Sepsis 1999;3:197–218 © 2000 Kluwer Academic Publishers. Manufactured in The Netherlands.

Structure and Fun ction of ImmunoglobulinsSpäth Structure and Function of Immunoglobulins

Peter J. Späth ZLB Central Laboratory, Blood Transfusion Service of the Swiss Red Cross, Bern, Switzerland

Abstract. Ef~cient elimination of pathogens from the host’s ef~cient screening and elimination [1–3]. Recognition body needs the cooperation of recognition/receptor mole- molecules can be various proteins in solution or on cell cules of adaptive and innate immunity. Receptors of innate surfaces. Receptors are membrane molecules which immunity are germline gene encoded and ~xed to recognize upon binding of their ligands induce alteration in cellu- a limited number of structures only.Structures on pathogens lar activities. In the frame of this review the secreted however are very diverse and they can undergo changes due to selection pressure. Some recognition proteins of adaptive recognition molecules of adaptive immunity are the immunity, i.e. immunoglobulin molecules, can be recognized immunoglobulins and the proteins on lymphocyte as biochemical transducers which reduce the diversity of membrane with variable regions are the receptors. antigenic epitopes of microbes to a few principal structures. The recognition molecules of innate immunity are, These principal structures are such that recognition/recep- among others, some of the complement proteins and tor molecules of innate immunity can cope with: complement the receptors are the Fc- and complement receptors of can be activated ef~ciently and receptors of the reticuloen- the reticuloendothelial system (RES). dothelial system (RES) can ensure ultimate elimination of Ultimate elimination of pathogens and senescent or pathogens, their debris and their metabolic products. The altered self utilizes the same machinery, the RES. Nev- structure of immunoglobulins perfectly ~ts their transducer ertheless, there is one fundamental difference between function: the bipolar molecules have variable regions for recognition of diversity of antigenic epitopes and have a few elimination of pathogens and of altered/senescent self: different constant regions which mediate effector functions. defense against pathogens is ef~cient only when a con- The ~rst part of this review focuses on the transducer func- trolled in_ammation can be generated, while the con- tion of high-af~nity, narrowly tuned in host defense and in tinuous recognition and elimination of altered/senes- elimination of senescent and altered self by low-af~nity cent self is not associated with in_ammation. Another cross-reactive immunoglobulins. general difference (with exceptions) is the binding In a second part the review gives an outlook on how af~nity and binding speci~city of recognition/receptor recognition by immunoglobulins of host’s structures may molecules which are involved in immunity against help to attenuate overshooting in_ammation (cytokines, pathogens and self: high and narrow for pathogens and complement) and tissue destruction by inappropriate com- low and cross-reactive for self. plement activation. Finally immunoglobulin preparations, which have been This short review focuses on some aspects of the used in clinic, will be mentioned brie_y. These have helped cooperation between germline gene encoded recogni- considerably to understand immunoglobulin function in hu- tion/receptor molecules of innate immunity (comple- mans. ment, RES) and the immunoglobulins of which the variable regions derive from somatic gene recombina- Key words. IgG, IgA, IgM, intravenous immunoglobulin, tion, insertion, deletion and hypermutation (acquired immunoglobulins, structure & function, therapy, host de- immunity). Furthermore, aspects of low af~nity and fense, attenuation of in_ammation, complement cross-reactivity of immunoglobulins for ~rst-line de- fense and for immunomodulation are discussed. Possi- ble mechanisms of immunomodulation in patients by IgG preparations are reviewed. Introduction General Aspects of Immunoglobulins Our immune system permanently screens the body for structures which are foreign or which are senescent or A. Immunoglobulins are biochemical altered self. Molecules, which are recognized as foreign transducers or senescent or altered self, are eliminated. Screening The function of immunoglobulins as biochemical trans- and elimination utilizes two types of recognition/recep- ducers is readily understandable when considering its tor molecules: (A) those encoded by germline genes (innate immunity) and (B) those encoded by genes which are able to recombine segments and undergo Address correspondence to: Peter J. Späth, ZLB Central Labora- hypermutations (adaptive immunity). Cooperation be- tory, Blood Transfusion Service of the Swiss Red Cross, CH-3000 tween both the germline-encoded and the adaptable Bern-22, Switzerland. Tel.: ϩ41 31 33 00 222; Fax: ϩ41 31 33 00 recognition/receptor system is needed to ensure most 633; E-mail: [email protected]

197 198 Späth

function in host defense. Microbes represent a continu- B. Common features of immunoglobulin ous challenge for our immune system. Microbes at structures and functions their surface display a very wide variety of antigenic There are ~ve classes (isotypes) of human immuno- epitopes which may change due to selection pressure. globulins: IgG, IgA, IgM, IgE, and IgD [5–8]. The IgG Regardless of how unique the antigenic epitopes of an and IgA isotypes are subdivided into subclasses (Table invader are, the invader and its debris have to be 1). IgG1 is considered to represent the prototype struc- phagocytosed by RES. This requires ef~cient binding ture of the four-chain immunoglobulin monomer com- of antigenic epitopes to receptors of the RES. Phago- posed of two identical heavy (H) and light (L) chains cytic cells are armed with germline gene encoded re- each [9–12] (Table 1, Figure 1). The c-chain of IgG1 ceptors. Such receptors might be suf~cient in number, myeloma immunoglobulin EU was the ~rst which was but they do not have a variable gene region and thus sequenced completely and its amino acid sequence is their speci~city is ~xed. Phagocyte receptors are not used as one of the references for numbering sequences able to adapt to the large, ever changing diversity of of other immunoglobulins [13]. The peptide chains of antigenic epitopes of microbes. The gap between diver- immunoglobulins form rigid domains whose number sity plus dynamics of antigenic epitopes and the germ- varies for the H chains, while it is always two for L line encoded receptors of phagocytes is bridged by the chains. The framework of the variable domain of the immunoglobulins. The Y to T shaped structure of im- N-terminal globular structure of the H- and L-chains munoglobulins [4] is perfectly adapted to allow to harbors the hypervariable regions, the “complemen- bridge this gap. tarity-determining residues” (CDRs), the region which

Table 1. Some major physicochemical properties of human immunoglobulin classes

IgG IgA IgM IgD IgE

Basic structure Monomer built by 2 identical heavy (H) and 2 yes yes yes yes yes identical light (L) chains (j or k) Molecular mass of the L-H-H-L monomer (Da) 150,000 160,000 190,000 176,000 183,00– (IgG3: 193,000a 170,000) Carbohydrate content (%) 3 7–12 7.5–10 9–12 12–13 Membrane-bound form known no no yes yes no Heavy chain (H) characteristics Class/Isotype ca l d e Number of subclasses 4 2 - - - c1,c2,c3,c4 a1, a2 Molecular weight (Da) 52,000 56,000 and ϳ60,000 56,213b 66,000 to c3: 58,000 52,000 72,500a Number of constant domains per heavy chain (CH)3 3 4 3 4 Additional 19 amino acid C-terminal domain of no yes yes no no heavy chains with additional penultimate Cys Amino acids building the hinge region c1: 15 a1: 26 none (however 58; rich in none (_exibility c2: 12c a2: 13c high _exibility lysine and of Fab c3: 62 in Cl2 and glutamic maintained) c4: 12 Cl3 domains) acid

Number of variable domains per heavy chain (VH)1 1 1 1 1 Number of hypervariable regions (CDRs) within framework of VH domain 4 4 4 4 4 Allotypes known yes yes yes no no Characteristics of L-H-H-L multimers Multimers of H2L2 con~guration in absence of no dimers, pentamers no no antigen binding tetramers (hexamers) Molecular weight of multimers (Da) (160,000)n 966,000– 971,000a Polypeptide chains in addition to H and L chains no J, SC J; (SCd)nono aMolecular mass range deduced from myeloma proteins bone myeloma protein with 512 amino acids c Ј restricted _exibility of F(ab )2 resulting dSC found with IgM on mucosa (predomominant in patients with IgA de~ciency) Structure and Function of Immunoglobulins 199

Fig. 1. Schematic representation of structure and function of immunoglobulins. Structure: a strongly simpli~ed, two-dimensional model of the four-chain IgG1 molecule is depicted: 1: light chain (L); 2: heavy chain (H); 3: variable region; 4: constant region; 5: hinge region; 6: Fab part; 7: Fc part. Variable domains (VL,VH) and constant domains are indicated by shadowed area. Function: Sche- matic representation of the transducer function of immunoglobulin molecules in host defence. The large diversity of antigenic epi- topes is recognised by the variable region (VL,VH) of the molecules (adaptive immunity). Through binding of immunoglobulins, the antigenic diversity is reduced to a number (isotypes) which the receptors of innate immunity can cope with (receptors of the RES) and recognition molecules (complement proteins) can bind to. Decoration of antigen-immunoglobulin complexes with complement opens the route for binding not only to Fc but also to the various complement receptors. FcxR: Fc receptors for various immunoglobulin iso- types; CRx: various complement receptors. C1q: subunit of the ~rst component of complement which recognises dense arrays of Fcc and Fcl. For further information, please consult Tables 1 to 3.

results from somatic recombination, random insertions The two functional regions of the immunoglobulin or deletions of nucleotides of the B lymphocyte V-gene molecules are joined via the hinge region. The hinge regions. CDRs are responsible for speci~city of the region provides conformational _exibility needed to antigen combining site [14]. VH has four and VL three achieve optimal antigen binding by the N-terminal CDRs. CDRs. Binding of activated C3 and C4 to IgG involves The nine different C-terminal constant regions of the upper hinge region [16] and probably parts of the immunoglobulins (classes and subclasses) are encoded ~rst constant region of the heavy chain [17]. by germline genes, are ligands for the various Fc-re- Taken together, the basic structure of immuno- ceptors (FcRs) of RES and mediate effector functions globulin molecules perfectly ~ts their role in host de- such as phagocytosis, antibody dependent cell-medi- fense which is that of a biochemical transducer with ated cytotoxicity (ADCC) and the release of reactive two principal functions: the Fab parts with their vari- oxygen intermediates, lysosomal hydrolases, arachi- able regions recognize and adapt to the widely diverse donate metabolites, and other mediators of in_amma- and ever changing antigen epitopes while the constant tion [15]. Ef~cient initial activation of complement via region mediate effector functions: they bind directly or the classical pathway of complement (see below) is a after decoration with complement proteins to the re- feature of Fc-parts of IgG and IgM. Initial activation ceptors of RES. The immunoglobulin molecules reduce via the alternative pathway can apparently be medi- diversity of pathogen antigens to a few principal struc- ated by constant domains of most immunoglobulin tures which can be dealt with by receptors of the in- classes (Table 2). nate immune system (Figure 2). 200 Späth

Table 2. Biologic properties of immunoglobulin classes

IgA IgM IgG monomers pentamers IgD IgE

Main function Ig of the Main Ig of Ig of the Marker of Mediator of imme- secondary mucous primary mature diate allergic antibody secretion antibody B cells responses; response response probably Ig of defense agains parasites Transplacental passage yes no no no no Activation by the (antigen-)aggregated yesa very likely yesb,c,d no no form of the classical pathway of complement not Activation by the (antigen-)aggregated form IgG4: yes controversial under certain ? yes of the alternative pathway of complement reports conditions: yese Acceptor molecule for activated component yes yes yes yes yes C4 and C3 of complement (monomers and antigen-complexed forms)f Anti-bacterial activity ϩϩϩϩ Anti-viral activity ϩϩϩϩ Binding to staphylococcal protein A yesg no no no no (IgG3: not) Binding to staphylococcal protein G all subclasses no no no no Binding to staphylococcal protein B no yes Polymeric, MHC class-I related receptor yesh yesi yesi ?? Fc receptors for the constant region (not involved in transcellular passage) yes yes (yesj) ? yes ADCC yes no Binding to mononuclear cells IgG1,IgG3: yes yes yes weak IgG4: weak IgG2: no Binding to neutrophils IgG1,IgG3: yes yes no no no IgG2,IgG4: no Binding to basophils and mast cells no no no no high af~nity Indication of immunomodulatory potency yes no yes ? ? Indication of an in_ammation attenuating effect yes yes yes ? ? ano complement activation by IgG4 because of Pro331 to Ser331 mutation [76] bone single pentamer in the “staple-like” form is considered to be able to activate the classical pathway of complement; pentamer in the disc form does not activate complement csteric con~guration of dense Fcl-parts is of importance for effector function: monomeric IgM, even when bound at high density to antigen, is not able to activate the classical pathway of complement [33]. dthe hexameric form, which is secreted by human plasma cells when not enough J chains are available (lymphoproliferation) or disul~de bridges can not be formed between l and J chains, is up to 20 times more ef~cient activator of classical pathway of complement and is a more ef~cient in mediating cytolysis e[101,102] fthe chance of an activated C3 or C4 molecule to bind to immunoglobulin is by several orders of magnitude higher when the molecules is an activator of complement goccurs between Cc2 and Cc3 domains; no binding of IgG3 subclass due to substitution of Arg435 to His htransplacental passage; recirculation by the endothel of the vasculature itranscytosis into exocrine secretions; not found on trophoblasts, i.e. no transplacental transport jdescribed so far on T lymphocytes only

C. The complement system enhances decisive factor in the elimination of invading pathogens, effector functions of immunoglobulins the destruction of pathogens and the initiation of an Immunoglobulins not only reduce diversity of antigenic in_ammatory process which enhances the former men- epitopes to the limited diversity of their Fc-parts, they tioned processes. In addition, it is important in removal also reduce diversity to structures which allow for of senescent or altered self [18]. Moreover, complement ef~cient cooperation with the complement cascade, a can be involved in mounting an immune response to protein system of innate immunity. Complement is a pathogens. Structure and Function of Immunoglobulins 201

Fig. 2. Outline of activation pathways of complement. Complement proteins given in italics depict regulatory proteins. P: properdin is a stabilizer of the ampli~cation loop C3-convertase; B: factor B (zymogen; active enzyme: Bb); D: enzyme factor D; C1-INH: C1- esterase inhibitor; H: factor H (cofactor), I: factor I (enzyme inactivating by cleavage C3b and C4b to iC3b and iC4b) CR1: comple- ment receptor 1 (CD35; cofactor). Non-covalent binding of C1q to dense arrays of IgG/IgM which have bound antigen, initiates the acti- vation of the classical pathway of complement. Immune complexes who have bound C1q can be ligands for the C1q-receptor. Deposition of C3b to immune complexes renders complexes to ligands for CR1. Activation of C3 through one of the three activation pathways leads to covalent binding of C3b to immune complexes. C3b can become a nucleation site for generation of new C3-conver- tases and further deposition of C3b to target (ampli~cation). Activation of C3 generates C3a. Activation of complement can further proceed beyond C3. Generation of C5a, formation of the membrane attack complex and eventually activation of the arachidonic acid pathway can be the consequence. APR: acute phase reaction.

1. Short outline of the complement system. The ampli~cation loop, i.e., the stability of the alternative complement system can be activated through three pathway C3-convertase. Alternative pathway C3-con- initial pathways: the classical pathway (C1qrs, C2 and vertase is a cofactor-enzyme complex formed by acti- C4), the lectin pathway (MBL, MSAP-1 and MSAP-2, vated C3 (C3b, cofactor) and enzyme Bb, which is a C2, C4) and the alternative pathway (factor D, factor cleavage product of zymogen factor B. This convertase B, properdin and C3). The main activators of the clas- activates additional C3 and resulting C3b can serve for sical pathway are immune complexes, of the lectin nucleation of a new convertase (ampli~cation). There is pathway carbohydrate structures with terminal man- evidence that dimers of C3b on target contribute much nose, fucose, galactose, N-acetyl-galactosamine and N- to the stability of the C3 convertase, among others acetyl-glycosamine (viruses, Gram-negative bacteria, because the C3 convertase stabilizing protein, proper- mycobacteria, yeasts), and of the alternative pathway din, which is a polymer, can bind to more than one C3b bacterial and viral surfaces rich in some sugars except cofactor molecules and thereby can better stabilize the terminal sialic acid (Figure 2). All pathways ~nally ampli~cation loop C3-convertase [18a]. activate C3, the central molecule of the complement The essential of the control of complement path- system. The ef~ciency of complement attack is ways, i.e., control of complement deposition, is the limi- re_ected in the amount of C3 deposited to targets. The tation of formation of new convertases or the reduction extent of C3 deposition is largely dependent on the of half-life of existing convertases (and of active C1, 202 Späth

which can be considered as a preformed convertase (Figure 3) [29–35]. Activation of the alternative path- built by cofactor C1q and zymogens C1r and C1s). Pro- way of complement does not require immunoglobulins teins of the _uid phase involved in control of comple- but the pathway activates far more rapidly in the pres- ment activation are C1-esterase inhibitor, C4-binding ence of antibody [36]. The ef~ciency of immunoglobulin protein, factor H and factor I while complement recep- mediated complement activation is determined by a tor 1 (CR1, CD35) is a control protein of C3-conver- number of factors: the intrinsic af~nity of the antibody- tases on cell surfaces. combining site, the relative mobility of its Fab-regions, Activation of C3 may be followed by activation of _exibility of bonds of antigen sites with respect to the the lytic pathway of complement (C5 to C9, membrane cell surface, and ~nally, the multiplicity of epitopes on attack complex, MAC). Association of C5b-7 to mem- the surface. An antibody of a single Ig isotype which brane and subsequent incorporation of C8 and mul- recognizes a single antigen albeit different antigenic timeters of C9 into the lipid bilayer punctures the epitopes on the antigen may have different comple- membrane and destroys the dysequilibrium of intra ment-mediated effects on a target surface [37]. Differ- and extracellular ion concentrations. Swelling and lysis ence in antibody with regard to utilization of comple- of cells are the consequence. Insertion of C5b-9 in a ment activation mechanism may decisively in_uence non-lytic manner into the membrane of nucleated cells the severity of an infectious episode [38]. may induce the arachidonic acid pathway cascade with Cooperation between immunoglobulins and comple- generation of potent mediators of in_ammation. Com- ment ~nally leads to immune complexes which can bind plement activation also results in the formation of via Fc-part and complement to phagocytic cells, if the anaphylatoxins C3a and C5a which are additional me- receptors are expressed on corresponding cells. The diators of in_ammation (Figure 2). simultaneous binding of immunoglobulin and comple- Covalent binding of C3b and C4b to target surface ment components to phagocytes renders phagocytosis prepares target for recognition by complement recep- insensitive to _uid phase monomeric immunoglobulins tor. Degradation products of C3b and C4b (iC3b, C3dg, [39]. Phagocytosis in presence of complement even af- iC4b and C4d), which remain covalently bound to tar- ter infusion of high doses of an intravenous IgG prepa- get, are ligands for complement receptors which exist ration (IVIgG) apparently is fully effective: patients on various cells 2 and 3, respectively. Their binding to with IgG concentration twice or more of normal do not complement receptors can induce a variety of ~nely suffer from higher frequency or longer duration of in- tuned cellular activities resulting in enhanced phago- fectious episodes. cytosis of pathogens by the RES. Cooperation of these A further consequence of complement deposition to receptors in uptake and killing of pathogens can be immune complexes is their enhanced solubility [40] and demonstrated by their selective blockage [19,20]. their ef~cient transport in the blood stream to the tis- sue resident macrophages of liver and spleen [41]. En- 2. Collaboration between immunoglobulins and hanced solubility of forming immune complexes is complement in host defense. The collaboration in achieved by alteration of the immune complex lattice host defense between complement and immunoglobu- because of the covalent binding of C3b [42]. The trans- lins (mainly IgG and IgM) is demonstrated in patients port is mediated in man by erythrocytes which bear a suffering from antibody de~ciency syndrome, who have low number of complement receptor 1 (CR1, CD35) per normal complement and patients with selective comple- red blood cell but due to the enormous surface of total ment defects and normal immunoglobulin levels. In RBC they provide a large transport capacity. Trans- both types of de~ciencies an enhanced frequency and port is ascertained by binding to CR1 of immune com- prolonged duration of bacterial infection is noted. In- plexes which bear C3b (C4b). While transporting C3b deed, almost all complement defects known predispose (C4b) decorated immune complexes, the second func- for bacterial infections [21]. Importance of complement tion of CR1 becomes operative: CR1 serves as cofactor in host defense is strengthened by the positive correla- for the inactivating enzyme factor I which cleaves C3b tion between in vitro resistance to complement of clini- (C4b) to the inactive molecule iC3b (iC4b). This inacti- cal isolates of pathogens and the ability of them to cause vation serves two purposes, it prevents those com- disease in humans having functional complement plexes which dissociate from the transporting RBS [22–26]. The importance of complement is further illus- from nucleating new C3-convertases and it generates trated by experimental infections of laboratory animals complement fragments on complexes which are opti- with or without impaired complement function [27,28]. mally suited to bind to CR3 (CD11b/CD18), which is a The biologic consequence of interaction of comple- membrane constituent of phagocytes (Figure 4). ment and immunoglobulins is very complex. The initial and ef~cient targeting of complement to surfaces can D. Physiology of immunoglobulins be mediated by antibodies through activation of the classical pathway of complement. Initiation of the clas- 1. Biologic origin of immunoglobulin. Immuno- sical pathway requires that immunoglobulins (G and globulins are secreted by plasma cells. Plasma cells M) provide a dense arrays of Fc domains which are derive from B lymphocytes. B lymphocytes become recognized by C1, the ~rst component of complement activated in a ~rst wave by trapping antigen through Structure and Function of Immunoglobulins 203

Fig. 3. Binding sites of complement component C1 (C1qr2s2) to dense arrays of IgG and IgM Fc-parts. It was hypothesised that C1q binds with its A-chain to IgG and B-chain to IgM ($). Involvement of the IgG amino acid sequence motif Glu-X-Lys-X-Lys in the inter- action with C1q is accepted. Pro331 has apparently a decisive role whether the above motif can become operative (IgG1, IgG2 and IgG3) or not (IgG4 with Ser331). It is less well established which residues of IgM are involved in C1q binding. This is because single site mutation may impair IgM polymerization. Most likely two clusters of residues are involved in binidng of C1q (the two lines which depict residues). The residues given in italics can’t be tested by mutations (no polymerization) but binding experiments with normal IgM imply their participation in C1q binding.

the B cell antigen receptor (BCR) complex. Pre-acti- served structures on pathogens, they can be termed vated B cells are then prone to proliferate and differ- “naturally occurring antibodies”. When the same im- entiate. munoglobulins recognize structures on host tissue they a) Origin of high-af~nity immunoglobulins for host can be termed “naturally occurring autoantibodies” defense. Antibodies for host defense are produced (NAbs). As pathogens and man share conserved anti- mainly by so called B-2 cells. Activation, differentiation gens, NAbs can participate in ~rst line defense. Re- and af~nity maturation can occur in a MHC class-inde- cently it was postulated that such antibodies are not pendent (no formation of germinal centers) and an only important in ~rst-line defense but may also direct MHC class-dependent manner with formation of ger- an immune response to non-self and may help to pre- minal centers. Hypermutations and gene rearrange- vent a strong immune response to conserved epitopes, ments of B cell variable region immunoglobulin genes in case conserved/self and non-self epitopes are located ascertain the ability of immunoglobulins to adapt to on the same antigen [43]. and to recognize the wide antigen diversity of microbes The presence of autoantibodies in healthy individu- with high af~nity. als is a paradox to the theory of clonal deletion and b) Origin of immunoglobulins which can provide clonal anergy of self-reacting lymphocytes. However, ~rst line defense, which react with self and which can such antibodies exist and obviously have a homeostatic express immunoregulatory properties. In humans (and function. Patients suffering from various diseases rodents) immunoglobulins can be detected with a wide might pro~t from infusion of these antibodies which cross-reactivity directed against structures conserved are present in commercial immunoglobulin prepara- during evolution. These antibodies are present in tions. The NAbs originate from B cells and can be germ-free animals nourished on a diet containing no positively selected from autoreactive B lymphocytes antigenic structures and thus can be termed “naturally as has recently been described in a mouse model [44]. occurring”. When such immunoglobulins recognize con- Self-reactive B lymphocytes are independent of T cell 204 Späth

Fig. 4. Transport of soluble immune complexes by erythrocytes to the tissue resident macrophages. Erythrocytes (E) bear the comple- ment receptor 1 (CR1, CD35) which binds C3b-decorated (C4b-decorated) immune complexes. CR1 is not only a complement binding protein, it is also a cofactor for factor I which cleaves and inactivates C3b to iC3b (C4b to iC4b). Cleavage and inactivation of C3b (C4b) occurs during the transport from the periphery to the tissue resident macrophages which can bind via CR3 (CD11b/CD18) the iC3b and iC4b bearing complexes.

help, they frequently express CD20 and CD5 (B-1a 2. Metabolism of immunoglobulins. Metabolism cells), have ~xed and biased repertoires and are not of immunoglobulin classes and subclasses differ consid- part of follicular structures [45,46]. B-1 cells appear erably (Table 3) and is a matter of structures. Elevated early in mouse ontogeny; they are the ~rst B lympho- catabolism can be due to susceptibility of the hinge cytes which populate mouse epithelium and the perito- region to proteases and susceptibility is in part associ- neum. During fetal development intraepithelial B-1 ated to the length of the hinge region. A prolonged cells appear to recognize and some times to be acti- half-life of IgG1, IgG2 and IgG4 is mediated by the vated by self-antigens [47]. B-1 lymphocytes can be action of a “protection receptor for monomeric IgG” isolated from peritoneal cavity of humans and their also termed FcRp which can bind IgG but not other phenotype is similar to that of mice [48]. About 63% of classes of immunoglobulins [50]. FcRp is a constituent the peritoneal B cells express surface antigen CD5. of endothelial cells, as was shown in knock-out mice CD5ϩ B lymphocytes produce (naturally occurring [51,52]. Endothelial cells internalize monomeric IgG auto) antibodies which use gene segments in germline and IgG complexes by pinocytosis. Subsequent to en- con~guration, are polyreactive, express low af~nity gulfment immune complexes are dissociated in the but can be of high avidity (IgM) and recognize a vide acidic environment endosomes. The liberated IgG and variety of self- and foreign antigens [49]. the pinocytosed monomeric IgG then bind to endoso-

Table 3. Some metabolic parameters of human immunoglobulin classes

IgG IgA monomer IgM pentamer IgD IgE

Mean serum concentration (g/L)a 12.5 3 1.5 0.03 1–5 ϫ 10Ϫ4 Normal range (g/L)a 6.9–14.0 0.88–4.1 0.34–2.1 Normal range (g/L)b 6.9–14.0 m: 0.9–4.1 m: 0.3–2.1 f: 0.7–3.7 f: 0.4–2.4 Synthetic rate (mg/kg body weight/day) 33 65 6.7 0.4 0.016 Fractional catabolic rate (% of IV pool 7 IgA1: 24 9 37 71 catabolised/day) (IgG3: 17) IgA2: 34 Half-life (days) 21 4.5–5.9 5 2.8–3 2.3–2.5 (IgG3: 7) (blood) Intravascular distribution 45% 42% 80% 75% 51% avalues of the diagnostic department ZLB standardized with CRM70 (95% con~dence interval) brecommended by the Federation of Swiss Clinical Laboratories [162] Structure and Function of Immunoglobulins 205

mal FcRp. FcRp subsequently redirects bound mono- A. Brief outline of some features of meric IgG to the endothelial cell surface. At neutral pH immunoglobulin classes E and D the IgG is released into the circulation [53]. Recently, IgD exists in membrane bound form (mlgD) and as a it was postulated the saturation of FcRp by exogenous monomer in the circulation (IgD). Binding of antigen to IgG could be a mechanism of action for removal of mlgD results in internalization and cell activation. Pos- disease-mediating antibodies [54]. sible collaboration of mlgD and complement receptors Transport of IgG through the placenta prepares the in activation of murine spleen lymphocytes was re- fetus to ~ght infections after birth. Immunoglobulin ported [57]. levels are maintained after birth by intestinal Fc re- Serum IgD can function as a typical antibody (see ceptor (FcRn). FcRn, FcRp and the placental IgG also Tables 1–3) [58]. Aggregated IgD myeloma pro- transporter all are MHC class-I-like molecules and teins are not able to activate the classical pathway of form heterodimers with b-microglobulin [55,56]. complement, while some are able to activate the alter- native pathway [59,60] Serum IgD has a vide range in concentration. To the best of my knowledge, the 10% of the human population with no detectable serum IgD is The Role of the Five Immunoglobulin not prone to disease. Periodic fever associated with per- Classes in Host Defense manent hypergammaglobulinemia D (IgD Ͼ100U/mL) may in most cases represent an inherited disease [61] To evaluate the therapeutic potential of immunoglobu- and is associated with febrile attacks, leukocytosis, lins, animal experiments can provide relevant results, neutrophilia, increased erythrocyte sedimentation rate but their implications for humans will always remain and leukocytoclastic vasculitis-like skin manifestations questionable. The most precise knowledge of immuno- with perivascular deposit of IgD and C3 [62]. Hyperim- globulin functions in man comes from the use of poly- munoglobulinemia D can be found in Behçet’s disease clonal immunoglobulin preparations. Immunoglobulin and idiopathic retinal vasculitis [63]. classes, which have been administered to humans in IgE is the immunoglobulin of allergic reactions. It is form of Ig preparations are listed in Table 4. No prepa- believed that IgE antibodies against certain parasites ration exists with relevant amounts of polyclonal IgE might be involved in immunity to parasites, since or IgD. Thus structure and function of IgD and IgE nematodes can induce elevated IgE levels. will be discussed brie_y only. In a prospective study of bone marrow transplanta-

Table 4. Some characteristics of immunoglobulin classes found in immunoglobulin preparations fractionated from pooled normal human plasma. For distribution of immunoglobulin classes in preparations, see Table 5.

Parameter / Ig IgG IgM IgA

Commercial preparations IVIgGs Pentaglobinc,e,f IgAbuling used in human studies (many)a,b Venimmun Nd,e,f Intravenous tolerability various methods b-propiolacton/UV treatment Not for intravenous achieved by (Pentaglobin) use limited S-sulfonation (Venimmun N) Stabilizer various ones; some preparations with glucose (Pentaglobin) glucose (100 mg/ml) mixtures of stabilizers glycine (Venimmun N) Pharmaceutical lyophilisate or liquid lyophilisate liquid (100 mg formulations protein/ml; 2 ml vials) aSome IVIgGs registered in Germany: Alphaglobin (Grifols), Endobulin (Immuno/Baxter; corresponds to Iveegam on the U.S. market), Gamma- Venin (Centeon/Aventis L.L.C.), Gammagard S/D (Baxter), Gammonativ (Pharmacia Upjohn), Immunglobulin Human DRK (German Red Cross), Intraglobin (Biotest), Intrimmun (Biotest Pharma), Octagam (Octapharma), Polyglobin-N (Bayer Corporation; corresponds to Gamimune-N on the U.S. market), Sandoglobulin (Novartis Pharma) bSome IVIgGs registered in the U.S.A.: Gammagard S/D (Baxter), Gammar-P.I.V. (Centeon/Aventis L.L.C.) Gamimune-N (Bayer Corporation; corresponds to Polyglobin-N on the German market), Iveegam (Immuno U.S., Inc.; corresponds to Endobulin on the German market), Panglobulin (American Red Cross; corresponds to Sandoglobulin), Polygam S/D (American Red Cross; corresponds to Gammagard S/D), Sandoglobulin (Novartis Pharmaceuticals), Venoglobulin-S & Venoglobulin-I (Alpha Therapeutic Corporation) cproduced and distributed in Germany by Biotest ddistribution in Germany by Centeon/Aventis ein the past a 20% by weight IgM concentrate (Gamma-M) for intramuscular application has been available from former Behringwerke AG, Marburg, Germany fBeside the two commercially available preparations enriched in IgM, reports from two experimental preparation not used in humans exist. One perparation was provided by Laboratoire de Fractionnement Biologique, France, was prepared from a pool of 2500 donors and is highly enriched in IgM [163]. The other preparation was from Biotest, Germany, and contained 35 g/L IgM, 12 g/L IgA and 3 g/L IgG [161]. gproduced by Immuno Vienna for experimental clinical use; presently not on the market 206 Späth

tion with 38 recipients, assessment of C-reactive pro- offers a multitude of preexisting low-af~nity, low-titer tein (CRP) and serum level of IgE was claimed to allow polyspeci~c IgM antibodies and a similarly primed B distinction between acute graft-versus-host disease cell population to meet the need for a defense as (GVHD) and an infectious episode: CRP was high and quickly and as ef~ciently as ever possible. As described IgE was low in infection and CRP was low and IgE above, immunoglobulins must provide densely packed high in acute GVHD without current infection [64]. Fc-parts to initiate effector functions for ef~cient de- Furthermore, in a prospective study of sepsis in fense. The few antibody molecules available at this trauma patients, IgE levels and peripheral eosinophil time point can’t build the Fc-density needed, except counts were reported to increase most after onset of the density is already pre-formed. In a pentameric IgM sepsis [65]. The increase does not seem to be related to Fcl densities are pre-formed. IgM is further suited for the severity of initial injury. The role of elevated total primary immune responses because in general it is IgE in severe traumatic injury is not clear although polyspeci~c, i.e., represents a “broad spectrum” anti- presence of speci~c anti-LPS IgE was associated with body which binds to multiple antigenic epitopes which a signi~cantly lower incidence of death and of renal can be diverse. Thus, preexisting IgM compensate failure [66]. For further information see Tables 1–3. their low af~nity by the high valency and cross-reactiv- ity. While IgM is the earliest isotype generated in an immune response, it tends to disappear later when B B. Structure and function of cells undergo immunoglobulin class switch. immunoglobulins M, G and A c) Serum IgM and complement in host defense. Immunoglobulin preparations make long-term obser- Theoretically, the preformed density of Fcl-parts of vations with repeated application of a given preparation free IgM should be suf~cient to activate (and when not possible, because their production under good manufac- appropriately controlled to consume) complement in ture practice (GMP) provides well standardized immu- blood. Free IgM assembled to pentamer has a disc-like noglobulin brands. Unfortunately, brand to brand dif- shape and does not activate the classical pathway of ferences in manufacturing processes do not always the complement system [74] unless it is bound to anti- allow to draw general conclusions from clinical experi- gen and takes a bent con~guration (staple form) [75]. ences with different brands of immunoglobulin prepara- The torsion of the molecule apparently exposes the tions [67–69]. C1q binding sites within the packed Fc-parts of IgM. The amino acid residues most likely involved in binding 1. Structure of IgM. IgM in the circulation is a poly- are within two clusters of the Cl3 domain (Figure 3) mer consisting of ~ve H2L2 chain subunits. The forma- [34,35,76]. tion of IgM pentamers needs the incorporation of the Receptors in humans for the Fc-part of IgM (FclR) J-chain (Table 1). The J chain is a 129 amino acid, 16 have so far only been reported on T lymphocytes in kDa, single chain glycopeptide with marked acidic humans and are absent on phagocytes. Thus, FclR- properties. In case of overproduction of IgM relative to mediated phagocytosis of IgM-coated pathogens ap- J-chains, hexameric, J-chain deprived IgM can appear parently does not occur. However, several complement in the circulation of diseased individuals (Table 2). It is receptors on human phagocytes exist: CR1 (CD35), not entirely clear, how the ~ve IgM monomers and the CR3 (CD11b/CD18) and CR4 (CD11c/CD18). As a con- J-chain are assembled. More recent publications favor sequence IgM-mediated complement deposition is es- a decisive role of Cys414 for polymerization and incor- sential for ef~cient clearance of IgM-coated targets poration of the J-chain [70,71]. which occurs via complement receptors [77]. d) Commercially available immunoglobulin prepa- 2. Function of IgM. a) Membrane associated IgM. rations enriched in IgM. Two immunoglobulin prepara- Membrane-bound IgM is a l2L2 molecule with l-chain tions containing more than 6% of IgM are on the mar- having an extra 25 transmembrane-spanning and an ex- ket (Tables 4 and 5) and both are for intravenous use. tra 3 amino acid cytoplasmatic sequence. Membrane-as- During large scale puri~cation of immunoglobulins sociated IgM is part of the B cell antigen receptor (BCR) from pooled plasma, it is inevitable that a small fraction complex. These recognition molecules have a wide spe- of the immunoglobulin undergoes structural changes ci~city and can bind with low af~nity to many different which upon infusion might activate the complement antigens. Simultaneous binding of complement deco- cascade already in the absence of binding to an antigen rated antigen to of the BCR complex and B cell comple- (unwanted, e.g. spontaneous complement activation). ment receptors drastically lowers the threshold for trig- Spontaneous, systemic complement activation may gering a B cell immune response [72]. On the other hand lead to severe adverse effects. To prevent spontaneous bridging of the BCR complex with FccRIIs by binding complement activation by preparations enriched in of antigen-antibody immune aggregates inhibits B cell IgM, the preparations currently on the market are proliferation and maturation [73]. chemically modi~ed: one product is treated with b- b) Serum IgM—The immunoglobulin of the innate propiolactone/UV light, the other by limited S-sulfona- and primary humoral immune response. During the tion (Table 4). b-propiolactone irreversibly modi~es ly- ~rst encounter with a pathogen, the immune system sine (Lys) and histidine (His) residues. The number of Structure and Function of Immunoglobulins 207

Table 5. Immunoglobulin class distribution in preparations highly enriched IgM preparation may prevent sponta- enriched in classes other than just IgG. For further neous complement activation [91] without signi~cant information concerning the preparations for human use, see loss of normal effector functions [92,93], while heating Table 4. of IgG preparations is well known to introduce a strong IgGa IgM IgA complement activation potential [94]. Further unex- Parameter / Ig (%)b (%) (%) pected effects of IgM may be encountered when the ~rst highly enriched IgM preparation with fully pre- served antigen binding and effector functions will be Normal human serum 80 7 13 tested in vivo. For example, it is generally assumed, c Pentaglobin (i.v. use) 76 12 12 that IgM is superior to IgG in treating bacterial infec- ϳ ϳ ϳ Venimmun N (i.v. use) 80 8 12 tions. The deca-valent structure of IgM should be opti- IgAbulin (topic application) 15.5–33.3 0.18–1.46 66.1–84.2 mally suited to recognize the multimeric structures of IgG preparations for bacterial surface and a single molecule bound should be i.v. used Ͼ97 traces Ͻ3 suf~cient to initiate complement activation. Bacteri- cidal activity of IgM in vitro indeed might show supe- aSplit products, monomers, dimers and oligomers rior quality over IgG although strain to strain vari- b Percent of total immunoglobulin ations might exist. Surprisingly, superiority of IgM c subclass distribution (according to manufacturer): IgG1: 62.6%; IgG2: over IgG or IgA in host defense could not always be 25.8%; IgG3: 4.0%; IgG4: 7.6% shown in in vivo experiments with isotype switched dsubclass distribution as close to WHO standard as possible; some IVIgG miss subclasses IgG3 or IgG4 antibodies (Table 6) [95–100]. Development of a highly enriched human IgM preparation may further pose problems when it comes to pre-clinical studies. Problems may arise from xeno- Lys side chains modi~ed per IgM monomer (l2L2) is 4.8 reactivity of human IgM. As xenoreactive IgM might in the average (6 for IgG). The number of altered His be involved in primary host defense, it would be con- residues is not known [78]. Limited sul~tolysis opens tradictory to eliminate rich antibodies to avoid xenore- disul~de bridges. Limited S-sulfonation for IgG was active reactions during pre-clinical studies. Xenoreac- reported to be reversible within hours after infusion tivity further rises questions about reported results [79]. To the best of my knowledge it has not been re- with human IgM obtained in non-human systems in ported what the effect of limited sul~tolysis on effector particular because xenoreactivity may involve not only function of IgM may be and how rapid the reversion of tissue but also molecules such as immunoglobulins. sul~tolysis may occur. Considering the importance of a Availability of IgM concentrates with fully pre- correct Cys-Cys-mediated reassociation of l-chains for served Fc and Fab functions will certainly provide proper biologic function of IgM, reversal of limited additional knowledge on humoral immunity of man and S-sulfonation of IgM must be considered potentially will open new possibilities in immunoglobulin therapy. problematic, since various possibilities exist for inter- Likewise, it will allow to verify in humans whether chain re-association of Cys residues [80]. IgM indeed can ef~ciently kill some bacterial strains A number of clinical studies with a preparation con- via activation of the alternative pathway of comple- taining IgG, IgM and IgA (IgMAG, Pentaglobin) have ment (Table 2) [101,102]. been performed, mainly aiming to support host defense against bacterial infections (see other chapters of this 3. Structure of IgA. The main immunoglobulin class issue) [81–88]. The rational behind these studies was in external secretions and on mucosa is secretory IgA based on immunochemical assessments of antibody tit- (sIgA). Secretory IgA is composed of 2 to 4 monomers ers in Pentaglobin. Results suggested equal or higher disul~de linked by joining (J) chains and a non-cova- IgM titers of agglutinating antibacterial antibodies lently associated secretory component (SC, also than IgG titers in an IVIgG preparation of the same termed secretory piece). The J chain is identical to J manufacturer [89]. chain of IgM. SC is a single, highly N-glycosylated 50 The main problem with the currently available to 90 kDa polypeptide with 20 cysteine residues. It is preparations enriched in IgM is their rather low con- the cleaved extracellular part of the polymeric IgA tent in IgM. It is dif~cult to believe that clinical ef~cacy receptor (see below). SC confers protection from pro- is due to IgM alone without any contribution from IgG, teolytic digestion of sIgA. the major constituent of both preparations containing In contrast to sIgA, IgA found in the circulation is to IgM, or even IgA. However, for theoretical reasons the 85-90% monomeric. The rest consists of 2 to 4 mono- potential of IgM for prophylaxis and treatment of in- mers joined by disul~de bridges via J chain, identical to fections is wide. Efforts are apparently made to de- J chain of sIgA. Plasma IgA is mostly IgA1 while sIgA velop IgM preparations with an IgM content Ͼ60% is up to 50% IgA2. IgA2 has two allotypic forms, [90]. Preparations highly enriched in IgM might be- A2m(1) and A2m(2). For further information see Tables have quite differently from what we are used to ob- 1 to 3. Receptors for IgA (FcaR or CD89) are expressed serve with IgG preparations. Indeed, heating of a on several cell types (see Chapter on Fc-receptors). 208 Späth

Table 6. Anti-bacerial activity of immunoglobulins of same speci~city but different isotypes in vitro and in animal models

Protecting effect Antibody directed against In vitro ef~ciency in animal models References

Mouse monoclonal antibodies P. aueruginosa O6-LPS, isotype switcheda IgMϾIgG2aϾIgG3ϾIgG2bϾIgG1b all more or less equalc [95] P. aueruginosa O-LPS / with complement IgGϾIgAϾIgMd all more or less equale [99] P. aueruginosa O-LPS / no complement IgAϾϾIgGϾϾIgMd IgGϷIgAϾϾϾIgMe,f [99] E. coli O-LPS IgGϾIgM IgGϾIgM [98] E. coli O-LPS (O18:K1:H7) IgGϾIgM IgGϾIgM [97] E. coli O-LPS IgMϾIgG2aϾIgGx IgMϾIgG2aϾIgGx [100] Immunoglobulins puri~ed from plasma of vaccinated volunteers P. aeruginosa / with complement IgAϾϾIgGϾIgMh all more or less equale [99] P. aeruginosa / no complement IgAϾIgGϾϾIgMg IgGϷIgAϾϾϾIgMe,f [99] P. aeruginosa / with complement / PMN IgGϭIgA ϾIgM not tested [96] P. aeruginosa / no complement / PMN IgGϾIgAϾϾIgM not tested [96] P. aeruginosa / with complement / monocytes IgAϾIgMϾIgG not tested (96) P. aeruginosa / no complement / monocytes IgAϾIgGϾϾIgM not tested (96) asimilar binding activities of all isotypes in ELISA systems with puri~ed P. aeruginosa It-1 LPS or heat killed bacteria bconcentration-dependent opsonophagocytic killing in vitro in presence of complement cmice challenged with 50% lethal doses of P. aeruginosa It-1 bacteria (burn wound sepsis and i.p. infection); infection-associated mortality assessed dPMN used for in vitro killing experiments eprotective levels for survival of neutropenic mice challenged with P. aeruginosa It-1 (IgG and IgA) and P. aeruginosa It-2 (IgM) fin vivo decomplementation by cobra venom factor treatment previous to challenge hmonocytes used in the in vitro killing experiments

4. Function of IgA in host defense. a) Function to (IgAbulin, Table 4) already exists [111–113] and will be secretory IgA. The role of sIgA in mucosal immunity is discussed elsewhere in this issue. discussed in detail elsewhere (this issue). The biologic origin of sIgA are submucosal plasma cells. These pro- 5. Host defense mediated by IgG preparations. duce multimeric IgA which by combining with the poly- The structure and general functions of IgG are out- meric IgA receptor at the basolateral membrane of epi- lined above, in Tables 1 to 3 and in Figure 1. thelial cells is transcytosed to the luminal surface with a With the introduction of large scale plasma frac- t1/2 of 30 min [103]. At the luminal surface the receptor is tionation by Cohn and Oncley [114,115] and the discov- cleaved to release IgA together with the bound secre- ery of agammaglobulinemia by Bruton [116], the road tory component [104,105]. IgA in cellular transit is able was open to investigate in man the function of human to neutralize viruses which might have infected those IgG in host defense. Early studies with intramuscular epithelial cells through which IgA is transported. preparations revealed a dose-dependent clinical effect: Secretory IgA binds to enteropathic bacteria and patients suffering from congenital antibody de~ciency viruses and by steric hindrance prevents close contact which were on a high-dose intramuscular schedule of of these microorganisms with epithelial cells. Secre- 0.05 g IgG/kg body weight per week had signi~cantly tory IgA reduces colonization, prevents translocation less acute infectious episodes than those who were and enhances immune exclusion of mucosal pathogens treated with lower doses. This observation triggered [106,107]. the development of IgG preparations which could be b) IgA and complement in host defense. The interac- applied intravenously (IVIgG). tion of IgA with complement is not entirely clari~ed yet. It is common sense that the quality of IVIgG prepa- There is good evidence that aggregated IgA does not ~x rations for prevention and treatment of (severe) infec- C1q [108]. IgA antibodies with altered oligosaccharide tions, among others, is associated to constant levels in side chains have been shown to be capable to ef~ciently various disease-relevant antibodies. To minimize _uc- activate the alternative complement pathway, making tuations in relevant antibody titers, the WHO recom- subpopulations of IgA antibodies potential participants mended to prepare IVIgG from plasma pools which in in_ammatory reactions [109,110]. When non-comple- combined at least 1000 donations. Today pool sizes ment activating IgA antibody is competing with IgG or have reached values between 10,000 to 50,000 or even IgM for binding to antigen competitive inhibition of higher numbers of donations. The general assumption complement activation can occur and serum resistance that such pool sizes would show constant titers in their of the pathogen may result (see below). anti-microbial antibodies could not be con~rmed by Some experience in host defense with a plasma some investigators [117]. The experience with one derived, IgA-enriched immunoglobulin preparation IVIgG preparation over the years shows considerable Structure and Function of Immunoglobulins 209

Table 7. Two examples of lot to lot variations of anti-microbial antibody titers in large pool IVIgG. Ranges of anti-poliovirus type 1 (IU/mL) and anti-HAV antibody titers (IU/mL) in lots of IVIgG fractionated over several years from pools of plasma from non-remunerated donations in the U.S.A. and in Germany are given. Antibody titers were assessed with validated methods in 6% protein solutions.

Anti-Polio type 1 Anti-HAV

1994 1995 1996 1997 1998 1994 1995 1996 1997 1998

USA USA Minimum 7.80 6.24 7.80 7.39 5.75 Minimum 11.9 8.60 8.60 8.60 8.10 Mean 14.7 12.7 13.3 13.5 12.4 Mean 18.1 16.3 16.3 16.6 15.0 Median 14.0 12.4 13.1 12.3 12.3 Median 18.0 16.2 16.2 16.4 14.5 Maximum 24.9 19.7 22.2 27.9 26.3 Maximum 28.1 25.9 25.0 40.9 25.3 Germany Germany Minimum 7.80 5.50 8.79 9.86 8.21 Minimum 23.6 21.2 21.3 12.9 22.8 Mean 13.7 14.0 16.1 17.2 17.9 Mean 32.0 30.2 32.7 35.2 33.0 Median 14.0 14.0 15.6 17.3 17.3 Median 32.0 29.9 31.6 34.4 32.6 Maximum 22.2 19.7 24.6 27.9 31.2 Maximum 43.3 46.9 54.4 51.9 57.8

The accuracy of determinations can be dedicated from stability testing. Ten lots kept at 4ЊC for 48 to 60 month were analyzed. The most pronounced difference in an individual lot was 18 IU/mL for anti-HAV antibody and 13.0 IU/mL for anti-Polio type I antibody, respectively.

consistency in antibody titers when the mean titers of tibodies which bind to bacterial surface at sites which do lots produced in one calendar year are compared. How- not allow complement dependent killing although com- ever, some lot to lot variation can’t be neglected even plement activation by bacteria-Ig complexes is normal when taking into account the variability of the test or even elevated [121]. Binding of IgG speci~c for pro- system. Consistency in mean antibody titers is seen tein III of serum-resistant Neisseria gonorrhoea, IgG with IVIgG prepared from plasma collected in differ- anti-gonococcal reduction protein (Rmp) to N. gonor- ent continents although continent to continent differ- rhoea and IgA speci~c for capsular polysaccharide on ences might exist, is seen with induced and acquired meningococci were described to mediate serum resis- antibodies and is detectable in all types of antibody tance [122–124]. The effect of antibodies mediating se- speci~city assessed for lot release (Table 7). rum resistance can be dependent on the ratio of lytic to blocking antibody, can be strain speci~c, and can be greater for one immunoglobulin isotype of lytic anti- Immunoglobulins that Bind to and body than for another. Help the Survival of Bacteria A. Secretory IgA that coats normal Immunoglobulins with gut _ora Prevention of pathogen-induced in_ammation of the Immunomodulatory Potential gut is in part due to the robust ecosystem of the gut A. Anti-toxin antibodies with strong _ora. The bacteria of the normal gut _ora are coated immunomodulatory potential with sIgA and these bacteria should undergo immune Neutralizing antibodies to superantigens can exert exclusion, however they do not. It was postulated, the anti-micorbial (anti-toxin) activity with strong immu- sIgA which coats the bacteria of the normal _ora may nomodulatory consequence. Superantigens are micro- help to maintain robustness of the bacterial ecosystem bial products which almost exclusively recognize the and may origin from B-1 cells (mice) which are diffe- Vb chain of TCR and bind directly to the MHC class II rent from conventional B cells (B-2 cells) which pro- molecule without antigen processing. The cross-link in duce af~nity matured, narrowly tuned IgA antibodies a non-MHC restricted manner of TCR Vb and MHC for host defense [118,119] (see above). class II by superantigens stimulates a strong cellular immune response in a large subset of T cells with spe- ci~c Vb gene segments. Antibodies in pooled immuno- B. Immunoglobulins that prevent killing globulin neutralize many of the superantigens and of pathogens therefore prevents the escape from MHC-restricted In case antibodies which are not activating complement proliferation of T lymphocytes and thus intervenes are competing with batericidal antibodies for antigen with the extraordinary immunostimulatory properties binding, pathogens may escape ef~cient destruction. of superantigens [125,126]. Such interaction may help The antibodies mainly involved are of the IgA isotype to reduce severity of conditions like Kawasaki disease [120]. Escape from destruction also may occur with an- [127]. 210 Späth

B. Attenuation of in_ammation by tokines. Further support for relevance of cytokine net- self-reacting autoantibodies work modulation is indicated by IVIgG induced altera- In_ammatory host responses to bacteria. their cell tion of in vitro production and release of cytokines wall components and metabolic products are mediated [136–140]. There is agreement that intact 7 S IgG is by the cells of the monocytes/macrophage lineage, best suited for alteration of cytokine production and/or neutrophils and complement. Activation of comple- release from cultured cells. Thus, there is indication for ment, induction of reactive oxygen intermediates, pro- Fab- and Fc-parts IgG to be involved in IgG-mediated in_ammatory cytokines and release of e.g. GM-CSF alteration in synthesis and release of cytokines from are potentially harmful when reactions can not be con- cell cultures. trolled appropriately by the host. Every measure Several studies on IVIgG induced changes in cyto- which is able to down regulate a multitude of these kine pro~les of patients with primary humoral immune reactions is potentially bene~cial for patients with se- defects exist. IVIgG apparently induce a short phase vere in_ammation. with release of pro-in_ammatory cytokines followed by The observation of platelet count rise in immune a prolonged phase with release of anti-in_ammatory thrombocytopenic purpura (ITP) following administra- cytokines. Indeed, in vivo alteration of cytokine syn- tion of IVIgG [128] was the advent of the therapeutic thesis and cytokine release was reported in 12 patients use of IVIgG in immunomodulation. In the meantime with congenital immunode~ciency in whom infusion of the anti-in_ammatory effect of high-dose IVIgG treat- IVIgG induced a brief elevation in pro-in_ammatory ment has been acknowledged even though not all as- cytokines (IL-8, TNFa), followed by a prolonged in- pects of this effect are entirely understood [129]. Today crease in anti-in_ammatory mediators (IL-1 receptor the therapeutic effect of IVIgG in immunomodulation antagonists, soluble receptors for TNFa and IL-6) and attenuation of in_ammation is attributed to natu- [141]. In another study intracellular cytokines were rally occurring autoantibodies (NAbs) and some non- assessed using _ow cytometry and ex vivo whole blood immunoglobulin proteins of the immune system present cultures prepared before and after replacement ther- in IVIgG. It is accepted that the anti-in_ammatory ef- apy of common variable immunode~ciency (CVID) and fect of IVIgG is multifactorial. Some of these effects are X-linked agammaglobulinemia (XLA) patients. In outlined below and it is shown that these effects are not CD4ϩ (and CD4ϩ28Ϫ) cells a signi~cant IL-2 and in restricted to IgG alone. CD8ϩ28Ϫ cells a signi~cant TNFa expression was ob- served in CVID but not in XLA patients while IFNc 1. Cytokine network modulating effect of IVIgG and CD69 expression remained unchanged [142]. In a preparations. The ~rst hint for a cytokine attenuat- further study of 12 patients with primary hypogam- ing effect of human polyclonal IgG was reported from maglobulinemia after a bolus of 0.4 g IgG/kg body Japan [130]. Recently, IVIgG preparations have been weight the effect of IVIgG administration on the IL-1 shown, both in vitro and in vivo, to profoundly affect the system was studied [143]. Following infusion an ele- homeostasis of the cytokine network, probably in a way vated level of IL-ra, an antagonist of IL-1, of anti-IL- which directs this network from disturbed to regulated 1a autoantibodies and a reduction in IL-1a in the circu- functioning. First of all, IVIgG contains small amounts lation was observed. In vitro studies on the release of of regulatory cytokines TGFb and IFNc [131,132]. The components of the IL-1 system from patient’s PBMC cytokines are biologically active, and their increase in indicated that administration of IVIgG in vivo may not the circulation after IVIgG administration can be dem- only be a potent down-regulator of proin_ammatory onstrated. Nevertheless, their therapeutic role as con- IL-1, but may also alter IL-1 stimulation of PBMC. stituents of IVIgGs remains to be evaluated. The effect of IVIgG on cytokine pro~les was further Antibodies directed against several cytokines were analyzed in patients with normal immunoglobulin lev- demonstrated in serum of healthy individuals, and in els. Circulating TNFa and IL-1b were serially as- IVIgG preparations. It was proposed that the anti- sessed before and after treatment with IVIgG of 21 in_ammatory effect of IVIgG may be related to neu- patients who suffered from Guillain-Barré syndrome. tralization of cytokines and alteration of cytokine syn- A reduction in pro-in_ammatory but no reduction in thesis and release [133,134]. Some of the anti-cytokine anti-in_ammatory cytokines was observed in patients autoantibodies show high af~nity to their antigens and receiving IVIgG. No such changes in circulating cyto- thus do not ~t the general feature of NAbs. Despite kines was observed in untreated patients or patients some investigations during the last years, the nature treated by plasma exchange [144]. Thus, one of the and role of anti-cytokine NAbs in vivo is not settled anti-in_ammatory effects of IVIgG may be the induc- [135]. The origin of these NAbs is probably a counter- tion of synthesis and release of anti-in_ammatory cy- regulatory mechanism to cytokine production, which tokines or cytokine antagonists. has a phase with release of pro-in_ammatory cytokines The activation of complement and the release of followed by a phase with release of anti-in_ammatory TNFa, IL-6 and IL-8 are important pathogenic factors cytokines. Therefore it is not surprising to ~nd anti- behind organ dysfunction in sepsis. Excessive produc- bodies to pro-in_ammatory cytokines and in the same tion and insuf~cient removal of cytokines due to mul- IVIgG preparation antibodies to anti-in_ammatory cy- tiorgan failure or sepsis are known to play a decisive Structure and Function of Immunoglobulins 211

role in progression of sepsis to septic shock. To show effect of IVIgG was most favourable, if infusion was conclusively the mechanism of an anti-in_ammatory ef- applied early after onset of an rMAS episode. This is fect of IVIgG in patients with severe trauma, burn or compatible with clinical observations in Kawasaki dis- sepsis was not possible yet. The in_ammation enhanc- ease, toxic epidermal necrolysis or dilating cardio- ing parameters in such conditions are apparently over- myopathy, all of which are diseases with a strong whelming and so complex that analytical keys and clini- in_ammatory component and all of which can pro~t cal observations fail to provide good data. Facing this from IVIgG infusion [145–147]. situation, a Bernese team was looking for severe in_ammatory conditions without microbial background 2. cytokine activity attenuating potential to study anti-in_ammatory effects of IVIgG. Twenty- of plasma-derived preparations enriched in IgM two consecutive patients with reactive macrophage ac- and IgA. The cytokine network modulating effect of tivation syndrome (rMAS) were analyzed. Patients immunoglobulins is obviously not restricted to IgG with rMAS (no neoplastic disorder or familial MAS as alone. In in vitro experiments a possible role of IgA in background) can acutely develop critical conditions prevention of in_ammation of the gut was reported. with ARDS, leak-syndrome, kidney failure without suf- Results were indicative for an anti-in_ammatory effect fering from bacterial infection or having the burden of of IgAbulin. IgAbulin was able to down-regulate in a large mass of narcotising tissue [144a]. In Figure 5 an dose dependent manner the release of TNFa and IL-6 example is given of how cytokine parameters can however not of GM-CSF from monocytes following change post infusion of IVIgG. The dramatic changes stimulation with heat-inactivated Haemophilus in- were associated with prompt relieve from life-threat- _uenzae b or LPS (E. coli) [148]. IgAbulin was further- ening condition. The study indicates that therapy with more able to inhibit receptor-dependent and inde- IVIgG can have a strong anti-in_ammatory potential in pendent generation of oxidative burst in human patients in an acutely deteriorating condition with hy- neutrophils and monocytes [149]. Finally the dose-de- peractive macrophages and excessive cytokine produc- pendent inhibition of release of pro-in_ammatory cy- tion. In patients who reacted to therapy, the clinical tokines TNFa and IL-6 by human peripheral blood

Fig. 5. Effect of IVIgG on cytokine pro~les in a patient with life-threatening reactive macrophage activation syndrome (rMAS). A 62 years old women was treated for rMAS with phenylbutazone (PB, 0.8g/d). Because of intestinal problems the patient stopped medica- tion. She was than hospitalised with rapidly deteriorating rMAS leading to “capillary leak”, ARDS, shock, kidney failure and severe coagulopathy. Administration of Sandoglobulin at a dose of 0.4g/kg b.w. over 72 hours (120 g total) is indicated by arrows. The life- threatening condition improved very rapidly. Sixteen days before IVIgG treatment TNFa was not detectable (normal Ͻ22 pg/mL), IL-6 level was 55 pg/mL (normal Ͻ 7 pg/mL), and IL-8 level was 78 pg/mL (normal Ͻ63 pg/mL). 212 Späth

monocular cells and adherent monocytes was paral- complement attack but is also able to slow down C3 leled by the release of IL-1ra and up-regulation of the activation in a speci~c manner by attenuating am- FcaR (CD89) [150]. pli~cation of C3 activation [159]. Attenuation of am- In mixed lymphocyte reaction (MLR) experiments pli~cation reduce the amount of C3a, C5a and arachi- a preparation which contains IgM, G and A (Pentaglo- donic acid metabolites liberated (Figure 2). All these bin) demonstrated signi~cant inhibition of alloantigen effects together with the potential for modulation of induced proliferation. The inhibitory capacity of the cytokine synthesis, release and activity may in their IgGMA preparation was more potent than the capacity sum make up the anti-in_ammatory potential of IVIgG of an IVIgG preparation. Assessment of cytokines in preparations. the culture supernatants provided evidence for modu- lation of IL-2 and IFNc production with a subsequent 4. Regulation of complement attack by IgA and impact on TNFa and IL-6 release [151]. IgM. Deviation of complement deposition from target tissue is apparently a feature of IgG, IgM and probably 3. IgG for attenuation of complement mediated IgA and is not a function associated to preceding anti- tissue destruction and in_ammation. Beside the gen binding. Deviation of complement deposition has no pro-in_ammatory cytokines anaphylatoxins C3a, C5a other prerequisite as close vicinity to a site where com- (C4a is no more considered to be of biological impor- plement is activated and the availability of structures to tance for in_ammation) and metabolites of arachidonic which C3b (C4b) can bind. All immunoglobulins which acid pathway are strong mediators of in_ammation can activate the alternative pathway provide such (Figure 2). Prevention of binding of anaphylatoxins to structures. When C4 uptake to a model immune com- their receptors can modulate in_ammation. Complexes plex was followed in vitro in presence of polyclonal IgG, of IgG and anaphylatoxins can be observed in human IgA1 and IgM, in vitro results indicated that on a serum and C3a can be separated from IgG of IVIgG weight and molar basis, monomeric serum IgA1 and preparations [152,153]. It is thus possible that IgG can IgM were far more active than IgG. The capacity of be a sink for C3a. sIgA to deviate complement attack was similar to that The interaction of complement with immunoglobu- of IgG [160]. In another in vitro study the enhanced lins is not limited to immunoglobulins which are com- complement-scavenging activity of IgM but not of IgA plexed with antigen. It is known that complement can could be con~rmed [161]. The better scavenging effect bind to monomeric IgG and IgG-C3b complexes are of IgM and the inability of IgA to deviate complement found in the circulation [154]. Covalently bound IgG- attack could be con~rmed in animal experiments when C3b are formed preferentially, despite activated C3 inhibition by IgM and IgG of C3-, C6- and C5b-9 deposi- (C4) forms ester bonds randomly within its short half- tion to rat glomeruli in a nephritis model were studied. life, the reason being that IgG is the second most abun- The immunomodulatory potentials of immunoglobu- dant protein in plasma and monomeric IgG molecules lins in human diseases are not mentioned completely have a low, but measurable af~nity to native C3 [155] without the list given in Table 8. It has to be kept in and activation of such C3 easily results in IgG-C3b com- mind that after the infusion of immunoglobulin prepa- plexes. Infusion of IVIgG furnishes an abundant rations all the effects mentioned in the text and in number of binding sites for the few C4b and many C3b Table 8 can become operative simultaneously. Which of generated. Thus, IVIgG can deviate complement depo- the functions become clinically relevant is dependent sition from tissue to the _uid phase [156]. In an in vivo on the immune condition of the recipient: immunologic model of purely complement-driven tissue destruction, parameters, which are deviated from the norm, may be the Forssman shock model of guinea pigs, attenuation of corrected while parameters within the norm remain complement attack by monomeric IgG was shown to be within their normal ranges and functions. Although the more effective with few but (very) high doses of IVIgG contribution of a single parameter may be of limited (1 to 2 g/kg body weight/d) than application of the same importance, the synergistic effect of all functions may dose fractionated into daily dosages over several con- be the essence of clinical effects of polyclonal poly- secutive days [157]. In vivo, in patients with derma- speci~c immunoglobulin preparations. tomyositis, IVIgG has been reported to inhibit deposi- tion of the C5b-9 membrane attack complex on the Conclusions endomysial capillaries by capturing C3b [158]. How- ever, explanation of the bene~cial effect of IVIgG in Immunoglobulin molecules can provide full transducer complement activation remains incomplete when men- function for host defense and immunomodulation only tioning deviation of complement attack from target as an intact, native molecule. This has implications for only. Deviation of complement activation from target to selection of IVIgG brand for prevention or treatment of the nearby surrounding does not reduce overshooting infectious diseases in humans. It is intriguing to envi- complement activation which generates anaphylatox- sage the use of preparations with high speci~city to ins and maintains a systemic in_ammation. Apparently support host defense. Such preparations could be mono- monomeric IgG of IVIgG is not only able to deviate clonal immunoglobulins or could be donor plasma de- Structure and Function of Immunoglobulins 213

Table 8. Immunomodulatory potential of various naturally occcurring immunoglobulins and their Ig classes. Those mechanisms which are not outlined in the text are summarized.

Self-antigens against which naturally occurring Biologic consequence of interaction between homeostatic immunoglobulins were described Ig isotype self-antigen and homeostatic antibody References

CD4 IgG Alteration of T cell function and T cell help with [164] possible effect on B cell repertoire; inhibition in vitro of infection CD4ϩ T cells by HIV CD5 IgG Potential for modulation of T cell functions and [165] for regulation of of B cell subsets expressing CD5 MHC class I IgG Alteration of T cell function and T cell help with [166] possible effect on B cell repertoire Idiotypes of membrane-bound or circulating IgG, IgM B cell repertoire switch. Control of expression of [167] immunoglobulins IgG autoreactivity (IgG; IgM) by high degree of variable region connectivity. Supposed to mediate reduction of diseases activity in conditions such as Guillain-Barré syndrome (IgG), Kawasaki disease (IgG), ANCA- associated systemic vasculitis (IgG, IgM) T cell receptor b-chain variable region and IgG T cell function and T cell help with possible effect [168] V-region frame on B cell repertoire The Fas/Fas-ligand system IgG Induction or inhibition of apoptosis in in vitro cell [145;169;170] cultures Inhibition of keratinocyte apoptosis in toxic epidermal necrolysis Neutral glycolipids of lymphocytes IgG Inhibition of lymphocyte proliferation [171] RGD sequences involved in adhesion IgG Inhibition of RGD-dependent adhesion processes [172] Hinge region of IgG1* IgG, IgA Inhibition of B cell proliferation [173]

Ј *Not to be mixed up with idiotypes. Antibodies which react with the hinge region of IgG1 do so with F(ab )2 fragments however not with Fab fragments. Anti-idiotypic antibodies react with both. An immunomodulatory potential of an IgGAM preparation was described recently [151]. It remains to be shown whether speci~c, F(ab) mediated reactions are involved.

rived polyclonal hyperimmune globulins. Very few of References the monoclonal preparations have reached approval by the authorities. The number of brands of hyperimmune 1. Fearon DT. Seeking wisdom in innate immunity. Nature preparations on the market is declining: logistic prob- 1997;388:323–324. lems, small production scales (high costs) and more 2. Fearon DT, Locksley RM. The instructive role of innate stringent registration policy of authorities may be rea- immunity in the acquired immune response. Science 1996; 272:50–54. sons for this situation. Arguments in favor of monoclo- 3. Bendelac A, Fearon DT. Innate immunity—Innate path- nals or hyperimmune preparations for passive transfer ways that control acquired immunity. Curr Opin Immunol of anti-microbial antibodies are: (1) lower costs because 1997;9:1–3. much less is needed and (2) the patient gets what he 4. Turner MW, Knox L. The subclasses of human immuno- needs. Firstly, the lower cost still have to be proven not globulin G. Immunol Today 1980;1:inserted folder. to be wishful thinking. Secondly, with low doses of 5. Nomenclature for human immunoglobulin. Bull World speci~c immunoglobulins to ~ght infections patients Health Organ 1964;30:447–449. probably may not really get what they need: patients 6. Rowe DS. IgD: A new class of human immunoglobulins. G might not pro~t from the anti-in_ammatory, immuno- Mal Infett Parassit 1966;18:Suppl-2. modulatory effect of immunoglobulins. Indeed, evi- 7. Ishizaka K, Ishizaka T, Hornbrook MM. Physico-chemical dence is solid enough to state that patients pro~t from properties of human reaginic antibody. IV. Presence of a unique immunoglobulin as a carrier of reaginic activity. J anti-in_ammatory effect of immunoglobulins (IgG) only Immunol 1966;97:75–85. when they are given at relative high doses. Thus, there 8. Nomenclature of human immunoglobulins. Bull World is agreement that for a mean range future large scale Health Organ 1973;48:373–374. production of native, fully active polyclonal immuno- 9. Porter RR. Separation and isolation of fractions of rabbit globulin preparations will stabilize costs while provid- gammaglobulin containing the antigenic combining sites. ing most _exibility in their clinical use. Nature 1958;182:670–671. 214 Späth

10. Porter RR. c-Globulin and antibodies. In: Putnan A, ed. The of C3b to the pneumococcal cell wall. J Immunol 1980; Plasma Proteins: Isolation Characterization and Function. 124:2502–2506. 1960:241–271. 27. Durack DT, Beeson PB. Protective role of complement in 11. Brambell FWR, Hemmings WA, Porter RR. The relative experimental Escherichia coli endocarditis. Infect Immun transmission of the fractions of papain hydrolyzed homolo- 1977;213–217. gous c-globulin from the uterine cavity to the foetal circula- 28. Miller TE, Phillips S, Simpson IJ. Complement-mediated tion in the rabbit. Proc Royal Soc London Series B 1960;151: immune mechanisms in renal infection. II. Effect of decom- 478–482. plementation. Clin Exp Immunol 1978;33:115–121. 12. Porter RR. Structural studies of immunoglobulins. Science 29. Duncan AR, Winter G. The binding site for C1q on IgG. 1973;180:713–716. Nature 1988;332:738–740. 13. Edelman GM, Cunningham BA, Gall WE, et al. The covalent 30. Tao MH, Can~eld SM, Morrison SL. The differential ability structure of an entire gammaG immunoglobulin molecule. of human IgG1 and IgG4 to activate complement is deter- Proc Natl Acad Sci USA 1969;63:78–85. mined by the COOH-terminal sequence of the CH2 domain. 14. Kabat EA, Wu TT, Bilofsky H. Evidence supporting somatic J Exp Med 1991;173:1025–1028. assembly of the DNA segments (minigenes), coding for the 31. Arya S, Chen F, Spycher S, et al. Mapping of amino acid framework, and complementarity-determining segments of residues in the C mu 3 domain of mouse IgM macromolecu- immunoglobulin variable regions. J Exp Med 1979;149:1299– lar assembly and complement-dependent cytolysis. JIm- 1313. munol 1994;152:1206–1212. 15. Unkeless JC, Shen Z, Lin CW, et al. Function of human Fc 32. Taylor B, Wright JF, Arya S, et al. C1q binding properties gamma RIIA and Fc gamma RIIIB. Semin Immunol 1995; of monomer and polymer forms of mouse IgM mu-chain 7:37–44. variants—Pro544Gly and Pro434Ala. J Immunol 1994;153: 16. Shohet JM, Pemberton P, Carrol MC. Identi~cation of a 5303–5313. major binding site for complement C3 in the IgG1 heavy 33. Chen FH, Arya SK, Rinfret A, et al. Domain-switched chain. J Biol Chem 1993;268:5866–5871. mouse IgM/IgG2b hybrids indicate individual roles for C2, 17. Anton LC, Ruiz S, Barrio E, et al. C3 binds with similar C3, and C4 domains in the regulation of the interaction of ef~ciency to Fab and Fc regions of IgG immune aggregates. IgM with complement C1q. J Immunol 1997; 159:3354– Eur J Immunol 1994;24:599–604. 3363. 18. Lutz HU, Bussolino F, Flepp R, et al. Naturally occurring 34. Sim RB, Reid KBM. C1 Molecular interactions with activat- anti-band-3 antibodies and complement together mediate ing systems. Immunol Today 1991;12:307–311. phagocytosis of oxidatively stressed human erythrocytes. 35. Perkins SJ, Nealis AS, Sutton BJ, et al. Solution structure Proc Natl Acad Sci USA 1987;84:7368–7372. of human and mouse immunoglobulin-M by synchrotron X- 18a. Jelezarova E, Lutz HU. Assembly and regulations of the ray scattering and molecular graphics modelling—A possi- complement ampli~cation loop in blood: The role of C3b- ble mechanism for complement activation. J Mol Biol 1991; C3b-IgG complexes. Mol Immunol 1999; submitted. 221:1345–1366. 19. Yang KD, Bathras JM, Shigeoka AO, et al. Mechanisms of 36. Ratnoff WD, Fearon DT, Austen KF. The role of antibody in bacterial opsonization by immune globulin intravenous: cor- the activation of the alternative complement pathway. relation of complement consumption with opsonic activity Springer Sem Immunopathol 1983;6:361–371. and protective ef~cacy. J Infect Dis 1989;159:701–707. 37. Joiner KA, Warren KA, Tam M, et al. Monoclonal antibodies 20. Smith CL, Baker CJ, Anderson DC, et al. Role of comple- directed against gonococcal protein I vary in bactericidal ment receptors in opsonophagocytosis of group-B strepto- activity. J Immunol 1985;134:3411–3419. cocci by adult and neonatal neutrophils. J Infect Dis 1990; 38. Fredlund H, Sjoholm AG, Selander B, et al. Serum bacteri- 162:489–495. cidal activity and induction of chemiluminescence of poly- 21. Ross C, Densen P. Complement de~ciency states and infec- morphonuclear leukocytes: Complement activation pathway tion: Epidemiology, pathogenesis and consequences of neis- requirements in defense against Neisseria meningitidis. Int serial and other infections in an immune de~ciency. Medi- Arch Allergy Immunol 1993;100:135–143. cine Baltimore 1984;63:243–273. 39. Fries LF, Siwik SA, Malbran A, et al. Phagocytosis of target 22. Schoolnik GK, Buchanan TM, Holmes KK. Gonococci caus- particles bearing C3b-IgG covalent complexes by human ing disseminated infection are restistant to the bactericidal monocytes and polymorphonuclear leucocytes. Immunology action of normal human serum. J Clin Invest 1976;58:1163– 1987; 62:45–45. 1173. 40. Schifferli JA, Barlotti SR, Peters DK. Inhibition of immune 23. McCabe WR, Kaijser B. Olling S, et al. Escherichia coli in precipitation by complement. Clin Exp Immunol 1980;45: bacteremia: K and O antigens and serum sensitivity of 387–394. strains form adults and neonates. J Infect Dis 1978;138: 41. Schifferli JA, Ng YG, Peters DK. The role of complement 33–41. and its receptor in the elimination of immune complexes. N 24. Casciato DA, Rosenblatt JE, Bluestone R, et al. Susceptibil- Engl J Med 1986;315:488–495. ity of isolates of bacteroides to the bactericidal activity of 42. Schifferli JA, Peters DK. Complement, the immune-com- normal human serum. J Infect Dis 1979;140:109–113. plex lattice, and the pathophysiology of complement-de~- 25. Wilkinson BJ, Sisson SP, Kim Y, et al. Localization of the ciency syndromes. Lancet 1983;II:957–959. third component of complement on the cell wall of encapsu- 43. Lutz HU. How pre-existing, germline-derived antibodies lated Staphylococcus aureus M: implications for the mecha- and complement may help induce a primary immune re- nisms of resistance to phagocytosis. Infect Immun 1979;26: sponse to nonself. Scand J Immunol 1999;49:224–228. 1159–1163. 44. Hayakawa K, Asano M, Shinton SA, et al. Positive selection 26. Winkelstein JA, Abramovitz AS, Tomasz A. Activation of C3 of natural autoreactive B cells. Science 1999;285:113–116. via the alternative complement pathway results in ~xation 45. Avrameas S. Natural autoantibodies: From ‘horror auto- Structure and Function of Immunoglobulins 215

toxicus’ to ‘gnothi seauton’. Immunol Today 1991;12:154– globulinemia D in idiopathic retinal vasculitis. Graefes Arch 159. Clin Exp Ophthalmol 1997;235:372–378. 46. Varela FJ, Coutinho A. Second generation immune net- 64. Saarinen UM, Strandjord SE, Warkentin PI, et al. Differen- works. Immunol Today 1991;12:159–166. tiation of presumed sepsis from acute graft-versus-host dis- 47. Melchers, F. Introduction to the annual report: 1998. Basel. ease by C-reactive protein and serum total IgE in bone mar- Basel Institute for Immunology - Annual Report 1999: pp. row transplant recipients. Transplantation 1987;44:540–546. 1–17. 65. Dipiro JT, Howdieshell TR, Hamilton RG, et al. Immuno- 48. Donze HH, Lue C, Julian BA, et al. Human peritoneal B-1 globulin E and eosinophil counts are increased after sepsis cells and the in_uence of continuous ambulatory peritoneal in trauma patients. Crit Care Med 1998;26:465–469. dialysis on peritoneal and peripheral blood mononuclear cell 66. Dipiro JT, Hamilton RG, Howdieshell TR, et al. Lipopoly- (PBMC) composition and immunoglobulin levels. Clin Exp saccharide-reactive immunoglobulin E is associated with Immunol 1997;109:356–361. lower mortality and organ failure in traumatically injured 49. Casali P, Notkins AL. CD5ϩ B lymphocytes, polyreactive patients. Clin Diagn Lab Immunol 1994;295–298. antibodies and the human B-cell repertoire. Immunol Today 67. Römer J, Morgenthaler J-J, Scherz R, et al. Characteri- 1989;10:364–368. zations of various immunoglobulin preparations for intrave- 50. Brambell FWR, Hemmings WA, Morris IG. A theoretical nous application. I. Protein composition and antibody con- model of gamma-globulin catabolism. Nature 1964;203:1352– tent. Vox Sang 1982;42:62–73. 1355. 68. Römer J, Späth PJ, Skvaril F, et al. Characterization of 51. Junghans RP, Anderson CL. The protection receptor for various immunoglobulin preparations for intravenous appli- IgG catabolism is the b2-microglobulin-containing neonatal cation. II. Complement activation and binding to staphylo- intestinal transport receptor. Proc Natl Acad Sci USA coccus protein A. Vox Sang 1982;42:74–80. 1996;93:5512–5516. 69. Jungi TW, Santer M, Lerch PG, et al. Effect of various

52. Christianson GJ, Brooks W, Vekasi S, et al. b2-microglobulin- treatments of gamma-globulin (IgG) for achieving intrave- de~cient mice are protected from hypergammaglobulinemia nous tolerance on the capacity to interact with human mono- and have defective antibody responses because of increased cyte Fc receptors. Vox Sang 1986;51:18–26. IgG catabolism. J Immunol 1997;159:4781–4792. 70. Wiersma EJ, Shulman MJ. Assembly of IgM. Role of di- 53. Raghavan M, Wang Y, Bjorkman PJ. Effects of receptor sul~de bonding and noncovalent interactions. J Immunol dimerization on the interaction between the class I major 1995;154:5265–5272. histocompatibility complex-related Fc receptor and IgG. 71. Wiersma EJ, Chen F, Bazin R, et al. Analysis of IgM struc- Proc Natl Acad Sci USA 1995;92:11200–11204. tures involved in J chain incorporation. J Immunol 1997;158: 54. Yu Z, Lennon VA. Mechanism of intravenous immune globu- 1719–1726. lin therapy in antibody-mediated autoimmune diseases. N 72. Dempsey PW, Allison MED, Akkaraju S, et al. C3d of com- Engl J Med 199;340:227–228. plement as a molecular adjuvant: Bridging innate and ac- 55. Raghavan M, Gastinel LN, Bjorkman PJ, The class I major quired immunity. Science 1996;271:348–350. histocompatibility complex related Fc receptor shows pH- 73. Tridandapani S, Kelley T, Cooney D, et al. Negative signal- dependent stability differences correlating with immuno- ing in B cells: SHIP Grbs Shc. Immunol Today 1997;18:424– globulin binding and release. Biochemistry 1993;32:8654– 427. 8660. 74. Poon PH, Phillips ML, Schumaker VN. Immunoglobulin M 56. Leach JL, Sedmak DD, Osborne JM, et al. Isolation from possesses two binding sites for complement subcomponent human placenta of the IgG transporter, FcRn, and local- C1q, and soluble 1:1 and 2:1 complexes are formed in solution ization to the syncytiotrophoblast: Implications for mater- at reduced strength. J Biol Chem 1985;260:9357–9365. nal-fetal antibody transport. J Immunol 1996;157:3317– 75. Feinstein A, Richardson N, Taussig MJ. Immunoglobulin 3322. _exibility in complement activation. Immunol Today 1986;7: 57. Sitia R, Rabellino EM, Sockell M, et al. A spatial association 169–174. between membrane IgD and the receptor for C3b (CR1) at 76. Painter RH. The binding of C1q to immunoglobulins. Be- the cell surface on murine B lymphocytes. J Immunol 1981; hring Inst Mitt 1993;131–137. 126:107–112. 77. Shigeoka AO, Jensen CJ, Pincus SH, et al. Absolute require- 58. Forsgren A, Grubb AO. Many bacterial species bind human ment for complement in monoclonal IgM antibody-mediated IgD. J Immunol 1979;122:1468–1472. protection against experimental infection with type III 59. Henney CS, Welschester HD, Terry WD, et al. Studies on group B streptococci. J Infect Dis. 1984;150:63–70. human IgD. II. The lack of skin sensitizing and complement 78. Stephan W, Dichtelmueller H, Schedel I. Eigenschaften und ~xing activities of immunoglobulin D. Immunochemistry Wirksamheit eines humanen Immunoglobulin M- Präparates 1969;6:445–449. für die intravenöse Anwendung. Arzneim Forsch/Drug Res 60. Konno T, Hirai H, Inai S. Studies in IgD-I. Complement 1985;35:933–936. ~xing activities of IgD myeloma proteins. Immunochemis- 79. Gronski P, Hofstaetter T, Kanzy EJ, et al. S-Sulfonation: A try 1975;12:773–777. reversible chemical modi~cation of human immunoglobulin 61. Drenth JP, Haagsma CJ, van der Meer JW. Hyperimmuno- permitting intravenous application. I. Physicochemical and globulinemia D and periodic fever syndrome. The clinical binding properties of S-sulfonated and reconstituted IgG. spectrum in a series of 50 patients. International Hyper-IgD Vox Sang 1983;45:144–154. Study Group. Medicine (Baltimmore) 1994;73:133–144. 80. Davis AC, Shulman MJ. IgM—Molecular requirements for 62. Boom BW, Daha MR, Vermeer BJ, et al. IgD immune com- its assembly and function. Immunol Today 1989;10:118–122. plex vasculities in a patient with hyperimmunoglobulinemia 81. Behre G, et al. Endotoxin concentrations and therapy with D and periodic fever. Arch Dermatol 1990;126:1621–1624. polyclonal IgM-enriched immunoglobulin in neutropenic 63. Kumano Y, Nagato T, Kurihara K, et al. Hyperimmuno- cancer patients with sepsis syndrome: Pilot study and in- 216 Späth

terim analysis of a randomized trial. Antiinfect Drugs lins G, M, and A against Pseudomonas aeruginosa lipopoly- Chemother 1995;13:129–134. saccharide. Infect Immun 1989;57:174–179. 82. Borleffs JC, Schellekens JF, Brouwer E, et al. Use of an 100. Oishi K, Koles NL, Guelde G, et al. Antibacterial and protec- immunoglobulin M containing preparation for treatment of tive properties of monoclonal antibodies reactive with Es- two hypogammaglobulinemic patients with persistent Cam- cherichia coli O111:B4 lipopolysaccharide—Relation to anti- pylobacter jejuni infection. Eur J Clin Microbiol Infect Dis body isotype and complement-~xing activity. J Infect Dis. 1993;12:772–775. 1992;165:34–45. 83. Haque KN, Zaidi MH, Bahakim H, IgM-enriched intrave- 101. Foreman KE, Bjornson AB. The alternative complement nous immunoglobulin therapy in neonatal sepsis. Am J Dis pathway promotes IgM antibody-dependent and -indepen- Child 1988;142:1293–1296. dent adherence of Bacteroides to polymorphonuclear leu- 84. Pilz G, Appel R, Kreuzer E, et al. Comparison of early kocytes through CR3 and CR1. J Leukoc Biol 1994;55: IgM-enriched immunoglobulin vs polyvalent IgG admini- 603–611. stration in score-identi~ed postcardiac surgical patients at 102. Bjornson AB, Detmers PA. The pentameric structure of high risk for sepsis. Chest 1997;111:419–426. IgM is necessary to enhance opsonization of Bacteroides 85. Schedel I, Dreikhausen U, Nentwig B, et al. Treatment of thetaiotaomicron and Bacteroides fragilis via the alterna- gram-negative septic shock with an immunoglobolin prepa- tive complement pathway. Microb Pathog 1995;19:117–128. ration: A prospective, randomized clinical trial. Crit Care 103. Mostov KE, Deitcher DL. Polymeric immunoglobulin recep- Med 1991;19:1104–1113. tor expressed in MDCK cells transcytoses IgA. Cell 1986; 86. Haque KN, Remo C, Bahakim H. Comparison of two types 46:613–621. of intravenous immunoglobulins in the treatment of neona- 104. Mestecky J, McGhee JR. Immunoglobulin-A (IgA)—Mo- tal sepsis. Clin Exp Immunol 1995;101:328–333. lecular and cellular interactions involved in IgA biosynthe- 87. Jackson SK, Parton J, Barnes RA, et al. Effect of IgM-en- sis and immune response. In: Dixon FJ, ed. Advances in riched intravenous immunoglobulin (Pentaglobin) on endo- Immunology. Orlando: Academic Press Inc., 1987:153–245. toxaemia and anti-endotoxin antibodies in bone marrow 105. Underdown BJ, Schiff JM. Immunoglobulin A: Strategic transplantation. Eur J Clin Invest 1993;23:540–545. defense initiative at the mucosal surface. Annu Rev Immu- 88. Poynton CH, Jackson S, Fegan C, et al. Use of IgM-enriched nol 1986;4:389–417. intravenous immunoglobulin (Pentaglobin) in bone marrow 106. Dickinson EC, Gorga JC, Garrett M, et al. Immunoglobulin transplantation. Bone Marrow Transplant 1992;9:451–457. A supplementation abrogates bacterial translocation and 89. Trautmann M, Held TK, Susa M, et al. Bacterial lipopolysac- preserves the architecture of the intestinal epithelium. Sur- charide (LPS)-speci~c antibodies in commercial human im- gery 1998;124:284–290. munoglobulin preparations: Superior antibody content of an 107. Maxson RT, Jackson RJ, Smith SD. The protective role of IgM-enriched product. Clin Exp Immunol 1998;111:81–90. enteral IgA supplementation in neonatal gut origin sepsis. J 90. Ng PK, O’Rourke PE, Andersen JD, et al. Process-scale Pediatr Surg 1995;30:231–233. puri~cation of immunoglobulin M concentrate. Vox Sang 108. Daha MR, Gorter A, Rits M, et al. Interaction of immuno- 1993;65:81–86. globulin-A with complement and phagocytic cells. Prog Clin 91. Bubb MO, Conradie JD. The importance of quaternary Biol Res 1989;297:247–261. structure in the expression of the C1-binding site of IgM. 109. Nikolova EB, Tomana M, Russell MW. The role of the carbo- Immunology 1976;31:893–902. hydrate chains in complement (C3) ~xation by solid-phase- 92. Tsay GC, Jesmok G. Heat treatment of IgM-containing im- bound human IgA. Immunology 1994;82:321–327. munoglobulins to eliminate non-speci~c complement activa- 110. Zhang W, Lachmann PJ. Glycosylation of IgA is required for tion. Miles Inc., Berkley Calif. United States Patent Oct, optimal activation of the alternative complement pathway 26(5,256,771). 1993. by immune complexes. Immunology 1994;81:137–141. 93. Tsay GC, Jesmok G. Heat-treated IgM antibody prepara- 111. Eibl MM, Wolf HM, Furnkranz H, et al. Prevention of nec- tions. Bayer Corporation, Elkhart Ind. (5,510,465), 1–14. rotizing enterocolitis in low-birth-weight infants by IgA- 1996. IgG feeding. N Engl J Med 1988;319:1–7. 94. Barandun S, Kistler P, Jeunet F, et al. Intravenous admini- 112. Hemmingsson P, Hammarström L. Nasal administration of stration of human gammaglobulin. Vox Sang. 1962;7:157–174. immunoglobulin as effective prophylaxis against infections 95. Pollack M, Koles NL, Preston MJ, et al. Functional proper- in elite cross-country skiers. Scand J Infect Dis 1993;25:783– ties of isotype-switched immunoglobulin M (IgM) and IgG 785. monoclonal antibodies to Pseudomonas aeruginosa lipo- 113. Lindberg K, Berglund B. Effect of treatment with nasal IgA polysaccharide. Infect Immun 1995;63:4481–4487. on the incidence of infectious disease in world-class canoe- 96. Pier GB, Thomas DM. Characterization of the human im- ists. Int J Sports Med 1996;17:235–238. mune response to a polysaccharide vaccine from Pseudo- 114. Cohn EJ, Strong LE, Hughes WLJ, et al. Preparation and monas aeruginosa. J Infect Dis 1983;148:206–213. properties of serum and plasma proteins. 1. A system for the 97. Kaufman BM, Cross AS, Futrovsky SL, et al. Monoclonal separation into fractions of the protein and lipoprotein com- antibodies reactive with K1-encapsulated Escherichia coli ponents of biological tissues and _uids. J Am Chem Soc lipopolysaccharide are opsonic and protect mice against le- 1946; 68:459–475. thal challenge. Infect Immun 1986;52:617–619. 115. Oncley JL, Melin M, Richert DA, et al. The separation of the 98. Kim KS, Kang JH, Cross AS, et al. Functional activities of antibodies, isoagglutinins, prothrombin, plasminogen and 1- monoclonal antibodies to the O side chain of Escherichia coli lipoprotein into subfractions of human plasma. J Am Chem lipopolysaccharides in vitro and in vivo. J Infect Dis 1988; Soc 1949;71:541–550. 157:47–53. 116. Bruton OC. Agammaglobulinemia. Pediatrics 1952;9:722– 99. Pier GB, Thomas D, Small G, et al. In vitro and in vivo 728. activity of polyclonal and monoclonal human immunoglobu- 117. Norrby-Teglund A, Basma H, Andersson J, et al. Varying Structure and Function of Immunoglobulins 217

titers of neutralizing antibodies to streptococcal superan- 135. Bendtzen K. Autoantibodies to cytokines. Eur J Clin Invest tigens in different preparations of normal polyspeci~c immu- 1998;28:300–301. noglobulin G: Implications for therapeutic ef~cacy. Clin In- 136. Andersson U, Bjoerk L, Skansen-Saphir U, et al. Pooled fect Dis 1998;26:631–638. human IgG modulates cytokine production in lymphocytes 118. Kroese FG, de Waard R, Bos NA. B-1 cells and their reac- and monocytes. Immunol Rev 1994;139:21–42. tivity with the murine intestinal micro_ora. Semin Immu- 137. Modiano JF, Amran D, Lack G, et al. Posttranscriptional nol 1996;8:11–18. regulation of T-cell IL-2 production by human pooled immu- 119. Bos NA, Bun JC, Popma SH, et al. Monoclonal immuno- noglobin. Clin Immunol Immunopathol 1997;83:77–85. globulin A derived from peritoneal B cells is encoded by 138. Nachbaur D, Herold M, Eibl B, et al. A comparative study both germ line and somatically mutated VH genes and is of the in vitro immunomodulatory activity of human intact reactive with commensal bacteria. Infect Immun 1996;64: immunoglobulin (7S IVIG), F(ab’)2 fragments (5S IVIG) 616–623. and Fc fragments. Evidence for post-transcriptional IL-2 120. Grif~ss JM, Jarvis GA. Interaction of serum IgA with com- modulation. Immunology 1997;90:212–218. plement components: The molecular basis of IgA blockade. 139. Amran D, Renz H, Lack G, et al. Suppression of cytokine-de- Adv Exp Med Biol 1987;216B:1303–1309. pendent human T-cell proliferation by intravenous immuno- 121. Joiner KA, Scales R, Warren KA, et al. Mechanism of action globulin. Clin Immunol Immunopathol 1994;73:180–186. blocking immunoglobulin-G for neisseria-gonorrhoeae. J 140. Schanz U, Hügle T, Gmür J. Additional inhibitory effects of Clin Invest 1985;76:1765–1765. intravenous immunoglobulins in combination with cyclo- 122. Rice PA, Vayo HE, Tam RM, et al. Immunoglobulin G anti- sporine A on human T lymphocyte alloproliferative response bodies directed against protein III block killing of serum-re- in vitro. Transplantation 1996;61:1736–1740. sistant Neisseria gonorrhoeae by immune serum. JExp 141. Aukrust P, Froland SS, Liabakk NB, et al. Release of cytok- Med 1986;164:1735–1748. ines, soluble cytokine receptors, and interleukin-1 receptor 123. Rice PA, McQuillen DP, Gulati S, et al. Serum resistance of antagonist after intravenous immunoglobulin administra- Neisseria gonorrhoeae. Does it thwart the in_ammatory re- tion in vivo. Blood 1994;84:2136–2143. sponse and facilitate the transmission of infection? Ann NY 142. Sewell WA, North ME, Cambronero R, et al. In vivo modu- Acad Sci 1994;730:7–14. lation of cytokine synthesis by intravenous immunoglobulin. 124. Hamadeh RM, Estabrook MM, Zhou P, et al. Anti-Gal binds Clin Exp Immunol 1999;116:509–515. to pili of Neisseria meningitidis: The immunoglobulin A 143. Aukrust P, Müller F, Svenson M, et al. Administration of isotype blocks complement-mediated killing. Infect Immun intravenous immunoglobulin (IVIG) in vivo-Down-regula- 1995;63:4900–4906. tory effects on the IL-1 system. Clin Exp Immunol. 1999; 125. Takei S, Arora YK, Walker SM. Intravenous immunoglobu- 115:136–143. lin contains speci~c antibodies inhibitory to activation of 144. Sharief MK, Ingram DA, Swash M, et al. I.v. immunoglobu- T-cells by staphylococcal toxin superantigens J Clin Invest lin reduces circulating proin_ammatory cytokines in Guil- 1993;91:602–607. lain-Barre syndrome. Neurology 1999;52:1833–1838. 126. Kaul R, McGeer A, Norrby-Teglund A, et al. Intravenous 144a. Emmenegger U, Frey U, Reimers A, Cottagnoud P. Späth immunoglobulin therapy for streptococcal toxic shock syn- PJ, Neftel KA. Serum ferritin levels and emergency treat- drome—A comparative observational study. Clin Infect Dis ment with intravenous immunoglobulin in fulminant reac- 1999;28:800–807. tive macrophage activation syndromes, submitted. 127. Leung DYM. Kawasaki syndrome: Immunomodulatory 145. Viard I, Wehrli P, Bullani R, et al. Inhibition of toxic epider- bene~t and potential toxin neutralization by intravenous mal necrolysis by blockade of CD95 with human intravenous immune globulin. Clin Exp Immunol 1996;104:49–54. immunoglobulin. Science 1998;282:490– 493. 128. Imbach P, Barandun S, D’Apuzzo V, et al. High-dose intra- 146. Furusho K, Sato K, Soeda T, et al. High dose intravenous venous gammaglobulin for idiopathic thrombocytopenic gammaglobulin for Kawasaki disease. Lancet 1983;II: purpura in childhood. Lancet 1981;1:1228–1231. 1359–1359. 129. National Institute of Health (NIH) Consensus Development 147. McNamara DM, Rosenblum WD, Janosko KM, et al. Intra- Conference. Intravenous immunoglobulin—Prevention and venous immune globulin in the therapy of myocarditis and treatment of disease. JAMA 1990;264:3189–3193. acute cardiomyopathy. Circulation 1997;95:2476–2478. 130. Iwata M, Shimozato R, Tokiwa H, et al. Antipyretic activity 148. Wolf HM, Eibl MM. The anti-in_ammatory effect of an oral of human immunoglobulin in preparation for intravenous immunoglobulin (IgA-IgG) preparation and its possible rele- use (IGIV) in experimental model of fever in rabbits. In: vance for the prevention of necrotizing enterocolitis. Acta Morell A, Nydegger UE, eds. Clinical Use of Intravenous Paediatr Suppl 1994;396:37–40. Immunoglobulin. London: Academic Press, 1986:327–338. 149. Wolf HM, Vogel E, Fischer MB, et al. Inhibition of receptor- 131. Lam L, Whitsett CF, McNicholl JM, et al. Immunologically dependent and receptorindependent generation of the respi- active proteins in intravenous immunoglobulin. Lancet 1993; ratory burst in human neutrophils and monocytes by human 342:678–678. serum IgA. Pediatric Res 1994;36:235–243. 132. Kekow J, Reinhold D, Pap T, et al. Intravenous immuno- 150. Wolf HM, Hauber I, Gulle H, et al. Anti-in_ammatory prop- globulins and transforming growth factor b. Lancet 1998; erties of human serum IgA: Induction of IL-1 receptor an- 351:184–185. tagonist and (CD89)-mediated down-regulation of tumour 133. Abe Y, Horiuchi A, Miyake M, et al. Anti-cytokine nature of necrosis factor-alpha (TNF-alpha) and IL-6 in human mono- natural human immunoglobulin: One possible mechanism of cytes. Clin Exp Immunol 1996;105:537–543. the clinical effect of intravenous immunoglobulin therapy. 151. Nachbaur D, Herold M, Gächter A, et al. Modulation of Immunol Rev 1994;139:5–9. alloimmune response in vitro by an IgM-enriched immuno- 134. Bendtzen K, Svenson M, Hansen M. Autoantibodies to cy- globulin preparation (Pentaglobin). Immunology 1998;94: tokines in IVIG. J Rheumatol 1993;20:2176–2177. 279–283. 218 Späth

152. Nezlin R, Freywald A. Complexes of IgG molecules and C3a to IgG autoantibodies of autoimmune patients and protects and C4a complement components in human serum. Eur J from experimental autoimmune disease. Blood 1997;90: Immunol 1992;22:1955–1957. 4004–4013. 153. Nezlin R. Detection of the C3a complement component in 164. Hurez V,Kaveri S-V,Mouhoub A, et al. Anti-CD4 activity of commercial gamma-globulins by dot blotting. J Immunol normal human immunoglobulin G for therapeutic use (intra- Meth 1993;163:269–272. venous immunoglobulin, IVIg). Therap Immunol 1994;1: 154. Jacobs RJ, Reichlin M. Generation of low m.w., C3-bearing 269–277. immunoglobulin in human serum. J Immunol 1983;130: 165. Vassilev T, Gelin C, Kaveri S-V, et al. Antibodies to the CD5 2775–2781. molecule in normal human immunoglobulins for therapeutic 155. Lutz HU, Stammler P, Fasler S. Preferential formation of use (intravenous immunoglobulins, IVIg). Clin Exp Immu- C3b-IgG complexes in vitro and in vivo from nascent C3b nol 1993;92:369–372. and naturally occurring anti-band 3 antibodies. J Biol Chem 166. Kaveri S, Vassilev T, Hurez V, et al. Antibodies to a con- 1993;268:17418–17426. served region of HLA class I molecules, capable of modulat- 156. Frank MM, Basta M, Fries LF. The effects of intravenous ing CD8 T cell-mediated function, are present in pooled immune globulin on complement-dependent immune dam- normal immunoglobulin for therapeutic use. J Clin Invest age of cells and tissues. Clin Immunol Immunopathol. 1992; 1996;97:865–869. 62:S82–S86 167. Hurez V, Kaveri SV, Kazatchkine MD. Expression and con- 157. Basta M, Kirshbom P,Frank MM, et al. Mechanism of thera- trol of the natural autoreactive IgG repertoire in normal peutic effect of high-dose intravenous immunoglobulin At- human serum. Eur J Immunol 1993;23:783–789. tenuation of acute, complement-dependent immune damage 168. Marchalonis JJ, Kaymaz H, Dedeoglu F, et al. Human auto- in a guinea pig model. J Clin Invest 1989;84:1974–1981. antibodies reactive with synthetic autoantigens from T-cell 158. Basta M, Dalakas MC. High-dose intravenous immuno- receptor beta-chain. Proc Natl Acad Sci USA 1992;89:3325– globulin exerts its bene~cial effect in patients with derma- 3329. tomyositis by blocking endomysial deposition of activated 169. Prasad NKA, Papoff G, Zeuner A, et al. Therapeutic prepa- complement fragments. J Clin Invest 1994;94:1729–1735. rations of normal polyspeci~c IgG (IVIg) induce apoptosis in 159. Lutz HU, Stammler P, Jelezarova E, et al. High doses of human lymphocytes and monocytes: A novel mechanism of immunoglobulin G attenuate immune aggregate-mediated action of IVIg involving the Fas apoptotic pathway. JIm- complement activation by enhancing physiologic cleavage of munol 1998;161:3781–3790.

C3b in C3bn-IgG complexes. Blood 1996;88:184–193. 170. Williams MA, Rhoades CJ, Lewis A, et al. Intravenous im- 160. Miletic VD, Hester CG, Frank MM. Regulation of comple- munoglobulin blocks nitric oxide synthesis and activation- ment activity by immunoglobulin. 1. Effect of immunoglobu- induced apoptosis in THP-1 macrophage cells. J Haematol lin isotype on C4 uptake on antibody-sensitized sheep eryth- 1999;84:254–255 (Abstract). rocytes and solid phase immune complexes. J Immunol 171. Brand A, Vuist WM, Van Schaik IN, et al. In vitro investi- 1996;156:749–757. gation of immunoglobulin treatment mechanisms in autoim- 161. Rieben R, Roos A, Muizert Y, et al. Immunoglobulin M-en- mune diseases. Clin Exp Rheumatol 1996;14(Suppl 15):S27– riched human intravenous immunoglobulin prevents com- S30 plement activation in vitro and in vivo in a rat model of acute 172. Vassilev TL, Kazatchkine MD, Van Huyen JP, et al. Inhibi- in_ammation. Blood 1999;93:942–951. tion of cell adhesion by antibodies to Arg-Gly-Asp (RGD) in 162. Scholer A, Fischbach F, Spichiger U, et al. Einheitliche Re- normal immunoglobulin for therapeutic use (intravenous im- ferenzbereiche (Normwerte) für häu~ge klinisch-chemische munoglobulin, IVIg). Blood 1999;93:3624–3631. Messgrössen. Schweizerische Ärztezeitung 1998;79:2619– 173. Terness P, Opelz G. Natural anti-immunoglobulin autoanti- 2622. bodies: Irrelevant by-products or immunoregulatory mole- 163. Hurez V, Kazatchkine MD, Vassilev T, et al. Pooled normal cules? Int Arch Allergy Immunol 1998;115:270–277. human polyspeci~c IgM contains neutralizing anti-idiotypes