Beyond Allotypes: The Influence of Allelic Diversity in Antibody Constant Domains

Polymorphic diversity in antibody constant domains has long been defined by allotypic motifs that cross react with the sera of other individuals. Improvements in sequencing technologies have led to the discovery of a large number of new allelic sequences that underlie this diversity. Many of the point mutations lie outside traditional allotypic motifs suggesting they do not elicit immunogenic responses. As antibodies play an important role in immune defense and biotechnology, understanding how this newly resolved diversity influences the function of antibodies is important. This review investigates the current known diversity of antibody alleles at a protein level for each antibody isotype as well as the kappa and lambda light chains. We focus on evidence emerging for how these mutations perturb antibody interactions with antigens and Fc receptors that are critical for function, as well as the influence this might have on the use of antibodies as therapeutics and reagents.

Immunoglobulin allotypes and RFLPs in disease association

Immunoglobulin heavy chain (Gm) and light chain (Km) allotypes have been extensively studied as possible markers of susceptibility to a range of immune-related diseases including malignancies, infectious diseases and autoimmune disorders. This review is concentrated on susceptibility to multiple sclerosis, systemic lupus erythematosus and insulin-dependent diabetes mellitus.

HLA, Gm, and Km polymorphisms and immunity to infectious diseases in South Amerinds

Isolated South Amerinds, a population at very high risk from infectious disease, mount good immune responses to pneumococcal polysaccharides, viral antigens and other immunogens. No unusual immunoglobulin allotype or HLA antigen, which might explain the high risk from infectious disease, was found among them. Responses are examined in relation to the immunogenetic markers that are most prevalent. Amerinds with Gm 1,2,17,21 responded less well than persons without this haplotype to 10 of 12 pneumococcal polysaccharides, and those who were homozygous at the HLA class I loci responded less well to viral antigens. However, these differences are not strong and there are few such findings relative to the number of possibilities examined. The most distinctive immunogenetic characteristic of these populations is their low level of polymorphism at all tested loci. Their susceptibility to infectious agents can be attributed to this genetic uniformity and a consequent ability of pathogens to adapt to the population.

Alloantibodies to human platelet glycoprotein antigens (HPA) and HLA class 1 in a cross section of Nigerian antenatal women

The prevalence of antibodies to human platelet antigens (HPA) and human leukocyte antigens (HLA) class 1 antigens among Nigerian pregnant women has not been reported in our country. This study was therefore aimed at screening the obstetric population for evidence of alloimmunization due to human platelet and HLA class 1 antigens. One hundred and forty four (144) pregnant women attending the obstetric clinic of Military Hospital, Port Harcourt, participated in the study. Their sera were tested for antibodies to HPA and HLA class 1 antigens using GTI PakPlus solid phase ELISA Kit. The total prevalence rate of antibody production was 60.5% (87 out of 144). Among the positive samples, 60 had platelet glycoprotein specific antibodies (41.7%) and 27 had HLA class 1 antibodies (18.8%). In 39.6% of the pregnant women, both platelet specific antibodies and HLA class 1 antibodies appeared. The prevalence of platelet specific glycoprotein antibodies were obtained as follows: GP 11b/111a 12 (8.3%), GP 1a/11a 35 (20.8%), GP Ib/IX 18 (12.5%) and GP IV 9 (6.3%). The prevalence of each platelet antibody subgroup was obtained as follows: anti-HPA-1a,-3a,-4a (4.2%), anti-HPA-1b,-3b,-4a (4.2%), anti-HPA-30 5a and anti-GP Ib/IX (12.5% each), anti-HPA-5b (8.3%) and anti-GP IV (6.3%). A high prevalence rate of human platelet arid cytotoxic antibodies has been observed in our obstetric population. There is need to establish platelet serology laboratory for the proper antenatal and postnatal management of pregnant mothers in this region.

Anaphylactic transfusion reaction associated with a possible anti-A2m(1)

A 42-year-old leukaemic black male developed shortness of breath, itching, hot flushes, substernal pain, marked hypotension, and cardiorespiratory arrest after the infusion of 50 ml of pooled platelet concentrates. The patient had had one previous and uneventful red blood cell transfusion. Serologic studies of this patient's post-transfusion serum showed the presence of an antibody against one denatured IgA2 protein with the phenotype A2m(1 + 2-). All of the platelet donors were A2m(1) positive. The patient was successfully transfused with platelets from donors with the phenotype A2m(1 - 2+). Although 35.8% of Blacks and 30.0% of Chinese are A2m(1) negative, this is the first reported transfusion reaction associated solely with the occurrence of a possible anti-A2m(1) in an individual of the type A2m(1 - 2+).

Immunoglobulin allotypes and IgG subclass antibody response to Aspergillus fumigatus in cystic fibrosis patients

BACKGROUND

A majority of patients with cystic fibrosis (CF) become colonised with Aspergillus fumigatus (Af.), but only a minority develops allergic bronchopulmonary aspergillosis (ABPA). ABPA is associated with increased levels of specific immunoglobulin G (IgG) anti-Af. antibodies with a characteristic IgG subclass distribution. We examined whether this characteristic immune response was under the influence of GM and KM allotypes, which are genetic markers (antigenic determinants) on gamma- and kappa-light chains, respectively.

METHODS

Sera from 233 CF patients were typed for seven GM determinants and two KM determinants. The types were correlated to IgG subclass anti-Af. antibody levels and to the presence or absence of Af. colonisation as well as ABPA.

RESULTS

The IgG2 antibody level was significantly higher in heterozygous GM (1,2,17 23 5,21 and 1,3,17 23 5,21) compared to homozygous GM allotypes (p = 0.02). Patients with the same allotypes tended to have higher IgG1 (p = 0.051). In patients with ABPA, being heterozygous for G1M and G3M was linked to higher IgG4 and lower IgG3 as compared to the other genotypes. The KM markers did not influence the antibody levels. The allotype GM(3 23 5), associated with atopic bronchial asthma, tended to make a relatively larger group in ABPA patients compared to non-ABPA and patients not colonised with Af. (p = 0.09).

CONCLUSIONS

An influence of the GM allotypes on the immune response to Af. and on the development of ABPA in patients with CF is suggested.

Demonstration of specific antibodies against infliximab induced during treatment of a patient with ankylosing spondylitis

Therapeutic proteins, such as infliximab, have revolutionized the treatment of many diseases during the last decade and more than 80 therapeutic proteins are currently approved for clinical use. However, all exogenous proteins have the potential to cause antibody formation. In order to ensure patient safety and the efficacy of therapeutic proteins, careful monitoring of the immunogenicity of therapeutic proteins is therefore necessary not only during preclinical trials, but also during the treatment of patients. Here, we report a clear-cut demonstration of the induction of anti-infliximab antibodies during the treatment of a patient with ankylosing spondylitis (AS). Assessment of anti-infliximab antibodies in sera obtained at various time periods were performed using a highly specific double antigen assay system developed in our laboratory. Immunoreactivity was found to be solely specific for infliximab. Because all sera obtained from the patient were found to be negative for the presence of human anti-mouse antibody (HAMA) and anti-human antibodies. The loss of effect of infliximab, as judged by observing the relapse of signs and symptoms of disease in the patient, seemed to be related with the appearance of antibodies. This study clearly demonstrates that monitoring for the induction of specific antibodies during clinical trials is an important issue for therapeutic proteins.

A Newly Discovered Fc Receptor that Explains IgG-Isotype Disparities in Effector Responses

The known IgG FcRs primarily mediate inflammation by interacting with IgG1, even though IgG2 isotypes tend to be more pathogenic. A novel FcgammaR that binds IgG2 but not IgG1 has just been identified, potentially explaining differences in biological activity that are seen with various IgG isotypes.

Positive selection of the peripheral B cell repertoire in gut-associated lymphoid tissues

Gut-associated lymphoid tissues (GALTs) interact with intestinal microflora to drive GALT development and diversify the primary antibody repertoire; however, the molecular mechanisms that link these events remain elusive. Alicia rabbits provide an excellent model to investigate the relationship between GALT, intestinal microflora, and modulation of the antibody repertoire. Most B cells in neonatal Alicia rabbits express V_Hn allotype immunoglobulin (Ig)M. Within weeks, the number of V_Hn B cells decreases, whereas V_Ha allotype B cells increase in number and become predominant. We hypothesized that the repertoire shift from V_Hn to V_Ha B cells results from interactions between GALT and intestinal microflora. To test this hypothesis, we surgically removed organized GALT from newborn Alicia pups and ligated the appendix to sequester it from intestinal microflora. Flow cytometry and nucleotide sequence analyses revealed that the V_Hn to V_Ha repertoire shift did not occur, demonstrating the requirement for interactions between GALT and intestinal microflora in the selective expansion of V_Ha B cells. By comparing amino acid sequences of V_Hn and V_Ha Ig, we identified a putative V_H ligand binding site for a bacterial or endogenous B cell superantigen. We propose that interaction of such a superantigen with V_Ha B cells results in their selective expansion.

Epistatic effects of immunoglobulin GM and KM allotypes on outcome of infection with hepatitis C virus

Immunoglobulin GM and KM allotypes-genetic markers of gamma and kappa chains, respectively-are associated with immune responsiveness to several infectious pathogens and with survival in certain viral epidemics. We hypothesized that GM and KM allotypes affect the outcome of hepatitis C virus (HCV) infection. To test this hypothesis, we serologically allotyped 100 persons with well-documented clearance of HCV infection and 198 matched persistently infected persons. None of the GM or KM phenotypes by itself was associated with the clearance or persistence of HCV infection. Particular combinations of these phenotypes, however, were significantly associated with the outcome of HCV infection. Subjects with GM 1,17 5,13 and KM 1,3 phenotypes were over three times (odds ratio [OR], 3.57; 95% confidence interval [CI], 1.44 to 8.87) as likely to clear the infection as the subjects who lacked these phenotypes. This GM phenotype had a similar association with clearance in the absence of KM 3 (OR, 2.75; 95% CI, 1.21 to 6.23). The presence of GM 1,3,17 23 5,13 phenotype (in the absence of KM 3) was associated with persistence (OR, 0.21; 95% CI, 0.06 to 0.77), while its absence (in the presence of KM 1,3) was associated with the clearance of infection (OR, 2.03; 95% CI, 1.16 to 3.54). These results show epistatic interactions of genes on chromosomes 14 (GM) and 2 (KM) in influencing the outcome of an HCV infection. Further investigations involving candidate genes (GM, KM, HLA, and Fcgamma receptors) and cellular and humoral immune responses to HCV epitopes are needed to understand the mechanisms underlying these associations.

Human/mouse cross-reactive anti-VEGF receptor 2 recombinant antibodies selected from an immune b9 allotype rabbit antibody library

Vascular endothelial growth factor (VEGF) and its receptors have been implicated in promoting solid tumor growth and metastasis via stimulating tumor-associated angiogenesis. Models of murine tumor angiogenesis and receptor-specific antibodies are required to evaluate roles of VEGF receptors in mouse models of human cancer. Human VEGFR2 (also known as KDR) and murine VEGFR2 (or Flk-1) share 85% amino acid sequence identity in their extracellular domain. We describe here the development of antibodies that cross-react with mouse and human VEGFR2. High-affinity, species cross-reactive, Fabs specific for KDR/Flk-1 were selected from an antibody phage display library generated from an immunized rabbit of b9 allotype. The selected chimeric rabbit/human Fabs were found to bind to purified KDR and Flk-1 with nanomolar affinity. Three of the selected Fabs detected KDR expression on human endothelial cells as well as Flk-1 on murine endothelial cells. The availability of anti-VEGFR2 Fab with species cross-reactivity will help to decipher the functional role of KDR/Flk-1 in tumor biology as well as facilitate the preclinical evaluation of the suitability of KDR/Flk-1 for drug targeting. This report underscores our earlier finding that b9 rabbits are excellent sources for high-affinity cross-reactive antibodies with therapeutic potential.

Immunoglobulin GM genes and IgG antibodies to cytomegalovirus in patients with systemic sclerosis

OBJECTIVE

To determine the role of GM and KM genes--genetic markers of immunoglobulin gamma and kappa chains, respectively--in humoral immunity to human cytomegalovirus (HCMV) in patients with systemic sclerosis (SSc; scleroderma).

METHODS

A total of 137 Caucasian patients with SSc and 145 ethnically matched controls were genotyped for GM f/3, z/17, n+/23+, n-/23-, KM 1, and KM 3 alleles by polymerase chain reaction-restriction fragment length polymorphism and direct DNA sequencing methods. IgG antibodies to HCMV were measured by an enzyme-linked immunosorbent assay.

RESULTS

In SSc patients, GM f,z genotypes were strongly associated with the occurrence of anti-HCMV IgG antibodies. The frequency of the GM f homozygotes was lower (42.2 vs 62.2%; p= 0.02; OR=0.4) and the frequency of the GM f,z heterozygotes was higher (51.1 vs 26.7%; p = 0.006; OR = 2.8) in SSc patients with IgG antibodies to HCMV than in subjects who lacked these antibodies. This association was not observed in the control group. KM and GM n genotypes were not significantly associated with the prevalence of these antibodies.

CONCLUSION

GM f,z alleles or alleles in linkage disequilibrium with them influence the generation of IgG antibodies to HCMV in patients with SSc.

Rabbit immune repertoires as sources for therapeutic monoclonal antibodies: the impact of kappa allotype-correlated variation in cysteine content on antibody libraries selected by phage display

The rabbit immune repertoire has long been a rich source of diagnostic polyclonal antibodies. Now it also holds great promise as a source of therapeutic monoclonal antibodies. On the basis of phage display technology, we recently reported the first humanization of a rabbit monoclonal antibody. The allotypic diversity of rabbit immunoglobulins prompted us to compare different rabbit immune repertoires for the generation and humanization of monoclonal antibodies that bind with strong affinity to antigens involved in tumor angiogenesis. In particular, we evaluated the diversity of unselected and selected chimeric rabbit/human Fab libraries that were derived from different kappa light chain allotypes. Most rabbit light chains have an extra disulfide bridge that links the variable and constant domains in addition to the two intrachain disulfide bridges shared with mouse and human kappa light chains. Here we evaluate the impact of this increased disulfide bridge complexity on the generation and selection of chimeric rabbit/human Fab libraries. We demonstrate that rabbits with mutant bas and wild-type parental b9 allotypes are excellent sources for therapeutic monoclonal antibodies. Featured among the selected clones with b9 allotype is a rabbit/human Fab that binds with a dissociation constant of 1nM to both human and mouse Tie-2, which will facilitate its evaluation in mouse models of human cancer. Examination of 228 new rabbit antibody sequences allowed for a comprehensive comparison of the LCDR3 and HCDR3 length diversity in rabbits. This study revealed that rabbits exhibit an HCDR3 length distribution more closely related to human antibodies than mouse antibodies.

Secondary heavy chain rearrangement: a mechanism for generating anti-double-stranded DNA B cells

The chronic graft-versus-host (cGVH) reaction results in a syndrome that closely resembles systemic lupus erythematosus (SLE). It is induced in nonautoimmune mice by the transfer of alloreactive T cells. The availability of anti-DNA transgenes allows us to study the genetic origins of autoantibodies in this model. We induced cGVH in two anti-DNA H chain site-directed transgenic mouse strains. This resulted in clonal expansion and selection of specific mutations in the anti-double-stranded (ds) DNA B cell population. These data, together with a high frequency of anti-dsDNA B cell clones recovered as hybridomas, suggested that anti-dsDNAs are the product of an antigen-driven immune response. Genetic analysis associated this response with the generation of anti-dsDNA B cells through secondary rearrangements that replaced the site-directed transgene (sd-tg) with endogenous VH genes.

Structural basis of allotypes of ecto-nucleotide pyrophosphatase/phosphodiesterase (plasma cell membrane glycoprotein PC-1) in the mouse and rat, and analysis of allele-specific xenogeneic antibodies

Ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPPs) have been implicated in bone calcification, type II diabetes, control of purinergic signalling and tumour invasion. The gene for the plasma cell membrane glycoprotein PC-1 in the mouse (Enpp1) has been known since 1970 to exist in two allelic forms, but their structural basis was heretofore unknown. We show that the Enpp1a and Enpp1b alleles differ by only two amino acids, at positions 650 and 679 in the C-terminal nuclease-like domain. Histidine 650 but not arginine 679 forms an essential part of the Enpp1a epitope recognized by monoclonal antibody IR-518. Sequences of LEW and LOU rats and the rat glioma cell line C6 differ from that of the mouse by about 60 amino acids. The LOU and C6 cell line sequences differ by only three amino acids, but differ from the LEW sequence by 10 amino acids. All three rat strains possess the mouse Enpp1b allele at positions 650 and 679. Despite numerous other differences from the mouse, rats immunized with Enpp1a mouse cells have generated monoclonal antibodies specific for the Enpp1a allele, suggesting that amino acids 650 and 679 may be particularly immunogenic. The cytoplasmic tails of the mouse and rat are highly conserved, but are significantly different from human cytoplasmic tails.

A structural perspective on MHC class I recognition by killer cell immunoglobulin-like receptors

Killer cell immunoglobulin-like receptors (KIR) play a critical role in the regulation of natural killer (NK) cell activity through their recognition of class I MHC molecules expressed on target cells. KIR recognition provides vital information to NK cells about whether a target cell should be lysed or spared. Understanding the molecular mechanism of this recognition has remained a strong focus of investigation. This has resulted in the crystal structures of several members of the KIR family and more recently the determinations of the three dimensional structures of KIR2DL2 and KIR2DL1 complexed with their respective ligands, HLA-Cw3 and HLA-Cw4. A strong structural conservation has been revealed both in the receptor design and in the overall mode of KIR binding to class I molecules. Nevertheless, distinct differences in the receptor binding sites allow for high specificity between ligands. Furthermore, unexpected similarities with T-cell receptor (TCR) recognition of MHC molecules are also observed. The detailed interactions between KIR and HLA-C molecules and their functional implications will be reviewed here.

Anti-fibrillin-1 autoantibodies in systemic sclerosis are GM and KM allotype-restricted

GM and KM allotypes--genetic markers of immunoglobulin (Ig) gamma and kappa chains, respectively--have been shown to play an important role in genetic predisposition to some autoimmune diseases. To determine their role in susceptibility to systemic sclerosis (SSc; scleroderma) and in the generation of anti-fibrillin-1 antibodies, 148 SSc patients and 191 controls were typed for several GM and KM allotypes by a standard hemagglutination inhibition method. IgG and IgM antibodies to fibrillin-1 were measured by radioimmunoassay. GM and KM phenotypes were not significantly associated with SSc. However, these determinants significantly influenced the production of anti-fibrillin-1 antibodies in SSc patients. In Caucasians, GM1,3,17 23 5,13,21 and GM3 23 5,13 phenotypes were associated with the presence and absence of IgG autoantibodies, respectively. The production of these autoantibodies was also associated with KM allotypes, KM1,3 heterozygosity being associated with response and homozygosity for the KM3 allele with nonresponse to fibrillin-1. In African-Americans, the KM1 homozygotes were associated with the absence of anti-fibrillin-1 antibodies and the KM3 homozygotes with the presence of autoantibodies. In this ethnic group, the GM1,17 5,13 phenotype was associated with the absence of IgM autoantibodies. This represents the first description of genetic control of autoimmunity to fibrillin-1 in scleroderma.

Immunoglobulin GM and KM allotypes in systemic lupus erythematosus

Genetic variation in immunoglobulin gamma (GM) and kappa (KM) chains was associated with systemic lupus erythematosus (SLE) in some studies. However, the data are conflicting, and only one study examined associations in African-Americans. We examined GM and KM allotypes, by race, in a population-based case-control study of SLE. Sera from patients (n = 222) and controls (n = 273) were typed for GM and KM allotypes by a hemagglutination inhibition method. GM phenotypes were not significantly associated with SLE in African-Americans or Caucasians. However, the frequency of KM phenotypes in Caucasian patients was significantly different from that in controls (p = 0.032). KM3,3 was associated with an increased risk, whereas KM1,3 was associated with a lower relative risk of SLE. In African-Americans, however, the pattern of associations with KM phenotypes differed from that in Caucasians, and the overall difference between patients and controls was not statistically significant.

Overcoming the poor immunogenicity of a protein by DNA immunization as a fusion construct

The production of antibodies against poorly immunogenic proteins is problematic. Often there is a failure to generate such antibodies. Furthermore, antibodies against other specificities are frequently induced. We describe a simple approach, analogous to conjugation to a protein carrier, whereby immunization with naked DNA was used to raise antibody to a highly homologous and poorly immunogenic allotypic protein. Deoxyribonucleic acid encoding the protein of interest was fused to DNA encoding the Fc region of a foreign Ig, resulting in increased immunogenicity. The potential applications of this approach include the production of antisera and mAb to allotypic variants, mutant proteins, and proteins that are highly conserved between species.

Central tolerance induction in natural immunoglobulin-allotype-specific T cells

While self toleance is induced to IgG(b)(2a) in Igh(b / b) mice, an anti-IgG(b)(2a) T cell activity emerges in their Igh(a / a) congenic counterparts. This activity is revealed by postnatal transfer of Igh(a / a) T splenocytes into Igh(a / b) F(1), in which total suppression of IgG(2a)(b) expression is established. Here, we sought to determine whether the natural T cell unresponsiveness to IgG(2a)(b) in Igh(b / b) mice involved a central tolerance. Based on the kinetics of postnatal thymic C(gamma2a)(b) gene expression in Igh(b / b) mice, we transplanted thymi from Igh(b / b) donors of diverse ages into tolerogen-free Igh(a / a) nu / nu recipients. The state of T cell tolerance or responsiveness to IgG(2a)(b) in these reconstituted nu / nu hosts was determined by monitoring the capacity of their splenocytes to induce suppression in Igh(a / b) F(1). These experiments demonstrated that: (i) in the Igh(a / a) nu / nu recipients of adult Igh(b / b) thymi, 33 to 65 % T splenocytes were from nu / nu recipient origin, but these peripheral Igh(a / a) T cells were rendered tolerant to IgG(2a)(b) during their differentiation through the adult Igh(b / b) thymi, (ii) circulating IgG(2a)(b) was not a prerequisite for this tolerance induction, (iii) Igh(b / b) thymic epithelium was unable to induce tolerance to IgG(2a)(b) and (iv) IgG(2a)(b)-producing / presenting cells, colonizing the Igh(b / b) thymi, were certainly responsible of full tolerance induction to IgG(2a)(b).

Diverse endogenous light chains contribute to basement membrane reactivity in nonautoimmune mice transgenic for an anti-laminin Ig heavy chain

Basement membrane proteins are targeted in a variety of pathologic autoimmune responses, yet little is known regarding the origins and regulation of this subset of pathogenic lymphocytes. To examine the generation and fate of B cells reactive with a matrix autoantigen, nonautoimmune C57BL/6 mice were rendered transgenic for a nephrotropic lupus anti-laminin immunoglobulin (Ig) H chain, termed LamH-Cmu. We previously reported recovery of two distinct phenotypes among LamH-Cmu-transgenic mice: progeny of founders M6 and M29 contained abundant transgene-expressing B cells but little anti-laminin Ig, whereas spontaneous autoreactivity was readily recovered from the M7 lineage that expressed minimal B-cell mIgM. To explore the spectrum of autoreactivity generated in vivo by different LamH-Cmu-endogenous L-chain combinations, we determined in vitro and in vivo antigen reactivity and L-chain V-region sequences of 17 LamH-Cmu-transgenic anti-laminin Igs. The results reveal a heterogeneous population of anti-laminin Igs with different fine specificities encoded by diverse endogenous L chains, encompassing nine different Vk gene families, 11 Vk genes, and three Jk genes. Many of the L chains are identical to known or putative unmutated germline Vk genes used to encode Igs reactive with self and foreign antigens in nonautoimmune and genetically autoimmune-prone mouse strains. These observations confirm that the LamH-Cmu H chain plays a dominant role in determining anti-laminin reactivity, and indicate that nonautoimmune B6 mice are fully capable of generating a diverse pool of basement-membrane-reactive B cells using unmutated Ig genes. When interpreted in the context of the divergent M6/M29 and M7 transgenic mouse phenotypes, our findings further suggest that these matrix-reactive lymphocytes are not spontaneously activated in vivo under normal circumstances.

Binding of bovine IgG2a and IgG2b allotypes to protein A, protein G, and Haemophilus somnus IgBPs

Immunoglobulin binding proteins (IgBPs) are thought to be virulence factors which enable pathogens to evade the host's immune response. Since bovine IgG2 is important in protection against pyogenic infections, the binding characteristics of Staphylococcus aureus protein A (PrA), streptococcal protein G (PrG), or Haemophilus somnus high molecular weight IgBPs to the two bovine IgG2 allotypes were examined. For PrA or PrG binding of IgG2, guinea pig red blood cells coated with specific IgG2a or IgG2b antibodies were used in a competitive binding inhibition assay with unlabeled and horseradish peroxidase-labeled PrA or PrG. To determine which sizes of H. somnus. IgBPs bind to the two IgG2 allotypes, immunoblots with H. somnus culture supernatant were probed with anti-DNP IgG2a and IgG2b. This detects only Fc binding because anti-DNP does not cross-react with H. somnus antigens. Both IgG2 allotypes bound equally well to PrA and PrG. However, IgG2b but not IgG2a bound to H. somnus high molecular weight IgBPs. The lack of differential binding of bovine IgG2 allotypes to PrA and PrG means that these IgBPs can be considered to be unbiased reagents in assays for detection of bovine IgG2 or for immunoaffinity purification. The differential binding of H. somnus IgBPs to the IgG2 allotypes indicates that animals having one allotype may be more resistant to H. somnus infection than animals having the other allotype.

Differential complement activation by bovine IgG2 allotypes

Immunoglobulin allotypes and complement (C) are known to be related to susceptibility to infection. Because bovine IgG2 is important in resistance to pyogenic infections and because its two allotypes, IgG2a and IgG2b, differ in sequence in the CH1, hinge, CH2, and CH3 regions, we tested the ability of these allotypes to initiate the bovine C cascade. Bovine IgG2a and IgG2b were standardized according to specific anti guinea pig red blood cell (GPRBC) ELISA activity using anti IgG2 reagents shown essentially unbiased for allotype. Complement activating activity of the allotypes was quantitated in a GPRBC lysis assay. With this system, IgG2b consistently had more than twice the activity in bovine C mediated lysis as compared with IgG2a. The fact that both EDTA and EGTA/Mg almost completely inhibited C mediated lysis of GPRBCs indicated that lysis was due to the classical pathway. Since antibody usually activates C by the classical pathway, this supports the supposition that activation was by the IgG2-GPRBC complexes. Flexibility analyses showed that IgG2b had a more rigid hinge than IgG2a, perhaps partially explaining the greater efficiency of IgG2b in C activation. Other mechanisms may include differences in glycosylation and in the amino acid at position 332. The difference in ability to activate C may mean that animals of the IgG2a allotype could be more susceptible to infection with extracellular pyogenic pathogens which are killed by C or by phagocytes after opsonization with IgG2 and C.

Crystal structure of the HLA-Cw3 allotype-specific killer cell inhibitory receptor KIR2DL2

Killer cell inhibitory receptors (KIR) protect class I HLAs expressing target cells from natural killer (NK) cell-mediated lysis. To understand the molecular basis of this receptor-ligand recognition, we have crystallized the extracellular ligand-binding domains of KIR2DL2, a member of the Ig superfamily receptors that recognize HLA-Cw1, 3, 7, and 8 allotypes. The structure was determined in two different crystal forms, an orthorhombic P212121 and a trigonal P3221 space group, to resolutions of 3.0 and 2.9 A, respectively. The overall fold of this structure, like KIR2DL1, exhibits K-type Ig topology with cis-proline residues in both domains that define beta-strand switching, which sets KIR apart from the C2-type hematopoietic growth hormone receptor fold. The hinge angle of KIR2DL2 is approximately 80 degrees, 14 degrees larger than that observed in KIR2DL1 despite the existence of conserved hydrophobic residues near the hinge region. There is also a 5 degrees difference in the observed hinge angles in two crystal forms of 2DL2, suggesting that the interdomain hinge angle is not fixed. The putative ligand-binding site is formed by residues from several variable loops with charge distribution apparently complementary to that of HLA-C. The packing of the receptors in the orthorhombic crystal form offers an intriguing model for receptor aggregation on the cell surface.

A single amino acid change makes the peptide specificity of B*3910 unrelated to B*3901 and closer to a group of HLA-B proteins including the malaria-protecting allotype HLA-B53

HLA-B*3910, which has only been found in African and African American individuals, differs from B*3901 by the single amino acid change of Cys67 to Tyr67. Sequence analysis of the B*3910-bound peptide pool and of several individual ligands revealed that this subtype has strong preference for peptides with Pro2. This is in contrast with the preference of B*3901 for peptides with basic residues (Arg and His) at this position, and indicates that the single amino acid substitution between B*3910 and B*3901 totally changes the repertoire of bound peptides. This is presumably due to the significant decrease in the size of the B pocket, and to its increased hydrophobicity, since Tyr67 takes part in this pocket. B*3910 is similar to various other class I proteins in its preference for peptides with Pro2 and nonpolar C-terminal residues, including HLA-B53, an antigen associated with protection against severe malaria. The role of these two motifs as major peptidic anchors suggests that B*3910 and HLA-B53 may bind common peptides.

Malononitrilamides 715 and 279 prolong rat cardiac allograft survival, reverse ongoing rejection, inhibit allospecific antibody production and interact positively with cyclosporin

A77 1726 is a malononitrilamide (MNA) and the active metabolite of leflunomide, which has been extensively investigated and shown to be a potent immunosuppressive drug. However, the half-life of A77 1726 is about 15-18 days in humans and leflunomide is therefore currently being developed for the treatment of autoimmune disease and not for transplantation. Search for analogues has led to the discovery of MNA 715 and 279, derivatives of A77 1726. Previous experimental experience of these compounds is still limited. The aim of the present study was to verify the efficacy of these MNAs concerning prevention and reversal of rejection, inhibition of antibody production and interaction with cyclosporin A (CsA). Heterotopic cardiac transplantation in DA to PVG rats was used. Subgroups of rats were given either CsA, MNA 715 or MNA 279 for 10 days, starting at either day 0 or day 4, or received no treatment. Titres of allospecific immunoglobulin M (IgM) and immunoglobulin G (IgG) were quantified by flow cytometry. Ten days of induction with MNA 715 or 279 produced significantly longer graft survival than in controls. Treatment from day 4 onwards, when acute rejection was established, rescued all grafts. Allospecific production of IgM or IgG was absent during MNA induction and was suppressed in animals receiving a rescue course of MNA. The transplant model was potentiated by addition of the immunomodulator quinolone-3-carboxamide (Linomide), which eliminates the effect of CsA and other immunosuppressants. The combined treatment with MNA and CsA was successful in overcoming the challenge of Linomide, demonstrating the additive effects of the two drugs. In conclusion, MNA 715 and 279 were shown to be potent immunosuppressants, preventing and reversing acute allograft rejection, inhibiting and suppressing allospecific antibody production, and the drugs interacted positively with CsA.

GM and KM immunoglobulin allotypes in a Spanish Pyrenean population: Val d'Aran

Four hundred and thirteen unrelated individuals (202 autochthonous and 211 non-autochthonous) of Val d'Aran (Catalan Pyrenees) have been analysed for the GM and KM immunoglobulin genetic system using the inhibition haemagglutination method. This population was defined by eight GM haplotypes (GM*3 23 5*, GM*3 5*, GM*1,17 21,28, GM*1,2,17 21,28, GM*1,17 5*, GM*1,17 5,6,11,24, GM*1,17 10,11,13,15 and GM*1,17 10,11,13,15,16) inferred from the 17 observed phenotypes. The Val d'Aran population frequencies conform to Hardy-Weinberg expectations. The frequencies of phenotypes and haplotypes show a definite homogeneity between the autochthonous and non-autochthonous people of Val d'Aran and 11 other Pyrenean populations (Mauléon, Macaye, St. Jean Pied de Port, Vallée de L'Ouzom, Gavarnie, Barèges, Luz St. Sauveur, Esparros, Camurac, Capcir and Pays de Sault) that have already been studied for the same allotypes. A factorial correspondence analysis was performed for the 12 autochthonous Pyrenean populations, showing a high frequency of the GM*3 23 5* haplotype in the three Pyrenean regions (Western, Central and Eastern), while the GM*1,17 21,28 haplotype is mainly found in the Central region, GM*3 5* in the Eastern and Western zones, and the GM*1,2,17 21,28 is mainly present in the Central and Eastern populations. The results show a relative regional homogeneity, so there is no evidence of a frequency gradient in the Pyrenean populations for the GM and KM genetic systems. It may, however, be noticed that the Central Pyrenean populations form a group, with one population (Vallée de l'Ouzom) isolated from the rest, probably because of its particular model of inheritance by which the heritage is passed to the first born without sex consideration. It has been possible to point out some differences in the genetic structure of the autochthonous and non-autochthonous Val d'Aran population and to place the autochthonous Aranese group among its Pyrenean neighbours.

Differential inhibition of B-cell development and xenoreactive natural antibody production by administration of anti-mu or anti-delta monoclonal antibodies in adult rats

BACKGROUND

Given the role of xenoreactive natural antibodies (XNA) in the pathogenesis of xenograft rejection, we tested whether the administration of anti-mu or anti-delta monoclonal antibodies (mAbs) in adult rats would suppress the generation of XNA.

METHODS

Adult LOU/C (Igkappa-1a) rats were treated with anti-mu or anti-delta mAbs after nonlethal total body irradiation and bone marrow transplantation from congenic LOU/C (Igkappa-1b) rats. The differentiation of donor bone marrow (BM)-driven Igkappa-1b+ B cells and XNA production were analyzed.

RESULTS

Both anti-mu and anti-delta mAbs arrested B-cell differentiation in the BM. In anti-mu-treated rats, there was a total depletion of donor-driven, peripheral Igkappa-1b+ B cells, secreting cells, and circulating XNA of the Igkappa-1b allotype. In anti-delta-treated rats, a significant number of Igkappa-1b+ B cells, which did not express membrane IgD, "escaped" deletion and partially repopulated peripheral lymphoid organs. This B-cell population was active in the production of XNA, as revealed by the high serum levels of XNA in these animals.

CONCLUSIONS

Anti-mu administration resulted in arrest of B-cell differentiation and in down-regulation of IgM and IgG XNA production in adult rats. These data suggest that the use of anti-mu mAbs may be a useful approach to suppress the production of XNA and prevent xenograft rejection. Furthermore, we suggest that the B-cell population responsible for the production of XNA in adult rats belongs to a B-cell lineage expressing low levels of membrane IgD and "escaping" deletion in the BM upon anti-delta treatment.

Variation in IgG1 heavy chain allotype does not contribute to differences in biological activity of two human anti-Rhesus (D) monoclonal antibodies

BACKGROUND

Pooled human anti-Rhesus D antiserum is currently administered for the prevention of RhD alloimmunization. Increased demand, and decreased supply, of donated pooled antiserum has led to the investigation of the suitability of human monoclonal anti-RhD antibodies for use in its place. However, it is unclear which biological properties of monoclonal antibodies are important for function in RhD-positive foetal red cell clearance and the prevention of alloimmunization. Various antibodies behave differently in a number of in vitro assays of biological function.

OBJECTIVES

To compare the function and structure of two human anti-RhD IgG1 monoclonal antibodies which differ in their ability to promote red cell lysis in vitro. In particular to examine whether the functional differences correlate to differences in the IgG1 heavy chain constant region (allotype).

STUDY DESIGN

We report here the cloning, characterization and re-expression in stable myeloma cell transformants of cDNAs coding for two such antibodies, secreted by the heterohybridoma cell lines ESD-1 (THERAD 03) and LHM 70/45.3 (THERAD 06). The cDNAs were then recombined to exchange portions of the Fc encoding regions and the recombinant antibodies were assayed in vitro to determine RhD-positive red cell-dependent activity.

RESULTS

Recombinant THERAD 03 and 06 antibodies behaved identically to the parent antibodies. The 'inactive' THERAD 06 did not have biological activity reconstituted by exchange with the THERAD 03 Fc regions, nor was THERAD 03 activity abolished by the reciprocal Fc region exchange.

CONCLUSIONS

Human monoclonal anti-RhD antibodies can be cloned and re-expressed in stable cell lines, and exhibit identical properties to the parent antibodies. Differences in biological activity cannot be attributed to differences in IgG1 heavy chain allotype.

The genetic basis for variation in antibody response to vaccines

Following a brief review of important concepts of vaccine response and vaccine immunology, recent reports on genetic determinants of vaccine response are reviewed. Recent data demonstrating significant associations with particular human leukocyte antigen genes and responsiveness to measles and hepatitis B vaccines are discussed, along with the influence of Km and Gm allotype genes on pneumococcal polysaccharide vaccines. These recent findings have important considerations for research, vaccine development, and clinical practice.

Opsonophagocytic and bactericidal activity mediated by purified IgG subclass antibodies after vaccination with the Norwegian group B meningococcal vaccine

To study how the different immunoglobulin (Ig)G subclass antibodies may confer protection against systemic meningococcal disease, we isolated IgG1, IgG2 and IgG3 antibodies from plasma from vaccinees immunized with the Norwegian meningococcal outer membrane vesicle vaccine. Four IgG1, one IgG2 and four IgG3 preparations were purified. The IgG2 and IgG3 subclass preparations were free from contaminating subclasses, whereas the IgG1 preparations contained from 0 to 14% of IgG2 and/or IgG3. Immunoblotting against whole-cell meningococcal antigens showed broad specificities of the various preparations, both within and between subclasses. These subclass preparations were tested for opsonophagocytic and bactericidal activity. As targets we used two different variants of the meningococcal vaccine strain, with low (44/76-SL) and high (44/76-1) expression of the outer membrane protein Opc. Using polymorphonuclear leucocytes as effector cells in the presence of human complement, all three IgG subclass preparations revealed high, and similar, opsonophagocytic activities against 44/76-SL, whereas against 44/76-1 the IgG2 preparation showed a reduced activity and most IgG3 preparations were slightly more active than the IgG1 preparations. Regarding bactericidal activity, all the three subclasses were highly active against 44/76-SL. Against 44/76-1 the bactericidal activities were somewhat more varied: all IgG1 and three IgG3 preparations exhibited higher activities than against 44/76-SL. Due to the low concentration in the IgG2 preparations, only a weak activity was seen against 44/76-1. One IgG3 preparation that was highly opsonophagocytic revealed no bactericidal activity against either of the two bacterial variants examined. In conclusion, we have shown that the IgG subclass effector functions differ from person to person, but that antibodies of IgG1, IgG2 and IgG3 subclasses, judged by their behaviour in the functional tests, may all contribute to protection against meningococcal disease.

Second symmetry in the BALB/c-C57BL/6 (B6) system, and anti-antiself antibodies in ageing B6 mice

Using an ELISA assay and inhibition of antibody mediated cytotoxicity we found that there was a higher level of anti-antiself activity in B6 anti-BALB/c alloimmune mice than in BALB/c anti-B6 mice. In contrast, when an inhibition of cellular cytotoxicity assay was used to assay for the activity, similar levels of anti-antiself antibodies were seen in B6 anti-BALB/c and BALB/c anti-B6 sera. Anti-antiself antibodies in alloimmune sera are not absorbed by the cellular immunogen as readily as are anti-foreign antibodies. These results are interpreted in terms of anti-antiself antibodies being directed mainly against T cell receptors specific for self. Anti-antiself antibodies are found also in old B6 mice, that are also known to make autoantibodies.

Bovine IgG2a antibodies to Haemophilus somnus and allotype expression

Bovine IgG2a has been implicated in protection against pyogenic infections, including those caused by Haemophilus somnus. To further investigate the role of IgG2a in defense against H. somnus, IgG1 and IgG2a antibodies were purified from antiserum against an immunodominant 40 kDa outer membrane protein (p40) of H. somnus, which was previously shown to passively protect calves against H. somnus pneumonia. The passive protective capacity of anti-p40 IgG1 or IgG2a was evaluated in vivo in calves. Purified anti-p40 IgG1 or IgG2a was incubated with H. somnus for 15 min before intrabronchial inoculation of calves. Bacteria incubated with anti-p40 IgG1 or IgG2a were inoculated into one caudal lung lobe and bacteria incubated with IgG1 or IgG2a from the respective preimmunization serum were inoculated into the contralateral lobe. The volumes of pneumonia in the right and left lungs were determined 24 h later. The difference in volume of pneumonia with H. somnus preincubated in IgG1 pre- and postimmunization anti p40 was less (16 cm3, P = 0.298) than the difference in volume of pneumonia with H. somnus preincubated in IgG2a pre- and postimmunization anti p40 (30 cm3, P = 0.146). Although the differences in lesion size between pre- and postimmunization serum were not statistically significant, the trend suggests IgG2a may be more protective than IgG1. To examine this further, the peptide specificity of these IgG1 and IgG2a antibodies to p40 was examined. After limited proteolysis of p40, IgG2a antibodies reacted with 2 peptides not recognized by IgG1 antibodies. Other peptides were recognized by both isotypes. Since these studies suggested that IgG2a may be important in protection against infection, we then investigated some aspects of the role of the 2 IgG2a allotypes, A1 and A2. In retrospective studies of age differences in expression of IgG2a allotypes, no heterozygotes were detected in calves of 60 d old or less, and fewer heterozygotes were detected in calves 61-120 d old than in cattle older than 270 d (P < 0.01). In a subsequent prospective study of the time course of allotype expression, Holstein calves shown to be heterozygotes expressed the IgG2aA1 allotype early but the IgG2aA2 allotype was not usually detected until 3 to 4 mo of age. Thus, both the retrospective and the prospective studies showed age related differences in expression of the IgG2aA1 and A2 allotypes. This could have implication in protection.

Role of repetitive antigen patterns for induction of antibodies against antibodies

Antibody responses against antibodies, such as rheumatoid factors, are found in several immunopathological diseases and may play a role in disease pathogenesis. Experience shows that they are usually difficult to induce experimentally. Antibodies specific for immunoglobulin constant regions (anti-allotypic) or for variable regions (anti-idiotypic) have been investigated in animal models; the latter have even been postulated to regulate antibody and T cell responses via network-like interactions. Why and how such anti-antibodies are induced during autoimmune diseases, has remained largely unclear. Because repetitively arranged epitopes in a paracrystalline structure of a viral envelope cross-link B cell receptors efficiently to induce a prompt T-independent IgM response, this study used immune complexes containing viruses or bacteria to evaluate the role of antigen pattern for induction of anti-antibody responses. We present evidence that antibodies bound to strictly ordered, but not to irregularly arranged, antigens dramatically enhance induction of anti-antibodies, already after a single immunization and without using adjuvants. The results indicate a novel link between anti-antibody responses and infectious agents, and suggest a similar role for repetitive self-antigens such as DNA or collagen involved in chronic immunopathological diseases.

Antibody to C1-inhibitor in a patient receiving C1-inhibitor infusions for treatment of hereditary angioneurotic edema with systemic lupus erythematosus reacts with a normal allotype of residue 458 of C1-inhibitor

Patients with hereditary C4 deficiency are likely to have severe lupus erythematosus. A patient with hereditary angioneurotic edema (HANE) and systemic lupus erythematosus (SLE) had a chronic deficiency in C4 because the hereditary deficiency in C1-inhibitor allowed the C1 in her serum to become activated and then inactivate C4. An attempt was made to repair the C4 deficiency as well as the deficiency in C1-inhibitor by giving infusions of human C1-inhibitor in the hope of inducing remissions of both HANE and SLE. During treatment, antibody to C1-inhibitor developed in the patient; this cleared when the infusions were stopped. During subsequent treatment with danazol alone, measurable C1-inhibitor developed in the patient's serum, but levels of C4 were never significantly increased. Antibody to normal C1-inhibitor was not expected to develop in the patient because she is heterozygous for this autosomal dominant trait. A normal allotype (VAL or MET 458), which would have been in the preparation used but which the patient does not synthesize because she can produce only one allotype (MET 458), appears to have been immunogenic. The antibody isolated from the patient's serum reacted with C1-inhibitor from a normal individual known to be homozygous for 458-VAL but not with one from a homozygote for MET-458.

Evaluation of monoclonal antibodies with specificity for human IgA, IgA subclasses and allotypes and secretory component. Results of an IUIS/WHO collaborative study

51 monoclonal antibodies (McAb) with putative specificity for human IgA, the IgA subclasses, Am allotypes or secretory component (SC) were evaluated for immunoreactivity and specificity by nine laboratories employing immunodiffusion, agglutination, immunohistological assays, immunoblotting and direct binding and competitive inhibition enzyme immunoassays. McAbs specific for IgA PAN (n = 24), IgA1 (n = 7), IgA2 (n = 3), IgA2m(2) (n = 2), non-IgA2m(2) (n = 4) and SC or secretory IgA (n = 5) were identified that were immunoreactive and specific in the assays employed. The McAbs identified as IgA- or SC-reactive were shown to be non-reactive to human IgG, IgM, IgD, IgE, kappa and lambda by direct binding and competitive inhibition immunoassays. Interestingly, no McAbs with restricted specificity for IgA2m(1) were identified. Some McAbs displayed higher affinity and/or better performance in one or several of the assay groups. The IgA- and SC-specific McAbs identified in this international collaborative study have potential as immunochemical reference reagents to identify and quantitate monomeric and polymeric IgA in human serum and secretions.

Skewed distribution of IgG Fc receptor IIa (CD32) polymorphism is associated with renal disease in systemic lupus erythematosus patients

OBJECTIVE

Fc gamma receptors of class IIa (Fc gamma RIIa) occur in 2 allelic forms, with either a low (IIa-R131) or a high (IIa-H131) affinity for complexed IgG2 and IgG3. This polymorphism might have implications for the handling of immune complexes. Therefore, we determined the distribution of the Fc gamma RIIa allotypes in patients with systemic lupus erythematosus (SLE), with or without a history of lupus nephritis.

METHODS

We studied 95 unrelated white European patients with SLE, as defined by the American College of Rheumatology criteria, 50 of whom had a history of lupus nephritis, and 69 healthy white European control subjects. Fc gamma RIIa allotypes were determined by immunophenotyping of blood monocytes.

RESULTS

It was found that lupus nephritis was significantly associated with the "low affinity" Fc gamma RIIa R/R131 allotype and with the R131 allele, compared with healthy controls. No significant association was found upon comparison of groups with and without nephritis.

CONCLUSION

SLE patients with a history of lupus nephritis have an abnormal distribution of Fc gamma RIIa allotypes. Fc gamma RIIa may well play a role in the pathogenesis of lupus nephritis, since IIa-R/R131 SLE patients seem to have a higher incidence of developing this complication.

The prevalence of red cell antibodies in pregnancy correlated to the outcome of the newborn: a 12 year study in central Sweden

BACKGROUND

All maternal red cell antibodies found during pregnancy in a 12 year period have been compiled. The efficacy of the current antenatal screening and management programme has been ascertained by reviewing the outcome of all newborns to these immunized mothers.

METHOD

Patient selection was carried out by computerised searching for all known records of registered antibodies during the study period. Each mother's obstetric record and her baby's hospital file was studied and relevant clinical treatment and laboratory data on both mother and child was recorded and analysed.

RESULTS

Eight hundred and twenty-one alloantibodies were detected in 629 immunized pregnant women with 753 fetuses. An overall antibody incidence of 0.57% was observed which included 373 clinically significant antibodies found in 261 mothers (0.24%). Multiple antibodies were present in 8.2% of all samples. Anti-D, by itself or in combination with other Rh-antibodies, caused more severe forms of hemolytic disease of the newborn (HDN) with 46% of all Rh-positive babies having phototherapy and 29% having exchange transfusion. Three of 18 Fya-positive infants required phototherapy and one required exchange transfusion and in the 16 Kell-positive babies, three required phototherapy and one required exchange transfusions.

CONCLUSIONS

Few antibodies to blood group antigens other than those in the Rhesus system were found to cause severe HDN. Antibodies that are generally considered non-significant did not cause HDN in this study. All antibodies that induced HDN were detected in time so that adequate measures could be taken to reduce the effects in the newborn. The antenatal screening and management programme currently in use is considered to be reliable.

Idiotypic restriction of murine monoclonal antibodies to a defined antigenic region of human thyroglobulin

In previous studies, we demonstrated that anti-human thyroglobulin (hTg) autoantibodies in patients with thyroid disorders exhibit a restricted epitopic specificity towards antigenic region II defined by its reactivity with four murine monoclonal antibodies (mAb 3, 6, 10, 15). To analyze the relationships between epitopic specificity and idiotypic expression of these mAb, two polyclonal anti-idiotypic sera were generated in rabbits by immunization with F(ab')2 fragments of mAb 3 and mAb 10. These anti-idiotypic preparations (AI 3 and AI 10) were tested against a panel of hTg-mAb produced in different strains of mice (HR BIOZZI and BALB/c). The idiotypic analysis showed that AI 3 and AI 10 specifically recognized framework-associated idiotopes as well as paratope-associated idiotopes shared by region II mAb. These results demonstrate that specificity for region II was strongly associated with a restricted idiotype suggesting a high sequence homology between V regions. In addition, naïve BALB/c mice immunized with AI 3 or AI 10 produced anti-hTg (Ab3) antibodies that recognize region II epitopes. These latter findings reveal that anti-Id contain a population of Ab2 beta carrying the internal image of region II epitopes.

Preferential expansion and survival of B lymphocytes based on VH framework 1 and framework 3 expression: "positive" selection in appendix of normal and VH-mutant rabbits

B cells with a rearranged heavy-chain variable region VHa allotype-encoding VH1 gene segment predominate throughout the life of normal rabbits and appear to be the source of the majority of serum immunoglobulins, which thus bear VHa allotypes. The functional role(s) of these VH framework region (FR) allotypic structures has not been defined. We show here that B cells expressing surface immunoglobulin with VHa2 allotypic specificities are preferentially expanded and positively selected in the appendix of young rabbits. By flow cytometry, a higher proportion of a2+ B cells were progressing through the cell cycle (S/G2/M) compared to a2- B cells, most of which were in the G1/G0 phase of the cell cycle. The majority of appendix B cells in dark zones of germinal centers of normal 6-week-old rabbits were proliferating and very little apoptosis were observed. In contrast, in 6-week-old VH-mutant ali/ali rabbits, little cell proliferation and extensive apoptosis were observed. Nonetheless even in the absence of VH1, B cells with a2-like surface immunoglobulin had developed and expanded in the appendix of 11-week-old mutants. The numbers and tissue localization of B cells undergoing apoptosis then appeared similar to those found in 6-week-old normal appendix. Thus, B cells with immunoglobulin receptors lacking the VHa2 allotypic structures were less likely to undergo clonal expansion and maturation. These data suggest that "positive" selection of B lymphocytes through FR1 and FR3 VHa allotypic structures occurs during their development in the appendix.

Anti-IL-4 antibody prevents graft-versus-host disease in mice after bone marrow transplantation. The IgE allotype is an important marker of graft-versus-host disease

Induction of a graft-vs-host reaction in irradiated (BALB/c X C57BL/6)F1 mice (CBF1 mice) with bone marrow cells (BMC) plus spleen cells of BALB/c mice leads to bone marrow transplantation--GVHD (BMT-GVHD). BMT-GVHD is characterized by liver disease, splenomegaly, and hypergammopathy. In addition, we found that increased serum IgE and IgG1 levels were correlated with BMT-GVHD such as liver disease and splenomegaly. The allotype of increased IgE levels in BMT-GVHD was IgEa of donor origin, not IgEb of host origin. We also found that in the thymus of murine BMT-GVHD, the CD4+ CD8+ double-positive T cells were decreased, but the CD4+ CD8- or CD4- CD8+ single-positive T cells were increased. Interestingly, double-positive T cells appeared in the spleen, suggesting that abnormal T cell differentiation existed in murine BMT-GVHD. When the recipients were treated with anti-IL-4 Ab (11B11), the increase of IgE and IgG1 was markedly reduced and liver disease and splenomegaly were also prevented. Moreover, abnormal T cell differentiation and maturation were suppressed. These observations suggest that IL-4 plays an important role in immunoregulation or pathogenesis of allogeneic effects, and 11B11 prevents immunodysfunction including T cell differentiation in the thymus or the spleen and autoimmune symptoms in murine BMT-GVHD.

A genetic marker of rabbit immunoglobulin VHa region: a109

A "new" rabbit immunoglobulin allotype belonging to the VHa series (a109) that seems particular to the Iberian O. cuniculus has been detected in a Portuguese wild rabbit population. This allotype was found in the wild population of Spain but not in those of France and Zembra island (Tunisia). Using antisera and monoclonal antibodies raised against already known VHa allotypes, we found that a 109 presents cross-reactivity with a1, a3, a100, a101, a107 and a108 allotypes. On the basis of studies of these cross-reactivities, we show that a109 is constituted of at least three variants (or subfamilies of variants) possessing determinants common with either a1 and a109, a3 and a109 or a1, a3 and a109 allotypes. These results are discussed according to recent data relative to generation of antibody diversity in rabbit.

T cell-induced Ig allotypic suppression in mice. Basis for emergence or tolerization, during the perinatal period, of natural T cells specific to the IgG2ab allotype

We have previously described an anti-IgG2ab T cell activity in normal Igha/a mice. Their congenic partner at the Igh locus (Ighb/b) and Igha/b hybrids bred from them, do not display this T cell activity but express IgG2ab. As these mice are supposed to possess the same genetic elements related to this potential T cell repertoire, only somatic selection mechanisms could be responsible for their different behavior. In this study, we investigated the basis for the emergence (in Igha/a mice) or tolerization (in Ighb/b-congenic mice and in Igha/b hybrids) of these natural anti-IgG2ab T cells. Stringent perinatal B cell deprivation in Ighb/b and Igha/b mice resulted in the emergence of anti-IgG2ab T cells, as these individuals could be subjected to autoimmune, T cell-mediated IgG2ab suppression. Furthermore, the acquisition of anti-IgG2ab T cell activity was drastically reduced in Igha/a mice, perinatally exposed to IgG2ab; thus, the presence of this allotype leads to tolerization of these specific T cells.

Heterogeneity of bovine IgG2. VI. Comparative specificity of monoclonal and polyclonal capture antibodies for IgG2a (A1) and IgG2a (A2)

The relative specificity of 26 randomly selected polyclonal and monoclonal anti-bovine IgG2 reagents for the A1 and A2 allotypic variants of IgG2a was evaluated in a direct RIA using the reagents as solid-phase capture antibodies (CAbs). More than 70% of these reagents were significantly allotype-biased and > 80% of those were positively biased to IgG2a (A1). Compared as the ratio of the ng of IgG2a (A1) bound versus ng IgG2a (A2) bound per 50 ng added (Krel), bias for IgG2a (A1) of six of these reagents was greater than two-fold. Compared in terms of their solid-phase equilibrium constants (Keq), differences as great as two-logs among these reagents were observed. Steward-Petty plots suggested that differences in Krel of a select panel of reagents was usually due to differences in Keq, but for two reagents with large differences in Krel, the existence of one population of CAbs recognizing an allotope and another recognizing common IgG2a determinants, was indicated. Eight of ten guinea pigs immunized with IgG2a (A1) responded with highly significant specificity bias for A1 whereas only two of 11 rabbits and two of ten guinea pigs immunized with IgG2a (A2) responded weakly with preference for IgG2a (A2). These results concur with the concept of the immunodominant nature of the A1 allotope, but also suggest that immunization with IgG2a (A2) might be a practical means of avoiding allotype bias in IgG2a reagents. The data indicate that the majority of randomly selected anti-bovine IgG2 reagents are allotype biased to the extent that when used as serological reagents to measure total IgG2 or bovine IgG2 antibody responses, the allotype of the animal tested rather than its total IgG2a concentration or IgG2 antibody titer, can determine the outcome of the serological test.

Detection of putative dopamine receptors in neurites outgrowing from locust central nervous system explants using anti-idiotypic dopamine antibodies

Organotypic cultures established from the third thoracic ganglion of locust embryo have been used to investigate dopamine receptors. In this in vitro system, neurites emerge directly from the explants and form a dense network around the explants, presenting cell surface freely exposed for experimental labelling. Polyclonal anti-idiotypic antibodies raised in rabbits to antibodies against dopamine conjugate, and previously found to bind to dopamine receptors, have been used to investigate putative dopamine receptors in these neurites. Immunocytochemical detection by light microscopy employing immunofluorescence labelling, was correlated with electron microscopy, using peroxidase staining. In addition to a location for dopamine receptors on the neurite surface, intracellular binding sites were also found in neurites. This internal labelling might represent an intracellular pool of dopamine receptor precursors. The labelling was specific in that it was not present when the anti-idiotypic dopamine antibodies were replaced with non-immune serum or when preincubation with conjugated dopamine preceded incubation with anti-idiotypic dopamine antibodies.

IgG3 reactive rheumatoid factor in rheumatoid arthritis: etiologic and pathogenic considerations

Rheumatoid factor (RF) is a polyclonal autoantibody directed against the Fc portion of IgG. Although the role of RF in patients with rheumatoid arthritis (RA) is unclear, immune complexes that form between RF and IgG can activate the classical complement (C) pathway, leading to pathogenic outcomes involving inflammatory events and tissue damage. The specificity of serum RF and RF produced by rheumatoid synovial cells (RSC) is different. Serum RF has specificity for rabbit IgG and human IgG subclasses IgG1, 2, and 4, but binds poorly to IgG3. The affinity of serum RF for IgG Fc is low, having an association constant of 10(4)-10(5) M-1. RSC RF, however, has specificity for human IgG and high avidity for IgG3. Because of this greater specificity and avidity for IgG3, and because RSC RF may be pathogenically more important than serum RF, an important role for IgG3-reactive RF in RA may exist. Binding of RF to IgG may be dependent on the allotype and glycosylation of IgG. Infectious agents present in RA patients may directly or indirectly induce the production of certain RF. In this communication, we review and expand on several observations examining the role of IgG3-reactive RF in RA including: 1) binding differences between RF derived from RSC and serum; 2) glycosylation characteristics of IgG and its interaction with RF; 3) apparent allotype dependent binding of IgG3-reactive RF; and 4) possible relationship between infectious agents and the production of IgG3-reactive RF. Taken together, these observations suggest an important role for IgG3-reactive RF in better understanding the etiology and pathogenesis of RA.