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Allergen Components Tests and What They Mean

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Allergen Components Tests and What They Mean Molecular Allergology: The Clinical Utility of Allergen Components Neal Bradshaw, Allergen Component Specialist April 2010 Overview • What are allergen components? • What type of diagnostics are there? • Back ground – allergen components • Study Work • Clinical Cases • ImmunoCAP ISAC How can molecular allergology improve my clinical practice? • What is triggering the reaction? • Is this true allergy or is the patient sensitised? • How severe is the reaction going to be? • How long will the allergy persist? • How can I rationalise oral food challenges? • Can I make immunotherapy more effective in this patient? Helping Patients Improve QoL AllergyAllergy diagnosisdiagnosis -- HistoricalHistorical overviewoverview ImmunoCAP Characterisation First allergens Diagnostic ISAC ® of IgE cloned recombinant goes global allergen panels Provocation testing RAST* First allergen chip 1880 1967 1988-91 1995-1999 2000 2007 In-vivo testing In-vitro testing Component-resolved diagnosis Limitations of Current Testing Current tests define allergen-containing sources, not specific allergenic molecules – Up to 50% of patients asymptomatic sensitisation1 – Up to 30% patients with false positive results in “open” challenges due to bias2 • The major challenge to clinicians is distinguishing sensitisation versus true allergy3 1. Chapman et al. Ann Allergy Asthma Immunol. 2006;96:S1-S68. 2. Nowak-Wegrzyn et al. Work Group Report: Open Food Challenge Testing. JACI 2009;123:S365-383. 3. Arbes et al. JACI 2005;116:377-383. Two Platforms • Allergen Components – ImmunoCAP Specific IgE – Over 85 different specific IgE component diagnostics • ImmunoCAP ISAC –21st Century allergy diagnostics – Protein array biochip – 103 individual components What is an allergen? ?? More than one protein! Ara h 1 Ara h 3 Ara h 2 Ara h 9 Ara h 8 Proteins of Peanut Whole allergen extracts vs components Extraction Extract ImmunoCAP Recombinant Technology Allergen raw material Purification Component ImmunoCAP Component Nomenclature Can f 1 Canis familiaris , allergen # 1 Prefix ”r” for recombinant or ”n” for native rCan f 1 ‐ nCan f 1 Protein groups Plant Foods Others PR‐10 proteins, Bet v 1 homologue Serum albumin’s •Heat labile protein •A common protein present in different biological fluids and solids e.g cow’s milk and beef, egg and chicken Profilins •Cross‐reaction between albumin from different anima species are well known. Cat and dog, cat and pork. •Highly cross‐reactive, present in most plants Storage proteins Enzymes •Proteins found in seeds • Including Bromelin and Pepsin •Often stable and heat resistant •Often associated with systemic and severe reactions Moulds • Limited cross reactivity LTP, lipid transfer protein • Useful for specific diagnosis •Stable to digestion and heat •Often associated with systemic and severe Others reactions in addition to OAS • Tropomyosin‐ A class of highly conserved Protein, heat stable • Egg ovomucoid ‐ Very heat stable and enzyme resistant CCD, cross‐reactive carbohydrates •Highly cross‐reactive, present in most plants •Seldom associated with clinical symptoms Venoms • Determine venom allergy in relation to specific Important: species for immunotherapy purposes Some species have very similar DNA and therefore share the same or similar allergen proteins. Plant Foods demonstrate high levels of cross reactivity between species e.g. wheat and grass PR-10 proteins Bet v 1‐homologous allergens PR-10 proteins, Bet • Tree pollen v 1 homologue •Fruits •Heat labile protein • Vegetables •Often associated with local symptoms •Nuts •Often associated with allergic reactions to fruits and vegetables in northern Europe Bet v1 Pr u p 1 Cor a 1 Ara h 8 Mal d 1 Gly m 4 Profilin’s Bet v 2‐homologous allergens Profilins •Tree pollen • Highly cross-reactive, •Fruits present in most plants • Vegetables •Seldom associated with •Nuts clinical symptoms but may • Grass Pollen cause demonstrable or • Weed Pollen even severe reactions in a small minority of patients Bet v 2 Phl p 12 Pru p 4 Hev b 8 LTPs non‐specific Lipid Transfer Proteins LTP, lipid transfer protein •Fruits • Vegetables •Stable to digestion and •Nuts heat • Weed pollen •Often associated with allergic reactions to fruits and vegetables in southern Europe •Often associated with systemic and severe Pru p 3 Ole e 7 reactions in addition to Cor a 8 Ara h 9 OAS Par j 2 Art v 3 Storage proteins Storage proteins • Legumes •Nuts •Proteins found in seeds •Grains and seeds •Often stable and heat resistant •Often associated with systemic and severe reactions 2 S albumin, Ara h 2 Gliadins 7 S globulin, Ses i 3 Alpha amylase inhibitors 11 S globulin, Gly m 6 Vicilin, Jug r 2 Rule of Thumb • Profilin and PR10 proteins o Highly cross reactive (PR 10 especially to Birch) o Often associated with less serve reactions e.g. OAS • nsLTP’s and Storage Proteins o Associated with more severe reactions o More heat/digestive enzyme resistant and therefore can be more often associated with OAS and well as digestive problems Tropomyosin • A class of highly conserved •Dust mite Protein • Cockroach • Physically associated with • Crustacean actin and myosin in muscle Fibres • Heat stable • Found in most edible parts of crustaceans Der p 10 Pen a 1 CCD (Cross Reactive Carbohydrate Determinants) • Many allergen are •Plants glycpcroteins •Venom • And therefore share similar glyco-epitopes •Dust mite • CCD’s therefore be highly cross reactive • these determinants are treated as foreign epitopes in humans they are considered highly immunogenic Peanut Peanut Allergen Components Ara h 1 Storage proteins Ara h 2 Storage proteins Ara h 3 Storage proteins Ara h 5 Profilin Ara h 8 PR-10 Ara h 9 LTP • Ara h1-3 are the major peanut allergens1 1.McDermott et al. Clin. Exp. Allergy 2007;37:753‐763. Peanut allergy in 3-5 year old children in UK 5 4 3 2 Prevalence % 1 P<0.001 0 1989 1995 1999 Birth cohort Sensitised Allergic Hourihane, 2007 MAAS Peanut Study MAAS 1085 born into unselected population based cohort 1029 attended 8-year Follow-up Inclusion criteria 11,8% were -SPT ≥ 3mm 110 children were peanut -sIgE>0.2 kUa/l peanut sensitized sensitised - Suggestive history 81 Oral Food Challenges The prevalence of clinical peanut allergy among sensitised subjects 22,4% Nicolaou,,Woodcook, Custovic et al. JACI 2010 Pattern of sensitisation to allergen components among peanut allergic and tolerant individuals True peanut allergy Cross-reactive sensitization Nicolaou et al. JACI 2010:125:191-197. Conclusion MAAS Peanut study • The majority of children considered peanut-sensitised on the basis of standard tests do not have peanut allergy • Ara h 2 was the most important predictor of clinical peanut allergy Clinical implications Measurement of IgE response to major peanut allergen Ara h 2 is more useful in predicting clinical allergy than currently used skin or blood tests Assessment of peanut allergy Peanut (SPT/specific IgE) + Ara h 2 Peanut: neg Peanut: pos Peanut: pos Ara h 2: neg Ara h 2: neg Ara h 2: pos Low risk for severe Risk for severe High risk for severe reactions to peanut reactions to peanut reactions to peanut Further testing: Further testing: In geographical Risk grading: areas where birch is Ara h 1 zzz common consider Ara h 3 zzz testing for Ara h 8 Ara h 9 zzz Ara h 8 zz CCD z Case: 7 year-old girl Consultation for regular control of eczema, rhinitis and food allergy Personal history • Eczema since childhood and uses steroid ointments • Allergic rhinitis against birch • Oral itching when eating peanuts and tree nuts • The parents want to know if it is ok if their daugher eats peanuts & tree nuts because recently no reactions to small amounts. IgE Hazelnut (f17): 78 kUA/l Peanut (f13): 0.40 kUA/l → Can we answer the parent’s question? Component testing Peanut f13 0.40 kUA/l Ara h 2 0.02 kUA/l Ara h 8 21.5 kU /l Markers of A Markers of primary cross Hazelnut f17 78 kU /l sensitisation A reactions Cor a 1 69.2 kUA/l Cor a 8 0.02 kUA/l PR-10 Birch t3 >100 kUA/l Interpretation Primarily cross reaction with birch If eating peanuts – mild reaction may occur ”May contain peanuts/nuts” label of less concern Treatment Epipen likely not needed Wheat Wheat allergy • Among the 6 foods responsible for most food allergic reactions in children • Extensive cross-reactions to grasses and fruits • What components are important? • Omega-5 gliadin • Linked Clinically to Exercised Induced Anaphylaxis12 1Palosuo et al J Allergy Clincal Immunol 1999;103:912-7 2 Ito et al Allergy 2008 63:1536 - 1542 Wheat - Omega-5 gliadin sIgE Tri a 19 (omega-5 gliadin) No Mild Moderate Severe 88 wheat sensitised japanese children, 44 had wheat allergy and 44 had no wheat allergy Ito et al , Allergy 2008 Wheat cases sIgE (kUA/L) protein wheat omega-5 gliadin wheat LTP profilin CCD age country (f4) (f416) * (g212) (Ro214) Symptoms Patient 1 65 Sweden 3,06 8,0 0,06 0,01 0,00 anaphylaxis Patient 2 32 Spain 6,14 0,08 0,11 0,14 4,95 no symptoms Patient 3 14 Spain 24,2 0,01 27,7 0,02 0,14 anaphylaxis Patient 4 29 Spain 2,32 0,02 0,11 7,8 0,14 no symptoms * Experimental ImmunoCAP Tri a 14 (LTP) and Tri a 19 (ω5‐gliadin) can help to discriminate wheat allergy from clinically irrelevant sensitisation C. Eriksson, unpublished data Egg • One of the most common allergies in infants and young children • Common clincal decision - reintroducing cooked egg back into the diet Major Egg Allergen Components1 Gal d 1 Ovomucoid Gal d 2 Ovalbumin Gal d 3 Conalbumin Gal d 4 Lysozyme 1, Bernhisel-Broadbent et al J Clin Allergy Immnol 1994;93;1047-59 Ovomucoid • Consists of 3 domains containing 3 disulfide bridges each (total 9 SS-bridges) • Very heat stable and resistance to proteases • Relative resistant to enzymatic degradation • High specific IgE concentrations to ovomucoid is associated with persistent egg allergy 1,2,3,4 1, Bernhisel-Broadbent et al.
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