europe, according to a tial instrument in determining ex- Also, potency of pollen from olive 20-year average, birch pollen is posure. and birch depended on the origin the dominant pollen with 2-times of emission as potency is deter- higher counts than grass pollen Geographical factors and mined by weather at the place of in almost all reported locations. pollen potency emission, not at the place of meas- Between locations, a 10-fold dif- Pollens are natural products and uring the pollen. Within Germany, ference of pollen load was noted like wine and strawberries their a constant 3-fold gradient of birch (Figure 2). “quality” depends on the climatic pollen potency is observed, with

36 Pollen allergens and geographical factors Global atlas oF allergy

Rotorod Durham Hirst-type S ection A - Allergy from genetics to mechanisms

Figure 1 Pollen monitoring networks across the world. Current pollen monitoring sites running for more than 6 years. Three different types of pollen counters are in use worldwide: Rotorod, Durham and Hirst-type traps. This makes pollen counts difficult to compare. Data from Europe were provided by U. Berger, European Aerobiology Network (EAN), Medical University Vienna, from USA by Jerome Schultz (AAAAI), from Russia by E. Severova, from Japan by R. Kishikawa, from South Africa by D. Byrman, from Israel by A. Eshel, from Saudi Arabia by H. Syed, from Azores by Rui Brandao, from Canada by F. Coates and from Australia by Janet Davies. For some countries data was not available. southern pollen being more po- Conclusion 3. Smith M, Jäger S, Berge U, Sikopari- tent that northern pollen. In the All investigated aeroallergens:pol- ja B, Hallsdottir M, Sauline I et al. same line, olive pollen from Spain len from birch, olive and grass, but Geographic and temporal variations in pollen exposure across Eu- released 5 times more Ole e 1 than also from cat, dog and horse vary rope. Allergy, In press 2014. Portugese olive pollen. at least 10-fold in allergen release within the same species. We ex- 4. Buters JTM, Thibaudon M, Smith The difference in pollen potency pect the same for other sources. M, Kennedy R, Rantio-Lehtimaa- could be due to two competing rip- ki A, Albertini R, et al. Release of Bet v 1 from birch pollen from 5 ening processes: allergen expres- KEY REFERENCES European countries. Results from 1. Langen U, Schmitz R, Steppuhn H. sion in pollen increases from zero the HIALINE study. [Prevalence of allergic diseases in Atmos Environ in the week before pollination to 2012;55:496-505. Germany: results of the German high numbers upon pollination Health Interview and Examina- 5. Galan C, Antunes C, Brandao R, (ripening of Bet v 1). Concomitant- tion Survey for Adults (DEGS1)]. Torres C, Garcia-Mozo H, Caeiro E, ly the anthers ripen too, and will Bundesgesundheitsblatt Gesund- et al. Airborne olive pollen counts release pollen when they are ripe heitsforschung Gesundheitsschutz are not representative of exposure to the major olive allergen Ole e 1. and weather is suitable. Thus, bad 2013;56:698-706. Allergy 2013;68:809-812. weather can result in late opening 2. Haahtela T, Holgate S, Akdis C. The biodiversity hypothesis and allergic 6. Buters JTM, Kasche A, Weichen- of anthers and consequently long disease: world allergy organization meier I, Schober W, Klaus S, ripening periods for the allergen, position statement. WAO Journal Traidl-Hoffmann C, et al. Year-to- resulting in more potent pollen. 2013;6:3. Year Variation in Release of Bet

Pollen allergens and geographical factors 37 Global atlas oF allergy

4,0 3,5 Bet v 1 3,0 2,5 2,0 1,5 1,0 0,5 Reykjavik 0,0 8

Leiden C

Siauliai

4,0 9 3,5 Bet v 1 3,0 Neustrelitz 2,5 2,0 Derby 1,5 6 1,0 1 0,5 4 G 0,0 3

11 E 13 Lodz

D 2

10 Strasbourg 12 Prague 5

Zurich AAsstetraecreaeaceae Soﬁa 4,0 4,0 4,0 4,0 4,0 BBetulaetulaceaeceae 3,5 Ole e 1 3,5 Ole e 1 3,5 Bet v 1 3,5 Bet v 1 3,5 Bet v 1 3,0 3,0 3,0 3,0 3,0 2,5 2,5 2,5 2,5 2,5 OleaOleaceaeceae 2,0 2,0 2,0 2,0 2,0 Thessaloniki 1,5 1,5 1,5 1,5 1,5 Poaceae 1,0 1,0 1,0 1,0 1,0 Poaceae 0,5 0,5 0,5 0,5 0,5 0,0 0,0 0,0 0,0 0,0 Madrid Figure 2 Pollen distribution and pollen potency across Europe. Size of the circles represents quantitative differences in the pollen index, colors represent different pollen species (families). Bar graphs represent the amount of allergen released - Allergy from genetics to mechanisms per pollen (potency) for the indicated locations.

v 1 Allergen from Birch Pollen: S ection A Evidence for Geographical Differ- ences between West and South Germany. Int Arch Allergy Immunol 2008;145:122-130. 7. Buters JTM, Weichenmeier I, Ochs S, Pusch G, Kreyling W, Boere AJ, et al. The allergen Bet v 1 in fractions of ambient air deviates from birch pollen counts. Allergy 2010;65:850- 858.

38 Pollen allergens and geographical factors Global atlas oF allergy

The underlying 4 mechanisms in allergy

Cezmi A. Akdis Swiss Institute of Allergy and Asthma Research Davos, Switzerland

The immune system forms an in- teractive network with tissues and Key messages

makes its decisions on the basis of S ection A signals coming from resident tissue • The early development of memory T and B cell responses and IgE cells, infectious agents, commensal production represent the sensitization phase of allergic reaction bacteria and almost any environ- • IL-4 and IL-13 are essential to induce class switching to IgE in B mental agents. The immunologic cells and for the production of allergen-specific IgE antibodies - Allergy from genetics to mechanisms basis of allergic diseases (Table 1) • Cross-linking of the IgE-FcεRI complexes on basophils and mast is observed in two phases: sensiti- cells and subsequent release of anaphylactogenic mediators is responsible for the immediate hypersensitivity reaction zation and development of mem- • Effector T and B cell and eosinophil infiltration of the affected ory T and B cell responses and IgE tissues is controlled by a chemokine network production and effector functions • Type 2 innate lymphoid cells play a role in eosinophilic inflammation related to tissue inflammation, tis- in mouse models and are observed in nasal polyp tissue in humans sue injury, tissue remodeling and • There is strong evidence on the defective allergen tolerance chronicity in asthma, atopic derma- mechanisms by T and B regulatory cells titis (AD) and allergic rhinitis (AR). • Epithelial barrier is leaky in asthma, chronic rhinosinusitis and Different disease endotypes may atopic dermatitis become apparent with different • Different disease endotypes show different dominant molecular dominant molecular mechanisms, mechanisms, biomarkers and therapy response to biologicals related biomarkers and response to biological therapy. In the sensitization phase, during tion. In the effector phase, when nosinusitis (CRS) patients as well the development of allergic dis- a new encounter with the allergen as keratinocytes in the skin of AD eases, effector Th2 cells produce causes cross-linking of the IgE- patients. Recent studies suggest IL-4, IL-5, and IL-13. IL-4 and IL- FcεRI complexes on sensitized ba- that tissue integrity is disturbed 13 induce class switching to the sophils and mast cells, they are ac- and allows penetration of aller- ε immunoglobulin heavy chain tivated and subsequently release gens, bacterial toxins and other in B cells and the production of anaphylactogenic mediators that particles through the epidermis, allergen-specific IgE antibodies are responsible for the immediate the lung and sinus epithelium, (Figure 1). Innate lymphoid cells hypersensitivity reaction. where they may activate the im- (ILC2) also provide Th2 cytokines. Defective epithelial barrier func- mune system leading to severe Allergen-specific IgE binds to the tion has been demonstrated for chronic inflammation in these dis- high-affinity FcεRI on the surface bronchial epithelial cells in the eases. Activation of the epithelial of mast cells and basophils, thus asthmatic lung, epithelial cells cells and release of IL-25, IL-31, leading to the patient’s sensitiza- in the sinus tissue of chronic rhi- IL-33 and TSLP contribute to type

The underlying mechanisms in allergy 39 Global atlas oF allergy

TABLE 1 2 responses of T cells and innate lymphoid cells (Figure 2). These Cellular and molecular events in allergic inflammation cytokines play a role in the pro- • Epithelial barrier defect in the skin and affected mucosas duction of allergen-specific IgE, eosinophilia, permissiveness of • Epithelial cell activation and their proinflammatory cytokines and chemokine production that induces inflammation and contributes to Th2 endothelium for the recruitment response: TNF-α, IL-13, IL-25, IL-31, IL-33, TSLP of inflammatory cells to inflamed tissues, production of mucus and • Chemokine release attracting Th2 cells and eosinophils decreased threshold of contrac- • Epithelial apoptosis and shedding in AD and asthma: IFN-γ, TNF-α, IL-32 tion of smooth muscle cells. • Innate lymphoid cell type 2 response: IL5, IL13 The discovery of ILCs has changed • Th2 response: IL-4, IL-5, IL-13, our perception of T cells as the major cytokine-secreting effec- • Eosinophilia: IL-5, IL-25, IL-33 tors of immunity and made us • Local and systemic IgE production: IL-4, IL-13 aware of completely unappreci- • Cross-linking of IgE receptor FcεRI on the surface of mast cells and baso- ated innate immune cell sources phils and their degranulation of effector cytokines. Particularly type 2 ILCs can contribute to Th2 • Smooth muscle, myofibroblasts activation, bronchial hyperreactivity in asthma: IL-4, IL-9, IL-13, IL-25, IL-33 type inflammation similar to Th2 cells in mouse models. Th1 cells • Angiogenesis in chronic inflammation: VEGF, IL-32 also efficiently contribute to the • Survival and reactivation of migrating inflammatory cells and their inter- effector phase in allergic diseases action with resident tissue cells and other inflammatory cells: IL-2, IL-4 with their role in apoptosis of the • Activation of other effector T cell subsets, such as Th9, Th17 and Th22 epithelium in asthma and AD. cells and their contribution to mucus production, tissue inflammation and In recent years, induction of im- regeneration. mune tolerance has become a

Th2 IgM Figure 1 In the sensitization phase - Allergy from genetics to mechanisms allergen-specific IgE antibodies are produced and bind to the IL-4 naive high-affinity FcεRI on the surface IgE B cell IL-13 of mast cells and basophils, thus S ection A memory leading to the patient’s sensitization. B cell IgE class When a new encounter with the switching ILC2 allergen causes cross-linking of the IgE-FcεRI complexes on sensitized IgE+ memory memory basophils and mast cells, they release B cell B cell anaphylactogenic mediators that expansion are responsible for the immediate allergens hypersensitivity reaction. B cell epitopes IgE Vasoactive amins FcεRI (histamine) Lipid mediators IgE (PGD2, PAF production LTC4, LTD4, LTE4) by plasma cells Cytokines degranulation (IL-3, IL-4, IL-5, IL-13) basophil Chemokines type 1 hypersensitivity

40 The underlying mechanisms in allergy

Figure1 Akdis Global atlas oF allergy S ection A - Allergy from genetics to mechanisms

Figure 2 Pathogenic mechanisms in allergic inflammation. Epithelial leakiness and activation and their proinflammatory cytokines and chemokines (TNF-α, IL-13, TSLP, IL-31, IL-33) production induces inflammation and contributes to Th2 response. Highly activated epithelial cells undergo apoptosis and shedding takes place. Chemokines are essential players for the recruitment of inflammatory cells, which is followed by survival and reactivation of migrating inflammatory cells and their interaction with resident tissue cells and other inflammatory cells. Innate lymphoid cells (ILC2) play a role in T and B cell activation and recruitment and are early providers of Th2 and T cell recruitment cytokines. Th2 type of an immune environment is characterized by IL-4, IL-5, IL-9, IL-13, IL-25, IL-33 production coming from Th2 cells and tissue cells. Eosin- ophilia is induced by IL-5, IL-25, IL-33. Local and systemic IgE production takes place in allergic patients with the involvement of IL-4, IL-13. Other effector T cell subsets, such as Th9, Th17 and Th22 cells also play partial roles in inflammation, mucus production and tissue healing. Smooth muscle, myofibroblasts activation and bronchial hyperreactivity is related to IL-4, IL-9, IL-13, IL-25, IL-33. Several chemokines, and arachidonic acid pathway molecules and other small molecules play roles in the inflammatory cell recruitment and further augmentation of the inflammatory cascades.

The underlying mechanisms in allergy 41 Global atlas oF allergy

Immune tolerance Allergy Autoimmunity IL-4 IL-5 IFN-γ TReg IL-9 TNF-α,β IL-17 IL-13

Th1 Th17 Th2

T-bet GATA-3 Figure 3 Concept development in T cell tolerance in allergy and autoimmunity. After the discovery Fox P3 of Th1 and Th2 cell subsets in 1986, it was thought that Th1 cells play a Th1 Treg Th2 role in infections and autoimmunity and Th2 cells in allergic disease. Both Transcription T-bet FoxP3 GATA-3 subsets were considered to have factors reciprocal roles in counter regulating Delayed type of hy- inhibition of Th1 and Th2 each other. After the introduction chronic persensitivity, mac- cells of Treg cells, it was demonstrated Major eosinophilic rophage activation inhibition of mo/mac that although there is reciprocal functions inflammation limited B cell help/ inhibition of DC matura- regulation between individual Th cell with high IgE inhibition tion peripheral tolerance subsets, Treg cells play a major role in the induction of immune tolerance Chronic intracellu- immunotherapy trans- arthritis in allergy, autoimmunity, organ Beneficial lar infections: leish- plantation autoimmunity autoimmunity transplantation, cancer, pregnancy, role maniasis, leprosy, allergy/asthma preg- helminth inf. chronic infections. virus infections nancy pregnancy

prime target for prevention and KEY REFERENCES immune responses in asthma. Nat treatment strategies for allergic 1. Akdis CA. Therapies for allergic Med 2012;18:673-683. diseases. Immune tolerance to inflammation: refining strate- 6. De Benedetto A, Rafaels NM, gies to induce tolerance. Nat Med McGirt LY, Ivanov AI, Georas SN, - Allergy from genetics to mechanisms allergens can be defined as estab- lishment of a long-term clinical 2012;18:736-749. Cheadle C, et al. Tight junction tolerance against allergens, which 2. Akdis M, Akdis, AC. Immune Tol- defects in patients with atopic dermatitis. J Allergy Clin Immunol immunologically implies changes erance. In: N Franklin Adkinson Jr BSB, Wesley Burks, William W 2011;127:773-786. S ection A in memory type allergen-specific 7. Soyka MB, Wawrzyniak P, Eiwegger T and B cell responses as well as Busse, Stephen T Holgate, Robert F Lemanske Jr, Robyn E O’Hehir, ed. T, Holzmann D, Treis A, Wanke K, et mast cell and basophil activation Middleton’s Allergy, 8th Edition, al. Defective epithelial barrier in thresholds that do not cause al- 2013. chronic rhinosinusitis: The regula- lergic symptoms anymore (Figure tion of tight junctions by IFN-gam- 3. Akdis M, Akdis CA. Mechanisms 3). T and B regulatory cells and ma and IL-4. J Allergy Clin Immunol of allergen-specific immunother- 2012;130:1087-1096. production of allergen-specific apy: multiple suppressor factors IgE-blocking IgG4 isotype anti- at work in immune tolerance to 8. Rebane A, Zimmermann M, Aab A, Baurecht H, Koreck A, Karelson bodies play an essential role in allergens. J Allergy Clin Immunol M et al. Mechanisms of IFN-gam- allergen tolerance. Similar mech- 2014;133:621-631. anisms of immune tolerance take ma-induced apoptosis of human 4. Akdis M, Burgler S, Crameri R, Ei- skin keratinocytes in patients with place in high dose allergen ex- wegger T, Fujita H, Gomez E, et al. atopic dermatitis. J Allergy Clin Im- posed bee-keepers and cat owners Interleukins, from 1 to 37, and in- munol 2012;129:1297-1306. (who do not develop allergy), after terferon-gamma: receptors, func- 9. Scanlon ST, McKenzie AN. Type 2 allergen-specific immunotherapy, tions, and roles in diseases. J Allergy innate lymphoid cells: new players and in individuals who naturally Clin Immunol 2011;127:701-721. in asthma and allergy. Curr Opin Im- outgrow allergic diseases. 5. Holgate ST. Innate and adaptive munol 2012;24:707-712.

42 The underlying mechanisms in allergy (overview) Global atlas oF allergy

Innate immune 5 response in allergy

Michael N. Teng Richard F. Lockey University of South Florida Tampa, USA

While the underlying inflammation in allergic asthma, allergic Key messages

rhinitis and atopic dermatitis is S ection A thought to result from the activity • Bronchial epithelial cells and skin keratinocytes play an important of Th2 cells, the innate (non-anti- role in asthma and atopic dermatitis gen specific) response to these in- • Type 2 innate lymphoid cells are essential for asthma progression sults provides key triggers for the • Dendritic cell subsets may play both pro and anti-inflammatory - Allergy from genetics to mechanisms initiation of the chronic inflamma- roles tion. • Epithelial cells, dendritic cells and innate lymphoid cells play a crucial role during the chronic phase of the allergic inflammation Innate immune responses begin by producing pro-inflammatory cytokines and chemokines that with sensing of insults by airway attract other inflammatory cells to affected tissues and skin epithelial cells. Non-spe- • Non-antigen specific innate immunity serves as the bridge to cific antigen recognition by epi- adaptive immune responses thelial cells occurs via pattern recognition receptors (PRR), which include both soluble (collectins) production are important for cells (ILC2, Neucytes) are impor- and cellular [Toll-like receptors antiviral defense. Airway epithe- tant for asthma pathogenesis. (TLR)] PRRs. Soluble PRRs recog- lial cells from subjects with asth- ILC2 are derived from a common nize the carbohydrate moieties ma have decreased levels of IFN lymphoid progenitor and related of microbes and can activate the production after viral infection, to NK and RORγt innate lymphoid complement cascade, initiating suggesting that IFN may play a cells (Figure 2). ILC2 respond to IL- inflammatory responses. Cellular protective role in preventing viral 25, IL-33, and TSLP stimulation by PRRs are better known for their asthma exacerbations. Production producing high levels of “Th2-type” interaction with pathogen-associ- of pro-inflammatory cytokines / cytokines (i.e., IL-5, -9, and -13) ated molecular patterns (PAMPs). chemokines (e.g., TNFα, IL-1, IL-6, upon stimulation. These cytokines Although TLRs are best known for IL-25, IL-33, TSLP) from epithelial can then activate eosinophils (via binding to products of microbes cells is the result of PRR activation IL-5, -13) and mast cells (via IL-9) and viruses, allergens also inter- of NFκB. as well as B and T lymphocytes act with TLRs (e.g., house dust Epithelial cells responding to aller- (Figure 1). In addition, secretion mite protein, Der p2 with TLR4). gen insult also produce IL-25, IL-33 of IL-13 induces mucus produc- Binding of TLRs and other cellular and thymic stromal lymphopoietin tion, smooth muscle contractility, PRRs triggers the production of (TSLP) (Figure 1). These cytokines and alternative activation of alve- interferon (IFN) and pro-inflam- have downstream effects on in- olar macrophages, which leads to matory cytokines and chemok- nate and adaptive immune cells. In amplification of IL-33 production. ines. Both type I and type III IFN particular, type 2 innate lymphoid ILC2 also secrete amphiregulin,

Innate immune response in allergy 43 Global atlas oF allergy

Allergens Mucus Viruses IFN

Airway epithelium

IL-25 IL-33 TSLP Areg Eosinophil IL-13 IL-9 DC IL-5 ILC2 IgE which may be involved in airway Mast cell remodeling. TSLP also drives the IL-4 maturation of immature lung dendritic cells (DC) to conventional

+ DC capable of presenting antigen CD4 T Th2 B to T cells. These allergen-activat- Figure 1 Innate immune response in asthma. Exposure to allergens or viruses ed DC then initiate the adaptive induces innate immune responses in airway epithelial cells. Viral infection in- immune responses characteristic duces type I and type III interferon (IFN) responses. Epithelial cells also secrete IL-25, IL-33, and TSLP, which activate type 2 innate lymphoid cells (ILC2) and of atopic airway disease. dendritic cells (DC). ILC2 cells produce “Th2-like” cytokines (e.g., IL-5, IL-9, and In summary, innate immunity plays IL-13). These cytokines then active eosinophils, mast cells, and goblet cells to a key role in initiating asthma. Rec- cause disease. ILC2 also produce amphiregulin (Areg) to induce airway remod- ognition of insults by AEC leads eling. Activated DC traffic to lymphoid organs to initiate T cell responses to the allergens/viruses to further disease pathogenesis. Adapted from ref. 3. to activation of ILC2, which produce Th2-type cytokines, and DC, which stimulate allergen-specific RORγt NK CD4+ T cell responses is necessary for asthma progression.

- Allergy from genetics to mechanisms KEY REFERENCES IL-7 1. Deckers J, Branco Madeira F, Ham- IL-15 mad H. Innate immune cells in asthma. Trends Immunol 2013;34:540-

S ection A Id2 547.

GATA3 2. Hirota JA, Knight DA. Human air- RORα way epithelial cell innate immunity: CLP ILCP γc cytokine ILC2 relevance to asthma. Curr Op Immu- Notch nol 2012;24:740-746. 3. Licona-Limon P, Kim LK, Palm MW, Flavell RA. Th2, allergy and group 2 GATA3 IL-4 innate lymphoid cells. Nat Immunol IL-5 2013;14:536-542. IL-9 4. Minnicozzi M, Sawyer RT, Fenton + IL-13 CD4 T Th2 MJ. Innate immunity in allergic disease. Immunol Rev 2011;242:106- Figure 2 Differentiation of ILC2 cells. ILC precursors (ILCP) are derived from 127. the common lymphoid progenitor (CLP) cells in an Id2-dependent process. ILCP 5. Vercelli D, Gozdz J, von Mutius E. are further differentiated into RORγt, NK, and ILC2 cells through the activities Innate lymphoid cells in asthma: of transcription factors (GATA3, RORα) and cytokines (IL-7, IL-15). CLP cells when innate immunity comes in a also differentiate into Th2 cells through thymic maturation. ILC2 and Th2 cells Th2 flavor. Curr Op Allergy Clin Im- secrete an overlapping set of cytokines. Adapted from ref. 3. munol 2014;14:29-34.

44 Innate immune response in allergy Global atlas oF allergy

6 Dendritic cells

Bart N. Lambrecht Gent University, Gent, Belgium

Key messages The adaptive immune response S ection A to allergens is characterized by a • Dendritic cells are one of the first immune cells that come into humoral arm (production of IgE contact with allergens at mucosal surfaces and can sample by B lymphocytes), and a cellular luminal antigens directly by extending dendrites across the

arm (CD8 and CD4 T lymphocytes epithelial barrier - Allergy from genetics to mechanisms that respond to the allergen in the • In the lymph node they report on the type of antigen encountered context of MHCI and MHCII mol- and subsequently induce CD4 T helper cell differentiation and ecules). Before adaptive immuni- CD8 T cell activation and transfer some of their encountered ty is induced to environmental or antigens to B cells food allergens, the allergen must • Lung and skin DCs also play a crucial role during the chronic get through the natural barriers of phase of the allergic inflammation, by producing chemokines the body (skin, mucus membranes) that attract other inflammatory cells to inflamed tissues and reach the cells of the immune • Unraveling how DCs induce and maintain Th2 immunity will system that are recirculating in provide new selective therapeutics targets for allergic diseases the lymph nodes (LN). Dendritic cells (DCs) are one of the first immune cells that come into contact epithelial cells and can sample lu- DCs originating from the lungs with allergens at mucosal surfac- minal antigens directly by extend- of house dust mite (HDM) al- es. In the lungs, intestine and skin, ing dendrites across the epithelial lergen-exposed mice are neces- DCs sit at the basolateral side of barrier (Figure 1). sary and sufficient to induce Th2 After antigen uptake, DCs migrate sensitization to HDM. Lung and to the draining LN and present the skin DCs also play a crucial role processed antigen to naïve T cells, during the chronic phase of the leading to clonal expansion and allergic response, by producing differentiation of antigen-specific chemokines that attract other in- T cells (Figure 2). Dendritic cells flammatory cells back to periph- arriving in the LN report on the eral tissues (Figure 2). In addition, type of pathogen or allergen that allergen-specific IgE and IgG1, has been encountered in the pe- through stimulation of FcεRI and riphery, and they subsequently FcγRIII respectively, target aller- induce CD4 T helper cell differen- gens to DCs thus boosting Th2 tiation (Figure 3), CD8 T cell acti- immunity further. During both Figure 1 Dendritic cells across the vation and transfer some of their sensitization and challenge, DCs epithelial barrier. encountered antigens to B cells. closely communicate with neigh-

Dendritic cells 45 Global atlas oF allergy

Figure 2 Role of dendritic cells in inflammation and T-cell polarisation.

Surface ligand Secreted

high IL-6 IL-4 OX40L Allergy/Parasites low IL-12 Th2 IL-5 CD86 T1/ST2L/IL-33 IL-13 Extracel, infections Jagged CCL2 ? TNFα

- Allergy from genetics to mechanisms ICOSL low IL-6 low IL-12 dim CD86 IL-2 IL-10 Tolerance IL-10 Treg dim CD80 Th0 TGFβ Fibrosis ? Jagged ? TGFβ

S ection A PGD2

high IL-6 Fungal infections Th17 IL-17 high TGFβ Autoimmunity

IL-23

high IL-6 IFN-γ α CD80 high IL-12 TNF Intracel. Infections Th1 Delta high IL-18 Cancer ICAM-1 CCL3 high IFNγ

Figure 3 Factors that affect T-cell differentiation.

46 Dendritic cells Global atlas oF allergy S ection A - Allergy from genetics to mechanisms Th2

Figure 4 The interaction of dendritic cells and epitelial cells drives the inflammatory process.

boring epithelial cells. Triggering ing the function of DCs in allergy cells initiate and maintain T help- of pattern recognition receptors constitutes a therapeutic avenue. er 2 cell-mediated immunity to on epithelial cells like the Toll-like However, eliminating the function house dust mite allergen. Immunity receptor 4 or protease activated of DCs completely would also in- 2013;38:322-335. receptors by allergens leads to the duce immunodeficiency, and it is 3. Lambrecht BN, Hammad H. The production of epithelial-derived much more important to unravel airway epithelium in asthma. Nat chemokines and cytokines (Fig- how DCs induce and maintain Th2 Med 2012;18:684-692. ure 4) that recruit DCs and that immunity selectively, to find new 4. Hammad H, Chieppa M, Perros F, program the DCs to induce Th2 therapeutics for allergy. Willart MA, Germain RN, Lambre- immune responses. Epithelial cells cht BN. House dust mite allergen and other innate immune cells also KEY REFERENCES induces asthma via Toll-like recep- make endogenous danger signals 1. Lambrecht BN, Hammad H. Lung tor 4 triggering of airway structural like uric acid, ATP and High Mobili- dendritic cells in respiratory viral cells. Nat Med 2009;15:410-416. ty Group Box 1 (HM-GB1) that can infection and asthma : from protec- 5. Kool M, Willart MA, van Nimwegen have the same effect on DCs. tion to immunopathology Ann Rev M, Bergen I, Pouliot P, Virchow JC Immunol 2012;30:243-270. et al. An unexpected role for uric Patients with atopic dermatitis, al- 2. Plantinga M, Guilliams M, Van- acid as an inducer of T helper 2 cell lergic rhinitis and asthma have in- heerswynghels M, Deswarte K, immunity to inhaled antigens and creased numbers of activated DCs Branco-Madeira F, Toussaint W inflammatory mediator of allergic armed with IgE in the inflamed et al. Conventional and mono- asthma. Immunity 2011;34:527- tissues. Not surprisingly, target- cyte-derived CD11b(+) dendritic 540.

Dendritic cells 47 Global atlas oF allergy

Natural killer cells and 7 natural killer-T cells

Günnur Deniz Istanbul University Istanbul, Turkey

Besides the heterogeneity of asthma pathogenesis, current knowl- Key messages edge underlines the dominance of a subgroup with Th2-like im- • Natural Killer (NK) cells display a potent regulatory function mune response and eosinophil- by secreting various cytokines or cell-to-cell contact and thus, ia. However allergic asthma may regulate innate and adaptive immune responses and maintain additionally involve innate, T cell immune homeostasis independent immune responses. • NK cells express subsets similar to T helper cells, such as NK1, Several different populations of NK2 and NK regulatory cells • Understanding the mechanisms enrolled in the development of innate lymphoid cells (ILC), in- allergic diseases are essential to develop strategies for treatment cluding natural killer (NK) cells, γδ and prevention T cells, and CD1-restricted NK1 • Recent developments in NK cell subsets support their role in cells have been previously impli- allergic diseases cated in the regulation of immune responses in the respiratory tract. - Allergy from genetics to mechanisms NK cells are innate lymphocytes, secreting and IFN-non-secreting nificantly higher, while γIFN- + NK which are a first line of defense NK cells strongly support this cells were not significantly lower against infection and cancer. The concept (Figure 1). The IFN-γ se- in allergic rhinitis patients com-

S ection A airways are a major route of en- creting NK subset showed a typ- pared to nonatopic controls. Since try of many important pathogens ical Th1-like cytokine pattern. In NK cells are important cells in in- into the body and the ability of contrast, the IFN-γ-non-secreting nate immunity and the initiation NK cells to respond rapidly to NK subset was composed of IL- of immune responses, their differ- infection suggests an important 4, IL-5 and IL-13-producing NK ent cytokine patterns may be im- role for these cells in acute pul- cells. These results demonstrate portant in changing the cytokine monary infection. Recent devel- that circulating NK cells retain milieu and the induction of T cell opments in our understanding effector subsets in humans with deviation. of NK cell subsets support their distinct cytokine profiles and may Natural killer-T (NK-T) cells are role in allergic diseases that may display different inflammatory unique CD1d-restricted T cells contribute to allergen-specific properties. In addition, it has been with NK cell surface markers. Th1 or Th2 cell generation as well reported that patients with aller- These cells may play an important induction or suppression of IgE. gic rhinitis had a higher percent- role in the pathogenesis of asthma. The in vivo and in vitro existence age and cytotoxicity of NK cells Invariant NK-T cells and not con- of human NK cell subsets, simi- compared to nonatopic patients. ventional MHC class II-restricted lar to Th1 and Th2 cells, with dis- The mean percentage of IL-4- and CD4+ T cells were found predomi- tinct cytokine patterns as IFN-γ IL-13-secreting NK cells were sig- nant in the lungs and bronchoalve-

48 Natural killer cells and natural killer-T cells Global atlas oF allergy

IL-22 NK22 IL-23 Protection of epithelial cell bariers

NK IL-2 NKreg IL-10, TGF-β

IL-12, IL-18 IL-4

Suppression of IgE NK2 production

IL-5, IL-13 S ection A NK1

Stimulation of IgE production - Allergy from genetics to mechanisms

IFN-γ Suppression of IgE production

Figure 1 NK cells are divided into four different subsets according to their cytokine secretion. NK cells have been detected in close contact to dendritic cells. NK cells grown in IL-12 and IL-18 (NK1) produce IFN-γ and inhibit IgE production, whereas NK cells grown in IL-4 (NK2) produce IL-5 and IL-13 and stimulate IgE production. NK reg cells produce IL-10 and TGF-β and suppress IgE production. IL-22 secreting NK22 subset might have a role in the protection of epithelial cell barriers. (Reprinted from J Allergy Clin Immunol, 132/3, Deniz G,van de Veen W, Akdis M. Natural killer cells in patients with allergic diseases, 527-35, Copyright 2013, with permission from Elsevier.)

olar lavage fluid of allergic asthma. 2. Pichavant M, Matangkasombut P, et al Regulatory NK cells suppress Although CD1d-restricted NK-T Dekruyff RH, Umetsu DT. Natural antigen-specific T cell responses. J cells might play a role in modulat- killer T cells regulate the develop- Immunol 2008;180:850-857. ing the asthmatic phenotype, they ment of asthma. Expert Rev Clin Im- 5. Deniz G, van de Veen W, Akdis M. are not the critical drivers of the munol 2009;5:251-260. Natural killer cells in patients with asthmatic response and at most 3. Mesdaghi M, Vodjgani M, Salehi allergic diseases. J Allergy Clin Im- play a modulatory role. E, Hadjati J, Sarrafnejad A, Bidad munol 2013;132:527-35. K et al. Natural killer cells in aller- 6. Deniz G, Akdis M, Aktas E, Blaser KEY REFERENCES gic rhinitis patients and nonatopic K, Akdis CA. Human NK1 and NK2 1. Scanlon ST, McKenzie AN. Type 2 controls. Int Arch Allergy Immunol subsets determined by purifica- innate lymphoid cells: new players 2010;153:234-238. tion of IFN-gamma-secreting and in asthma and allergy. Curr Opin Im- 4. Deniz G, Erten G, Kücüksezer UC, IFN-gamma-nonsecreting NK cells. munol 2012;24:707-712. Kocacik D, Karagiannidis C, Aktas E Eur J Immunol 2002;32:879-884.

Natural killer cells and natural killer-T cells 49 Global atlas oF allergy

Innate lymphoid 8 cells

Hirohisa Saito National Research Institute for Child Health & Development Tokyo, Japan

Definition and ontogeny Innate lymphoid cells (ILCs) are the Key messages cells having lymphoid morphology, but lacking recombination acti- • Innate lymphoid cells (ILCs) have lymphoid morphology, but lack vating gene (RAG)-dependent re- rearranged antigen receptors and myeloid and dendritic cell arranged antigen receptors. They markers also lack myeloid and dendritic • ILCs are derived from a committed ILC precursor cell markers (Lineage – (Lin-)). Ac- • Group 1 ILCs (ILC1s) release INF-γ, but not Th2 and Th17 cording to these definition, natural cytokines under the influence of IL-12 and IL-18 killer (NK) cells and lymphoid tis- • Group 2 ILCs (ILC2s) may play a role in allergic diseases and sue-inducer (LTi) cells are included eosinophilic inflammation by releasing the Th2 cytokines IL- into the ILC population. NK cells 5, IL-9 and IL-13, when stimulated with IL-25, IL-33 and thymic mediate initial immune responses stromal lymphopoietin against viruses and cancer cells. • Group 3 ILCs (ILC3s) may play a role in some chronic allergic LTi cells are essential for the for- diseases by releasing the Th17 cytokines IL-17 and IL-22

- Allergy from genetics to mechanisms mation of lymph nodes. ILCs can be divided into three but not IL-17, while NCR-‑ ILC3s ance against nematodes. Although groups. Group 1 ILCs (ILC1s) are are capable of producing IL-17, Th2 cells are a major source of defined by their capacity to pro-

S ection A but not IL-22. However, it should type 2 cytokines during asthmatic duce Th1 cytokine IFNγ and the be noted that some NCR-‑ILC3s and allergic reactions, ILC2s also inability to produce Th2 cell- and contribute to disease pathology, TH17 cell-associated cytokines. can also produce IL-22. Recently, especially where IL-25, IL-33 and They develop under the influence it was suggested that ILCs are de- TSLP are released by inflamed and of IL-12 and IL-18. Group 2 ILCs rived from a committed ILC pre- damaged epithelia. Human ILC2s (ILC2s) are capable of producing cursor, which is developmentally have similar properties with their Th2 cytokines (IL-5, IL-9 and IL-13) unrelated to NK and LTi cells. murine counterparts. In addition, in response to epithelium-derived human ILC2s express CRTh2 (che- cytokines IL‑25, IL‑33 and thym- Role of ILCs in allergy moattractant receptor-homolo- ic stromal lymphopoietin (TSLP). ILC2s include Lin- SCA1+ natural gous molecule expressed on Th2 Group 3 ILCs (ILC3s) can produce helper cells found in fat-associat- cells) on their surface. Th17 cytokines IL-17 and/or IL-22 ed lymphoid clusters, Lin-SCA1+ in the presence of IL-1β and IL-23. nuocytes and Lin-SCA1- innate IL-17-producing ILC3s play a role Some ILC3s express the natural helper 2 cells derived from lymph in neutrophilic inflammation in a cytotoxicity triggering receptor nodes of IL-25 and/or IL-33-inject- particular endotype of asthma via (NCR) NKp46 (NCR+ ILC3s). The ed or N. brasiliensis-infected mice. production of IL-1β by macrophag- NCR+ ILC3s can produce IL-22, ILC2s are important in host resist- es stimulated with damage-associ-

50 Innate lymphoid cells Global atlas oF allergy

CLP

B cell

α4β7+ T cell

α4β7? S ection A

γ high PLZFhigh NKP LTiP ROR t ILCP - Allergy from genetics to mechanisms

Gfi1 RORγt T-bet RORγt GATA3 RORα

NCR+ IL-12 ILC3 - IL-18 NCR NK LTi ILC2 ILC1 ILC3

IL-12 IL-23 IL-25 IL-12 IL-23 IL-18 IL-1β IL-33 IL-18 IL-1β TSLP

IL-17 IL-5 IFNγ IL-9 IFNγ IL-22 IL-17 IL-22 IL-13

Figure 1 Ontogeny of innate lymphoid cells (ILCs). A committed ILC precursor (ILCP) having a high level of transcriptional factor PLZF (2) can give rise to ILC1s, ILC2s and ILC3s, but not to LTi cells and NK cells, which originate from a α4β7+ common progenitor shared with the three ILC lineages. Development of ILC2s depends on the transcription factors Gfi1, GATA3 and RORα. ILC3s require the transcription factor RORγt for their development and function. Although NCR+ ILC3s can give rise to ILC1s if stimulated with IL-12 and IL-18, the differentiation pathway of ILC1s is not fully understood yet.

Innate lymphoid cells 51 Global atlas oF allergy

Protease PAMPs Allergen

Goblet cell hyperplasia DAMPs IL-25 IL-33 IL-13 TSLP IL-22 Macrophage

IL-1β ILC3 ILC2

IL-17 IL-5 - Allergy from genetics to mechanisms Neutrophilic Eosinophilic Inflammation Inflammation

S ection A Figure 2 The role of ILCs in allergy. Epithelial tissues can release IL-25, IL-33 and TSLP in response to protease allergens such as house dust mites or papain, DAMPs, PAMPs and TH2 cytokines. In response to the epithelium-derived cytokines ILC2s can release IL-13, which induces inflammation and remodeling (such as goblet cell hyperplasia) in the tissue, and IL- 5, which can induce eosinophilic inflammation. ILC3s release IL-17, which can induce neutrophilic inflammation, and IL-22, which inhibits the release of ILC2-activating cytokines.

ated molecular patterns (DAMPs) KEY REFERENCES 3. Walker JA, Barlow JL, McKenzie and/or pathogen-associated mo- 1. Spits H, Artis D, Colonna M, Diefen- AN. Innate lymphoid cells--how lecular patterns (PAMPs). The bach A, Di Santo JP, Eberl G, et al. did we miss them? Nat Rev Immunol expression of the IL-10 family Innate lymphoid cells-a proposal 2013;13:75-87. for uniform nomenclature. Nat Rev cytokine IL-22, which is capable 4. Kim HY, Lee HJ, Chang YJ, Picha- Immunol 2013;13:145-149. of being released from ILC3s, LTi vant M, Shore SA, Fitzgerald KA, et 2. Constantinides MG, McDonald BD, cells or Th17 cells, is increased in al. Interleukin-17-producing innate Verhoef PA, Bendelac A. A commit- chronic allergic inflammation in ted precursor to innate lymphoid lymphoid cells and the NLRP3 in- the lung and skin. IL-22 inhibits cells. Nature 2014 [Epub ahead flammasome facilitate obesity-as- the production of ILC2-activating of print Feb 9] doi: 10.1038/na- sociated airway hyperreactivity. cytokines, IL-25 and IL-33. ture13047. Nat Med 2014;20:54-61.

52 Innate lymphoid cells and allergy Global atlas oF allergy

9 Mast cells

Stephen J. Galli Stanford University Stanford, USA

What are mast cells? In humans and other vertebrates, Key messages

mast cells reside in virtually all S ection A tissues, often close to epithelial • Mast cells develop in essentially all tissues from precursors that surfaces (e.g., the skin, respira- circulate in the blood tory system, and gastrointesti- • Mast cells are major sources of histamine and other products nal tract) and near blood vessels, (mediators) that contribute to anaphylaxis and other allergic - Allergy from genetics to mechanisms nerves, smooth muscle cells and disorders fibroblasts. Mast cell precursors • Mast cells can be rapidly activated (within minutes) to release are generated in the bone mar- mediators when allergens are recognized by IgE antibodies row, circulate in the blood, and bound to IgE receptors (FcεRI) on the cells’ surface then enter the tissues where they • Mast cells also can be activated to release mediators by many complete their maturation, be- agents that act independently of IgE coming cells with many prominent • Mast cells can have beneficial roles in enhancing resistance to cytoplasmic granules (Figure 1A animal venoms and in host defense against certain parasites & C). These granules are storage sites for mast cell products (often called “mediators”) that, when re- of allergic diseases or parasite in- of the IgE-bound FcεRIs, signaling leased by the cell, have powerful fections, and in other settings. the cells to release their products effects on other cell types. Mast (Figure 1B & D). Mast cells also can cell granules contain most of the How can mast cells be be activated independently of IgE, body’s histamine and virtually all activated to release their e.g., by products of microorgan- of its heparin, as well as a variety products? isms, certain neuropeptides, and of proteases (Table 1). When mast Mast cells express on their sur- compounds present in animal ven- cells are “activated” (i.e., stimulat- face hundreds of thousands of oms (Table 2). ed to release their products), they high affinity receptors (FcεRI) that When large numbers of mast cells release histamine, heparin and strongly bind the Fc portion of IgE are rapidly activated by the sys- proteases by “degranulation” (Fig- antibodies. Individual mast cells temic distribution of an allergen ure 1B & D), and they also secrete can bind IgEs which recognize in subjects who have IgE recog- many other mediators that are not any of a variety of different aller- nizing that allergen, anaphylaxis stored, but are synthesized by the gens derived from pollens, foods, can occur within minutes. Such activated cells, including leukot- dust mites, medicines, etc. Such IgE-dependent anaphylaxis is ab- rienes, prostaglandins, cytokines, mast cells can be activated when sent or markedly diminished in chemokines and peptide growth they encounter any antigens that mice genetically lacking mast cells factors (Table 1). Mast cell num- cross-link two adjacent IgE mole- (even though they have basophils, bers can increase in tissues at sites cules, which results in aggregation another bone marrow-derived cell

Mast cells 53 Global atlas oF allergy

Figure 1 (A, C) A resting mast cell (shown in a transmission electron micrograph in A and as a cartoon in C) contains many cytoplasmic granules (indicated by arrows in A) and has allergen-specific IgE (yellow symbols in C) bound to FcεRI receptors (green symbols in C) on its surface (B, D). When allergen (red symbols in D) is recognized by adjacent IgE antibodies bound to the mast cell’s FcεRI receptors, this aggregates the FcεRIs on the cell’s surface, activating the mast cell to release its granule contents at points where the granules fuse with the plasma membrane (indicated by arrows in a transmission electron micrograph in B and as a cartoon in D). Such activated mast cells also secrete newly synthesized products that are not stored in the granules. (Modified from Fig. 9.44 in Parham P. The Immune System. 3rd edition, Copyright 2009 from The Immune System by Parham. Reproduced by permission of Garland Science/Taylor & Francis LLC. The electron micrographs in A & B are courtesy of Ann M. Dvorak.)

TABLE 1 Mast Cell Products

Products Biological effects*

- Allergy from genetics to mechanisms Stored preformed in • Increases vascular permeability and blood vessel dilatation granules and secreted • Contracts airway smooth muscle Histamine upon activation (in • Causes itching and pain minutes) • Influences immune responses and the function of some nerves

S ection A • Anticoagulant Heparin • Required for storage of other products in granules Proteases (e.g., • Degrade certain proteins and peptides, including components of tryptase, chymase, animal venoms carboxypeptidase • Regulate tissue remodeling A3) • Converts angiotensin I to angiotensin II (chymase) Synthesized and se- • Regulate migration and function of leukocytes creted upon activation • Increase vascular permeability Lipid mediators (beginning in minutes • Induce constriction or dilatation of blood vessels (depending on (e.g., leukotrienes, for lipid mediators, the type of mediator) prostaglandins) extending over hours • Contract or relax smooth muscle (airways, gastrointestinal tract) for peptide products†) • Enhance mucus secretion Cytokines, chemok- • Many effects on other cells (both leukocytes and tissue structural ines, peptide growth cells) that can promote or suppress inflammation and/or tissue re- factors modeling * Only some of the many biological effects of these products are listed. † Some of these can be present in granules and therefore also can be released rapidly upon mast cell activation.

54 Mast cells Global atlas oF allergy

TABLE 2 Mechanisms of mast cell activation*

Activation mechanisms† Settings in which this occurs Comments

Anaphylaxis, allergic rhinitis, The site of mast cell activation depends on the Cross-linking of IgE bound to mast cell atopic dermatitis, allergic site of exposure to the antigen; in anaphylaxis, surface FcεRI by multivalent antigen asthma, some types of urti- there is systemic distribution of the offending recognized by the IgE caria antigen throughout the body.

Reaction of microbial products or products of damaged or dead cells Various types of viral or bac- Exposure of mast cells to some of these prod- with receptors (Toll-like receptors or terial infections; diverse set- ucts cells can influence how the mast cells re- other pattern recognition receptors) tings in which cell damage or spond to other activation signals, such as IgE on the mast cell surface or inside the cell death occurs and antigen. mast cell

Endogenous peptides that can activate some Reaction of endogenous peptides Various disease processes or types of mast cells include certain neuropep- with receptors for those peptides on mechanisms of host defense tides, endothelin-1, and products of comple- the mast cell surface that maintain health ment activation (C3a, C5a). S ection A Some of these venom peptides are structur- ally similar to endogenous peptides that can Reaction of exogenous peptides with Envenomation by venomous also activate mast cells; mast cell proteases receptors on the mast cell surface reptiles released when the activated mast cells de- - Allergy from genetics to mechanisms that recognize such peptides granulate can degrade and thereby reduce the toxicity of some components of the venoms.

* In addition to mechanisms that activate mast cells, certain stimuli can diminish the extent of mast cell activation. † Mast cells activated by IgE and specific antigen can release many or all of the products listed in Table 1. By contrast, other activation mechanisms can result in the relatively selective release of granule-stored products (e.g., in response to certain peptides) or cytokines, chemokines and growth factors (e.g., in response to certain microbial products). type that can bind IgE), showing mast cells did not develop in order shansky K, Lichtman MA, Beutler that mast cells importantly con- to cause disease. Likely beneficial E, Kipps TJ, Seligsohn U, Prchal JT, tribute to this acute, catastroph- roles of mast cells include enhanc- eds. Williams Hematology, 8th ed. ic and potentially fatal reaction. ing host resistance to some par- New York: McGraw-Hill Medical, Through effects of released mast asites and other pathogens and 2010;63:915-932. cell products on inflammation enhancing innate and acquired re- 2. Galli SJ, Tsai M. IgE and mast and structural cells in the affected sistance to certain animal venoms. cells in allergic disease. Nat Med tissues (Table 1), IgE-dependent Mast cells also have the potential 2012;18:693-704. mast cell activation can contribute to limit the pathology associated 3. Reber L, Marichal T, Galli SJ. New to late phase reactions (that devel- with certain innate or acquired models for analyzing mast cell op hours after allergen exposure) immune responses through the functions in vivo. Trends Immunol and to the features of chronic al- production of mediators with an- 2012;33:613-625. lergic inflammation (e.g., in allergic ti-inflammatory or immunosup- asthma). pressive effects. 4. Marichal T, Starkl P, Reber LL, Kale- snikoff J, Oettgen HC, Tsai M, Metz Do mast cells contribute KEY REFERENCES M, Galli SJ. A beneficial role for to health, or only to 1. Galli SJ, Metcalfe DD, Arber DA, Immunoglobulin E in host defense disease? Dvorak AM. Basophils and mast against honeybee venom. Immunity From an evolutionary perspective, cells and their disorders. In: Kau- 2013;39:963-975.

Mast cells 55 Global atlas oF allergy

10 Basophils

Hajime Karasuyama Tokyo Medical and Dental University Tokyo, Japan

Basophils are the least abundant granulocytes, and represent less Key messages than 1% of peripheral blood leukocytes. They were first document- • Basophils have long been neglected in immunological studies, ed by Paul Ehrlich more than 100 owing to their small numbers and phenotypic similarity to mast years ago, but their functional sig- cells nificance remained enigmatic for a • The finding that basophils secrete large quantities of Th2 long time. Basophils share certain cytokines (IL-4 and IL-13) ended the long-held view of basophils features with tissue-resident mast as minor relatives of mast cells with little function • Basophils normally circulate in the blood, and are recruited to cells, including the presence of ba- affected tissues in various allergic disorders, including allergic sophilic granules in the cytoplasm, rhinitis, chronic urticaria, atopic dermatitis, and asthma the surface expression of IgE re- • Recent development of analytical tools in mouse models has ceptor (FcεRI), and the release of identified pivotal and nonredundant roles for basophils in a chemical mediators in response variety of immune responses, including allergy to various stimuli (Table 1). There-

- Allergy from genetics to mechanisms fore, they have often erroneously been considered as minor and re- mast cells may play distinct roles in allergic reactions. Indeed, baso- dundant relatives or precursors of in vivo, no definitive evidence for phils have been demonstrated to tissue-resident mast cells. Indeed,

S ection A it has been provided until recently. infiltrate affected tissues in var- in clinical settings, basophils have Basophils release preformed his- ious allergic disorders, including been used, as surrogates of less tamine, newly synthesized leukot- allergic rhinitis, chronic urticaria, accessible tissue mast cells, for the in vitro quantification of immedi- riene C4, and Th2 cytokines (IL-4 atopic dermatitis, and asthma. ate-type response to allergens in and IL-13), all of which are involved However, the overwhelming influx allergic patients. TABLE 1 Basophils circulate in the periph- Difference between basophils and mast cells eral blood, and are rarely present in peripheral tissues under home- Basophils Mast cells ostatic conditions, in contrast to Place of birth bone marrow bone marrow mast cells. The half-life of circulating basophils is estimated at Place of maturation bone marrow peripheral tissues approximately 2 days, while mast Anatomical localization peripheral blood peripheral tissues cells survive for months in periph- Life span short (several days) long (weeks or months) eral tissues. Although these differ- Proliferation capability - + ences suggest that basophils and

56 Basophils Global atlas oF allergy

Basophils Basophils in Basophils in in diseases protective immunity regulation of immunity

Protection against Promotion of Allergy Ectoparasites Th2 cell differentiation

Basophils function as IL-4 Allergic rhinitis Tick infestation producers and antigen-presenting cells Chronic cutaneous allergic inflammation Systemic anaphylaxis Protection against Enhancement of Eosinophilic esophagitis Endoparasites humoral memory response etc. Basophil-derived factors Helminth infection stimulate memory B and T S ection A cells

Generation of - Allergy from genetics to mechanisms Autoimmunity M2-type macrophage

Basophil-derived IL-4 Lupus nephritis acts on monocytes and macrophages

Figure 1 Previously unappreciated roles of basophils revealed by mouse studies. of eosinophils in these responses parasites (ticks and intestinal hel- KEY REFERENCES has long overshadowed the signif- minths), and regulation of innate 1. Karasuyama H, Mukai K, Obata K, icance of basophil infiltration and and acquired immunity (gener- Tsujimura Y, Wada T. Nonredun- it has remained uncertain whether dant roles of basophils in immunity. ation of Th2 cells and M2-type Annu Rev Immunol 2011;29: 45-69. basophils play a crucial role or are macrophages, and enhancement just redundant with mast cells. 2. Falcon, F.H., Knol, E.F., Gibbs, B.F. of humoral immunity) (Figure 1). The role of basophils in the patho- Recent development of analyti- Of note, the number of basophils genesis of allergic disease. Clin Exp cal tools for basophil function in recruited to affected tissues of Allergy 2011;41:939-947. vivo, including basophil-deficient model mice is much smaller than 3. Schroeder JT. Basophils: emerging roles in the pathogenesis of mice, has identified pivotal and that of eosinophils, as observed in nonredundant roles for basophils allergic disease. Immunol Rev allergic patients, suggesting that 2011;242:144-160. in a variety of immune responses basophils may also play key roles in mouse models, such as allergic 4. Siracusa MC, Kim BS, Spergel JM, in the development and exacerba- Artis D. Basophils and allergic in- reactions (allergic rhinitis, chronic tion of human allergic disorders in flammation. J Allergy Clin Immunol cutaneous allergic inflammation, 2013;132:789-801. spite of their paucity. Therefore, systemic anaphylaxis, and eosin- 5. Voehringer D. Protective and basophils and their products could ophilic esophagitis), autoimmun- pathological roles of mast cells ity (lupus nephritis), protective be promising targets for the treat- and basophils. Nat Rev Immunol immunity against infections with ment of allergic disorders. 2013;13:362-75.

Basophils 57 Global atlas oF allergy

11 Eosinophils

Hans-Uwe Simon University of Bern Bern, Switzerland

Eosinophils are terminally differentiated granulocytic effector Key messages cells that produce and store biologically active molecules, includ- • Eosinophils are multifunctional cells ing cytotoxic proteins, lipid medi- • Eosinophilia in allergic diseases is largely mediated by IL-5- ators, chemotactic peptides, and producing T cells cytokines. They are considered as • Eosinophils can cause organ dysfunction by both cytotoxicity multifunctional cells able to mod- and fibrosis ulate both innate and adaptive • Specific anti-eosinophil therapies have been shown to be effective in asthma immunity (Fig. 1). Eosinophils are generated in the bone marrow under the influence of eosinopoie- tins (IL-3, IL-5, GM-CSF), released to peripheral blood upon matura- that reduce eosinophil numbers bronchoconstriction. Moreover, eosinophils can amplify T helper tion, and mainly reside in the he- are usually effective in allergic dis- 2 immune reactions by the gener- - Allergy from genetics to mechanisms eases. Moreover, the numbers of matopietic and lymphatic organs, eosinophils in sputum have been ation of cytokines. A role for eo- such as the bone marrow, spleen, shown to predict the success of sinophils in experimental asthma lymph nodes, and thymus. The anti-eosinophil therapies in asth- has been demonstrated in eosino- normal eosinophil blood count

S ection A matic patients. For example, tai- phil-deficient mice, which demon- ranges from 50 to 500 x 109/L. loring of asthma treatment based strated reduced T cell recruitment Eosinophil numbers can increase on sputum eosinophils is effective and mucus production, as well as in various inflammatory reactions, in decreasing asthma exacerba- reduced bronchial hyperreactivity. including allergic diseases. Several tions. proposals for the classification of Eosinophils also play a role in tis- eosinophil-related disorders have The exact role of eosinophils in sue repair and remodeling pro- been published. In allergic diseas- the pathogenesis of allergic dis- cesses. Specific anti-eosinophil es, eosinophilia is largely mediat- eases is currently a topic of inten- treatment by using anti-IL-5 an- ed by IL-5 - producing T cells. sive research. In asthma, eosin- tibodies was associated with re- ophil-derived cytotoxic proteins duced fibrosis in allergic asthma Clinical observations point to a and reactive oxygen species have and eosinophilic esophagitis. The potential role of eosinophils in the been shown to damage bronchial peribronchial fibrosis was also pathogenesis of allergic diseases. epithelial cells, leading to a bar- reduced in experimental asthma Eosinophil numbers in blood and rier defect. Eosinophils are also a induced in eosinophil-deficient eosinophil tissue infiltration of- source of lipid mediators, such as mice. Therefore, eosinophils can ten correlate with the severity of leukotriene C4 and platelet-ac- contribute to organ dysfunction the disease. Therefore, therapies tivating factor, which can cause by both cytotoxicity and fibrosis.

58 Eosinophils Global atlas oF allergy

A Bone B marrow Blood Tissue Activation

IL-5 GM-CSF IL-3

C S ection A Granule proteins Killing of pathogens DNA & ROS tissue damage - Allergy from genetics to mechanisms

Activation Cytokines Immune regulation Lipid mediators

Cytokines Remodeling MMP-9

Figure 1 Tissue infiltration and role of eosinophils in diseases. (A) Eosinophils originate from multipotent and lineage- restricted hematopoietic progenitor cells. They mature in the bone marrow under the influence of eosinophilopoietic cytokines (IL-3, IL-5, and GM-CSF). Mature eosinophils are released in the peripheral blood and can infiltrate inflammatory tissues as it occurs in allergic diseases. At sites of inflammation, eosinophils are activated and their apoptosis is delayed (reviewed by Geering B, Stoeckle C, Conus S, Simon HU. Living and dying for inflammation: neutrophils, eosinophils, basophils. Trends Immunol 2013;34:398-409). Under non-inflammatory conditions, eosinophils undergo apoptosis without infiltration of organs outside the hematopoietic and lymphatic systems. (B) An example of eosinophil tissue infiltration: Eosinophil infiltration of the dermis in a patient with drug allergy. The tissue section was stained with hematoxylin and eosin (original magnification x63). (C) Eosinophils are multifunctional cells. Following activation of eosinophils, they release granule proteins and reactive oxygen species (ROS), which are able to kill pathogens, but also tissue cells possibly causing organ dysfunction. Eosinophils additionally release mitochondrial DNA, which forms together with granule proteins eosinophil extracellular traps (reviewed by Simon D, Simon HU, Yousefi S. Extracellular DNA traps in allergic, infectious, and autoimmune diseases. Allergy 2013;68:409-416). By releasing cytokines and lipid mediators, eosinophils are further involved in immune regulation and remodeling events.

KEY REFERENCES al on criteria and classification of allergy. Ann Rev Pharmacol Toxicol 1. Simon D, Simon HU. Eosinophilic eosinophilic disorders and related 2014;55:in press. disorders. J Allergy Clin Immunol syndromes. J Allergy Clin Immunol 2007;119:1291-1300. 2012;130:607-612. 4. Rosenberg HF, Dyer KD, Foster PS. Eosinophils: changing perspectives 2. Valent P, Klion AD, Horny HP, Rou- 3. Radonjic-Hoesli S, Simon HU. fosse F, Gotlib J, Weller PF et al. Novel targeted therapies for eo- in health and disease. Nat Rev Im- Contemporary consensus propos- sinophil-associated diseases and munol 2013;13:9-22.

Eosinophils 59 Global atlas oF allergy

12 T cells

Carsten B. Schmidt-Weber Technical University Munich and Helmholtz Center Munich, Germany

Immune memory - good against bugs, bad for Key messages allergic and autoimmune diseases • Allergy is dependent on the immunologic memory as it re-occurs The potency of the immune mem- regularly ory is assumed to be a key event • Allergic symptoms correlate with T cell activation particularly of in the evolution that allowed the the Th2 type success of larger organisms over • T cells do also react to allergens in asymptomatic patients and smaller sized creatures and gen- may mediate allergen tolerance by active immune suppression erated longer-lived organisms. However, the ability to remember pathogens has also its downsides. variability and, thus, an extend- memory cells are able to quickly ed repertoire of TCRs that cover expand and reproduce an immune A key feature of allergy is that most determinants of our environ- response that has been proven to the symptoms occur again every ment is generated. Apart from the be successful. It is anticipated that season. This is similar to the im- sophisticated structure of TCRs, the generation of memory cells is - Allergy from genetics to mechanisms munologic feature that memoriz- the activation and differentiation underlying successful immuniza- es determinants on pathogens or of these cells is integrating mul- tions (vaccination) against infec- other harmless structures such tiple signals from the tissue, the tious agents. Hyposensitisation as autoantigens or allergens. The S ection A immune system and the external by allergen-specific immunother- inappropriate immune response environment. This integration pro- apy (AIT) may also be governed by caused by dysregulation of the im- cess involves antigen-presenting memory populations. munologic tolerance is underlying cells (APC) that need to digest the autoimmune and allergic diseases. environmental allergen/antigen Decision making in the Both memory and immune toler- and present it in a molecule with immune system ance are mediated by T lympho- similar high diversity as the TCR. The decision making process is cytes, which recognize immu- Major histocompatibility com- subject of immunology research nogenic structures by the T-cell plexes, (MHC) bring the digested and has the intention to solve the receptor (TCR). This receptor is peptides to the surface of the APC “black box” of immune tolerance characterized by a very high varia- and also deliver additional signals mechanisms. The goals are to bility that is generated by multiple that are essential for the activa- prevent the loss of immune tol- gene-segment cassettes that are tion or deactivation of T cells. The erance by means of public health alternatively rearranged to gen- successful activated T cell will di- initiatives (e.g. pollution control, erate a final gene product. Further vide and after the termination of dietary advices etc.), to increase variation is introduced by a flexi- an immune response some cells effectiveness of specific immuno- ble fusion process that increases (memory cells) will remain. These therapy and similar vaccination

60 T cells Global atlas oF allergy

spec. spongiosis remodeling, bronchiale itch immediate type acute inflammation asymptomatic immunity unspec. immunity hypersensitivity reactions anti- "remodeling"? reactions shedding inhibition of MHC airway - microbial tissue S ection A I & II "remodelling" homeostatis Figure 1 Different T cell phenotypes arise from naïve (resting, not antigen-experienced T cells) upon activation by antigen-presenting cells and by decision cytokines (not shown). The figure highlights a variety of responding cells both of

the immune system as well as from non-immune (mesenteric) origin. - Allergy from genetics to mechanisms

strategies and to develop new Terminating immune immunology. J Allergy Clin Immunol therapies that prevent severe tis- responses 2007;120:247-254. sue damage as it occurs in the gut, This holds particularly true for 2. Stott B, Lavender P, Lehmann S, skin and airways. The decision of the immune system. T regulatory Pennino D, Durham S, Schmidt-We- the immune system is reflected by (Treg) cells represent a key discov- ber CB. Human IL-31 is induced by the T lymphocyte activity, mainly ery that falls into this category, as IL-4 and promotes TH2-driven in- by their secreted mediators, in- they are actively suppressing oth- flammation. J Allergy Clin Immunol terleukins (IL). Interleukins are er immune cells particularly Th1, 2013;132:446-54 e5. typically of the “Th2”-type includ- -2 and-17 cells. In fact, healthy 3. Eyerich S, Onken AT, Weidinger ing IL-4, IL-5 and IL-13, whereas individuals are showing immune S, Franke A, Nasorri F, Pennino D, autoimmune or pathogen-trigged activation in vitro, suggesting that et al. Mutual antagonism of T cells T cells usually express “Th1- or mechanisms exist that keep these causing psoriasis and atopic ecze- Th17-type” IL’s and interferons processes under asymptomatic ma. N Engl J Med 2011;365:231- (IFN) such as IFN-γ or IL-17. IL-4 control. Novel immune regulato- 238. produced by T cells is essential for ry T cell phenotypes are hypothe- 4. Akdis M, Verhagen J, Taylor A, Kar- the production of IgE, the diagnos- sized to mediate anti-inflammato- amloo F, Karagiannidis C, Crameri tic key parameter in the detection ry signals also to tissue cells. AIT is R, et al. Immune responses in of allergies. The interleukins have assumed to generate Treg cells and healthy and allergic individuals are various functions and are charac- future research and novel phar- characterized by a fine balance be- terizing the regulatory impact of maceutical strategies are aiming tween allergen-specific T regulato- T cells on other immune cells and to reinforce these mechanisms in ry 1 and T helper 2 cells. J Exp Med on tissue cells. The exploration order to re-construct immune tol- 2004;199:1567-1575. of T cell mediated signals on tis- erance under minimal influence on 5. Pennino D, Bhavsar PK, Effner R, sue cells is just beginning and it is anti-pathogen responses. Avitabile S, Venn P, Quaranta M, already revealed that T cells can et al. IL-22 suppresses IFN-gam- directly mediate tissue pathology KEY REFERENCES ma-mediated lung inflammation such as epithelial damage or colla- 1. Schmidt-Weber CB, Akdis M, Akdis in asthmatic patients. J Allergy Clin gen deposition (Figure 1). CA. TH17 cells in the big picture of Immunol 2013;131:562-570.

T cells 61 Global atlas oF allergy

13 B cells

Azza Abdel-Gadir Talal Chatila Harvard Medical School Boston, USA

B cells are crucial in allergic diseases by virtue of their production Key messages of allergen-specific IgE antibodies, which play a key role in instigat- • By their production of allergen-specific IgE antibodies B cells ing immediate hypersensitivity contribute to the pathophysiology of a wide range of allergic reactions and contribute to the diseases + pathophysiology of a wide range • CD4 Th2 cells that produce IL-4 and express CD40L orchestrate of allergic diseases ranging from the IgE-switch and differentiation of B cells asthma, atopic dermatitis, food • The recently described B regulatory cells inhibit over-activated immune responses and drug allergy, amongst others. • Elucidating mechanisms regulating the bifurcation of B cell IgE-production by B cells entails responses into B regulatory versus IgE-producing cells holds class-switch recombination at the promise for therapeutic interventions immunoglobulin heavy chain locus into the IgE heavy chain (Cε). CD4+ Th2 cells that produce IL-4 and of each pathway to the generation given to regulatory B (Breg) cells - Allergy from genetics to mechanisms express CD40L orchestrate the of disease-promoting pathogenic that inhibit over-activated im- differentiation of IgE-switched B IgE antibodies remains to be es- mune responses. Several groups cells. It has been suggested that tablished (Figure 1). have proposed that a reduction there are two pathways for IgE

S ection A in Breg cells worsens symptoms production after secondary expo- The highly variable correlation be- of allergic disease such as contact sure to antigen. tween the levels of allergen-spe- hypersensitivity and anaphylax- cific IgE antibodies and suscepti- The first involves the differen- is. Breg cells are characterized by bility to anaphylaxis indicates that tiation of IgE-switched plasma their production of the negative other factors, such as IgG antibod- cells from IgG1+ precursors by regulatory cytokines, IL-10 and ies, have profound influences on sequential switching from Cγ1 TGF-β. An increased number of IgE-mediated responses. Immuno- to Cε, leading to the production IL-10-producing B cells has been therapy to aeroallergens has been of high affinity IgE antibodies by found in S. mansoni worm infection shown to stimulate the production somatic hypermutation (affinity and the in vivo transfer of these of allergen-specific IgG1 and IgG4 maturation). The second pathway cells prevents recipient mice from antibodies, that protect against involves the direct differentiation anaphylaxis. Breg cells proliferate disease by inhibiting allergen in- of IgE+ memory B cells generated when stimulated with the milk an- teraction with FcεRI-bound IgE on during the primary immune re- tigen casein in milk tolerant but mast cells and basophils, thus pre- sponse into plasma cells, leading not in milk allergic patients. Akdis venting their degranulation. to a robust recall IgE antibody re- and colleagues recently found in- sponse. The relative contribution Recently, much attention has been creased suppressive IL10+ Breg

62 B cells Global atlas oF allergy

cells in non-allergic beekeepers undergoing allergen-specific immunotherapy and high-dose venom exposure. They revealed that Breg cells are specifically developing into IgG4-producing plasma cells (Figure 2). Thus, elucidating mechanisms regulating the bifurcation of B cell responses into Breg versus IgE producing cells holds promise for therapeutic interventions.

KEY REFERENCES 1. Larché M, Akdis CA, Valenta R. Im- munological mechanisms of allergen-specific immunotherapy. Nat Rev Immunol 2006;6:761-771.

2. Xiong H, Dolpady J, Wabl M, Cu- S ection A rotto de Lafaille MA, Lafaille JJ. Figure 1 Pathways for the generation of memory B cells. The interaction of Sequential class switching is re- Th2 cells with allergen-specific B cells may lead to switching into either IgE+ or quired for the generation of high

IgG1+ memory B cells. The former would differentiate directly to IgE+ plasma affinity IgE antibodies. J Exp Med - Allergy from genetics to mechanisms cells upon recall responses, while the latter would first undergo switching from 2012;209:353-364. Cγ1 to Cε before further differentiating into plasma cells. 3. Talay O, Yan D, Brightbill HD, Straney EE, Zhou M, Ladi E, et al. IgE+ memory B cells and plasma cells generated through a germinal-center pathway. Nat Immunol 2012;13: 396–404. 4. Lee JH, Noh J, Noh G, Choi WS, Cho S, Lee SS. Allergen-specific transforming growth factor-β-producing CD19(+)CD5(+) regulatory B-cell (Br3) responses in human late eczematous allergic reactions to cow’s milk. J Interferon Cytokine Res 2011;31: 441–449. 5. Amu S, Saunders SP, Kronenberg M, Mangan NE, Atzberger A, Fal- lon PG. Regulatory B cells prevent and reverse allergic airway inflammation via FoxP3-positive T regulatory cells in a murine model. J Allergy Clin Immunol 2010;125: 1114–1124. 6. van de Veen W, Stanic B, Yaman G, Wawrzyniak M, Sollner S, Akdis DG, et al. IgG4 production is confined to Figure 2 Opposing actions of IgE and IgG4 in allergic responses. Allergen- human IL-10-producing regulatory specific IgG4, generated during immunotherapy, blocks the interaction of B cells that suppress antigen-spe- allergens to IgE and abrogates IgE-dependent effector responses. Regulatory cific immune responses. J Allergy B cells may promote tolerance by differentiating into allergen-specific IgG4- Clin Immunol 2013;131:1204– producing plasma cells. 1212.

B cells 63 Global atlas oF allergy

Immunoglobulin E and 14 other antibodies in allergy

Hannah Gould Yih-Chih Chan King’s College London London, United Kingdom

Immunoglobulin E (IgE) is one of five antibody classes, IgM, IgD, Key messages IgG, IgA and IgE, in mammals (Fig- ure 1). There are four subclasses • Antibodies of the IgE class are central to the allergic response. of IgG (IgG1-4) and two of IgA • IgE antibodies are synthesized and secreted by allergen-specific (IgA1, IgA2), making a total of 9 B cells that have undergone heavy-chain class switching to IgE nine different classes including and differentiated into IgE-secreting plasma cells the subclasses in humans. • IgE binds to FcεRI on mast cells and antigen (in this case allergen)- presenting cells to sensitize the cells for allergen activation Every person can produce an anti- • The immediate symptoms of allergy are caused by the release body to recognize virtually any po- of potent physiological mediators produced by the allergen- tential antigen by a combination of activated mast cells, while the activated antigen-presenting cells mechanisms. The initial repertoire indirectly induce new allergen-specific B cells to produce more IgE of IgMs generated in the bone • Allergen immunotherapy can generate allergen-specific antibo- marrow by “V(D)J” gene recombi- dies of IgG and IgA classes to compete with IgE for allergens nation and junctional nucleotide

- Allergy from genetics to mechanisms variation is highly diverse and is further adapted by antigen stimu- immunoglobulin gene (Figure 2). potent molecules that cause the lation of the B cells in the immune This changes the antibody class symptoms of allergy. The activat- response. This results in cell prolif-

S ection A and the way it is able to engage dif- ed antigen-presenting cells stim- eration and the formation of ger- ferent effector cells in the immune ulate T helper 2 (Th2) cells, which minal centers in lymphoid tissues, response. Germinal center reac- in turn induce the production of where they undergo two process- tions may also occur in the target more allergen-specific antibodies es: somatic hypermutation (SHM) organs of allergy. in a positive feedback loop primed and class switch recombination by allergen. (CSR). SHM introduces point mu- Antibodies of the IgE class are tations in the antigen-binding central to the allergic response Antibodies of the same or cross-re- sites, which may increase or de- (Figure 3). They are synthesized acting specificity, but another an- crease affinity for antigen result- and secreted by IgE-expressing tibody class can compete with IgE ing in selection of high-affinity B cells that have differentiated for antigen binding to prevent or mutants that compete for antigen into IgE-secreting plasma cells. suppress the allergic response. in a process called affinity matu- IgEs bind to mast cells and anti- This may occur in specific allergen ration. CSR replaces the constant gen-presenting cells bearing the immunotherapy, which stimulates region of the heavy-chain with one high-affinity IgE receptor, FcεRI, to a modified Th2 response, causing of another class encoded in a tan- sensitize the cells for allergen ac- a massive up-regulation of IgG4 dem array downstream from the tivation. Allergen-activated mast and IgA2. Some of these antibod- VDJ sequence in the expressed cells release the physiologically ies may recognize the allergen and

64 Immunoglobulin E and other antibodies in allergy Global atlas oF allergy

Figure 1 All five antibody classes have the same basic “immunoglobulin” structure with two heavy- and two light-chains, each with variable-regions (white) containing the antigen-combining site and class-specific constant-regions shown in different colors. The distinctive ε constant region of the IgE heavy-chain is shown in green. Carbohydrates attached to the protein are depicted as small purple circles. The different constant-regions are encoded in a tandem array in the germ line immunoglobulin heavy- chain gene locus on human chromosome 14, downstream from the heavy-chain variable-region of the expressed heavy- chain gene.

Figure 2 Class switch recombination is required to express IgE. The immunoglobulin heavy-chain locus contains S ection A the rearranged variable (VDJ) region linked to a transcriptional enhancer (E) and a series of three elements required for expression of the complete heavy-chain, an “intervening” exon (I), - Allergy from genetics to mechanisms a switch region (S) and a constant region (C). During class switch recombination the VDJ, I and proximal part of S are recombined with the distal part of S within another germ line gene cassette (I, S, and C distinguished by Greek letters corresponding to the newly expressed antibody class). The intervening sequence is deleted and the ends join to form a circle. Prior to recombination, specific cytokines stimulate germ line gene transcription from the I exon promoters of the two genes that subsequently undergo recombination. The germ line gene transcript corresponding to the gene to be expressed helps to instigate the subsequent recombination. The I exon promoter in the switch circle, now attached to the previously expressed gene, remains transiently active, producing a circle transcript whose sequences can be used to identify the genes that recombined. The new immunoglobulin gene in the shortened chromosome is expressed from the VDJ promoter, leading to the synthesis of the immunoglobulin heavy-chain mRNA and protein. The light-chain is unchanged after heavy-chain recombination. compete with IgE. It is thought KEY REFERENCES nal-centre reactions in allergic in- that immune deviation to IgG4 flammation. Trends Immunol 2006; 1. Gould HJ, Sutton BJ. IgE in allergy 27:446-52. and IgA2 allergen specificities and asthma today. Nat Rev Immu- 3. Matsuoka T, Shamji MH, Dur- may contribute to the success of nol 2008; 8:205-17. ham SR. Allergen immunotherapy specific allergen immunotherapy 2. Gould HJ, Takhar P, Harries HE, and tolerance. Allergol Int 2013; (Figure 4). Durham SR, Corrigan CJ. Germi- 62:403-13.

Immunoglobulin E and other antibodies in allergy 65 Global atlas oF allergy

Figure 3 IgE binds very tightly to mast cells and antigen-presenting cells through its high-affinity receptor, FcεRI. Specific allergen crosslinking of the IgE-receptor complex on mast cells induces cell degranulation with the release of mediators leading to the allergic response and also the production of IL-4 and IL-13 and expression of CD40L by the antigen-presenting cells and mast cells. These cytokines lead to B cell proliferation and further switching to IgE in B cells expressing other isotypes in a positive feedback loop, resulting the generation of even more IgE.

Figure 4 Natural exposure to allergens may induce allergen- specific IgE production in sensitive individuals by stimulation of antigen- presenting cells in a T helper 2 (Th2) - Allergy from genetics to mechanisms immune response. This IgE sensitizes effector cells (mast cells, basophils and eosinophils) and the generation of allergen-specific IgE by B cells. S ection A Exposure to high-doses of allergens through immunotherapy induces IL- 10/IL27 release from dendritic cells leading to suppression of the Th2 by deviation of T cell differentiation into the T helper 1 cell and T regulatory (Treg) cell pathways. The resultant cytokines, IFN-γ IL-12, IL-10 and TGF-β lead to the generation of allergen-specific IgG4 and IgA2 antibodies that compete with IgE for allergens.

66 Immunoglobulin E and other antibodies in allergy Global atlas oF allergy

Role of superantigens 15 in allergic diseases

Donald Y. M. Leung National Jewish Health Denver, USA

Atopic dermatitis (AD) is the most common chronic skin disease in the Key messages

general population. It often pre- S ection A sents during early childhood and • Staphylococcus aureus is a major trigger of atopic dermatitis and is the prelude to development of may contribute to severity of rhinosinusitis and asthma food allergy, asthma and allergic • S. aureus exacerbates allergic diseases by secreting virulence rhinitis. A majority of AD patients factors such as superantigens and alpha toxin - Allergy from genetics to mechanisms have a systemic and skin direct- • Staphylococcal virulence factors alter host responses to ed Th2 immune response lead- allergens and microbes ing to allergen sensitization and • Th2 skin immune responses and filaggrin deficiency increases the propensity of atopic skin to become colonized and infected increased skin colonization with with S. aureus Staphylococcus aureus (S. aureus). These patients also have a defect in the terminal differentiation of proteins such as filaggrin, and de- stimulates cytokine release from their skin keratinocytes leading to creased expression of antimicro- antigen-presenting cells (Figure reduced expression of skin barrier bial peptides needed for skin host 3). Evidence supporting a role for defense against invading bacteria superantigens in AD include the and viruses. Reduced barrier func- observation that most AD pa- tion is due to a combination of gene tients make IgE antibodies direct- mutations encoding skin barrier ed against superantigens found proteins such as filaggrin with the on their skin and the presence of downregulation of epithelial dif- these IgE antibodies to superan- ferentiation protein levels induced tigens correlate with skin disease by Th2-type cytokines and IL-22. severity. Basophils and skin mast Loss of filaggrin has been linked to cells from patients with anti-su- enhanced allergen penetration into perantigen IgE release histamine the skin, increased S. aureus growth on exposure to superantigens, but Figure 1 Child with atopic dermati- and S. aureus infection (Figure 1). not in response to superantigens tis superinfected with superantigen Staphylococcus aureus triggers and to which they have no specific secreting Staphylococcus aureus. maintains skin inflammation in AD IgE. Importantly, the superanti- (Reprinted from J Allergy Clin Immu- via the production of virulence fac- gen, staphylococcal enterotoxin B nol, 125/1, Boguniewicz M, Leung DY. tors, such as superantigens and al- (SEB), can induce eczematoid skin Recent insights into atopic dermatitis pha toxin (Figure 2). and implications for management of in- changes when applied to the skin. fectious complications, 4-13, Copyright Superantigens are potent poly- After stimulation by SEB, T reg- 2010, with permission from Elsevier.) clonal T cell activators that also ulatory cells lose their immuno-

Role of superantigens in allergic diseases 67 Global atlas oF allergy

reduction of skin inflammation. AD patients with S. aureus infection should receive antibiotics as this may reduce the severity of their skin disease. Together, these observations fulfill Koch’s postu- lates and support a role for staphylococcal superantigens in AD. There is also increasing data suggesting that in certain clinical sit- uations, S. aureus may contribute to severity of rhinosinusitis and asthma, by augmenting the airway inflammation and promoting polyclonal local IgE formation, and by inducing corticosteroid resistance. Figure 2 Virulence factor production by S. aureus (Reprinted from J Allergy Clin Immunol, 125/1, Schlievert PM, Strandberg KL, Lin YC, Peterson ML, Leung DYM. Secreted virulence factor comparison between methicillin-resistant and methicillin- KEY REFERENCES sensitive Staphylococcus aureus, and its relevance to atopic dermatitis, 39-49, 1. Boguniewicz M, Leung DY. Recent Copyright 2010, with permission from Elsevier.) insights into atopic dermatitis and implications for management of infectious complications. J Allergy Clin Immunol 2010;125: 4-13. 2. Ong PY, Ohtake T, Brandt C, Strick- land I, Boguniewicz M, Ganz T, et al. Endogenous antimicrobial peptides and skin infections in atopic dermatitis. N Engl J Med 2002;347:1151- 1160. 3. Irvine AD, McLean WHI, Leung DY. Filaggrin Mutations Associated - Allergy from genetics to mechanisms with Skin and Allergic Diseases. N Engl J Med 2011;365:1315-1327. 4. Gittler JK, Shemer S, Suárez- Fariñas M, Fuentes-Duculan J, S ection A Gulewicz KJ, Wang CQF, et al. Pro- gressive activation of TH2/TH22 cytokines and selective epidermal proteins characterizes acute and Figure 3 Model comparing activation of CD4+ T cells and macrophages by the chronic atopic dermatitis. J Allergy superantigen, SEB, compared with antigenic peptide activation of the same cells. Clin Immunol 2012; 130:1344-54. In comparison to peptide activation, SEB causes polyclonal T cell stimulation. (Reprinted from J Allergy Clin Immunol, 125/1, Schlievert PM, Strandberg KL, Lin YC, 5. Schlievert PM, Strandberg KL, Lin Peterson ML, Leung DYM. Secreted virulence factor comparison between methicillin- YC, Peterson ML, Leung DYM. Se- resistant and methicillin-sensitive Staphylococcus aureus, and its relevance to atopic creted virulence factor comparison dermatitis, 39-49, Copyright 2010, with permission from Elsevier.) between methicillin-resistant and methicillin-sensitive Staphylococ- suppressive activity, suggesting a become corticosteroid resistant cus aureus, and its relevance to novel mechanism by which super- and to secrete IL-31, a highly pru- atopic dermatitis. J Allergy Clin Im- antigens could augment T-cell ac- ritogenic cytokine that induces ec- munol 2010;125:39-49. tivation and skin inflammation in zema in animal models. 6. Boguniewicz M, Leung DY. The ABC’s of managing patients with patients with AD. Superantigens Treatment of AD patients should severe atopic dermatitis. J Allergy also selectively induce T cells to focus on skin barrier repair with Clin Immunol 2013;132: 511-512.

68 Role of superantigens in allergic diseases Global atlas oF allergy

Cytokines in 16 allergy

Lars K. Poulsen National University Hospital Copenhagen, Denmark

Cytokines are soluble proteins or peptides that act as the hormones Key messages

- messengers - of the immune sys- S ection A tem and between other cells of the • Cytokines act as messengers of the immune system with other body. They confer cell-to-cell com- cells of the body munication which may take place • Various groups of cytokines are responsible for the sensitisation between adjacent cells (juxtacrine) to an allergen and for eliciting the allergic inflammation. - Allergy from genetics to mechanisms or cells in different organs of the • There are sensing cytokines, T cell instructing cytokines, effector cytokines, resolving cytokines and chemokines body (para- or endocrine). A cy- • The integrated actions of the cytokines in development, tokine signal is delivered via a re- elicitation and eventually resolving the inflammation is called the ceptor on the surface of a cell, and cytokine network of allergy since different cells may express the same receptor, a cytokine can have several functions (pleiotropy) cells - followed by a number, but (CD4+) cell to develop into dif- depending on the target cell. Also more and similar molecules have ferent kinds of cells, each of them a target cell may have receptors been discovered, so instead of just equipped for different kinds of im- for several similar cytokines al- interleukin-1 (IL-1), we now have mune response: IL-12 and γ-inter- lowing for . redundancy IL-1α, IL-1β and IL-1RA (= Interleu- feron will produce T helper cells There are more than 100 de- kin 1 Receptor Antagonist). type 1 (Th1) that helps fighting bacteria and viruses, IL-4 leads to scribed cytokines and their names Various groups of cytokines are Th2 cells which fights large mul- are not easy to cope with, since no responsible for the different ticellular parasites like worms, unified nomenclature exists. Some phases of the allergic sensitization but unfortunately also create the are named after where they were (building up the allergic immune allergic immune response. Oth- first found and/or their function, response) and elicitation (reactions er Th-cell types such as Th17 such as thymic stromal lymphopoi- upon exposure to an allergen): etin (TSLP), others after the first (believed to be active in fighting function identified, like Granulo- The sensing cytokines: IL-33, IL-25, bacterial or fungal infections, but cyte-Macrophage Colony Stimu- TSLP. These are released from unfortunately also involved in au- lating Factor (GM-CSF), and some the epithelial cells of the mucous toimmune diseases), and T regu- may even have several names giv- membranes and signals to the al- latory (dampening the inflamma- en to them by different research lergen-presenting dendritic cells tion) also exists. to take up incoming allergens and groups. An attempt to unify the T-cell effector cytokines in allergy bring them to the lymph nodes. nomenclature has been made by are the cytokines by which Th- the word interleukin - meaning The T-cell instructing cytokines will cells exerts their action: Th2 cells messengers between white blood instruct undifferentiated T helper release IL-4 and IL-13 which in-

Cytokines in allergy 69 Global atlas oF allergy

Viruses Allergens Airway epithelial cells

TSLP, IL-4 IL-25, IL-33 IL-4 IL-13

CXCL1 IL-17 Dendritic cell T 0 cell T 2 cell CXCL8 IL-23 H H B cell IL-22 TGFβ IL-4 IL-10 TGFβ IgE TGFβ IL-12 TGF β IL-5 IL-6 IFNγ

TH17 cell

TNF IFN β Neutrophil TH1 cell Treg cell Eosinophil TH9 cell MMP IL-9 Neutrophil elastase • Basic proteins ROS Mucus • Cysteinyl leukotrienes • Cytokines Mast cell Epithelial cells • Histamine • Cysteinyl leukotrienes • Prostagladins Blood vessel Fibroblasts Smooth muscle cells • Cytokines

- Allergy from genetics to mechanisms Figure 1 The complex interplay of cytokines in allergic inflammation: red - sensing cytokines; green - T-cell instructing cytokines; violet - T-cell effector cytokines; blue - Resolving cytokines; pink - Chemokines.

structs B-cells to produce the al- Chemokines is a special group of tically by the so-called biological

S ection A lergy antibody IgE, IL-5 that stim- cytokines that attract leukocytes therapeutics where cytokine ac- ulates the bone marrow to form to the site of inflammation, and tions are antagonized. the eosinophilic granulocyte, and the immune system uses these to IL-9 that together with IL-13 cre- move leukocytes in the tissues, KEY REFERENCES 1. Galli SJ, Tsai M, Piliponsky AM. The ates the allergic inflammation e.g. when they have left the blood- stream. development of allergic inflamma- in the lung as is the case in asthma. tion. Nature 2008; 454:445-454 The integrated actions of the cy- The resolving cytokines such as 2. Poulsen LK, Hummelshoj L. Trig- tokines in development, elicita- IL-10 and Transforming Growth gers of IgE class switching and tion and eventually resolving the allergy development. Ann Med Factor (TGF-β) comprise a small inflammation is called the cytokine 2007;39:440-456. but important group of cytokines network of allergy. Since several of 3. Williams CM, Rahman S, Hubeau that down-regulates the allergic these cytokines play a profound C, Ma HL. Cytokine pathways inflammation, restoring the home- role in allergy, many attempts are in allergic disease. Toxicol Pathol ostasis of the immune system. being made to use this therapeu- 2012;40:205-215.

70 Cytokines in allergy Global atlas oF allergy

Cell migration and 17 chemokines

Cristiana Stellato Gilda Varricchi Gianni Marone University of Salerno University of Naples University of Naples Salerno, Italy Federico II, Italy Federico II, Italy

The immune system relies on a tightly regulated migration pro- Key messages

cess for the ordered compart- S ection A mentalization of immune cells • Cell migration in the immune system is a highly regulated, within the lymphoid organs, for multi-step process involving adhesion molecules, chemotactic implementation of the homeo- factors and their receptors and is necessary for the homeostatic static immune surveillance as well immune surveillance as well as for the coordinated recruitment - Allergy from genetics to mechanisms as for an appropriate response to of inflammatory cells at sites of inflammation environmental insults through • Chemokines represent a superfamily of small proteins that regulate immune cell trafficking and the recruitment and innate and adaptive effector reactivation of specific leukocyte cell types to sites of inflammation sponses. Circulating leukocytes • Chemokines are divided in four subclasses – CC, CXC, CX3C and tissue-dwelling immune cells and C – and activate cell targets through class-specific seven- proceed from hematopoietic to transmembrane chemokine receptors vascular compartments and into • Dysregulation of the chemokine system plays a crucial role in tissue sites through receptor-me- chronic inflammatory diseases, metabolic disorders, cancer and diated, multi-step processes in- aging volving many classes of traffick- • Antagonism of chemokine receptors has so far shown partial ing molecules, including adhesion success as therapeutic strategy, and is now assisted by research molecules (selectins and integrins) toward more specific downstream regulatory pathways with their counterligands and che- modulating the chemokine network moattractants, either lipid-derived or belonging to the chemokine superfamily. It is the combinatorial whose first identified member, members sharing the same recep- nature of the diverse patterns of CXCL8, was initially characterized tor (Table 1). The ensuing signal- expression and activation of these by its potent and specific leukocyte ing involves multiple and diverse molecules and their receptors on chemoattractant activity – hence pathways that are highly recep- immune and structural cells, to- the name, derived from ‘chemot- tor-, cell type- and context-specif- gether with their modulation in actic cytokines’. Chemokines are ic and produce diverse functional response to environmental clues, divided into the CXC, CC, CX3C outcomes. Among these, the con- as in case of inflammatory or tu- and C subfamilies based on the trol of immune cell trafficking in morigenic settings, that ultimately number and spacing of conserved homeostasis and the regulation of provides a high level of specificity cysteine residues. They bind to the leukocyte recruitment, phenotype in cellular trafficking. seven-transmembrane, G-protein and activation in innate and adap- Chemokines constitute a su- coupled receptors that are specif- tive immune responses remains perfamily of small polypeptides, ic for each subclass, with multiple a defining and pivotal function of

Cell migration and chemokines 71 Global atlas oF allergy

TABLE 1 Nomenclature of Chemokine Families and Paired Receptors

Standard Chromo- Human Chemokine Standard Chromo- Human Chemokine name some ligand receptor(s) name some ligand receptor(s) CCR1, CCR5 CXC-chemokines CCL3L3 17q21.1 LD78β (CD195) CXCL1 4q21.1 GROα/MGSAα CXCR2>CXCR1 CCL4 17q12 MIP-1β CCR5 (CD195) CXCL2 4q21.1 GROβ/MIP-2α CXCR2 CCL4L1 17q12 LAG-1 CCR5 (CD195) CXCL3 4q21.1 GROβ/MIP-2β CXCR2 CCL4L2 17q12 CCL4L CCR5 (CD195) CCR1, CCR3, CXCL4 4q21.1 Platelet Factor-4 CXCR3 (CD183) CCL5 17q12 RANTES CCR5 (CD195) CXCL4L1 4q12-q21 PF4V1 CXCR3 (CD183) CCL6* CCR1, CCR2, CXCL5 4q21.1 ENA-78 CXCR2 CCL7 17q11.2 MCP-3 CCR3 CCR3, CCR5 CXCL6 4q21.1 GCP-2 CXCR1,CXCR2 CCL8 17q11.2 MCP-2 (CD195) CXCL7 4q21.1 NAP-2 CXCR2 CCL9* CXCL8 4q21.1 IL-8 CXCR1,CXCR2 CCL10* CXCL9 4q21.1 MIG CXCR3 (CD183) CCL11 17q11.2 Eotaxin CCR3 CXCL10 4q21.1 IP-10 CXCR3 (CD183) CCL12* CXCL11 4q21.1 I-TAC CXCR3 (CD183) CCL13 17q11.2 MCP-4 CCR2, CCR3 CCR1, CCR5 CXCL12 10q11.21 SDF-1α/β CXCR4 (CD184) CCL14 17q12 HCC-1 (CD195) CXCL13 4q21.1 BCLC CXCR5 CCL15 17q12 HCC-2 CCR1, CCR3 CXCL14 5q31.1 BRAK CXCR4 (CD184) CCL16 17q12 HCC-4 CCR1, CCR2

- Allergy from genetics to mechanisms CXCL15* CCL17 16q13 TARC CCR4 CXCL16 17p13 SR-PSOX CXCR6 CCL18 17q12 PARC Unknown CXCL17 19q13.2 DMC Unknown CCL19 9p13.3 ELC CCR7 (CD197)

S ection A C-chemokines CCL20 2q36.3 MIP-3α, LARC CCR6 XCL1 1q24.2 Lymphotactin/α XCR1 CCL21 9p13.3 SLC CCR7 (CD197) XCL2 1q24.2 Lymphotactin/β XCR1 CCL22 16q13 MDC CCR4

CX3C-chemokines CCL23 17q12 MPIF-1 CCR1

CX3CL1 16q13 Fractalkine CX3CR1 CCL24 7q11.23 Eotaxin-2 CCR3 CC-chemokines CCL25 19p13.3 TECK CCR9 CCL1 17q11.2 I-309 CCR3 CCL26 7q11.23 Eotaxin-3 CCR3 CCL2 17q11.2 MCP-1 CCR2 CCL27 9p13.3 CTACK CCR10 CCR1, CCR5 CCL3 17q12 MIP-1α CCL28 5p12 MEC CCR3/CCR10 (CD195) CCR1, CCR5 CCL3L1 17q21.1 LD78β (CD195) *No human ortholog described Modified from Bachelerie et al., Pharmacol. Rev. 66: 1-79, 2014, with update on Pubmed Library and Genebank.

72 Cell migration and chemokines Global atlas oF allergy S ection A - Allergy from genetics to mechanisms

Figure 1 . The association of CC and CXC chemokines (CCL and CXCL indicated by outer arrows, member numbers listed in the outer gray circle) and their receptors (listed in pink circle below ) to a selection of diseases, gained from animal models and from data obtained in human samples and in clinical trials. Abbreviations: Sep, Sepsis; RA, Rheumatoid arthritis; T, Transplant; IBD, Inflammatory Bowel Disease; Onc, Oncology; SLE, Systemic Lupus; MS, Multiple Sclerosis; Ath Scl, Atherosclerosis; COPD: Chronic Obstructive Pulmonary Disease; AMD, Acute macular degeneration; NP, Neuropathic pain; Asth, Asthma; At. Derm, Atopic dermatitis; Hep, Hepatitis; Panc, Pancreatitis; Pso, Psoriasis; GVHD, Graft vs Host disease. (Reprinted with permission from Garin and Proudfoot, Exp. Cell. Res. 317: 602-612, 2011.) the chemokine superfamily. The cell types, with CXC members act- while CC chemokines shape leu- key role of chemokines in chronic ing on effector functions relevant kocyte trafficking and function in inflammatory diseases is now firm- in diseases characterized by neu- Th2-dependent, eosinophil-rich ly established (Figure 1). In these trophilic, Th1- and Th-17-driven inflammatory processes such as contexts, the CXC and CC sub- responses, such as COPD, multiple allergic asthma, early-stage atopic classes, though with overlaps, seg- sclerosis, Crohn’s disease and spe- dermatitis, eosinophilic gastroin- regate their control over different cific phenotypes of severe asthma; testinal diseases (Figure 2). Among

Cell migration and chemokines 73 Global atlas oF allergy

Asthma

COPD - Allergy from genetics to mechanisms S ection A

Figure 2 Involvement of chemokines and chemokine receptors in the inflammatory response present in bronchial asthma and COPD . In asthma, dendritic- and epithelial-derived chemokines elicited by the inhaled allergens recruit and activate Th2 cells and eosinophils through CCR4 and CCR3, respectively, contributing to the generation of an IgE-mediated inflammatory response. In COPD, chemokines released from lung epithelial cells and macrophages following exposure to cigarette smoke and/or pollutants generate a neutrophilic/monocytic-enriched infiltrate driven by Th1/Th17 cells that contributes to the inflammatory response and determins lung structural damage. Reprinted( by permission from Macmillan Publishers Ltd: Nat Rev Immunol, Barnes PJ, Immunology of asthma and chronic obstructive pulmonary disease, 8,183-192, copyright 2008.)

74 Cell migration and chemokines Global atlas oF allergy

the CC chemokines, CCL2/Mono- Inhibition of leukocyte recruit- tion: present and future therapeu- cyte Chemoattractant Protein-1 ment is a major mechanism of glu- tic targets. Nat Immunol 2005;6: (MCP-1) is a non-redundant, po- cocorticoids’ anti-inflammatory 1182-1190. tent regulator of monocytes, ba- action and a major goal for novel 3. Charo IF, Ransohoff RM. The many sophils and dendritic cells and par- therapies selectively targeting ticipates to the Th2 polarization specific recruitment pathways. roles of chemokines and chemok- of memory T cells. The CX3C and Antagonism of chemokine-me- ine receptors in inflammation. N the C subfamilies are represented diated functions offers major Engl J Med 2006;354:610-621. by a single member, CX3CL1/frac- challenges, partly due to member 4. Garin A, Proudfoot AE. Chemok- talkine, which is the only cell mem- redundancy in each subclass, but ines as targets for therapy. Exp Cell brane-associated chemokine, and mostly to the complexity of the 2011;317:602-612. lymphotactin, respectively. control of their expression, which Res spans from transcriptional to post- 5. Islam SA, Luster AD. T cell homing Chemokines’ range of regulatory translational and extracellular ma- to epithelial barriers in allergic dis- competences has been widened trix-dependent mechanisms, that over the last decades, as almost ease. Nat Med 2012;18:705-715. are diversely affected in specific all cell types, including structural 6. Fan J, Heller NM, Gorospe M, disease settings. Antagonism of cells such as fibroblasts, endothe- single chemokine receptors has Atasoy U, Stellato C. The role of lial and epithelial cells, as well as so far shown only partial success post-transcriptional regulation in S ection A tumor cells have been found to as therapeutic strategy, and is chemokine gene expression in in- express regulated profiles of func- now flanked by research toward flammation and allergy. tional chemokine receptors. By Eur Respir J more specific downstream regu- 2005;26:933-947. regulating cell proliferation, differ- - Allergy from genetics to mechanisms latory pathways modulating the entiation and apoptosis functions, 7. Bachelerie F, Ben-Baruch A, Bur- chemokine network. and – either directly or indirectly khardt AM, Combadiere C, Farber – controlling angiogenesis and ex- KEY REFERENCES JM, Graham GJ et al. International tracellular matrix remodeling, the 1. Rot A, von Andrian UH. Chemok- Union of Pharmacology. LXXXIX. chemokine system is also central ines in innate and adaptive host de- Update on the extended family of to cancer-related inflammation, fense: basic chemokinese grammar chemokine receptors and introduc- angiogenesis, tumor cell survival for immune cells. Annu Rev Immunol and invasiveness, and is critically 2004;22:891-928. ing a new nomenclature for atypi- involved in the step-wise process 2. Luster AD, Alon R, von Andrian UH. cal chemokine receptors. Pharma- of wound healing. Immune cell migration in inflamma- col Rev 2014;66:1-79.

Cell migration and chemokines 75 Global atlas oF allergy

Complement-Mediated 18 Regulation of the Allergic Response

Marsha Wills-Karp Johns Hopkins Bloomberg School of Public Health Baltimore, USA

Asthma is thought to arise as a result of aberrant T helper type 2 Key messages (Th2)-polarized immune responses to innocuous environmental al- • The phylogenetically ancient complement activation system is lergens, however the mechanisms activated in the lungs of asthmatic individuals driving these aberrant immune re- • Several environmental triggers of asthma including allergens, air sponses remain elusive. As a phy- pollutants, cigarette smoke, and viruses activate the complement logenetically ancient immune sys- system and mediate Th2-driven immune responses tem, the complement activation • Genetic polymorphisms in the C3 and C3aR1 genes are associated with susceptibility to the development of asthma in system, is a sophisticated network children and adults of soluble and membrane-bound • Modification of complement activation pathways may provide a proteins. It has evolved to recog- novel strategy for the treatment of asthma nize “danger or pattern-associated molecular patterns” expressed by foreign organisms through “hard- to directly activate complement tiate recruitment and activation of - Allergy from genetics to mechanisms wired” pattern recognition recep- at the airway surface. Genetic de- various inflammatory cells asso- tors (PRRs). Activation of these letion of C3 in animal models has ciated with asthma pathogenesis PRRs culminates in the generation been shown to protect against the (Figure 4). of C3 and the production of two

S ection A development of allergen-, pollut- pro-inflammatory anaphylatoxins, In humans, segmental allergen ant-, and RSV-induced asthmat- C3a and C5a, which induce inflam- provocation resulted in a signifi- ic responses and Th2 cytokine mation and the membrane attack cant increase in C3a levels in the production suggesting that C3a complex, which lyses foreign cells. bronchoaveolar lavage of asth- production at the airway surface The anaphylatoxins C3a and C5a matics, with no change in healthy serves as a common pathway for are potent pro-inflammatory me- volunteers. This differential pro- the induction of Th2-mediated diators that bind to specific cell duction of C3a between individu- inflammatory responses thereby surface receptors and regulate als with asthma and those without driving and/or exacerbating the many processes observed in asth- asthma suggest that there may be disease (Figure 1, 2, 3). The exact ma including leukocyte activation, alterations in the genetic control mechanisms by which C3 regu- smooth muscle contraction, and of the production of, the activation lates allergic responses are un- of, or the response to various com- mucus secretion. known, but current evidence sug- plement components that may un- Consistent with a role for C3-C3a gests that C3a can both enhance derlie susceptibility to asthma. In- in asthma, exposure to a variety of antigen uptake by antigen-pre- deed, associations between single environmental triggers of asthma senting cells, thereby enhancing nucleotide polymorphisms (SNPs) in animal models has been shown sensitization to allergens, and ini- in the C3 gene and atopic asthma

76 Complement-mediated regulation of the allergic response Global atlas oF allergy

B 1.4 A 3.0 * 1.2 2.5 ) 1.0 3 2.0 0.8 ( µ g/g) 1.5 200 0.6

PC 1.0 ** 0.4 Cells/ml (x10 0.2 0.5 0.0 0.0 PBS C3 +/+ C3 -/- IL-4 IFN-γ Figure 1 Allergen-induced asthma is C3 dependent. A) The effect of C3 deficiency on airway hyperresponsiveness (AHR) in anesthetized C3−/− and C3+/+ mice. AHR was assessed 24 hrs after the last challenge and is expressed as the

provocative concentration of ACh (in micrograms per gram) that increased baseline airway resistance 200% (PC200). B) IL-4- and IFN-γ-producing cells in the lungs from C3−/− (■) and C3+/+ littermates (□) were quantitated 24 h after the last Ag challenge. (Reproduced from Drouin SM, Corry DB, Kildsgaard J, Wetsel RA. 167:4141-4145, Copyright 2001 with permission from the American Association of Immunologists.).

C 800

* S ection A

600 O * sec) 2 - Allergy from genetics to mechanisms 400

200 APTI (cm H

0 PBS wt PM wt PBS C3-/- PM C3-/- Figure 2 Air pollution exposure-induced airway hyperresponsiveness is C3-dependent. Lung sections from PM-exposed mice were stained with anti-C3 mAb (A) or (B) isotype control antibodies. Specific C3 staining is observed in the airway epithelial layer. C) Airway responsiveness (APTI) to acetylcholine stimulation is significantly reduced in C3-deficient mice after particulate matter (PM) exposure as compared to PM-exposed wildtype mice. (P < 0.05). (Reproduced from American Journal of Respiratory Cell and Molecular Biology, the official journal of the American Thoracic Society, Walters DM, Breysse PN, Schofield B, et al., 27, 413-418, Copyright 2002 with permission from American Thoracic Society). A B 1000 ** 1200 *

900 750 O - sec 2 600 500 cm H 300 250

0 0 +/+ -/- +/+ -/- Complement C3 Mature B cells Figure 3 Respiratory syncytial virus-induced airway hyperresponsiveness is C3-dependent. Airway hyperresponsiveness in wildtype and C3- and B cell-deficient mice challenged with RSV 7 days after immunization with formalin-fixed RSV. (A) B6129F2 WT (C3+/+) and C3 deficient (C3−/−), and (B) C57BL/10 (B+/+) and B10 μMT (B−/−) mice. AHR to acetylcholine challenge is defined by the time-integrated rise in peak airway pressure. Reproduced( from Journal of Experimental Medicine, Polack FP, Teng MN, Collins PL, et al., 196, 859-65, Copyright 2002 with permission from The Rockefeller University Press).

Complement-mediated regulation of the allergic response 77 Global atlas oF allergy

Epithelial Cell

Genetic Eos C3 SNPs C3aR ASM DC C3 C3a Ag C3aR Th2 Environment Complement al Production Airway Triggers and C3aR Activation Contraction Allergens Viruses Ozone PM Mast ETS Cell

Figure 4 Complement activation pathways regulate Th2-mediated immune responses. Following airway exposure to a variety of environmental triggers of asthma in genetically susceptible individuals, C3 is produced and secreted by airway epithelial cells lining the airways. C3 is cleaved into its active form, C3a, presumably by proteases either contained in the allergens or produced by the epithelium. C3a then binds to its receptor, C3aR1 on antigen presenting cells, enhancing uptake of antigen by these cells. Antigen-loaded APCs then drive the differentiation of naïve T cells to Th2 cells. Th2 cytokines in turn recruit and active the effector cells of the allergic response, eosinophils and mast cells. During the effector phase of the response, C3a can bind its receptor on these effector cells enhancing their recruitment and activation. Growth factors and bronchoactive substances from these cells lead to increased airway smooth muscle growth and contractile capacity.

have been reported in children of allergic diseases. Further inves- Prince GA, Exner M, Regele H, et al. and adults. Interestingly, the fre- tigations into the mechanisms by A role for immune complexes in en- quency of these SNPs is high, sug- which C3a modules allergic asth- hanced respiratory syncytial virus gesting that these polymorphisms ma may offer novel therapeutic disease. J Exp Med 2002;196:859- 865. may have conferred evolutionary approaches for the treatment of - Allergy from genetics to mechanisms advantage in the past and perhaps asthma. 4. Wills-Karp M. Complement activa- in protection from parasitic infection pathways: a bridge between innate and adaptive immune re- tions. KEY REFERENCES sponses in asthma. Proc Am Thorac 1. Drouin SM, Corry DB, Kildsgaard 2007;4:247-251. S ection A Although we are in the initial stag- Soc J, Wetsel RA. Cutting edge: the es of understanding the role of 5. Barnes KC, Grant AV, Baltadzhieva absence of C3 demonstrates a D, Zhang S, Berg T, et al., Variants in complement pathways in asthma role for complement in Th2 effec- the gene encoding C3 are associ- pathogenesis, one may postulate tor functions in a murine model of ated with asthma and related phe- that changes in the activation of pulmonary allergy. 2001; J Immunol notypes among African Caribbean specific complement components 167:4141-4145. families. Genes Immun 2006;7:27- due to differences in exposure 2. Walters DM, Breysse PN, Schofield 35. to different environmental trig- B, Wills-Karp M. Complement Fac- 6. Hasegawa K, Tamari M, Shao C, gers or to genetic alterations in tor 3 mediates particulate matter– Shimizu M, Takahashi N, et al. Var- complement family genes or the induced airway hyperresponsive- iations in the C3, C3a receptor and convergence of both of these fac- ness. Am J Respir Cell Mol Biol 2002; C5 genes affect susceptibility to tors may play an important role in 27:413-418. bronchial asthma. Hum Genet 2004; susceptibility to the development 3. Polack FP, Teng MN, Collins PL, 115:295-301.

78 Complement-mediated regulation of the allergic response Global atlas oF allergy

Lipid mediators of 19 hypersensitivity and inflammation

Marek Sanak Jagiellonian University Medical College Kraków, Poland

Since the discovery that bronchoconstriction and edema can Key messages

be mediated by cysteinyl leukot- S ection A rienes, lipid mediators attracted • Lipid mediators regulate both the physiological status and much attention in allergology. The inflammation in the airways • Cysteinyl leukotrienes and prostaglandin D are the best studied biological effect of a lipid media- 2 tor is determined by its receptor inflammatory mediators of hypersensitivity and allergic disorders - Allergy from genetics to mechanisms affinity and intracellular signal • Other lipid mediators, like pro-inflammatory eoxins and anti- transduction, and receptors dif- inflammatory lipoxins also participate in allergic reaction • A class of phospholipid and ceramide mediators interact with fer in their specificity and cellular immune response in allergy distribution. Lipid mediators of inflammation are difficult to study due to their complex metabolism, piratory epithelium also secretes rhinosinusitis. Patients with aspi- chemical similarities and rapid in- 15-hydroxyeicosapentaenoic acid rin-exacerbated respiratory dis- activation. Their levels in airways (15-HETE) to its basal surface. ease (AERD) overproduce pros- can be measured in bronchial or Upon stimulation with Th2 cy- taglandin D , but this finding is nasal lavage, induced sputum or 2 tokines (IL-4, IL-13), the asthmat- also present in other eosinophilic exhaled breath condensate, while ic respiratory epithelium under- phenotypes of asthma. During an systemic production can be as- goes mucous cell metaplasia with aspirin provocation test, bron- sessed in urine. amplication of the production of choconstriction is mediated by a Regulation of the airways tonus, 15-HETE. 15-HETE can be metab- further increase in the local and secretion or inflammation involves olized to eoxins, isomers of cystei- systemic production of cysteinyl numerous mediators (Figures 1 nyl leukotrienes. The concentra- leukotrienes, a unique feature of tion of eoxins (EXC , EXD and and 2). Respiratory epithelium 4 4 this disease. produces prostaglandin E (PGE ), EXE4) is increased together with 2 2 The integrity of the lung function secreted to the apical surface. It cysteinyl leukotrienes in children with asthma. Moreover, EXD and is maintained by PGE , which in- has been recently demonstrated 4 2 EXE leves correlate with bronchi- hibits inflammation at physiologi- that excessive PGE can impair 4 2 cal concentrations. PGE can pro- phagocytic clearance of solid par- al hyperreactivity . 2 mote tissue injury in high doses. ticles by alveolar macrophages. A One of the asthma phenotypes decreased number of carbon par- is characterized by an overpro- Other lipid mediators are released ticles in alveolar macrophages and duction of cysteinyl leukotrienes. by activated cells only. They act increased systemic production of These asthmatics have hypersen- as highly bioactive autacoids ca-

PGE2 metabolites were report- sitivity to non-steroidal anti-in- pable of chemoattraction of neu- ed in children with asthma. Res- flammatory drugs and chronic trophils (12-HETE, leukotriene B4)

Lipid mediators of hypersensitivity and inflammation 79 Global atlas oF allergy

ins are also generated from polyunsaturated fatty acids by reactive oxygen species in a non-enzymatic reaction. A separate class of lipid mediators are phospholipids and ceramides. Platelet-activating factor, a phosphatydylcholine ether of alkyl-acetyl glicerol is the most potent mediator of anaphylaxis and bronchoconstriction. Cer- amides are abundant constituents of the cell membrane mediating apoptosis. Lipid mediators can bridge inflammation with the cellular immune response in allergic disorders.

KEY REFERENCES 1. Brugha RE, Mushtaq M, Round T, Figure 1 Main classes of inflammatory lipid mediators in the airways are Gadhvi DH, Dundas I, Gaillard E, et cysteinyl leukotrienes, eoxins and prostaglandins. Platelet activating factor and al. Carbon in airway macrophages ceramides are also released during allergic reaction. from children with asthma. Thorax 2014 in press. 2. Jakieła B, Gielicz A, Plutecka H, Hubalewska M, Mastalerz L, Bo- chenek G, et al. Eicosanoid biosynthesis during mucocilliary and mucous metaplastic differentiation of bronchial epithelial cells. Prostaglandins Other Lipid Mediat 2013;106:116-23. 3. Sachs-Olsen C, Sanak M, Lang AM, - Allergy from genetics to mechanisms Gielicz A, Movinckel P, Lødrup Carlsen KC, et al. Eoxins: a new inflammatory pathway in childhood asthma. J Allergy Clin Immunol

S ection A 2010;126:859-867. 4. Sanak M, Gielicz A, Bochenek G, Kaszuba M, Niżankowska-Mogil- nicka E, Szczeklik A. Targeted eicosanoid lipidomics of exhaled breath condensate provide a distinct pattern in the aspirin-intolerant asthma phenotype. J Allergy Clin Immu- nol 2011;127:1141-1147. Figure 2 Lipid mediators are produced in airways by structural and 5. Haworth O, Levy BD. Endogenous inflammatory cells. In general, tissue infiltrating inflammatory cells produce lipid mediators in the resolution of pro-inflammatory mediators, while structural ones produce anti-inflammatory airway inflammation. Eur Respir J mediators. Excessive production of lipid mediators by respiratory epithelial 2007;30:980-950. cells and alveolar macrophages also promotes inflammation. 6. Vadas P, Gold M, Perelman B, Liss GM, Lack G, Blyth T, et al. Plate- or eosinophils and lymphoid cells (lipoxins, resolvins, protectins) let-activating factor, PAF acetylhy- (PGD2). Some can provide termi- and their biosynthesis requires drolase, and severe anaphylaxis. N nation signals for inflammation cell interaction . Bioactive oxylip- Engl J Med 2008;358:28-35.

80 Lipid mediators of hypersensitivity and inflammation Global atlas oF allergy

Lipid mediators in 20 resolution of allergic inflammation

Evangelos Andreakos Academy of Athens Athens, Greece

Persistent non-resolving inflammation underlies the pathogen- Key messages

esis of allergic diseases including S ection A rhinitis and asthma, and deter- • Non-resolving inflammation underlies the pathogenesis of mines both the intensity of the allergic diseases symptoms and the chronicity of • Resolution of inflammation is an active, finely orchestrated and the disease. Yet, the mechanisms complex process - Allergy from genetics to mechanisms controlling resolution of inflam- • Resolution of inflammation involves anti-inflammatory, immune mation have only recently started regulatory, cell death and lipid mediator-related mechanisms to become elucidated. • ω3-derived specialized proresolving lipid mediators (SPMs) such as protectins, resolvins and maresins are key mediators of Resolution is an active and highly inflammation resolution orchestrated process of similar • Allergic diseases are associated with defects in the generation of complexity to the onset and pro- SPMs gression of inflammation. It starts • Synthetic SPMs or compounds triggering their production are early in the inflammatory re- promising therapeutics for the treatment of allergic diseases sponse and involves the induction of anti-inflammatory/regulatory networks aiming at terminating genation of arachidonic acid into vate inflammatory cells, promote pro-inflammatory signalling, and prostaglandins and leukotrienes apoptotic cell and tissue debris biosynthetic circuits triggering the that occurs during the initiation of clearance, and repair damaged tis- production of specialized prore- an inflammatory response is fol- sue, altogether leading to the res- solving lipid mediators (SPMs) lowed by the generation of lipox- toration of homeostasis. essential for return to homeosta- ins, lipids with anti-inflammatory Notably, ω3-derived SPMs also sis. The relative balance between and proresolving properties, in possess antimicrobial function. pro-inflammatory, anti-inflamma- a process termed ‘lipid mediator PD1 is induced by antiviral TLRs tory and proresolving respons- class switching’. As the inflam- and exhibits potent antiviral ac- es, influenced by environmental matory response progresses, the tivity, while several resolvins and exposures and lifestyle factors, production of additional SPMs protectins enhance antibacterial eventually determines whether derived from ω3 PUFAs such as defences. This has significant im- the inflammatory response will protectins, resolvins and mares- plications for the role of lipid me- persist or terminate. ins ensues (Figure 1). These act in diators in allergic disease exacer- Central to the resolution of inflam- a stereospecific manner through bations, which are often triggered mation are bioactive lipids derived G protein-coupled receptors to by infections. The biosynthesis of from ω3 and ω6 polyunsaturated reverse vasodilation and suppress SPMs is dependent on lipoxygen- fatty acids (PUFA). The early oxy- leukocytic cell infiltration, de-acti- ase-5 and lipoxygenase-12,15,

Lipid mediators in resolution of allergic inflammation 81 Global atlas oF allergy

Onset Resolution ω-6 ω-3

Lipoxins Prostaglandins Resolvins Leukotriennes Protectins

Termination Initiation Inflammatory response (Time) Return to homeostasis

Figure 1 Generation of eicosanoids and specialized proresolving lipid mediators as inflammation progresses. As the inflammatory response proceeds, the production of additional proresolving lipids derived from ω3 PUFAs such as protectins, resolvins and maresins ensues. These act in an orchestrated manner to terminate inflammation and ensure the transition to homeostasis.

Airway lumen

Pollutants Smoke Allergen Virus Respiratory INDUCERS OF PRORESOLVING epithelium LIPID MEDIATORS TLR agonists ω Viruses 3 DHA, EPA Type 2 inflammation ω6 Lipoxins AA Protectins Protectins Resolvins Resolvins Maresins - Allergy from genetics to mechanisms Maresins ILCs Cyto NEU Vasoconstriction Th2 Suppression of cell influx Cell deactivation e I kines T cell apoptosis Antimicrobial defences Vasoconstriction S ection A EOS

Chronic inflammation MAC Increased efferocytosis Apoptotic cell clearance Production of IL-10 Tissue restitution Atopy RESOLUTION

Figure 2 Proresolving activities of ω3/ω6 polyunsaturated fatty acid (PUFA)-derived bioactive lipids in respiratory allergies. Specialized proresolving lipid mediators (SPMs) are generated in response to viral infection, Toll-like receptor (TLR) stimulation or type 2 inflammation. SPMs act in concert to reverse vasodilation, prevent leukocytic cell infiltration, de-activate inflammatory cells including Th2 cells and innate lymphoid cells (ILCs), upregulate macrophage efferocytic function and antimicrobial defences, promote clearance of apoptotic cells and debris, and repair damaged tissue, eventually restoring homeostasis. AA, arachidonic acid; DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; EOS, eosinophil; MAC, macrophage; NEU, neutrophil. (Adapted from Andreakos E. Asthma exacerbations: a molecular dichotomy between antiviral and pro-inflammatory responses revealed.;EMBO Mol Med. 2012;4(12):1231-3. Reprinted with permission under the Creative Common Attribution License or equivalent.)

82 Lipid mediators in resolution of allergic inflammation Global atlas oF allergy

key enzymes that carry out the tients with asthma, and low PD1 ogy of asthma. Annu Rev Physiol oxygenation of PUFAs. Substrate levels have been observed during 2009;71:489-507. availability, temporal expression acute exacerbations. PD1 and re- 3. Levy BD, Serhan CN. Resolution and activation of these and other solvins D1 and E1 have been fur- of acute inflammation in the lung. key enzymes ultimately determine ther used to promote resolution of Annu Rev Physiol 2014;76:467-492. which SPMs will be produced, allergic airway inflammation in ex- 4. Koltsida O, Karamnov S, Pyrillou where and when. perimental mouse models. On the K, Vickery T, Chairakaki AD, Tam- basis of current data, SPMs can There is emerging evidence that affect multiple processes during vakopoulos C et al. Toll-like re- SPMs are essential for the reso- an allergic response as depicted in ceptor 7 stimulates production of lution of allergic inflammation. Figure 2. In conclusion, although specialized pro-resolving lipid me- Lipoxin A4 (LXA4) has been found it its early days, the field of res- diators and promotes resolution in nasal secretions of patients with olution of inflammmation raises of airway inflammation. EMBO Mol allergic rhinitis or chronic rhinosi- expectations for the application Med 2013;5:762-775. nusitis, as well as bronchoalveolar of SPMs or substances triggering 5. Morita M, Kuba K, Ichikawa A, Na- lavage and exhaled breath con- their production for the treatment kayama M, Katahira J, Iwamoto R, densate of patients with asthma, of allergic diseases. et al. The lipid mediator protectin and low LXA4 levels have been linked to the severity of the dis- D1 inhibits influenza virus replica- KEY REFERENCES S ection A ease. LXA4 has also has been tion and improves severe influenza. 1. Barnig C, Cernadas M, Dutile S, Cell 2013;153:112-125. shown to inhibit IL-13 production Liu X, Perrella MA, Kazani S et al. by human innate lymphoid cells Lipoxin A4 regulates natural killer 6. Serhan CN, Chiang N, Van Dyke TE. Resolving inflammation: dual an- and resolve allergic inflammation cell and type 2 innate lymphoid cell - Allergy from genetics to mechanisms in rodents. Similarly, protectin D1 activation in asthma. Sci Transl Med ti-inflammatory and pro-resolution (PD1) has been detected in ex- 2013;5:174ra26. lipid mediators. Nat Rev Immunol haled breath condensate from pa- 2. Hamid Q, Tulic M. Immunobiol- 2008;8:349-361.

Lipid mediators in resolution of allergic inflammation 83 Global atlas oF allergy

Allergy and the 21 epithelial barriers

Stephen T. Holgate University of Southampton Southampton, UK

Asthma is a disorder largely restricted to the conducting airways Key messages characterised by episodic bronchoconstriction superimposed on • The epithelium in chronic asthma resembles a chronic wound a background of airway hypere- with impaired barrier function sponsiveness and is generally re- • This manifests as enhanced susceptibility to injury by viruses, pollutants and allergens and aberrant repair to sustain sponsive to bronchodilator drugs. inflammation and remodelling Airway inflammation is another • Recapitulation of morphogenetic epithelial growth and characteristic of asthma which, to transcription factors suggest persistent activation of the a variable extent, is responsive to epithelial mesenchymal trophic unit (EMTU) corticosteroids and often associ- • A new approach to prevention and treatment might aim to ated with allergy. increase airway resilience rather than focusing on suppressing This concept of allergy driving an inflammation once present IgE, mast cell and eosinophilic in- • Inadequate epithelial tight junction assembly has been demonstrated in asthma, atopic dermatitis and chronic rhinosinusitis

- Allergy from genetics to mechanisms flammation in asthma has been heavily underpinned by involvement of the Th2 subtype of T cells capable of releasing an array of cy- Activation of the tion (Figure 1). We referred to this

S ection A tokines and chemokines linked to epithelial mesenchymal interaction as activation of the the allergic cascade. trophic unit epithelial mesenchymal trophic In addition to inflammation, the unit (EMTU) since many of the sig- However, this simplistic approach pathology of asthma is dominat- nalling mechanisms are similar to has not been rewarded by thera- ed by structural changes includ- those engaged in lung morphogen- peutics targeting individual coming epithelial damage and mucous esis in the developing foetal lung. ponents of the allergic cascade, metaplasia, angiogenesis, smooth which while identifying selective muscle proliferation and angio- Enhanced susceptibility subgroups of “responders”, has genesis. In 2000, we proposed that of the asthmatic not provided a ubiquitous series these structural features were epithelium to injury of treatments where “one size the consequence of the airways The airways in chronic asthma fits all”. These less than encour- resembling a chronic wound in are more susceptible to injury as aging findings raise the question which epithelial damage is accom- revealed by the majority of novel whether the current Th2 model panied by aberrant production genes discovered by GWAS being for asthma adequately explains of growth factors and mediators preferentially expressed in the the disease in its very wide range that not only drive remodelling, epithelium. There is also strong of manifestations. but also sustain chronic inflamma- genetic and gene expression evi-

84 Allergy and the epithelial barriers Global atlas oF allergy S ection A

Figure 1 Schematic representation of the activated epithelial mesenchymal trophic unit (EMTU) in active asthma. - Allergy from genetics to mechanisms Increased susceptibility of the epithelium to environmental injury such as biologically active allergens, respiratory viruses and pollutants together with a delayed repair response leads to the secretion of a range of growth factors, cytokines and chemokines that both drive airway wall remodelling and sustain chronic airway inflammation. From( Holgate S.T. Arshad SH, Roberts GC, Howarth PH et al. A new look at the pathogenesis of asthma. Clin Sci. 2009; Reprinted with permission under the Creative Common Attribution License or equivalent.) dence that anti-oxidant pathways explains viral exacerbations of ly for 14 days almost abolishes the in the asthmatic airways are de- asthma, the relatively weak effect post-viral exacerbation in parallel fective leading to enhanced tissue of corticosteroids and the mixed with maintaining biomarkers of damage on exposure to viruses neutrophilic/eosinophilic inflam- anti-viral defence in respiratory and pollutants. Even under basal matory profile. The primary defect secretions. conditions, the asthmatic epithe- appears to be in the first step of lium shows enhanced expression induction of the anti-viral protec- The asthmatic epithelium of biomarkers of apoptosis (e.g. tive cytokines interferons (IFNs) displays impaired healing caspases, P85 fragment of PARP) β and λ after ds viral RNA binds The epithelium also contributes indicating loss of resilience. to microsomal TLR3 (Figure 2). At to persistence of asthma through least part of this defect can be ac- enhancing remodelling pathways Asthmatic airways, both in chil- counted for by the enhanced basal in the form of aberrant epithelial dren and adults, are more vulner- production of TGFβ to reduce repair. Over expression of the epi- able to common and usually innoc- SMAD3 phosphorylation and in- dermal growth factor (EGF) family uous respiratory viruses such as crease nuclear inhibitory signals of receptors and their phosphoryl- rhinoviruses (RVs) adenoviruses provided by SOCS1 and 3. Since ation in the asthmatic epithelium and coronaviruses. When infect- exogenous IFNβ could restore de- increases in proportion to disease ed with major or minor subclass fective anti-viral defence to asth- severity and is not accompanied by RVs, asthmatic epithelial cells fail matic epithelium in vitro, inhaled appropriate proliferative respons- to eliminate the virus adequately IFNβ could be a novel therapeutic es as a consequence of mobilisa- leading to enhanced replication, for severe exacerbations. Indeed, tion of cell cycle inhibitors such as shedding and cytotoxic cell death waf when administered at the first P21 to the epithelial nuclei where with pro-inflammatory media- sign of a common cold in severe they inhibit cell cycling. The net tor release. Such a mechanism asthma inhaled IFNβ1α given dai- result of this is delayed epithelial

Allergy and the epithelial barriers 85 Global atlas oF allergy

Figure 2 In chronic asthma, there is a defect innate immunity at the level of defective production of interferons when toll-like receptors such as TLR3, TLR5 and TLR7 become activated by viral nucleic acids as the first step in triggering an anti-viral response. This results in virus survival, replication and eventual cytotoxic destruction of epithelial cells with release of inflammatory mediators that contribute to exacerbations. The defect appears to be in Step 1 of the anti-viral cascade involving defective interferon regulatory factor (IRF) 3 signalling to the interferon genes with low production of IFN induction, reduced signalling via the common IFN receptor and, therefore, reduced IRF7 amplification of the antiviral cascade in Step 2. The IRF7 pathway itself remains intact. For this reason a small amount of exogenous IFNβ acting via the common IFN receptor can restore a full anti-viral response as shown in the left bottom panel. It is upon this principle that inhaled IFNb1ais being developed for the prevention/treatment of severe asthma exacerbations. (From Holgate S.T. Arshad SH, Rob- erts GC, Howarth PH et al. A new look at the pathogenesis of asthma. Clin Sci. 2009; Reprinted with permission under the Creative Common Attribution License or equivalent). - Allergy from genetics to mechanisms

healing following environmental the epithelial barrier function is Is asthma a disorder of insults and enhanced pro-fibrotic, persistently deranged in asthma epithelial sensing of the S ection A myogenic and angiogenic growth at the level of junctional integrity. inhaled environment? factor production such as TGFβ The defective barrier function in Such a “pro-asthmatic” epithelium PDGFs, IGFs, FGFs and VEGFs to asthmatic epithelium persists in may have its origin in the way the drive structural remodelling (5). differentiated epithelial cell cul- epithelium senses the inhaled en- The epithelium of asthmatic chil- tures following repeated passage vironment, with altered sensitiv- dren displays similar characteris- indicating an intrinsic abnormality ity being predetermined through tics and when grown as a monolay- linked to enhanced mucous meta- altered expression of transcrip- er and physically injured displays plasia, reduced cilia-genesis and tion factors involved in foetal lung slower and incomplete restitution reduced innate immune respon- morphogenesis such as SPDEF suggesting that the abnormality is siveness. Increased permeability increase secondary to FoxA2 and intrinsic to the asthmatic epitheli- is enhanced by T cell interactions NKX2-1 (TTF-1) decrease. Path- um irrespective of age. within the epithelium as well as way analyses have now shown the actions of “biologically active” that in addition to regulating the Inadequate epithelial allergens (e.g. proteases), viral in- “set point” for epithelial mucus tight junction assembly in fection and pollutant exposure, production, the same transcrip- asthma all of which perturb tight junction tion factors are also implicated in There is increasing evidence that functions. orchestrating innate immune de-

86 Allergy and the epithelial barriers Global atlas oF allergy S ection A - Allergy from genetics to mechanisms

Figure 3 Schematic representation of the role of epithelial transcription factors involved in morphogenesis of the foetal lung such as SPDEF, FoxA2 and TTF1 interacting with key transcription factors of the allergic cascade such as STAT6 in driving mucous metaplasia and orchestrating both chronic Th2-type inflammation and tissue remodelling. In asthma, the ‘set’ point for responding to environmental insults is altered to reduce airway resilience and augment the chronic wound scenario depicted in figure 1 and on the right side of the above figure.Reproduced ( with permission from Holgate S.T. The sentinel role of the airway epithelium in asthma pathogenesis. Immunol Rev 2011; 242: 205-219, with permission from Willey Blackwell.). fence (including IFN responses to KEY REFERENCES 937-947. viral infection) and inflammatory 1. Holgate S.T. Stratified approaches 4. Holgate ST. Innate and adaptive to the treatment of asthma. pathways such as those leading to Br J Clin immune responses in asthma. Nat Pharmacol 2013;76: 277-291. Med 2012;18: 73-83. Th2-type allergic responses (Fig- 2. Holgate ST, Davies DE, Lackie PM, 5. Xiao C, Puddicombe SM, Field S, ure 3). Wilson SJ, Puddicombe SM, Lordan Haywood J, Broughton-Head V, JL. Epithelial-mesenchymal inter- This leads to the overall conclu- Puxeddu I,et al Defective epithelial actions in the pathogenesis of asth- barrier function in asthma. J Allergy sion that the different asthma sub- ma. J Allergy Clin Immunol 2000;105 Clin Immunol 2011;128: 549-556. types have their origin in the way (2 Pt 1): 193-204. 6. Maeda Y, Chen G, Xu Y, Haitchi the airway epithelium “reads” the 3. Wark PA, Johnston SL, Bucchieri F, HM, Du L, Keiser AR, et al. Airway environment and translates this Powell R, Puddicombe S, Laza-Stan- epithelial transcription factor NK2 ca V, et al. Asthmatic bronchial epi- along discrete pathways to vari- homeobox 1 inhibits mucous cell thelial cells have a deficient innate metaplasia and Th2 inflammation. able disease manifestations and immune response to infection with Am J Respir Crit Care Med 2011; responses to interventions. rhinovirus. J Expt Med 2005;201: 184:421-429.

Allergy and the epithelial barriers 87 Global atlas oF allergy

Epithelial proteases 22 and allergic diseases

Ömer Kalayci Hacettepe University School of Medicine Ankara, Turkey

Proteases are composed of a group of molecules with diverse Key messages physiological and pathological effects. The human body is equipped • Proteases are physiologically important digestive enzymes with a variety of protease inhib- and generate peptides from precursor proteins. However, itors that counteract and thus both proteases and protease inhibitors can be active players in control the activity of proteases. inflammation However, these protease inhibi- • Proteases can be endogenous and exogenous. Almost all inhalant tors can be active participants of allergens such as pollens, mites and fungi have protease activity. inflammation. • Proteases exert their activity through Protease Activated Receptors, PAR 1-4, which are highly relevant in asthma and Proteases are naturally present in other allergic diseases all organisms. Depending on their • Proteases disrupt tight junctions between the cells, can catalytically active site, they are penetrate into the tissue and directly activate the cells apart termed as serine, cysteine, aspar- from the classical flow of immunological mechanisms tic and metalloproteases. Endog- - Allergy from genetics to mechanisms enous proteases are produced by inflammatory cells, most im- ical processes including allergic of goblet cells and increased mu- portantly by mast cells (chymase, diseases (Table 1). cous production (Figure 1). tryptase), neutrophils (cathep- S ection A sin, elastase) and epithelial cells The action of proteases can be me- Some activities of proteases are (thrombin). Almost all allergens in- diated through Protease Activat- PAR-independent and are ba- cluding house dust mites, pollens, ed Receptors (PAR) 1-4. They are sically a function of exogenous fungi and cockroach and many G protein-coupled receptors and proteases. They increase pro-in- are present almost on all cell types. bacteria, such as staphylococcus flammatory cytokine production PAR-dependent action of proteas- aureus, and viruses such as rhino- by airway epithelial cells, activate es results in: increased release of virus and influenza have signifi- eosinophils and increase mucus pro-inflammatory cytokines by cant protease activities. production. epithelial cells, endothelial cells, Physiologically, proteases func- inflammatory cells, keratinocytes Their highly relevant activity for tion as digestive enzymes, gen- and fibroblasts; enhancement of allergic diseases is the effect of erate active peptides from their IgE production; angiogenesis; in- proteases on epithelial tight junc- precursors and drive innate im- creased cell migration, infiltration tions and adhesion molecules. munity against multicellular or- and degranulation of inflamma- Through their ability to disrupt ganisms such as parasites, which tory cells; proliferation and con- occludin and claudin molecules are too large to be phagocytosed. traction of airway smooth muscle and to activate MMP9 (which ac- They also participate in patholog- cells; proliferation and activation tivates other cellular proteases),

88 Epithelial proteases and allergic diseases Global atlas oF allergy

TABLE 1 Proteases in inflammation proteases can penetrate through the intracellular junctions in the Source Protease Mode of action Actions mucosal epithelial barrier and ep- Exogeneous Pollens PAR dependent Disruption of tight junctions idermis. This allows the penetra- Fungi PAR independ- Disruption of barrier function tion of the allergenic molecules Mites ent Th-2 adjuvants into the tissues, where they can Cockroach Secretion of pro-inflamma- exert their protease as well as immune stimulating activities. This Hymenoptera tory cytokines Promotion of IgE synthesis recently emerging concept raises Bacteria the intriguing possibility that pro- Activation of Viruses tease activities of the allergens epithelial cells may be critical not only for the keratinocytes maintenance of tissue inflamma- inflammatory cells tion observed in allergic diseases, airway smooth muscle but may also be important in the Endogenous Thrombin Mostly PAR Activation of inception of allergic diseases. In addition, this initial penetration Plasmin dependent Endothelial cells may be subsequently followed by Tyrptase Epithelial cells the stimulation of a variety of cell S ection A Chymase Keratinocytes types without the classical IgE and Plasmin Fibroblasts other cellular immune mechanism. Kallikrein Airway smooth muscle

Trypsin All inflammatory cells KEY REFERENCES - Allergy from genetics to mechanisms 1. Jacquet A. Interactions of airway Elastase Glandular secretion epithelium with protease allergens Cathepsin G in the allergic response. Clin Exp Al- lergy 2011;41:305-311. 2. Birben E, Sackesen C, Turgutoglu N, Kalayci O. The role of SPINK5 in asthma related physiological events in the airway epithelium. PAR PAR Respir Med 2012;106:349-55. disruption of tight junctions 3. Takai T, Shigaku I. Barrier Dys- function Caused by Environmen- tal Proteases in the Pathogenesis of Allergic Diseases. Allergol Int Stimulation of epithelium 2011;60:25-35.

PAR

mast cell eosinophil endothelium neutrophil

exogenous protease endogenous protease

airway smoth muscle Figure 1 The action of proteases mediated trough Protease Activated Receptors (PAR).

Epithelial proteases and allergic diseases 89 Global atlas oF allergy

Mechanisms of immune 23 regulation in allergy

Willem van de Veen Mübeccel Akdis Swiss Institute of Allergy and Asthma Research Davos, Switzerland

Allergy is characterized by dominant allergen-specific Th2 re- Key messages sponses, and consequent IgE induction. Many factors influence • Immune tolerance to allergens have been studied in individuals the pathophysiology of allergic receiving allergen-specific immunotherapy (AIT) and high dose diseases, including genetic sus- allergen exposure models such as beekeepers and cat owners ceptibility, route/time/dose of • Early basophil and mast cell desensitisation is the first event of allergen exposure, structural fea- immune tolerance to allergens tures of the allergen and microbial • Induction of allergen-specific T regulatory (reg) cells exposure. characterized by the expression of multiple suppressor factors; CD25, CTLA-4, PD1, RUNX, HR2, IL-10 and TGF-beta is essential The immunoregulatory mecha- • Induction of IL-10-producing Breg cells after high dose Ag nisms that can mediate tolerance exposure and AIT was described, together with increased towards allergens in humans have allergen-specific IgG4 production, which is specifically confined been subject to intensive research to IL-10-producing Breg cells during the last decades. These • Decreased eosinophil, mast cell and basophil migration and - Allergy from genetics to mechanisms mechanisms have been studied in activation in the affected tissues also occurs during allergen allergic patients receiving aller- tolerance gen-specific immunotherapy (AIT) as well as in healthy individuals, S ection A who are exposed to high-doses in the induction and maintenance pression of antigen-presentation of allergens, such as beekeepers of tolerance towards allergens. capacity of DCs. IL-10 also sup- and cat owners. These human in These cells produce immunoreg- presses mast cell and eosinophil vivo models have demonstrated ulatory cytokines such as IL-10 activation, thereby interfering that the mechanisms leading to and TGF-β. TGF-β is a pleiotropic with early and late phase allergic peripheral tolerance to allergens cytokine that has a wide range of responses. Both Treg and Breg include early desensitization of functions including suppression cells contribute to IgG4 produc- mast cells and basophils, induc- of B and T cell proliferation and tion and suppression of IgE pro- tion of T regulatory (reg) and Breg differentiation, as well as control duction. Inducible IL-10-produc- cells, regulation of allergen-spe- of airway inflammation and air- ing B regulatory 1 (Br1) cells are cific immunoglobulin production way remodeling. IL-10 is a key an- skewed towards the production of and interference with migration ti-inflammatory cytokine, which anti-inflammatory IgG4 antibod- and activation of eosinophils, mast inhibits effector T cell activation ies. These cells may play a role in cell and basophils in the allergic directly through suppression of tolerance induction to allergens, tissues. co-stimulatory pathways in T as an increase in the frequency of Treg and Breg cells play a key role cells, and indirectly through sup- IL-10-producing B cells specific for

90 Mechanisms of immune regulation in allergy Global atlas oF allergy

Suppression of Th2 cell homing to tissues Endothelial cells Figure 1 Role of Treg and Breg cells in the suppression of allergic IgG4 production inflammation. Treg cells and their cytokines mainly IL-10 and TGF-β IgG4 production suppress Th2 type immune responses TReg and control allergic diseases in Br1 IL-10 B cell TGF-β many ways. Black arrows show the regulatory and suppressive effects of Treg cells on: B cells by inducing IL-10 IgG4 and IgA and suppressing IgE; on Th2 cell by suppressing proliferation and homing to tissues; on mast cells, IL-4 basophils and eosinophils via direct Th2 IL-13 and indirect suppressive effects; mast cell basophil eosinophil and on epithelial cell activation and IL-3 IL-4 proinflammatory properties by IL-5 direct and indirect suppression. In IL-9 addition, Br1 cells, which produce IL-10 suppress effector T cells and S ection A contribute to IgG4 synthesis. Direct and indirect suppressive effects on mast cells, basophils and eosinophils - Allergy from genetics to mechanisms the bee venom allergen phospholi- regulates both Th1 and Th2-type tivation during allergen-specific pase A2 was observed in bee ven- responses. Therefore, HR2 ap- immunotherapy by histamine re- om allergic patients, who received pears to be a key mediator in the ceptor 2. J Allergy Clin Immunol AIT. suppression of Th2 responses and 2012;130:1153-1158. 4. van de Veen W, Stanic B, Yaman G, The susceptibility of mast cells induction of tolerance towards allergens. Intensive research in the Wawrzyniak M, Söllner S, Akdis DG and basophils to allergen-induced et al. IgG4 production is confined to degranulation is reduced already area is essential to fully uncover human IL-10-producing regulatory after the first injection of AIT. This the molecular pathways of aller- B cells that suppress antigen-spe- may be the result of subclinical lev- gen tolerance. cific immune responses. J Allergy els of degranulation of these cells Clin Immunol 2013;131:1204- caused by allergen, leading to the KEY REFERENCES 1212. increased activation thresholds 1. Meiler F, Zumkehr J, Klunker S, 5. Akdis CA, Akdis M. Mechanisms of Rückert B, Akdis C.A, Akdis M. observed during in vitro measure- allergen-specific immunotherapy. J In vivo switch to IL-10-secreting ments. Furthermore, rapid up-reg- Allergy Clin Immunol 2011;127:18- T regulatory cells in high dose 27. ulation of histamine receptor allergen exposure. J Exp Med (HR) 2 was observed in basophils 6. Radulovic S, Jacobson MR, Durham 2008;205:2887-2898. SR, Nouri-Aria KT. Grass pollen during the first 6 hours of venom 2. O'Mahony L, Akdis M, Akdis CA. immunotherapy induces Foxp3-ex- immunotherapy. HR2 triggering Regulation of the immune response pressing CD4+ CD25+ cells in the could suppress FcεRI-mediated and inflammation by histamine and nasal mucosa. J Allergy Clin Immunol basophil degranulation. Histamine histamine receptors. J Allergy Clin 2008;121:1467-1472. can be released from mast cells Immunol 2011;12:1153-1162. 7. Akdis M, Akdis CA. Therapeutic and basophils that are activated 3. Novak N, Mete N, Bussmann C, manipulation of immune tolerance during AIT and can regulate T cell Maintz L, Bieber T, Akdis M et al. in allergic disease. Nat Rev Drug Dis- responses as well. HR2 negatively Early suppression of basophil ac- cov 2009;8:645-660.

Mechanisms of immune regulation in allergy 91 Global atlas oF allergy

Neuro-immune 24 regulation of allergic inflammation

Harald Renz Philipps-University of Marburg Marburg, Germany

The pathophysiology of asthma is complex and heterogeneous Key messages showing inter- as well as intra-individual variability. In addition to • Dysbalanced neurogenic responses may contribute to the the profound dysregulation in in- pathogenesis of allergic diseases and other inflammatory nate and adaptive immune func- diseases tions, dysbalanced neurogenic re- • The axon reflex participates in the acute inflammatory response sponses substantially contribute in rhinitis or asthma and is aggravated in asthmatic patients, due to the disease (Figure 1). to a high degree of neuronal plasticity • Increased neurotrophin levels were described in the asthmatic Airway hyper-responsiveness is patients where they play a critical role in maintaining eosinophilia considered a hallmark of asth- and Th2 driven inflammation, mast cell activation and enhance ma. The contractility of airway IgE production by B cells smooth muscle cells is controlled • There is an urgent need for the development of biomarkers by several types of neurons in- assessing the state of neurogenic dysregulation in asthmatic cluding sympathetic (adrenergic), patients together with the development of novel therapeutic - Allergy from genetics to mechanisms parasympathetic (cholinergic) and approaches aiming to re-establish the neurogenic homeostasis non-adrenergic, non-cholinergic (NANC) neurons. These types of neurons are part of the complex S ection A innervation network of the airways and the lung. Nervous Neurons control lung function via System the axon reflex (Figure 2). This is best described for sensory neu- Allergic rons, which pick up stimulatory Neurotrophins signals in the airways and transmit Phenotype them via the sensory neurons to the central nervous system (CNS). Immune Stimuli able to excite these neu- System rons include unspecific pollutants such as tobacco smoke particles, ozone and NO2 as well as signals driven from microbes and allergens. Cell damage caused by viral Figure 1 Neurotrophins contribute to bi-directional communication between infection and replication is an im- nervous and immune system.

92 Neuro-immune regulation of allergic inflammation Global atlas oF allergy

Trigger Stimulus Allergens Virus(RSV) Ozone Cigarette smoke Airway

Epithelium

Sensory Neuropeptides ganglion

Neuro-Inflammation S ection A • plasma-extravasation • bronchoconstriction • chemotaxis

• activation of immune cells - Allergy from genetics to mechanisms • mast cell-degranulation CNS

Figure 2 Neurogenic inflammation – The axon reflex.

portant trigger of the axon reflex. Low-affinity High-affinity binding Efferent signals are sent back NGF BDNF from the cell body of the neurons NT-3 NT-4 BDNF to the lung periphery. Within the NGF NT-4 NT-3 cell bodies, neuropeptides are produced and stored. Afferent firing of the neurons triggers not Cell membrane only the production, but also the retrograde transport of these neuropeptides back to the site of irritation and activation. These locally released peptides (includ- p75NTR TrkA TrkB TrkC ing tachykinins, neurokinins and others) play an important role in p75NTR ↔ Trk Cooperation? mediating acute pro-inflammatory events such as vasodilatation, recruitment of inflammatory cells, Figure 3 Neurotrophins and receptors. activation of mast cells and eosinophils and others. Therefore, the axon reflex is one important example of how neurons actively participate in the acute inflammatory response in rhinitis or asthma.

Neuro-immune regulation of allergic inflammation 93 Global atlas oF allergy

TABLE 1 model of allergic airway inflammation and asthma. Eur J Immunol The family of NGF and its receptors in bronchial asthma 1998;28:3240-3251. augmentation of TH-2 inflammation (NGF, p75) 4. Braun A, Lommatzsch M, Manns- anti-apoptic signals (NGF, BDNF, p75) feldt A, Neuhaus-Steinmetz U, Fischer A, Schnoy N, et al. Cellular • eosinophils sources of enhanced brain-derived • pulmonary plasma cells neurotrophic factor production in a mouse model of allergic inflam- acute broncho-constiction (NGF, p75) mation. Am J Respir Cell Mol Biol neuronal control of airway hyperresponsiveness (BDNF) 1999;21:537-546. epithelial wound healing 5. Kerzel S, Päth G, Nockher WA, Quarcoo D, Raap U, Groneberg DA, et al. Pan-neurotrophin receptor The axon reflex is aggravated in (observed in sputum, BAL, tissue, p75 contributes to neuronal hyper- asthmatic patients, due to a high blood). Further mechanistic stud- reactivity and airway inflammation degree of neuronal plasticity ob- ies carried out both in human and in a murine model of experimental served in many chronic diseases. mice models further revealed that asthma. Am J Respir Cell Mol Biol The development of the peripher- NGF and BDNF play a critical role 2003;28:170-178. in maintaining eosinophilia and al neuronal network, the state of 6. Nassenstein C, Braun A, Erpen- Th2-driven inflammation, mast activation, and the differentiation beck VJ, Lommatzsch M, Schmidt of neurons and various subtypes cell activation, while enhancing S, Krug N, et al. The neurotrophins is tightly controlled by another IgE production by B cells. There- nerve growth factor, brain-derived group of mediators termed neuro- fore, neurotrophins are consid- neurotrophic factor, neurotro- trophins (Figure 3). Neurotrophins ered major players in the overall phin-3, and neurotrophin-4 are belong to a family of mediators, maintenance of an already existing survival and activation factors for which control neuronal functions inflammatory response (Table 1). eosinophils in patients with aller- and exert also important effector There is an urgent need for the gic bronchial asthma. J Exp Med mechanisms on many other cells development of better diagnostic 2003;198:455-467. including immune cells. The pro- tools to assess the state of neu- - Allergy from genetics to mechanisms 7. Abram M, Wegmann M, Fokuhl V, totype of the neurotrophin family rogenic dysregulation in asthmat- Sonar S, Luger EO, Kerzel S, et al. is the nerve growth factor (NGF). ic patients. The development of Nerve growth factor and neurotro- The brain-derived neurotrophic novel biomarkers should go hand factor (BDNF) and other mem- phin-3 mediate survival of pulmo-

S ection A in hand with the development nary plasma cells during the aller- bers of this family have also been of novel therapeutic approaches gic airway inflammation. J Immunol extensively studied. Neurotro- aiming to re-establish neurogenic 2009;182:4705-4712. phins signal through two different homeostasis in this disease. types of receptors, the pan-neu- 8. Sonar SS, Schwinge D, Kilic A, rotrophin-receptor p75 and the KEY REFERENCES Yildirim AO, Conrad ML, Seidler K, high-affinity neurotrophin recep- 1. Nockher WA1, Renz H. Neurotro- et al. Nerve growth factor enhanc- tors TRKA, B and C. These recep- phins in allergic diseases: from neu- es Clara cell proliferation after lung tors are also expressed at various ronal growth factors to intercel- injury. Eur Respir J 2010;36:105- degrees and extend on cells of the lular signaling molecules. J Allergy 115. Clin Immunol 2006;117:583-589. innate and the adaptive immune 9. Hahn C1, Islamian AP, Renz H, system. 2. Nockher WA1, Renz H. Neurotro- Nockher WA. Airway epithelial phins and asthma: novel insight An important step forward in bet- into neuroimmune interaction. J Al- cells produce neurotrophins and ter understanding the neurogenic lergy Clin Immunol 2006;117:67-71. promote the survival of eosin- component in asthma was the de- 3. Braun A, Appel E, Baruch R, Herz ophils during allergic airway in- scription of increased neurotro- U, Botchkarev V, Paus R, et al. Role flammation. J Allergy Clin Immunol phin levels in asthmatic patients of nerve growth factor in a mouse 2006;117:787-794.

94 Neuro-immune regulation of allergic inflammation Global atlas oF allergy

United airways and 25 immune regulation

Claus Bachert University of Ghent Ghent, Belgium

It is well established that the upper and lower airways are linked Key messages

together, we therefore, call them S ection A “United Airways”. The develop- • The upper and lower airways are often diseased together ment of asthma mostly begins • A high percentage of young children with asthma are sensitized early in life time, and asthma man- to inhalant allergens ifests before the age of 16 years; • There is an increased risk of developing late-onset asthma in - Allergy from genetics to mechanisms usually, this early-onset asthma chronic rhinosinusitis patients is preceded by rhinitis symptoms. • These patients are often non-atopic, but express IgE to staphylococcal enterotoxins Over 80% of young children with • Apart from inhalant allergens, staphylococcal enterotoxin– asthma are allergen sensitized, specific IgE is related to asthma and atopy in this age group increases disease morbidity. Addi- tionally, atopy plays a critical role often suffer from sinus disease diators and cytokines. With the in the inception of asthma attacks with symptoms such as nasal ob- Th2 cells being prominent, an eo- in this age group, in particular dur- struction, loss of smell and facial sinophilic type of inflammation is ing viral infection. Also in later life, pain/headache. CRS can be differ- orchestrated, which involves key rhinitis is a powerful predictor of entiated into CRS without nasal interleukins (ILs) such as IL-4 and asthma, and atopy significantly in- polyps (CRSsNP) and with nasal IL-5. Very similar mechanisms, creases the risk for asthma devel- polyps (CRSwNP), based on symp- although patients with CRSwNP opment in late-onset asthma. toms (loss of smell is typical for often are non-atopic, also prevail A recent Europe-wide epidemio- CRSwNP, headache and facial pain in late-onset asthmatics with si- logic study on the prevalence of are typical for CRSsNP), nasal en- nus disease. Among the group of chronic rhinosinusitis (CRS), a dis- doscopy (presence of bilateral na- nasal polyps, especially the IL-5 ease manifesting in the nose and sal polyps) and CT scanning. From positive endotype, predominantly paranasal sinuses, confirmed the those phenotypes, CRSwNP has showing an eosinophilic inflamma- well-known association between a clearly increased risk of asthma tion, bears a high risk of asthma allergic rhinitis and early-onset comorbidity in Caucasian popula- comorbidity (up to 70%). In these asthma, but also demonstrated a tions. patients, serum total IgE often clearly increased risk of suffering Allergic airway disease is charac- is increased, independent of the from late-onset asthma in CRS terized by the mucosal synthesis atopic status of the patient. IgE patients. Thus, whereas younger of IgE molecules, which arm den- antibodies to Staphylococcus au- patients with asthma frequently dritic cells and mast cells. These reus superantigens (SE-IgE) can complain of allergic rhinitis symp- armed cells upon contact with be detected in a large proportion toms, older patients with asthma the allergen, release specific me- of these patients in the upper air-

United airways and immune regulation 95 Global atlas oF allergy

Figure 1 The association (relative risk ratio with 95% confidence interval) of early- and late-onset asthma with nasal allergies (early-onset) and chronic rhinosinusitis (late-onset). (Reproduced with permission from Jarvis D, Newson R, Lotvall J,et al. Asthma in adults and its association with chronic rhinosinusitis: The GA2LEN survey in Europe. Allergy 2012;67:91-98, - Allergy from genetics to mechanisms with permission from Willey Blackwell)

S ection A SAE-IgE

0 1

IFNg Cases: 15 Figure 2 Classification tree for Controls:10 comorbid asthma in patients with 0 1 5.8 (1.8 29.6) nasal polyps: SE-IgE positivity (categorical classifying determinant) is associated with a significantly increased risk to suffer from co- IL 17 Cases: 0 morbid asthma. (Reprinted from J Controls: 14 0.12 (0.03 3) Allergy Clin Immunol, 126/5, Bachert 0 1 C, Zhang N, Holtappels G,Presence of IL-5 protein and IgE-antibodies to staphylococcal enterotoxins in nasal Cases: 3 Cases: 6 polyps is associated with co-morbid Controls:17 Controls: 4 asthma, 962-968, Copyright 2010, with Ref. 5.1 (1.4 38) permission from Elsevier.)

96 United airways and immune regulation Global atlas oF allergy

1.0 Diagnostic tools in asthma should include questions on nasal and sinus symptoms, blood eosinophils, Controls total IgE and specific IgE abs to Non-severe 0.5 inhalant allergens and SEs also in SE-IgE Neg non-atopic subjects. The treat- GP-IgE Pos ment of the upper airways in these 0.0 HDM-IgE Pos patients might furthermore sup- HDM-IgE Neg port the management of the lower SE-IgE Pos airways, and therefore should be GP-IgE Neg part of the individual therapeutic -0.5 Severe strategy.

KEY REFERENCES -1.0 1. Shaaban R, Zureik M, Soussan D, Neukirch C, Heinrich J, Sunyer J, -1.0 -0.5 0.0 0.5 1.0 et al. Rhinitis and onset of asthma: Figure 3 Multiple correspondence analyses factor map with 95% confidence a longitudinal population-based

ellipses situating relationships between parameters and disease severity. SE study. Lancet 2008;372:1049- S ection A IgE is situated near severe asthma, whereas GP and HDM IgEs are situated 1057. near non-severe asthma. ( Reprinted from J Allergy Clin Immunol, 130/2, Bachert 2. Jarvis D, Newson R, Lotval J, C,van Steen K, Zhang N,Specific IgE against Staphylococcus aureus enterotoxins: an Hastan D, Tomassen P, Bousquet PJ,

independent risk factor for asthma, 376-381, Copyright 2012, with permission from - Allergy from genetics to mechanisms Bousquet J, et al. Asthma in adults Elsevier.) and its association with chronic rhinosinusitis: The GA2LEN survey in Europe. Allergy 2012;67:91-98. 3. Bachert C, Zhang N, Holtappels G, De Lobel L, van Cauwenberge P, Shixi L, et al. Presence of IL-5 protein and IgE-antibodies to staphylococcal enterotoxins in nasal polyps is associated with co-morbid asthma. J Allergy Clin Immunol 2010;126:962-968. 4. Bachert C, van Steen K,Zhang N, Holtappels G,, Cattaert T, Maus B, Figure 4 Odds ratios for asthma presence for each of the tertiles of serum et al. Specific IgE against Staphylo- SE-IgE in a pan-European study involving app. 3000 patients. The concentration coccus aureus enterotoxins: an in- of SE-IgE is significantly associated with an increased risk of suffering from dependent risk factor for asthma. J asthma (Reproduced with permission from Tomassen P, Jarvis D, Newson R, et al. Allergy Clin Immunol 2012;130:376- Staphylococcus aureus enterotoxin specific IgE and its association with asthma in 381. the general population: a GA²LEN. Study. Allergy 2013;68:1289-97, with permission 5. Tomassen P, Jarvis D, Newson R, from Willey Blackwell.) Van Ree R, Forsberg R, Howarth ways, but also with increasing se- ies are also associated with an P, et al. Staphylococcus aureus en- verity of asthma in serum. SE-IgE increased risk of asthma in the terotoxin specific IgE and its asso- antibodies are significantly asso- general European population, ac- ciation with asthma in the general population: a GA²LEN. Study. Aller- ciated with severe asthma, oral cording to a recent epidemiolog- gy 2013;68:1289-97 corticosteroid use and hospitali- ic study investigating more than 6. Fokkens WJ, Lund VJ, Mullol J, zations within the last 12 months, 55000 patients. Local IgE there- and lung function parameters. Bachert C, Alobid I, Baroody F et fore needs to be recognized as an al. European Position Paper on Rhi- As well as IgE antibodies to in- important mediator of disease of nosinusitis and Nasal Polyps 2012. halant allergens, SE-IgE antibod- the airways. Rhinol Suppl 2012;23:1-298.

United airways and immune regulation 97 Global atlas oF allergy

Genetics of 26 allergy

Stephan Weidinger University Hospital Schleswig-Holstein Kiel, Germany

Atopic diseases (eczema, asthma, rhinitis) affect an increasing num- Key messages ber of individuals worldwide and represent a major global health • Epidemiological and genetic research has provided firm evidence problem. Epidemiological and ge- for the existence of genetic determinants of atopic diseases with netic research has provided firm reported heritability estimates of up to 80% evidence for the existence of ge- • Atopic diseases are complex, polygenic traits, influenced by netic determinants of atopic dis- multiple disease genes eases with reported heritability • Results from studies using high density association mapping estimates of up to 80% (Figure 1). suggest that epithelial events and innate immune function are Atopic diseases are typical com- major drivers of pathogenesis plex, polygenic traits, which are • The detection of molecular interactions between susceptibility thought to be influenced by mul- genes and environmental triggers over time and the elucidation tiple disease genes. As for other of epigenetic factors as potentially underestimated source of complex traits, the identification hidden heritability will be major tasks for the next years

- Allergy from genetics to mechanisms of these genes is hampered by considerable phenotype and locus heterogeneity, incomplete pene- tary alterations of structural pro- intermediate molecular mecha- trance and interaction with most- teins and innate immune function nisms of immune mechanisms and

S ection A ly unknown non-genetic factors, are major drivers of pathogenesis. inflammation and illustrating the as well as by the yet incompletely With the exception of few sin- need for a more accurate classifi- understood interrelation of these gle loci exerting large effects on cation of allergic diseases based diseases with each other and with some phenotypes, e.g. filaggrin on their phenotypic and molecu- intermediate traits like IgE. Only null mutations on atopic dermati- lar basis (Figure 3). Of note, the recently, it has become possible tis (Figure 2), the majority of loci observed increase in prevalence to systematically unravel the poly- displays rather modest effects of atopic diseases is not primar- genic etiology of complex human when considered in isolation, and ily genetic, but rather due to the diseases by high density associa- the despite impressive progress in dramatic changes of environmen- tion mapping, which has allowed the field, only a small proportion tal conditions and modern health a breakthrough in the definition of the total heritability is yet ex- hazards that trigger a genetic of disease genes with an unprec- plained by known risk variants. It vulnerability into action. The de- edented richness of findings and is further becoming clear that ge- tection of molecular interactions a surprisingly high degree of re- netic risk factors overlap between between susceptibility genes and producibility. For allergic diseases, traditional entities rather than environmental triggers over time results from such studies suggest providing direct discriminators and the elucidation of epigenetic that epithelial events, e.g. heredi- suggesting shared and potentially factors as potentially underesti-

98 Genetics of allergy Global atlas oF allergy

1 MZ DZ H: 0.82-0.96 0,8 0,86 H: 0.60-0.79 0,76 H: 0.55-0.71 H: 0.40-0.65 0,6 0,65 0,6

0,4 H: 0.30-0.40 0,34

0,2 0,21 0,19 0,16 0,13 0,08 0 S ection A AtopicEkzem Asthma Crohn T2D T1D dermatitis - Allergy from genetics to mechanisms Figure 1 A genetic predisposition to the development of asthma, allergic rhinitis, and atopic dermatitis (AD) has been confirmed by numerous epidemiological studies with the strongest evidence delivered by twin studies, which show a distinctly higher concordance rate among monozygotic twins as compared to dizygotic twin pairs (for AD: 0.72-0.77 vs 0.15-0.23), and segregation analyses, which suggest that genetic factors account for more than 80% of the variance in the susceptibility to AD.

R2447X

2282del4 3321delA Q1701X E2422X S2554X S3269X

R501X 3222del4 3702delG Q1790X Q2417X S3247X K4671X

441delA 1249insG R826X 4271delAA 6950del8 S2889X K4021X

N C

3673delC R1474X 6834del5 7945delA 11029delCA

R1140X S1695X 5757del4 S2706X R4307X Q3683X

Q1256X E1795X 7267delCA 11033del4

5360delG 6867delAG

Figure 2 The strong association of low-frequency FLG null mutations with atopic dermatitis is one of the most robust genotype-phenotype linkages observed in complex human genetic disorders, and illustrates the importance of epithelial barrier defects in the development of allergic disease.

Genetics of allergy 99 Global atlas oF allergy

FLG IL2/IL21 HLA-DRB1 PRR5L CLEC16A TNFRSF6B SLC9A4 RAD50/IL13 C11orf30 ZNF652

1 2 3 4 5 6 7 8 9 10 11 12 1314 1415 1516 16 17 18 19 2021 22

Crohn‘s disease Ulc. colitis Asthma Rheum. arthritis Allergic rhinitis Multiple sclerosis Ulc. colitis Celiac disease Type 1 diabetes Atopy Psoriasis Ulcerative colitis Type 1 diabetes Crohn‘s disease Atopy IgE levels Vitiligo Atopy NOD2- IBD Glioma

Psoriasis ALL Asthma

Crohn‘s disease

strong correlation agonistic association moderate correlation antagonistic association

Figure 3 The majority of established risk loci for atopic dermatitis are also implicated in the development of other immune mediated-diseases with both agonistic and antagonistic effects.

mated source of this hidden her- Ruschendorf F, Patone G et al. A 2010;363:1211-1221. itability will be major tasks for the common variant on chromosome 5. Paternoster L, Standl M, Chen next years. 11q13 is associated with atopic CM, Ramasamy A, Bonnelykke dermatitis. Nat Genet 2009;41:596- K, Duijts L et al. Meta-analysis of KEY REFERENCES 601. genome-wide association stud- 1. Ellinghaus D, Baurecht H, Es- 3. Irvine AD, McLean WH, Leung DY. ies identifies three new risk loci parza-Gordillo J, Rodriguez E, Filaggrin mutations associated for atopic dermatitis. Nat Genet - Allergy from genetics to mechanisms Matanovic A, Marenholz I, H et with skin and allergic diseases. N 2012;44:187-192. al. High-density genotyping study Engl J Med 2011;365:1315-1327. 6. Weidinger S, Baurecht H, Naumann identifies four new susceptibility 4. Moffatt MF, Gut IG, Demenais F, A, Novak N. Genome-wide associa- loci for atopic dermatitis. Nat Genet Strachan DP, Bouzigon E, Heath tion studies on IgE regulation: are S ection A 2013;45:808-812. S, et al. A large-scale, consorti- genetics of IgE also genetics of at- 2. Esparza-Gordillo J, Weidinger S, um-based genomewide associa- opic disease? Curr Opin Allergy Clin Folster-Holst R, Bauerfeind A, tion study of asthma. N Engl J Med Immunol 2010;10:408-417.

100 Genetics of allergy Global atlas oF allergy

Epigenetics of 27 Allergy

R. Sharon Kimberly Morvarid Kari C. Chinthrajah Vu Tavassoli Nadeau Stanford University Stanford, USA

Epigenetics is the study of herit- able changes in gene activity that Key messages

are not caused by changes in the S ection A DNA sequence (Figure 1). These • Epigenetic modifications result in changes in the expression include modifications to the struc- of genetic material and can occur by three processes: DNA ture supporting the DNA called methylation, histone modification or microRNA mediated changes histones. Histone modification • Like genetics, epigenetic marks are inherited with each cell - Allergy from genetics to mechanisms (adding or removing acetyl groups) division and can persist through generations and may account in determines DNA packaging and part for the increased prevalence of allergic disease the cell’s ability to access and read • Genes in immune cells responsible for disease can be the associated sequence. DNA can epigenetically modified by variables such as environmental also be modified directly by adding exposures, diet, and the microbiome a methyl group to cytosine bases, • Identical twins with discordant asthmatic status have been which may restrict access to the shown to have different epigenetic marks on key immunologic DNA for transcription into mRNA. genes in their genome Finally, gene expression can be regulated at the post-transcriptional level by microRNAs, which studies, in which one twin suf- cumulative effect over multiple can further modify mRNA tran- fered from asthma and the other generations (Figure 4). This is par- did not. Asthmatic twins were scripts and histones to alter the ticularly relevant when consider- found to exhibit DNA methyla- expression of genes (Figure 2). ing the epidemiology of allergic dis- tion patterns that differed from ease, which seems to be amplified Many environmental factors are their healthy counterpart. Most with subsequent generations. At thought to regulate gene expres- notably, they had increased meth- the population level, allergic sen- sion through these mechanisms ylation and decreased expression sitization seems to have occurred and studies are ongoing to identify of the FOXP3 gene, which is im- in waves. The first wave was char- specific exposures and pathways portant for the anti-inflammatory acterized by allergic rhinitis and of effect (Figure 3). One of the function of T regulatory cells. Ad- asthma in industrialized countries main characteristics of epigenetic ditionally, they showed decreased (US, UK, Australia), more than 50 changes is that it is passed on to function of non-allergic effector T years ago. The second wave is now daughter cells with each cell divi- cells through methylation of the food allergy. Interestingly, devel- sion so it may have a long lasting IFN-gamma gene. oping countries are currently just effect on cell function. Furthermore, there is evidence seeing the first wave. This implies The importance of epigenetics in that some epigenetic marks can be that factors such as pollution, diet, determining allergic phenotype transmitted from parents to chil- and lifestyle may be driving epige- was illustrated in identical twin dren trans-generationally, with netic changes in different parts of

Epigenetics of allergy 101 Global atlas oF allergy

ACTIVE GENE (Euchromatin)

DNA Histone tails Chromatin methylation acetylation remodeling

TET DNMT HAT HDAC ATP-dependent enzymes

Figure 1 Different epigenetic mechanisms determine a gene’s active vs silenced state. DNA methylation involves SILENCED adding a methyl group DNA GENE base cytosine (red circle). (Heterochromatin) This prevents gene access to transcription factors and promotes other epigenetic changes. Histones, which are the world that are skewing people large molecules that act as a scaffold for DNA strands, can be modified on their tails. Modification such as histone acetylation (green stars) can avourf towards an allergic phenotype. histone molecules to spread apart, allowing for an open DNA structure called Epigenetics is an exciting and ex- euchromatin. Other histone modifications have been shown to favour a very panding field of asthma and allergy condensed state (heterochromatin) in which DNA transcription is impossible. research that provides new insight Chromatin remodelling is an active process that requires the intervention into our understanding of these of various ATP-dependent enzymes. (HAT = Histone acetyltransferase; complex syndromes, and possibly TET = Ten-eleven translocation dioxygenase; DNMT = DNA useful biomarkers for diagnosis methyltransferase; HDAC = Histone deacetylase). and characterization of various al-

lergic sub-phenotypes. RNA-induced silencing complex miRNA duplex KEY REFERENCES - Allergy from genetics to mechanisms 1. Kohli A, Garcia MA, Miller RL, Ma- her C, Humblet O, Hammond SK, et al. Secondhand smoke in combination with ambient air pollution ex- S ection A posure is associated with increased CpG methylation and decreased expression of IFN-γ in T effector cells and Foxp3 in T regulatory cells in children. Clin Epigenetics 2012;4:17. ribosome 2. Amarasekera M, Prescott SL, Palm- Blocked er DJ. Nutrition in early life, im- protein mRNA synthesis mune-programming and allergies: the role of epigenetics. Asian Pac J mRNA degradation Allergy Immunol 2013;31:175-182. 3. Martino D, Prescott S. Epigenetics Figure 2 MicroRNA (miRNA) is transcribed from eukaryotic DNA with RNA and prenatal influences on asthma polymerase to form a double-stranded structure. Further processing of the and allergic airways disease. Chest miRNA results in a structure with other proteins essential to miRNA’s function, 2011;139:640-647. shown here as the three blue geometric shapes. This complex is called an 4. Begin P, Nadeau KC. Epigenetic RNA-induced silencing complex, or RISC. The RISC will bind to complementary regulation of asthma and allergic mRNA sequences and has 2 modes of action: one, it can occlude and prevent disease. Allergy, Asthma & Clinical translation of the mRNA into functional proteins; two, it can recruit other Immunology 2014 proteins to degrade the bound mRNA.

102 Epigenetics of allergy Global atlas oF allergy

Environmental Exposures Constituting Prenatal Epigenetic Changes to Immunity Pollution Food

Folate Tobacco n-3 Polyunsatu- rated Fatty Acids Pollution Anti-oxidants

Bacteria Figure 3 Environmental factors such as Farming pollution, food, agriculture and microbiota

have been shown to have significant impli- S ection A Viruses cations on early immune programming and development. Prenatal exposure to these Pets Probiotics elements is postulated to cause epigenetic changes to genes and signaling pathways Agriculture Microbiota of fetal immunity that may have lasting - Allergy from genetics to mechanisms effects during the child’s life. Trans-generational Amplification Hypothesis

Figure 4 Figure A depicts a transgenerational model of atopic disease predisposition that is solely based on environmental stressors. This model predicts that environmental pressure directly correlates with an increase in Figure A baseline genetic risk for disease only for generations that lived during the changed environment. Figure B illustrates an epigenetic transgenerational inheritance model wherein a change in environment not only increases baseline risk for disease but also induces epigenetic changes in subsequent generations as shown in animal models. This could lead to an amplification of the atopic disease that lasts up to two generations after return to normal environment.

Figure B

Epigenetics of allergy 103 Global atlas oF allergy

Endotypes of 28 allergic diseases

Ioana Agache Cezmi A. Akdis Transylvania University Swiss Institute of Allergy and Asthma Brasov, Romania Research, Davos, Switzerland

The heterogeneity of allergic diseases in relation to clinically Key messages significant outcomes, including response to treatment, has been • The heterogeneity of allergic diseases in relation to clinically established beyond any doubt. significant outcomes, including response to treatment, pushed However, current guidelines ig- towards the development of the concept of phenotypes and nore disease heterogeneity and endotypes causal pathways, leading to unsuc- • There are several benefits of using endotypes such as stratified cessful clinical “bulk” trials or con- treatment and better characterization of subjects in genetic and tradictory results in epidemiologic epidemiologic studies and clinical trials for drug development and genetic surveys. • Several endotypes can be described for asthma, rhinitis and chronic rhinosinusitis based on the mechanisms of inflammation, In the beginning, disease pheno- driving cause, genetic factors, tissue-related factors and types describing clinical and mor- response to treatment phologic characteristics as well • Translation of biomarkers into pathway-specific diagnostic as unique responses to treatment tests is essential and should guide the design of future clinical - Allergy from genetics to mechanisms have been developed to address trials, incorporating both longitudinal and mechanism-tailored the complexities of the disease. endpoints Phenotypes are clinically rele- • Stratified treatment should be endotype-, biomarker- and vant observable characteristics outcome-driven S ection A in terms of presentation, triggers, and treatment response, but do not necessarily relate to or give derstanding of pathophysiological (Figure 2). insights into the underlying pathomechanisms of allergic disease. The ideal biomarker should be logical mechanism. For most of the New and expensive biological pathway-specific, reproducible, allergic diseases heterogeneous therapies for allergic diseases are easily measurable, and affordable. and mechanisms of the disease-re- emerging that are highly effica- Biomarker research is increasingly lated metabolic, inflammatory, cious only for a selected group of shifting towards multidimensional immunological, and remodeling patients. The response to targeted approaches, in which the clinical pathways have been described, interventions in allergic disease value of a combination of various and defined as a disease endotype. may vary among individuals or for markers is studied. Translation of There are several benefits of en- the same individual in relation to biomarkers into pathway-specific dotyping in a clinical setting (Fig- outcome measures (dissociated diagnostic tests is essential and ure 1). In addition, aligning mouse effect). Therefore, targeted treat- should guide the design of future models to human endotypes is a ment should be both biomark- large clinical trials, incorporating more relevant approach to the un- er-driven and outcome-driven both longitudinal and mechanism

104 Endotypes of allergic diseases Global atlas oF allergy

In epidemiological trials: subgrouping of asthma cohorts using endotypes may better determine the incidence, prevalence, morbidity, mortality and health-care resources utilisation related to asthma.

In genetical studies: relating endotypes to genes may yield more specific associations.

In drug-related trials: refining inclusion criteria using endotypes may identify patient subgroups with particular benefit from existing as well as new treatments. This could result in a substantial improvement in asthma care.

It is anticipated that in the future endotype-tailored treatment (stratified medicine) could lead to measurable improvement in the optimization of care of individual cases and hopefully result in an improvement in health care costs by applying specific treatments S ection A only to those who will benefit from it. - Allergy from genetics to mechanisms Figure 1 Potential advantages of endotyping. (Reproduced with permission from Agache I, Akdis C, Jutel M, Virchow JC, Untangling asthma phenotypes and endotypes. Allergy. 2012;67:835-46, with permission from Willey Blackwell.)

Response to a targeted antiasthmatic drug

Genetic and epigenetic Immune-inflammatory Remodeling phenotype Efficacy at the target site background pathway (ASM, epithelium) of the drug formulation

inter- and intraindividual differences in response (dissociated effect)

biomarker outcome driven treatmen driven treatment

Figure 2 Response to targeted treatment in asthma. (Reproduced from Agache IO. From phenotypes to endotypes to asthma treatment. Curr Opin Allergy Clin Immunol. 2013 Jun;13:249-56.)

Endotypes of allergic diseases 105 Global atlas oF allergy

TABLE 1 tailored endpoints. The selection of outcome measures is difficult, Th2 high and Th2 low asthma endotypes as it must reflect the mechanistic Endotype Biomarker intervention and should be relevant for both the population as a Th2 high IgE driven (atopic Total serum IgE whole and for the particular indi- and non-atopic) IgE on DC Sputum total or specific IgE vidual. While endotype-driven thera- IL-4/IL-13 driven Serum periostin Sputum IL-13 peutic strategies are becoming IL-4 rc α SNPs increasingly successful in asthma, only feeble attends were made for IL-5/eotaxin driven Sputum/blood eosinophils other allergic diseases. In addition, FeNO the issues related to the dissociat- Eotaxin 2 ed effect and drug efficacy at the PGD2 driven ? target site remain unresolved.

Aspirin intolerant Sputum/urine leukotrienes and For asthma the “Th2 high” and prostaglandins “Th2 low” endotypes are well recognized and used to ascribe spe- Mast cell/IL-9 driven) ? cific treatment. Several subtypes Eosinophilic obese Sputum IL-5 of the Th2-high and Th2-low en- asthma Submucosal eosinophils dotypes can be described based on the main operating molecular Asthmatic Eosinophilic inflammation mechanism (Table 1). granulomatosis (Th1 Corticosteroid resistance driven) ? Autoimmunity markers Applying the same model to allergic and non-allergic rhinitis Innate immune TSLP response driven IL-33/ST-2 could prove as successful in promoting personalized approaches, Th2 low Neutrophilic (Th17/ Sputum neutrophilia especially for the severe forms of IL-8/purinergic Low IgE the disease. The well recognized inflammation driven) Low eosinophils link between rhinitis and asthma - Allergy from genetics to mechanisms High reversibility should be integrated and tackled Paucigranulocytic No inflammation (sputum/bronchial within the framework provided by (EMTU driven) biopsies) endotypes. Prominent remodeling S ection A Rhinitis endotypes can be defined Small airways Flow, resistance, ventilation heterogeneity in relation to the background in- disease Alveolar inflammation flammation or in terms of treat- Microbioma Non-eosinophilic exacerbation-prone ment responsiveness. The follow- asthma ing endotypes can be proposed PCR evidence of infections for allergic rhinitis: eosinophilic or Th2 (IL-4/IL-13) inflammation; Innate IR driven BAL/sputum TNF-α steroid-responsive, anti IgE re- Non-eosinophilic L-Arg/ADMA sponsive, anti IL-5 responsive, obese asthma anti IL-4/IL-13 responsive. For non-allergic rhinitis the defini- Abbreviations: tion of endotypes (eosinophilic or ADMA = asymmetric dimethyl arginine; BAL = broncho-alveolar lavage; EMTU = neutrophilic inflammation, steroid epithelium-mesenchyme trophic unit; FeNO = fractional exhaled nitric oxide; L-Arg responsive or resistant) should = L-arginine; PCR = polymerase chain reaction; SNPs = single-nucleotide polymorphisms include the driving cause: superantigens, local IgE production, autoantibodies. In the same line a

106 Endotypes of allergic diseases Global atlas oF allergy

PRACTALL document described of children with cow’s milk allergy chow JC. Untangling asthma phe- several endotypes for chronic rhi- can be distinguished by casein- notypes and endotypes. Allergy nosinusitis (CRS) characterized and milk-specific IgE levels, milk 2012;67:835-846. by differences in responsiveness specific basophil reactivity, and 4. Akdis CA, Bachert C, Cingi C, Dyke- to treatment, including topical milk SPT mean wheal diameters. wicz MS, Hellings PW, Naclerio RM intranasal corticosteroids and bi- In another study IL-25 was found et al. Endotypes and phenotypes of chronic rhinosinusitis: a PRACTALL ological agents, such as anti–IL-5 highly elevated only in children document of the European Acade- and anti-IgE mAb (Figure 2). Some with a clinical response to peanut, my of Allergy and Clinical Immu- of the described CRS endotypes suggesting a role for IL-25 in the nology and the American Academy were based on different biomark- pathogenesis of peanut allergy of Allergy, Asthma & Immunology. ers linked to underlying mecha- and as a biomarker of a severe at- J Allergy Clin Immunol 2013;131: nisms. opic phenotype. 1479-1490. Atopic dermatitis (AD) is a chron- 5. Wollenberg A, Seba A, Antal AS. For drug allergy several pheno- Immunological and molecular tar- ic inflammatory skin disease with types were described for the hy- gets of atopic dermatitis treat- complex genetic and immunolog- persensivity to non-steroidal an- ment. Br J Dermatol 2014 Apr 11. ical mechanisms. Several endo- ti-inflammatory drugs (NSAIDS): doi: 10.1111/bjd.12975. [Epub types can be proposed according aspirin-exacerbated respiratory ahead of print] to the inflammatory background disease, aspirin-exacerbated cuta- 6. Mu Z, Zhao Y, Liu X, Chang C, Zhang S ection A such as Th2/IL-22/periostin high neous disease, multiple NSAID-in- J. Molecular Biology of Atopic Der- or Th17/Th1 high or in relation to duced urticaria/angioedema, matitis. Clin Rev Allergy Immunol the expression of fillagrin, MATT single NSAID-IgE reactions and 2014. [Epub ahead of print] or vitamin D pathway genes muta- single NSAID T cell responses, 7. Ford LS, Bloom KA, Nowak- - Allergy from genetics to mechanisms tions. For the Th2 type AD serum which differ in terms of the path- Węgrzyn AH, Shreffler WG, Masi- periostin is related to disease se- ogenic pathways involved, as well lamani M, Sampson HA. Basophil reactivity, wheal size, and immuno- verity. Targeting both the inflam- as the mediators released after globulin levels distinguish degrees matory-immune dysregulated provocation tests. of cow's milk tolerance. J Allergy pathways or the barrier defect Clin Immunol 2013;131:180-186. holds future promise. Several new Key References 8. Aalberse JA, van Thuijl AO, Meijer targets such as toll-like recep- 1. Lotvall J, Akdis CA, Bacharier LB, Y, de Jager W, van der Palen-Merk- tors, type 2 innate lymphoid cells Bjermer L, Casale TB, Custovic A us T, Sprikkelman AB et al.Plasma and tight junction proteins are et al. Asthma endotypes: a new IL-25 is elevated in a subgroup emerging. Promising new thera- approach to classification of dis- of patients with clinical reactiv- peutic agents in the near future ease entities within the asthma ity to peanut. Clin Transl Allergy syndrome. are sphinganin, cannabinoids and J Allergy Clin Immunol 2013;3:40. 2011;127:355–360. highly targeted monoclonal anti- 9. Ayuso P, Blanca-López N, Doña I, bodies. 2. Agache IO. From phenotypes to Torres MJ, Guéant-Rodríguez RM, endotypes to asthma treatment. Canto G et al. Advanced pheno- For food allergy phenotypes Curr Opin Allergy Clin Immunol typing in hypersensitivity drug re- prove useful for predicting severe 2013;13:249-256. actions to NSAIDs. Clin Exp Allergy reactions. Different phenotypes 3. Agache I, Akdis C, Jutel M, Vir- 2013;43:1097-1109.

Endotypes of allergic diseases 107 Global atlas oF allergy

Animal models of 29 allergic disease

Remo Frei Liam O’Mahony Swiss Institute of Allergy and Asthma Research Davos, Switzerland

Animal models have been developed for almost all types of aller- Key messages gic disease such as asthma, allergic rhinitis, food allergy, anaphylax- • A wide range of animal models exist for a variety of allergic is, atopic dermatitis and allergic diseases conjunctivitis. These models are • Animal models are particularly useful for identifying novel important to examine the mech- cellular and molecular immunological mechanisms of allergy anism of the disease, the activity • No single animal model completely recreates all the aspects of an of a variety of genes and cellular allergic response pathways, define the role of environmental factors (such as the microbiota), predict the safety of of the allergen with substances the features of allergy. This is very (e.g. LPS), which stimulate the in- new drugs before being used in important to take into account nate immune response. Certain when choosing the correct model clinical studies, define the patho- protocols require the combina- to address the specific experimen- genic pathways and suggest new tion of allergen with an adjuvant,

- Allergy from genetics to mechanisms tal question. For example, chronic therapeutic options. The correct for example aluminium hydroxide exposure models are required to animal model should reflect the (ALOH3, Alum), which is one of the examine many of the structural disease pathophysiology as close- preferred adjuvants in respiratory changes associated with allergic ly as possible and new models are

S ection A allergy models. The sensitization, responses within the airways. essential for the development of challenge and analysis parameters new therapies. of murine allergy models are sum- Notwithstanding the limitations of these models, several studies Laboratory mice do not usually marized in Figure 1. carried out in animal models have spontaneously develop allergies Although murine models of aller- given important clues that explain and a range of sensitization and gy provide important insights into the pathophysiological conditions challenge protocols have been the disease mechanisms, there related to the disease status. For developed. The number of sensiti- are some limitations that should instance, the role of Th2 type cy- zations and challenges is decisive be considered. In addition to the tokines and T regulatory cells in for the development of acute or genetic and physiological differ- the pathogenesis of allergy have chronic forms of these models. The ences between humans and mice, been particularly well-studied in nature of the allergic disease and there are also limitations due to animal models. inflammatory response is directly complexity of this disease. In oth- influenced by the genetic back- er words, mice do not develop al- Human clinical studies remain the ground of the mice, the allergen, lergy. One can replicate important gold standard for determining the type of the sensitization and chal- components of the disease, but no clinical efficacy of new therapeu- lenge protocol and contamination single model accurately models all tic approaches. Murine models

108 Animal models of allergic disease Global atlas oF allergy

Sensitization

Food allergy Respiratory allergy Skin allergy

Challenge

Spleen Colon Spleen Lymph nodes Lung Serum Lymph nodes S ection A

Analyses Bronchoalveolar IgE lavage - Allergy from genetics to mechanisms Ear thickness

Differential Flow Re- Lung function qPCR Histology cell count cytometry stimulation

Figure 1 Overview of the experimental steps commonly used in allergy models. Allergy mouse models typically comprise a sensitization, a challenge, and an analyses phase. After sensitization, allergic responses are provoked, depending on the model, by oral application (food allergy), by inhalation (respiratory allergy), or by skin contact (skin allergy) with the allergen. The severity and mechanisms of the allergic response are determined using a variety of technologies, focused on the relevant model organs or using functional assessments such as lung function testing or ear thickness measurements. will continue to provide important 2008;1:213-220. mechanistic clues, while improved 3. Lyons A, O’Mahony D, O’Brien F, models may extend our under- MacSharry J, Sheil B, Ceddia M et standing of the basic mechanisms al. Bacterial strain-specific induc- for examining new therapeutic op- tion of Foxp3+ T regulatory cells is tions. protective in murine allergy models. Clin Exp Allergy 2010;40:811- Key References 819. 1. Fuchs B, Braun A. Improved mouse models of allergy and allergic asthma--chances beyond ovalbumin. Curr Drug Targets 2008;9:495-502. 2. Nials AT, Uddin S. Mouse models of allergic asthma: acute and chronic allergen challenge. Dis Model Mech

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