Immunoglobulin allotypes (GM and KM) and their interactions with HLA antigens in autoimmune diseases: a review

Coming together at the hinges: Therapeutic prospects of IgG3

The human IgG3 subclass is conspicuously absent among the formats for approved monoclonal antibody therapies and Fc fusion protein biologics. Concern about the potential for rapid degradation, reduced plasma half-life, and increased immunogenicity due to marked variation in allotypes has apparently outweighed the potential advantages of IgG3, which include high affinity for activating Fcγ receptors, effective complement fixation, and a long hinge that appears better suited for low abundance targets. This review aims to highlight distinguishing features of IgG3 and to explore its functional role in the immune response. We present studies of natural immunity and recombinant antibody therapies that elucidate key contributions of IgG3 and discuss historical roadblocks that no longer remain clearly relevant. Collectively, this body of evidence motivates thoughtful reconsideration of the clinical advancement of this distinctive antibody subclass for treatment of human diseases. Abbreviations: ADCC - Antibody-Dependent Cell-mediated CytotoxicityADE - Antibody-dependent enhancementAID - Activation-Induced Cytidine DeaminaseCH - Constant HeavyCHF - Complement factor HCSR - Class Switch RecombinationEM - Electron MicroscopyFab - Fragment, antigen bindingFc - Fragment, crystallizableFcRn - Neonatal Fc ReceptorFcγR - Fc gamma ReceptorHIV - Human Immunodeficiency VirusIg - ImmunoglobulinIgH - Immunoglobulin Heavy chain geneNHP - Non-Human Primate.

The forgotten tale of immunoglobulin allotypes in cancer risk and treatment

Monoclonal antibody (mAb) has fulfilled the promise of being the "Magic Bullet" in oncology with the clinical success of mAbs against CD20, Her-2/neu, epidermal growth factor receptor, vascular endothelial cell growth factor and others in a variety of cancers. Most manufacturers of mouse-human chimeric antibodies (and most immunologists) have treated the constant region of human immunoglobulin (Ig) as if it were naturally monomorphic and therefore not immunogenic in humans. In fact, the constant region of Ig heavy and light chain is highly polymorphic, and yet Ig haplotypes are usually not defined by genome-wide association studies nor are they considered to be important for optimizing mAb therapy. We hereby summarize evidence that Ig allotypes are important and biologically relevant in that they contribute to the etiopathogenesis of many malignant, infectious, and autoimmune diseases. Because Ig allotypes differ from each other in engaging Fc receptor, we argue that future development of effective mAb therapy for cancer should take a patient-specific approach by using the correct allotype for each patient to maximize the efficacy of this therapy.

Immunogenetics as a tool in anthropological studies

The genes coding for the main molecules involved in the human immune system--immunoglobulins, human leucocyte antigen (HLA) molecules and killer-cell immunoglobulin-like receptors (KIR)--exhibit a very high level of polymorphism that reveals remarkable frequency variation in human populations. 'Genetic marker' (GM) allotypes located in the constant domains of IgG antibodies have been studied for over 40 years through serological typing, leading to the identification of a variety of GM haplotypes whose frequencies vary sharply from one geographic region to another. An impressive diversity of HLA alleles, which results in amino acid substitutions located in the antigen-binding region of HLA molecules, also varies greatly among populations. The KIR differ between individuals according to both gene content and allelic variation, and also display considerable population diversity. Whereas the molecular evolution of these polymorphisms has most likely been subject to natural selection, principally driven by host-pathogen interactions, their patterns of genetic variation worldwide show significant signals of human geographic expansion, demographic history and cultural diversification. As current developments in population genetic analysis and computer simulation improve our ability to discriminate among different--either stochastic or deterministic--forces acting on the genetic evolution of human populations, the study of these systems shows great promise for investigating both the peopling history of modern humans in the time since their common origin and human adaptation to past environmental (e.g. pathogenic) changes. Therefore, in addition to mitochondrial DNA, Y-chromosome, microsatellites, single nucleotide polymorphisms and other markers, immunogenetic polymorphisms represent essential and complementary tools for anthropological studies.

Pathways: Strategies for susceptibility genes in SLE

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder marked by an inappropriate immune response to nuclear antigens. Recent whole genome association and more focused studies have revealed numerous genes implicated in this disease process, including ITGAM, Fc gamma receptors, complement components, C-reactive protein, and others. One common feature of these molecules is their involvement in the immune opsonin pathway and in phagocytic clearing of nuclear antigens and apoptotic debris, which provide excessive exposure of lupus-related antigens to immune cells. Analysis of gene-gene interactions in the opsonin pathway and its relationship to SLE may provide a system-based approach to identify additional candidate genes associated with disease able to account for a larger part of lupus susceptibility.

Antigen-specific influence of GM/KM allotypes on IgG isotypes and association of GM allotypes with susceptibility to Plasmodium falciparum malaria

BACKGROUND

Plasmodium falciparum malaria is a complex disease in which genetic and environmental factors influence susceptibility. IgG isotypes are in part genetically controlled, and GM/KM allotypes are believed to be involved in this control.

METHODS

In this study, 216 individuals from Daraweesh, an area of seasonal malaria transmission in Sudan, were followed for nine years for malaria infection. Total IgG and IgG isotypes against four malaria antigens, MSP2-3D7, MSP2-FC27, AMA1, and Pf332-C231 were measured in plasma obtained from the cohort at the end of the study, during the dry malaria-free period. The GM/KM allotypes of the donors were determined.

RESULTS

The GM 1,17 5,13,14,6 phenotype was associated with a higher incidence of malaria compared with the non-1,17 5,13,14,6 phenotypes (P = 0.037). Paradoxically, the carriers of the GM 1,17 5,13,14,6 phenotype had significantly higher baseline levels of total IgG and non-cytophilic IgG isotypes as compared to non-carriers. The KM allotypes influence on IgG isotypes level was limited. Finally, the differences in the baseline concentrations of total IgG and IgG isotypes between the different GK/KM phenotype carriers were antigen-dependent.

DISCUSSION

The results show that GM but not KM allotypes appeared to influence host susceptibility to uncomplicated malaria as well as the antibody profile of the donors, and the carriers of the GM 1,17 5,13,14,6 phenotype were the most susceptible

CONCLUSIONS

The GM allotypes have significant influence on susceptibility to uncomplicated P. falciparum malaria and antigen-dependent influence on total IgG and IgG subclasses.

Human immunoglobulin allotypes: possible implications for immunogenicity

More than twenty recombinant monoclonal antibodies are approved as therapeutics. Almost all of these are based on the whole IgG isotype format, but vary in the origin of the variable regions between mouse (chimeric), humanized mouse and fully human sequences; all of those with whole IgG format employ human constant region sequences. Currently, the opposing merits of the four IgG subclasses are considered with respect to the in vivo biological activities considered to be appropriate to the disease indication being treated. Human heavy chain genes also exhibit extensive structural polymorphism(s) and, being closely linked, are inherited as a haplotype. Polymorphisms (allotypes) within the IgG isotype were originally discovered and described using serological reagents derived from humans; demonstrating that allotypic variants can be immunogenic and provoke antibody responses as a result of allo-immunization. The serologically defined allotypes differ widely within and between population groups; therefore, a mAb of a given allotype will, inevitably, be delivered to a cohort of patients homozygous for the alternative allotype. This publication reviews the serologically defined human IgG allotypes and considers the potential for allotype differences to contribute to or potentiate immunogenicity.

Recombinant human hepatitis B vaccine initiating alopecia areata: testing the hypothesis using the C3H/HeJ mouse model

Untoward effects of human vaccines suggest that recombinant hepatitis B vaccine may induce alopecia areata (AA) in some patients. Similar untoward immunological effects may also account for AA-like diseases in domestic species. In this study, the C3H/HeJ spontaneous adult onset AA mouse model was used to test the role, if any, of recombinant hepatitis B vaccine on the initiation or activation of AA. Initial experiments demonstrated no effect on induction of AA in young adult female C3H/HeJ mice (P = 0.5689). By contrast, older females, those at the age when AA first begins to appear in this strain, had a significant increase (P = 0.0264) in the time of onset of AA, suggesting that the vaccine may initiate disease in mice predisposed to AA. However, larger vaccine trials, which included diphtheria and tetanus toxoids as additional controls, did not support these initial result findings and suggest that AA associated with vaccination may be within the normal background levels of the given population.

Immunoglobulin gene polymorphisms are susceptibility factors in clinical and autoantibody subgroups of the idiopathic inflammatory myopathies

OBJECTIVE

To investigate possible associations of GM and KM markers with adult and juvenile forms of the idiopathic inflammatory myopathies (IIMs) in Caucasian and African American patients.

METHODS

We performed serologic analyses of polymorphic determinants associated with immunoglobulin gamma heavy chains (GM) and kappa light chains (KM) in large populations of Caucasian patients (n= 514 [297 adults and 217 children]) and African American patients (n=123 [73 adults and 50 children]) with IIM representing the major clinical and autoantibody groups.

RESULTS

For Caucasian patients with dermatomyositis (DM), the Gm 3 23 5,13 phenotype was a risk factor in both adults (odds ratio [OR] 2.2, corrected P [Pcorr]=0.020) and children (OR 2.2, Pcorr=0.0013). Of interest, the GM 13 allotype was a risk factor for juvenile DM in both Caucasian subjects (OR 3.9, Pcorr<0.0001) and African American subjects (OR 4.8, Pcorr=0.033). However, the Gm 1,3,17 5,13,21 phenotype was a risk factor for juvenile DM in Caucasian subjects but not African American subjects. Among the IIM autoantibody groups, Gm 3 23 5,13 was a risk factor in Caucasian adults with anti-Jo-1 autoantibodies (OR 3.4, Pcorr=0.0031), while the GM 3 allotype was protective in adults with anti-threonyl-transfer RNA synthetase or anti-U RNP autoantibodies (OR 0.1, Pcorr=0.047 and OR 0.2, Pcorr=0.034, respectively). In contrast, GM 6 was a risk factor in African American adults with anti-signal recognition particle autoantibodies (OR 7.5, Pcorr=0.041).

CONCLUSION

These data suggest that polymorphic alleles of GM and KM loci are differentially associated with IIM subgroups defined by age, ethnicity, clinical features, and autoantibody status, and expand the list of immune response genes that are possibly important in the pathogenesis of myositis.

Genetic interactions of KIR and G1M immunoglobulin allotypes differ in obese from non-obese individuals with type 2 diabetes

We analyzed the natural killer cell immunoglobulin-like receptor (KIR) genes and immunoglobulin allotypes in the development of type 2 diabetes (T2D) based on body mass index (BMI) measurements (obese vs. non-obese) in Puerto Rican Americans. Genetic interactions between the KIR haplotype A homozygotes (HAH) and its fraction containing two inhibitory receptors 2DL3 and 2DL1 and the activating receptor 2DS4 with immunoglobulin allotypes were studied. We found a significant association between the HAH and T2D (p=0.002; OR=7.97) and its interaction with the immunoglobulin allotype z: GM f/f (-) (p=<0.0001; OR, not determined) only in non-obese individuals. This association were due to the interactions between the 2DL3/2DL3, 2DL1/2DL1, and 2DS4 fragment with GM f/f (-) in T2D patients (p=0.0017; OR=3.45). Analysis based on BMI demonstrated associations in both obese (p=0.037; OR=2.43; 95% CI=0.97-6.31) and non-obese individuals (p=<0.0001; OR=8.38; 95% CI=2.49-29.31). By contrast, the interaction of the GM allotype f/f (-) with the HAH fragment was associated with T2D only in non-obese individuals (p=<0.0001; OR=18.2; 95% CI=3.71-113.4). As expected, interaction of both HAH and its fragment with HLA-C group's ligands were significant. We used informative short tandem repeats (STRs) that distinguish major populations to determine genetic admixture and found that there was no genetic stratification in our cohort. Our findings are consistent with the possibility of an autoimmune and/or innateimmune component in the pathogenesis of T2D: NK receptors with chronic inflammation in obese and genetic interactions with G1M allotype in T2D non-obese possibly mediating autoimmunity.

Genetic factors affecting the occurrence, clinical phenotype, and outcome of autoimmune hepatitis

Autoimmune hepatitis is a polygenic disorder of unknown cause in which the genetic risk factors that affect occurrence, clinical phenotype, severity, and outcome still are being clarified. The susceptibility alleles in white North American and northern European patients reside on the DRB1 gene, and they are DRB1*0301 and DRB1*0401. These alleles encode a 6 amino acid sequence at positions 67-72 in the DRbeta polypeptide chain of the class II molecules of the major histocompatibility complex. This sequence is associated with susceptibility, and lysine at position DRbeta71 is the key determinant. Molecular mimicry between foreign and self-antigens may explain the loss of self-tolerance and the occurrence of concurrent immune diseases in anatomically distant organs. Disease severity is associated with the number of alleles encoding lysine at DRbeta71 (gene dose) and the number of polymorphisms, including those of the tumor necrosis factor-alpha gene, cytotoxic T lymphocyte antigen-4 gene, and tumor necrosis factor-receptor superfamily gene, that can modify the immune response. Individuals in different geographic regions may have different susceptibility alleles that reflect indigenous triggering antigens, and these may provide clues to the etiologic agent. Knowledge of the genetic predispositions for autoimmune hepatitis may elucidate pathogenic mechanisms, identify etiologic agents, characterize susceptible populations, foresee outcomes, and target new therapies. These lessons may be applicable to autoimmune disease in general.

A biased Gm haplotype and Gm paraprotein allotype in multiple myeloma suggests a role for the Gm system in myeloma development

The association between a particular Gm haplotype and susceptibility to multiple myeloma (MM) is not clear. The reason is probably because no investigations have so far been carried out on the relationship between the Gm haplotype, which represents the inherited combination of IgG Gm allotypes, and the Gm allotype expressed at the IgG paraprotein (M-component), which reflects the enhanced gene expression within the haplotype in MM. We studied the incidence of Gm allotypic markers present in IgG subclasses in the serum from 52 patients with MM and in parallel with the isolated IgG paraproteins. The results showed that 84.6% of the patients were heterozygous for haplotypes Gm(a; z; n-; g;)/Gm(f; n+/n-; b1; b0; b5) and 15.3% were homozygous for Gm(f; n/n-; b1; b0; b5), while no homozygous Gm(a; z; n-; g) individuals were found among the studied patients. The incidence of these combinations in the healthy population in Serbia is 34%, 66% and < 1%, respectively. Subjects with Gm(a; z; n-; g)/Gm(f; n+/n-; b1; b0; b5) combination are over 10 times [odds ratio (OR) = 10.69; 95% confidence interval 1.67-68] as likely to be affected by the disease as the subjects with homozygous Gm(f; n+/n-; b1; b0; b5) combination (OR = 0.35, 95% confidence interval 0.06-2.23). However, despite the Gm heterozygosity, most of the Gm(a; z; n-; g;)/Gm(f; n+/n-; b1; b0; b5) positive patients with MM (86.3%) had IgG paraprotein with the allotypic marker from the Gm(f; n+/n-; b1; b0; b5) haplotype. Together with patients homozygous for this haplotype, the relative number of patients with serum IgG paraprotein carrying allotypic marker from the Gm(f; n/n-; b1; b0; b5) haplotype was 88.5%. These results suggest that the development of an M-component could be related to a disturbance on chromosome 14q32 carrying the Gm (f; n+/n-; b1; b0; b5) set of genes.

Interaction of KIR Genes and G1M Immunoglobulin Allotypes Confer Susceptibility to Type 2 Diabetes in Puerto Rican Americans

The susceptibility to type 2 diabetes (T2D) involves genetic factors. We studied the distribution of KIR and MHC class I ligands phenotype and genotype frequencies, as well as immunoglobulin KM and GM allotype frequencies in a group of patients (N = 95) with T2D and ethnically matched healthy controls (N = 74) with Puerto Rican ethnic background. We found a slight increase of the 2DL3/2DL3 homozygous genotype in T2D. Moreover, the association between 2DL3/2DL3 genotype was significant in the presence of 2DS4 (pC = 0.01). Also, we observed an epistatic effect of the interaction of 2DL3/2DL3, 2DS4 with allele z of G1M in T2D (pC = 0.004, OR = 3.60, 95% CI, 1.62-8.10). This genetic interaction between KIR and G1M allotypes, associated with T2D, was also significant by multiple logistic regression analysis (p < 0.0001, OR = 4.90, 95% CI, 2.12-11.3). We did not detect population stratification using unlinked short tandem repeat (STR) markers, demonstrating that the patients and controls were ethnically matched. Hence, we have demonstrated in this study an epistatic interaction between KIR genes and the G1M allotype that influences the susceptibility to T2D in Puerto Rican Americans. Our findings are important for understanding the autoimmune or innate immune inflammatory-mediated mechanisms involved in the pathogenesis of T2D.

Immunoglobulin GM and KM genotypes in Korean patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by immune complex deposition. We genotyped immunoglobulin allotypes of G1M (f,z), G2M (n+,n-), G3M (b,g) and KM (1,3) in 142 Korean patients with SLE and 200 healthy controls to investigate the role of the allotypes in SLE. The allele frequency of G1M (z) was significantly higher in patients with SLE as compared to the healthy controls (94.6% vs. 84.3%, corrected P = 0.0004, OR 3.30, 95% CI 1.71-6.88). The frequency of G2M (n-) allele was also higher in patients with SLE (95.3% vs. 88.3%, corrected P = 0.008, OR = 2.71, 95% CI 1.38-5.72). Distribution of the tested allele frequencies for G3M and KM were not different between the patients and controls. In the respect of antibody production, there was increased genotype frequency of G1M (z/z) in anti-Sm(-) SLE (P = 0.023 vs. control, P = 0.042 vs. anti-Sm (+) SLE). In conclusion, particular genotypes at G1M (f,z) and G2M (n+,n-) loci are significantly associated with SLE. These immunoglobulin genes may contribute to the etiology of SLE and production of autoantibodies.

Immunoglobulin GM and KM allotypes and prevalence of anti-LKM1 autoantibodies in patients with hepatitis C virus infection

GM and KM allotypes-genetic markers of immunoglobulin (Ig) gamma and kappa chains, respectively-are associated with humoral immunity to several infection- and autoimmunity-related epitopes. We hypothesized that GM and KM allotypes contribute to the generation of autoantibodies to liver/kidney microsomal antigen 1 (LKM1) in hepatitis C virus (HCV)-infected persons. To test this hypothesis, we characterized 129 persons with persistent HCV infection for several GM and KM markers and for anti-LKM1 antibodies. The heterozygous GM 1,3,17 23 5,13,21 phenotype was significantly associated with the prevalence of anti-LKM1 antibodies (odds ratio, 5.13; P=0.002), suggesting its involvement in this autoimmune phenomenon in HCV infection.

Genetic factors in pemphigus

Epidemiological studies performed in different ethnic populations and family studies, notably based on a partial phenotype of the autoimmune process, indicate that genetic factors are involved in the occurrence of pemphigus. However, the precise heritability remains uncertain in the absence of twin concordance rate studies. Among the different strategies available to identify genetic factors participating in autoimmune disease susceptibility, only population studies based on case-control design have been performed in pemphigus. These studies consistently showed that MHC locus, in particular HLA class II alleles, are associated with pemphigus vulgaris and pemphigus foliaceus. Other genes of the MHC locus may also participate in disease susceptibility as shown by studies using microsatellite markers across different regions of the MHC. It is likely that other non-MHC genes are involved in the pathogenesis of pemphigus. In particular, involvement of a polymorphic variant of desmoglein 1 gene was shown to be associated with pemphigus foliaceus and to interact in an epistatic manner with MHC class II genes to contribute to the autoimmune process. Other candidate genes to which a role can be assigned in the disease pathogenesis should be considered to design case-control or family-based association studies. Genome scan studies which require a large number of multiplex families to reach statistical power, should also be considered in the endemic form of pemphigus foliaceus because of the high number of familial cases.

Immunoglobulin GM and KM genotypes in hepatitis C virus infection

Hepatitis C virus (HCV) is a major health problem, affecting over 170 million people worldwide. HCV causes a wide spectrum of liver disease, varying from persistent to asymptomatic infection. To evaluate the role of immunoglobulin (Ig) GM and KM genes in HCV infection, 191 HCV-infected Thai subjects were studied. These included 43 individuals with transient HCV infection and 148 individuals with persistent chronic HCV infection. The controls consisted of 134 healthy individuals. Several GM and KM alleles were determined by polymerase chain reaction-based methods. The frequency of G1M(f) homozygotes was lower (52.4% vs. 64.2%, P = 0.03) and the frequency of G1M(z) homozygotes was higher (10.5% vs. 3.7%, P = 0.02) in patients than the respective frequencies in controls. These results suggest that GM genotypes make a significant contribution to the risk of acquiring HCV infection.

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.

Epistatic effects of genes encoding immunoglobulin GM allotypes and interleukin-6 on the production of autoantibodies to 60- and 65-kDa heat-shock proteins

Immunoglobulin GM and KM genes have been associated with antibody responses to a variety of antigens. A promoter-region polymorphism of interleukin-6 (IL-6) gene (-174 G/C) has been shown to be associated with antibody responses to heat-shock proteins (hsp) 60 and hsp65. To examine the possible epistatic effects of these unlinked genetic systems on the autoimmune responses to hsp60 and hsp65, 176 healthy Caucasian subjects from Finland were genotyped for several allelic determinants of GM, KM, and IL-6 genes by PCR-RFLP methods. IgG antibodies to hsp60 and hsp65 were measured by an ELISA. Significant interactive effects of GM f,z and IL-6-174 genotypes were noted for both anti-hsp60 (P=0.002) and anti-hsp65 (P=0.038) antibody levels. Since these autoantibodies have been implicated in susceptibility to coronary heart disease and carotid atherosclerosis, the associations reported here might be relevant to the etiology of these diseases.

Major locus on mouse chromosome 17 and minor locus on chromosome 9 are linked with alopecia areata in C3H/HeJ mice

Alopecia areata is an autoimmune disease that targets actively growing (anagen) hair follicles in humans, mice, rats, dogs, horses, and cattle. C3H/HeJ mice spontaneously develop alopecia areata from 5 mo of age and older in females and later in males. Frequency of disease approached 20% in a colony by 18 mo of age. C57BL/6J mice do not develop alopecia areata. A segregating F2 population of female mice (n=1096) was generated from crossing these two strains. Alopecia areata (n=138) and clinically normal (n=214) mice were genotyped at 12 mo of age using 211 microsatellite probes. The peak logarithm of odds ratio score on mouse chromosome 17 (10.9) was around marker D17Mit134 at 16.9 cM from the centromere. The mouse histocompatibility locus, H2, the mouse equivalent of human leukocyte antigen in humans, was a likely candidate. Twelve-month-old C3H.SW-H2b/SnJ mice (C3H/HeJ congenic mice in which the H2k purported susceptibility locus was replaced with the H2b purported resistance locus) did not develop alopecia areata, supporting this locus as being important in alopecia areata. A suggestive linkage was also found on mouse Chromosome 9 (logarithm of odds ratio score 2.0) around D9Mit206, 20 cM from the centromere. The interval on mouse Chromosome 17 contains several orthologous genes potentially associated with human alopecia areata.

Immunoglobulin KM genes in Guillain-Barré syndrome

Guillain-Barré syndrome is associated with antecedent Campylobacter jejuni infection. Only a minority of the infected individuals, however, develops the disease, implying a role for genetic factors in conferring susceptibility. To determine the role of immunoglobulin KM genes (genetic markers of the constant region of kappa chains) in the etiology of this syndrome, we genotyped 83 patients and 196 healthy controls from Norway for KM1 and KM3 alleles by polymerase chain reaction-restriction fragment length polymorphism. The frequency of KM3 homozygotes was significantly increased in patients compared with controls (86.7% vs. 74%, P=0.01, odds ratio=2.3). Conversely, the frequency of KM1/KM3 heterozygotes was significantly decreased in patients compared with controls (13.3% vs. 26%, P=0.01, odds ratio=0.4). These results suggest that KM genes may be relevant to the etiology of Guillain-Barré syndrome.

Immunoglobulin kappa light chain gene alleles are not associated with primary Sjögren's syndrome

The immunoglobulin kappa (Km) light chain gene is polymorphic and is believed to play a role in the pathology of infectious and autoimmune diseases. Polymorphisms within the constant region of the Km gene encode three alleles designated Km1, Km1,2 and Km3. Previous studies using serological detection of Km allotypes reported associations between specific Km allotypes, systemic lupus erythematosus and the presence of anti-La antibodies, yet these findings were not confirmed in other studies. In order to more precisely define any associations between Km alleles and anti-Ro/La antibodies we used the polymerase chain reaction and restriction fragment length polymorphisms for Km genotyping in a large cohort of patients with primary Sjögren's syndrome (SS). No associations were observed between specific Km alleles and primary SS when compared with a control population, nor within serologically defined subsets of SS patients. We conclude that Km alleles are not associated with primary SS or the Ro/La autoantibody response.

Evidence for a locus (IDDM16) in the immunoglobulin heavy chain region on chromosome 14q32.3 producing susceptibility to type 1 diabetes

Type 1 diabetes results from autoimmune destruction of pancreatic islet beta-cells, possibly initiated or exacerbated by viral infections. Recent studies have demonstrated that antibodies towards enterovirus and autoantibodies towards islet cell components develop in the long preclinical phase of type 1 diabetes. We therefore hypothesised that susceptibility to type 1 diabetes could be influenced by genetic factors controlling production of antiviral antibodies or autoantibodies or both. To search for evidence of linkage or association (linkage disequilibrium) between type 1 diabetes and the immunoglobulin heavy chain (IGH) region, 351 North American and British families with > or =2 diabetic children were genotyped for IGH region microsatellites. Using affected sibpair analysis, significant evidence for linkage was obtained for three markers close to the IGH gene cluster (P values 0.004, 0.002, 0.002). No evidence was found for association using family-based methods. To attempt to confirm these findings, a smaller dataset (241 families, 138 with > or =2 diabetic children) from Denmark, a more genetically-homogeneous population, was genotyped for one marker only. These families showed no linkage, but significant evidence for association (P = 0.019). This study suggests that a locus (assigned the symbol IDDM16) in the IGH region, possibly an IGH gene, influences susceptibility to type 1 diabetes.

Parental GM and HLA genotypes and reduced birth weight in patients with Turner's syndrome

We investigated a possible influence on birth weight in Turner's syndrome of many clinical, hormonal, genetic and immunogenetic variables. We considered 97 patients with Turner's syndrome. Patients with parents with identical GM (Gamma heavy chains Marker) phenotype had a significantly lower birth weight than those with parents with different GM phenotype. Karyotype other than 45,X, HLA (Human Leukocyte Antigen) parental sharing, mother-patient compatibility and elevated 17-hydroxyprogesterone (17OHP) serum level after adrenocorticotropin hormone (ACTH) and absence of heart and kidney malformations and lymphedema were associated with a lower birth weight, but not significantly. Multiple interactions showed that the presence of an identical GM phenotype in parents, together with other conditions (karyotype other than 45,X, adrenal dysfunction, HLA parental sharing, mother-child compatibility, KM(3) [Kappa light chains Marker] phenotype) resulted in a further decrease of birth weight. These data might suggest a negative effect of genetic similarity on intrauterine growth in Turner's syndrome.

Genetics of type 1 diabetes mellitus

At least 20 different chromosomal regions have been linked to type 1 diabetes (T1D) susceptibility in humans, using genome screening, candidate gene testing, and studies of human homologues of mouse susceptibility genes. The largest contribution from a single locus (IDDM1) comes from several genes located in the MHC complex on chromosome 6p21.3, accounting for at least 40% of the familial aggregation of this disease. Approximately 30% of T1D patients are heterozygous for HLA-DQA1*0501-DQB1*0201/DQA1*0301-DQB1*0302 alleles (formerly referred to as HLA-DR3/4 and for simplification usually shortened to HLA-DQ2/DQ8), and a particular HLA-DQ6 molecule (HLA-DQA1*0102-DQB1*0602) is associated with dominant protection from the disease. There is evidence that certain residues important for structure and function of both HLA-DQ and DR peptide-binding pockets determine disease susceptibility and resistance. Independent confirmation of the IDDM2 locus on chromosome 11p15.5 has been achieved in both case-control and family-based studies, whereas associations with the other potential IDDM loci have not always been replicated. Several possibilities to explain these variable results from different studies are discussed, and a key factor affecting both linkage and association studies is that the genetic basis of T1D susceptibility may differ between ethnic groups. Some future strategies to address these problems are proposed. These include increasing the sample size in homogenous ethnic groups, high throughput genotyping and genomewide linkage disequilibrium (LD) mapping to establish disease associated ancestral haplotypes. Elucidation of the function of particular genes ('functional genomics') in the pathogenesis of T1D will be a most important element in future studies in this field, in addition to more sophisticated methods of statistical analyses.

Transfer of vitiligo after allogeneic bone marrow transplantation

Adoptive transfer of donor immunity has been demonstrated in animals after bone marrow transplantation (BMT). In humans, several autoimmune diseases have been similarly transferred. Although BMT may, per se, be associated with a modulation of the recipient's immune system, which could trigger or even cause autoimmune diseases, both animal experiments and experience with humans show the likeliness of adoptive transfer of donor immunity to the recipient. We describe a patient with multiple myeloma in whom generalized vitiligo developed within 3 months after allogeneic BMT from his HLA-matched sister with vitiligo. We believe that a form of adoptive transfer of donor immunity to the recipient might play a role in the development of vitiligo. In spite of this, neither de novo development of vitiligo in a genetically predisposed patient nor autoimmune phenomena associated with graft-versus-host disease can be completely excluded as a contributing factor for development of vitiligo in our patient. To our knowledge, this is the first case report of transfer of vitiligo after BMT from a donor with vitiligo.

Understanding the pathogenesis of autoimmune hepatitis

OBJECTIVES

The aim of this study was to review the pathogenic mechanisms of autoimmune hepatitis, identify gaps in knowledge, and focus future investigative efforts.

METHODS

The study was based on a review of all relevant articles on the mechanisms of autoimmunity in autoimmune liver disease from 1980 to 2000, extraction of pertinent concepts from the medical literature; and integration of evolving paradigms of pathogenesis with personal experiences and investigations.

RESULTS

Autoimmune hepatitis is a consequence of autoantigen exposure, genetic predisposition, and defective immunoregulatory mechanisms. Autoantigen is optimally presented by class II molecules of the major histocompatibility complex that have lysine residues at position DRbeta71 of the antigen-binding groove. Cytokines and non-disease-specific autoimmune promoters modulate immune reactivity. Cell-mediated and antibody-dependent mechanisms contribute to hepatocyte injury.

CONCLUSIONS

Multiple disturbances in the homeostatic mechanisms that preserve self-tolerance are likely in autoimmune hepatitis. Future investigations must focus on individual determinants of autoantigen presentation, immunocyte activation, and liver cell destruction. Findings can then be integrated into a comprehensive knowledge base that may be applicable to other autoimmune diseases.

Update on the genetics of the idiopathic inflammatory myopathies

A number of lines of investigation suggest that, as is likely the case for other autoimmune diseases, the idiopathic inflammatory myopathies (IIM) develop as a result of specific environmental exposures in genetically susceptible individuals. Current data imply that multiple genes are involved in the etiology of these complex disorders. Targeted gene studies and whole genome approaches have begun to identify several genetic risk factors for autoimmune diseases, but the rarity and heterogeneity of the IIM have limited our knowledge of their associated genes. Current findings suggest that human leukocyte antigen (HLA) genes on chromosome 6, particularly HLA DRB1*0301 and the linked allele DQA1*0501, have the strongest associations with all clinical forms of IIM in white patients. Different HLA alleles, however, may confer risk or protection for myositis in distinct ethnic, serologic, and environmental exposure groups. Non-HLA genetic risk factors, which have been documented for other autoimmune diseases, are now being identified for the IIM. These include polymorphic genes encoding immunoglobulin heavy chains (defined by serologic markers known as Gm allotypes), cytokines and their receptors, and certain proteins that accumulate in the myocyte vacuoles of inclusion body myositis patients. Selected allelic polymorphisms of interleukin-1 receptor antagonist variable number tandem repeats and genes for tumor necrosis factor alpha and interleukin-1 alpha also have recently been associated with IIM. The pathogenic bases for the differences among the many clinically, pathologically and immunologically defined syndromes known as the IIM will be elucidated through a better understanding of the multiple genes that define risks for their development, as well as through investigations of gene-gene and gene-environment interactions.

Genetic markers of immunoglobulins and diabetes mellitus in the multiracial population of New Caledonia. The CALDIA Study Group

GM and KM immunoglobulin allotypes, which are the markers, respectively, of the constant parts of the heavy and the light chains of the IgG1, IgG2 and IgG3 subclasses, have been analysed in diabetic mellitus patients and controls living in New Caledonia. We tested 40 Europeans, 256 Melanesians and 44 Polynesians, as well as their 340 matched controls, in order to search for a genetic susceptibility at those polymorphic loci. All the subjects were tested for G1M (1, 2, 3, 17), G2M (23), G3M (5, 6, 10, 11, 13, 14, 15, 16, 21, 24, 28) and KM (1) by the classical hemagglutination method. The frequencies of GM haplotypes and KM alleles have been estimated by a maximum likelihood method. The results are in favour of no influence of the GM and KM loci. The prevalence of diabetes mellitus varies in the populations of New Caledonia: Polynesians are at much higher risk than Melanesians or Europeans. The GM haplotype distribution differs among ethnic groups; so they provide a useful marker to measure genetic admixture. The higher prevalence of diabetes observed among New Caledonians of European origin compared to the prevalence in Europe may be explained by genetic admixture with neighbouring Pacific populations, notably Polynesians (Asian haplotypes are present at a frequency of 9.4%). So, the genetic admixture should be measured in any genetic epidemiological study.

Association of KM genotype with bullous pemphigoid

Association of kappa light chain immunoglobulin allotypes with bullous pemphigoid was examined in 101 Caucasian patients. Km alleles were determined by polymerase chain reaction amplification followed by restriction enzyme digestion. The frequency of Km(3)/Km(1,2)kappa light-chain genotype was found to be significantly associated with the disease, while that of the Km(3)homozygous genotype was significantly higher in patients with both anti-BPAG1 and anti-BPAG2 autoantibodies.

Susceptibility to coeliac disease in Tunisian children and GM immunoglobulin allotypes

Coeliac disease is a malabsorption disorder of the small intestine resulting from ingestion of gluten. The immunogenetic component is clearly demonstrated by the association of the disease with human leukocyte antigens (HLA). Among other candidate genes are the GM allotypes, which are the markers of the constant parts of heavy chains of the subclasses IgG1, IgG2 and IgG3. GM immunoglobulin allotypes have been analysed in 131 unrelated Tunisian children with coeliac disease. All patients and their parents were tested for G1M(1, 2, 3, 17), G2M(23) and G3M(5, 6, 10, 11, 13, 14, 15, 16, 21, 24, 28) by the classical haemagglutination method. Genotypes and haplotypes were deduced from phenotypes in patients and their parents. Transmission disequilibrium tests were performed in 79 informative families. The GM*3;..;5* haplotype was transmitted more often (23) than not (8) by heterozygous parents (chi 2 = 7.26; P = 0.007). This difference remained significant after correction for multiple testing. This study provides evidence for association and linkage between GM and coeliac disease. It suggests that GM or genes close to GM play a role in the development of the disease.

Immunoglobulin allotype gene polymorphisms in systemic sclerosis: interactive effect of MHC class II and KM genes on anticentromere antibody production

OBJECTIVE

To examine potential interactions between immunoglobulin (Ig)-allotype gene polymorphisms and susceptibility to systemic sclerosis (SSc) as well as serological expression in SSc patients.

METHODS

IgG heavy chain allotypes G1M(f, z), G2M(n+, n-), G3M(b, g) and Ig light chain allotype KM(1, (1, 2), 3) were genotyped in 105 Japanese SSc patients and 47 race matched normal controls using polymerase chain reaction (PCR) based methods. Associations of each Ig allotype with SSc related antinuclear antibodies were examined in combination with or without MHC class II alleles.

RESULTS

GM/KM genotypic and allelic frequencies were similar in SSc patients and in normal controls. Frequencies of G1M(f) and G2M(n+) were significantly decreased in anticentromere antibody (ACA) positive SSc patients compared with ACA negative SSc patients (p = 0.04 and 0.02, respectively). Conversely, the presence of DQB1*0501 and KM(1, 2) significantly increased the risk of ACA positivity.

CONCLUSION

Ig allotype gene polymorphisms were not associated with susceptibility to SSc. Instead, the results suggested that MHC class II and KM genes are associated with autoimmune responses by interactively promoting the production of ACA.

The pathogenesis of Graves' disease

Graves' disease, one of the autoimmune thyroid diseases, is caused by the production of IgG autoantibodies directed against the thyrotropin receptor. These antibodies bind to and activate the receptor, causing the autonomous production of thyroid hormones. Despite recent improvements in our understanding of the cellular and molecular basis of autoimmunity, our currently available treatments for Graves' disease have remained largely unchanged over the last 50 years. Nevertheless, new concepts in immune system regulation hold out the prospect in the future for intervention designed to modify, and possibly cure, the underlying disease process.