HLA similarities indicate shared genetic risk in 21-hydroxylase autoantibody positive South African and United States Addison's disease.

Genetic similarities between patients from the United States and South African (SA) Addison's Disease (AD) strengthen evidence for genetic association. SA-AD (n = 73), SA healthy controls (N = 78), and US-AD patients (N = 83) were genotyped for DQA1, DQB1, DRB1, and HLA-B alleles. Serum was tested for the quantity of 21OH-AA and IFNα-AA at the Barbara Davis Center. Although not as profound as in US-AD, in SA-AD 21OH-AA + subjects the predominantly associated risk haplotypes were DRB1*0301-DQB1*0201 (DR3), DRB1*04xx-DQB1*0302 (DR4), and the combined DR3/4 genotype. DQB1*0302 associated DRB1*04xx haplotypes conferred higher risk than those DRB1*04xx haplotypes associated with other DQB1 alleles. We found negative association in 21OH-AA + SA-AD for DQA1*0201-DQB1*0202 and DQA1*0101-DQB1*0501 vs SA controls, and positive association for DQA1*0401-DQB1*0402 vs US-AD. Apart from the class II DR3 haplotype, HLA-B8 did not have an independent effect; however together DR3 and HLA-B8 conferred the highest risk vs 21OH-AA negative SA-AD and SA-controls. HLA-B7 (often with DR4) conferred novel risk in 21OH-AA + SA-AD vs controls. This study represents the first comparison between South African and United States AD populations utilizing genotyping and serology performed at the same center. SA-AD and US-AD 21OH-AA + patients share common HLA risk haplotypes including DR4 (with HLA-B7) and DR3 (with HLA-B8), strengthening previously described HLA associations and implicating similar genetic etiology.

The insulin gene is transcribed in the human thymus and transcription levels correlated with allelic variation at the INS VNTR-IDDM2 susceptibility locus for type 1 diabetes.

Type 1, or insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease associated with loss of tolerance to several pancreatic islet cell molecules, including insulin, glutamic acid decarboxylase (GAD), ICA69 and the tyrosine phosphatase IA-2 (refs 1-3). Among several predisposing loci, IDDM2 maps to the insulin gene (INS) VNTR (variable number of tandem repeats) minisatellite on chromosome 11p15 (refs 4-9). Allelic variation at this VNTR locus correlates with steady-state levels of INS mRNA in pancreas and transfected rodent cell lines, but it is difficult to reconcile the association of lower INS mRNA levels in the pancreas with class III VNTRs that are dominantly protective from IDDM. We show that during fetal development and childhood, mRNAs for insulin and other islet cell autoantigens (GAD, ICA69, IA-2) are expressed at low levels in the human thymus. Critically, we also detect proinsulin and insulin protein. VNTR alleles correlate with differential INS mRNA expression in the thymus where, in contrast to the pancreas, protective class III VNTRs are associated with higher steady-state levels of INS mRNA expression. This finding provides a plausible explanation for the dominant protective effect of class III VNTRs, and suggests that diabetes susceptibility and resistance associated with IDDM2 may derive from the VNTR influence on INS transcription in the thymus. Higher levels of (pro)insulin in the thymus may promote negative selection (deletion) of insulin-specific T-lymphocytes which play a critical role in the pathogenesis of type-1 diabetes.

Confirmation of novel type 1 diabetes risk loci in families.

AIMS/HYPOTHESIS: Over 50 regions of the genome have been associated with type 1 diabetes risk, mainly using large case/control collections. In a recent genome-wide association (GWA) study, 18 novel susceptibility loci were identified and replicated, including replication evidence from 2,319 families. Here, we, the Type 1 Diabetes Genetics Consortium (T1DGC), aimed to exclude the possibility that any of the 18 loci were false-positives due to population stratification by significantly increasing the statistical power of our family study. METHODS: We genotyped the most disease-predicting single-nucleotide polymorphisms at the 18 susceptibility loci in 3,108 families and used existing genotype data for 2,319 families from the original study, providing 7,013 parent-child trios for analysis. We tested for association using the transmission disequilibrium test. RESULTS: Seventeen of the 18 susceptibility loci reached nominal levels of significance (p < 0.05) in the expanded family collection, with 14q24.1 just falling short (p = 0.055). When we allowed for multiple testing, ten of the 17 nominally significant loci reached the required level of significance (p < 2.8 × 10(-3)). All susceptibility loci had consistent direction of effects with the original study. CONCLUSIONS/INTERPRETATION: The results for the novel GWA study-identified loci are genuine and not due to population stratification. The next step, namely correlation of the most disease-associated genotypes with phenotypes, such as RNA and protein expression analyses for the candidate genes within or near each of the susceptibility regions, can now proceed.

The HLA-B 3906 allele imparts a high risk of diabetes only on specific HLA-DR/DQ haplotypes.

AIMS/HYPOTHESIS: We investigated the risk associated with HLA-B*39 alleles in the context of specific HLA-DR/DQ haplotypes. METHODS: We studied a readily available dataset from the Type 1 Diabetes Genetics Consortium that consists of 2,300 affected sibling pair families genotyped for both HLA alleles and 2,837 single nucleotide polymorphisms across the major histocompatibility complex region. RESULTS: The B*3906 allele significantly enhanced the risk of type 1 diabetes when present on specific HLA-DR/DQ haplotypes (DRB1 0801-DQB1 0402: p = 1.6 × 10(-6), OR 25.4; DRB1 0101-DQB1 0501: p = 4.9 × 10(-5), OR 10.3) but did not enhance the risk of DRB1 0401-DQB1 0302 haplotypes. In addition, the B 3901 allele enhanced risk on the DRB1 1601-DQB1 0502 haplotype (p = 3.7 × 10(-3), OR 7.2). CONCLUSIONS/INTERPRETATION: These associations indicate that the B 39 alleles significantly increase risk when present on specific HLA-DR/DQ haplotypes, and HLA-B typing in concert with specific HLA-DR/DQ genotypes should facilitate genetic prediction of type 1 diabetes, particularly in a research setting.

No association of vitamin D intake or 25-hydroxyvitamin D levels in childhood with risk of islet autoimmunity and type 1 diabetes: the Diabetes Autoimmunity Study in the Young (DAISY).

AIMS/HYPOTHESIS: The aim of the study was to investigate the association between vitamin D intake and status and the risk of islet autoimmunity (IA) and subsequent type 1 diabetes in children at increased risk of type 1 diabetes. METHODS: The Diabetes Autoimmunity Study in the Young (DAISY) in Denver, CO, USA, has been following children at increased risk of diabetes since 1993. As of February 2011, 198 children developed IA during follow-up of 2,644 DAISY children. Vitamin D intake and plasma 25-hydroxyvitamin D [25(OH)D] were measured longitudinally. Proportional hazards regression analyses of time to IA, or type 1 diabetes in IA-positive children, were conducted, with vitamin D intake and 25(OH)D as time-varying covariates. HRs were calculated for a standard deviation difference in exposure, with adjustment for confounders. RESULTS: Intake of vitamin D was not associated with the risk of IA (adjusted HR 1.13; 95% CI 0.95, 1.35; p = 0.18) nor progression to diabetes in IA-positive children (adjusted HR 1.30; 95% CI 0.91, 1.86; p = 0.15). Moreover, 25(OH)D level was not associated with the risk of IA (adjusted HR 1.12; 95% CI 0.88, 1.43; p = 0.36), nor progression to diabetes in IA-positive children (adjusted HR 0.91; 95% CI 0.68, 1.22; p = 0.54). In the 128 children in whom we measured 25(OH)D at 9 months of age, 25(OH)D was not associated with risk of IA (n = 30 IA-positive children) (adjusted HR 1.02; 95% CI 0.96, 1.07; p = 0.58). CONCLUSIONS/INTERPRETATION: Neither vitamin D intake nor 25(OH)D levels throughout childhood were associated with the risk of IA or progression to type 1 diabetes in our population.

CHOP deletion does not impact the development of diabetes but suppresses the early production of insulin autoantibody in the NOD mouse.

C/EBP homologous protein (CHOP) has been proposed as a key transcription factor for endoplasmic reticulum (ER) stress-mediated ß-cell death induced by inflammatory cytokines in vitro. However, the contribution of CHOP induction to the pathogenesis of type 1 diabetes is not yet clear. To evaluate the relevance of CHOP in the pathogenesis of type 1 diabetes in vivo, we generated CHOP-deficient non-obese diabetic (NOD.Chop (-/-)) mice. CHOP deficiency did not affect the development of insulitis and diabetes and apoptosis in ß-cells. Interestingly, NOD.Chop (-/-) mice exhibited a delayed appearance of insulin autoantibodies compared to wild-type (wt) mice. Adoptive transfer with the diabetogenic, whole or CD8(+)-depleted splenocytes induced ß-cell apoptosis and the rapid onset of diabetes in the irradiated NOD.Chop (-/-) recipients with similar kinetics as in wt mice. Expression of ER stress-associated genes was not significantly up-regulated in the islets from NOD.Chop (-/-) compared to those from wt mice or NOD-scid mice. These findings suggest that CHOP expression is independent of the development of insulitis and diabetes but might affect the early production of insulin autoantibodies in the NOD mouse.

Detection of four diabetes specific autoantibodies in a single radioimmunoassay: an innovative high-throughput approach for autoimmune diabetes screening.

Highly sensitive and specific radioimmunoassays have been validated for autoantibodies reacting with the four major autoantigens identified so far in autoimmune diabetes. However, the analysis of this large number of autoantigens has increased the costs and time necessary for complete autoantibody screenings. Our aim was to demonstrate that it is possible to detect the immunoreactivity against a combination of four different autoantigens by a single assay, this representing a rapid, low-cost first approach to evaluate humoral autoimmunity in diabetes. By using this novel multi-autoantigen radioimmunoassay (MAA), in subsequent steps we analysed 830 sera, 476 of known and 354 of unknown diabetes-specific immunoreactivity, collected from various groups of individuals including type 1 and type 2 diabetes patients, autoantibody-positive patients with a clinical diagnosis of type 2 diabetes (LADA), prediabetic subjects, individuals at risk to develop autoimmune diabetes, siblings of type 1 diabetic patients, coeliac patients and healthy control subjects. All sera reacting with one or more of the four autoantigens by single assays also resulted positive with MAA, as well as eight of 24 type 1 diabetic patients classified initially as autoantibody-negative at disease onset based on single autoantibody assays. In addition, MAA showed 92% sensitivity and 99% specificity by analysing 140 blinded sera from type 1 diabetic patients and control subjects provided in the 2010 Diabetes Autoantibody Standardization Program. MAA is the first combined method also able to evaluate, in addition to glutamic acid decarboxylase (GAD) and tyrosine phosphatase (IA)-2, insulin and islet beta-cell zinc cation efflux transporter (ZnT8) autoantibodies. It appears to be particularly appropriate as a first-line approach for large-scale population-based screenings of anti-islet autoimmunity.

Dimorphic histopathology of long-standing childhood-onset diabetes.

AIMS/HYPOTHESIS: Childhood diabetes is thought to usually result from autoimmune beta cell destruction (type 1A) with eventual total loss of beta cells. Analysis of C-peptide in children characterised at diabetes onset for autoantibodies shows heterogeneous preservation of insulin secretion in long-standing diabetes. The aim of this study was to characterise the pancreases of childhood-onset diabetes in order to define the pathological basis of this heterogeneity. METHODS: We evaluated 20 cadaveric organ donor pancreases of childhood-onset long-term patients for disease heterogeneity and obtained corresponding C-peptide measurements. RESULTS: Pancreases from the majority of cadaveric donors contained only insulin-deficient islets (14 of 20). The remaining six patients (30%) had numerous insulin-positive cells within at least some islets, with two different histological patterns. Pattern A (which we would associate with type 1A diabetes) had lobular retention of areas with 'abnormal' beta cells producing the apoptosis inhibitor survivin and HLA class I. In pattern B, 100% of all islets contained normal-appearing but quantitatively reduced beta cells without survivin or HLA class I. CONCLUSIONS/INTERPRETATION: Our data demonstrate that C-peptide secretion in long-standing diabetic patients can be explained by two different patterns of beta cell survival,possibly reflecting different subsets of type 1 diabetes.

Aging in man. Linear increase of a novel T cell subset defined by antiganglioside monoclonal antibody 3G5.

A new human T cell subset defined by antineuronal ganglioside mAb 3G5 increases linearly with advancing age in man. The percentage of circulating 3G5+ T cells in 21 normal individuals, quantitated by cytofluorograph analysis, increases linearly from age 7 (23-30%) to age 84 (58%) (r = 0.85, p less than 0.001). The antigen on T cells has the biochemical properties of a ganglioside that migrates between GM1 and GM2 ganglioside markers on TLC. The 3G5 subset represents the first T cell subset that reflects aging in man.

A monoclonal antibody (3G5)-defined ganglioside antigen is expressed on the cell surface of microvascular pericytes.

The identification of microvascular pericytes in vitro relies principally on morphological characteristics and growth dynamics, as there is a paucity of immunochemical markers for these cells. Consequently, an attempt was made to identify mAb reagents that would aid in both the rapid identification and enrichment of retinal capillary pericytes in vascular cell cultures. A panel of mAbs raised by xenogeneic immunization of mice with various tissues was screened for immunoreactivity with dissociated cultures of bovine retinal capillary pericytes. Two antibodies from the panel (3G5 and HISL-8) were seen to react with pericytes by indirect immunofluorescence. The mAb 3G5 was selected for further study. mAb 3G5 did not react with dissociated cultures of smooth muscle cells, endothelial cells, or retinal pigmented endothelial cells. The pericyte 3G5 antigen was insensitive to the action of trypsin; therefore, mAb 3G5 was used to selectively purify pericytes from trypsinized mixed retinal cell cultures by flow cytometry. 3G5+ pericytes (representing 8% of cells in a mixed retinal cell culture) were enriched at least nine-fold to represent greater than 70% of cells. The mAb 3G5 stained retinal capillaries in vivo with a fluorescence distribution consistent with pericyte staining. The 3G5 antigen of cultured pericytes was found to be a glycolipid of mobility intermediate between ganglioside markers GM1 and GM2.

Major histocompatibility complex restriction fragment length polymorphisms define three diabetogenic haplotypes in BB and BBN rats.

Class I and II major histocompatibility complex (MHC) probes can be used to subdivide diabetes-prone BB rats and their BBN control strain, coderived from the same outbred colony by selection against diabetes. Class II probes (A-alpha in particular) distinguish four restriction fragment length polymorphisms (RFLP), termed 1a, 1b, 2a, and 2b, in the BBN population, only one of which (2a) is found in BB rats. The degree of class II RFLP in the population studied is RT1.B-alpha greater than or equal to RT1.B-beta greater than RT1.D-alpha greater than or equal to RT1.D-beta, suggesting that intra-class II region dynamics may be different in rats compared with mice. A class I probe (S16) absolutely distinguished BB from BBN rats, since all BB rats exhibit an RFLP pattern termed 2a0, while 2a BBN rats can be subdivided into 2a1 and 2a2 forms. Serologic evaluation has shown that 2a0, 2a1, and 2a2 rats express RT1.AuBu, 1a rats express RT1.AaDa, and 1b rats express neither RT1a nor RT1u at the loci tested. A breeding study was carried out to determine the diabetogenicity of the MHC-defined RFLP's. As expected, the BB-derived 2a0 is diabetogenic. The BBN-derived 2a1 and 2a2 RFLPs are also diabetogenic, while 1a and 1b rats do not carry MHC-linked diabetogenic genes. The MHC-linked diabetes gene acts in a functionally recessive manner, since there is a 10-fold higher incidence in homozygotes than in heterozygotes. Analysis of the RFLP patterns leads us to hypothesize that the 2a1 RFLP results from a crossover between 1a and 2a0 MHCs and that the diabetogenic MHC-linked gene is on the class II side of Qa and T1. The availability of three diabetogenic MHC haplotypes should help localize the MHC-linked diabetogenic gene of rats.

Two genes required for diabetes in BB rats. Evidence from cyclical intercrosses and backcrosses.

The BB rat develops a syndrome of autoimmune diabetes similar to Type I diabetes of man. It also has a severe T cell lymphopenia. As part of an ongoing breeding program to transfer the diabetogenic genes of the BB rat onto inbred rat strain backgrounds, diabetic animals were used in a backcross (BC)- intercross (IC)-backcross breeding scheme with Brown Norway (BN), Lewis (L), and Wistar-Furth (WF) inbred rats. We have used monoclonal antibodies to analyze both lymphopenia and major histocompatibility (MHC) antigens (the RT1 locus in the rat) in relation to the development of diabetes. To examine T cell subsets we used a panel of monoclonal antibodies, in particular W3/25 and OX19 , which discriminate the abnormal phenotype better than W3/13. In our breeding program, at least two independent genes or gene complexes are required for the expression of diabetes. One gene determines the lymphopenia, is inherited by simple autosomal recessive genetics and is not linked to the MHC. The second gene is linked to the MHC. Both genes are necessary, but neither gene is sufficient by itself for the development of diabetes.

Antigen-dependent immunotherapy of non-obese diabetic mice with immature dendritic cells.

Immunotherapy can be used to induce immunological tolerance by a number of different protocols. During the last decade the ability to use tolerogenic dendritic cells (DCs) to prevent autoimmunity has received much attention. Many studies have attempted to use immature or semi-mature DCs to induce tolerance in the non-obese diabetic (NOD) mouse model of human type 1 diabetes. However, most studies to date have used protocols in which generation of DCs involved a culture step in fetal bovine serum (FBS)-supplemented medium which may affect tolerance induction in a non-specific fashion. Indeed, several studies have shown that DCs cultured in the presence of FBS will induce a powerful T helper type 2 (Th2) immune response towards FBS-related antigens which can suppress an ongoing immune response. Hence, this may interfere with diabetes development in the NOD mouse by induction of immune deviation rather than by antigen-specific tolerance. In order to test whether antigen-specific tolerance induction by DC therapy is feasible in the NOD mouse, we therefore generated immature DCs using autologous serum [normal mouse serum (NMS)-supplemented cultures] instead of FBS, and we show that these DCs can protect NOD mice from diabetes, if pulsed with insulin-peptide antigens before adoptive transfer. Our data therefore support that DC therapy is able to prevent diabetes in the NOD mouse in an antigen-specific manner.

rs2476601 T allele (R620W) defines high-risk PTPN22 type I diabetes-associated haplotypes with preliminary evidence for an additional protective haplotype.

Protein tyrosine phosphatase non-receptor type 22 (PTPN22) is the third major locus affecting risk of type I diabetes (T1D), after HLA-DR/DQ and INS. The most associated single-nucleotide polymorphism (SNP), rs2476601, has a C->T variant and results in an arginine (R) to tryptophan (W) amino acid change at position 620. To assess whether this, or other specific variants, are responsible for T1D risk, the Type I Diabetes Genetics Consortium analyzed 28 PTPN22 SNPs in 2295 affected sib-pair (ASP) families. Transmission Disequilibrium Test analyses of haplotypes revealed that all three haplotypes with a T allele at rs2476601 were overtransmitted to affected children, and two of these three haplotypes showed statistically significant overtransmission (P=0.003 to P=5.9E-12). Another haplotype had decreased transmission to affected children (P=3.5E-05). All haplotypes containing the rs2476601 T allele were identical for all SNPs across PTPN22 and only varied at centromeric SNPs. When considering rs2476601 'C' founder chromosomes, a second haplotype (AGGGGC) centromeric of PTPN22 in the C1orf178 region was associated with protection from T1D (odds ratio=0.81, P=0.0005). This novel finding requires replication in independent populations. We conclude the major association of PTPN22 with T1D is likely due to the recognized non-synonymous SNP rs2476601 (R620W).

Autoimmune polyendocrine syndrome type 1 (APS-1) as a model for understanding autoimmune polyendocrine syndrome type 2 (APS-2).

Autoimmune polyendocrine syndromes type 1 and 2 (APS-1 and APS-2) are diverse in regards to their component diseases and immunologic features of pathogenesis. Animal models and human studies highlight the importance of alleles of HLA (human leukocyte antigen)-like molecules determining tissue specific targeting that with the loss of tolerance leads to organ specific autoimmunity. Knowledge of the syndromes and component diseases allows clinicians to recognize and prevent illness prior to morbidity. With the current understanding of the syndromes, a paradigm for diagnosis, screening and treatment can be established. Once genetically susceptible individuals are identified screening for autoantibodies can be performed. Amongst autoantibody positive individuals, monitoring for physiologic decompensation, with a goal of treating prior to morbidity and in some cases mortality, follows. With continued basic and clinical research, therapies aimed at treating the underlying autoimmunity and disease prevention should become possible.

Two novel AIRE mutations in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) among Indians.

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a rare recessive disorder resulting from mutations in the autoimmune regulator (AIRE) gene. There is no information on AIRE mutations in Indians. In a cross-sectional study, nine patients (eight families), from four referral hospitals in India, were studied for AIRE mutations by direct sequencing. We screened for new mutations in 150 controls by allele-specific PCR. The patients had 1-7 known components of APECED. Three patients had unusual manifestations: presentation with type 1 diabetes; chronic sinusitis and otitis media; and facial dysmorphism. All patients carried homozygous, probably recessive, AIRE mutations. Two unrelated patients from a small in-bred community (Vanika Vaisya) in south India carried an unreported missense mutation, p.V80G, in the N-terminal caspase recruitment domain. Another unique mutation, p.C302X, resulting in a truncated protein with deletion of both zinc-finger domains, was detected in a patient from Gujarat. Neither mutation was detected in controls. Other mutations, previously described in Caucasians, were: 13 base pair deletion (p.C322fsX372) in 4 (38%), and Finn-major (p.R257X) and p.R139X (Sardinian) mutation in one subject each. In conclusion, in this first series of APECED in Indians, we detected AIRE mutations previously reported in Caucasians, as well as unique mutations. Of these, p.V80G is possibly an ancestral mutation in an in-bred community.

Insulin2 gene (Ins2) transcription by NOD bone marrow-derived cells does not influence autoimmune diabetes development in NOD-Ins2 knockout mice.

Insulin is a critical autoantigen for the development of autoimmune diabetes in non-obese diabetic (NOD) mice. About 80% of NOD females and 30-40% of NOD males develop diabetes. However, Insulin2 (Ins2) knockout NOD mice develop autoimmune diabetes with complete penetrance in both sexes, at an earlier age, and have stronger autoimmune responses to insulin. The severe diabetes phenotype observed in NOD-Ins2-/- mice suggests that lack of Ins2 expression in the thymus may compromise immunological tolerance to insulin. Insulin is a prototypical tissue specific antigen (TSA) for which tolerance is dependent on expression in thymus and peripheral lymphoid tissues. TSA are naturally expressed by medullary thymic epithelial cells (mTEC), stromal cells in peripheral lymphoid tissues and bone marrow (BM)-derived cells, mainly CD11c(+) dendritic cells. The natural expression of TSA by mTEC and stromal cells has been shown to contribute to self-tolerance. However, it is unclear whether this also applies to BM-derived cells naturally expressing TSA. To address this question, we created BM chimeras and investigated whether reintroducing Ins2 expression solely by NOD BM-derived cells delays diabetes development in NOD-Ins2-/- mice. On follow-up, NOD-Ins2-/- mice receiving Ins2-expressing NOD BM cells developed diabetes at similar rates of those receiving NOD-Ins2-/- BM cells. Diabetes developed in 64% of NOD recipients transplanted with NOD BM and in 47% of NOD mice transplanted with NOD-Ins2-/- BM (P = ns). Thus, NOD-Ins2-/- BM did not worsen diabetes in NOD recipients and Ins2 expression by NOD BM-derived cells did not delay diabetes development in NOD-Ins2-/- mice.

Progression to diabetes in nonobese diabetic (NOD) mice with transgenic T cell receptors.

The T cell receptor (TCR) requirements in the pathogenesis of insulin-dependent diabetes were examined with transgenic NOD mice bearing nondisease-related TCR alpha and beta chains. In both TCR beta and TCR alpha beta transgenic NOD mice the beta chain transgene was expressed by > 98% of peripheral T cells. The alpha chain transgene was also highly expressed. Insulitis developed in both sets of transgenic animals with most of the lymphocytes in the lesion expressing the transgenic beta chain and with depletion of the endogenous TCR V beta genes. Nonetheless, NOD animals transgenic for TCR beta and TCR alpha beta developed diabetes similar to controls. Thus, skewing the TCR repertoire did not diminish autoimmune susceptibility in NOD mice.

Linkage of faulty major histocompatibility complex class I to autoimmune diabetes.

Pancreatic islet cells are the targets of an autoimmune response in type I diabetes. In the nonobese diabetic (NOD) mouse model of autoimmune diabetes, expression of major histocompatibility complex (MHC) class I proteins was inversely correlated with diabetes; in this mouse a mutation in the MHC class II-linked gene for the putative MHC class I peptide transporter was also present. Mice deficient in MHC class I expression because they do not produce beta 2-microglobulin also developed late onset autoimmune diabetes. In cells from humans with type I diabetes expression of MHC class I was decreased; subsets of prediabetics categorized as most likely to become hyperglycemic also had low MHC class I. T cell responses to self antigens are faulty in diabetics. In sets of genetically identical twins that are discordant for diabetes, the defect appeared to reside with the antigen presenting cell. Thus, a lack of surface MHC class I protein is associated with autoimmune diabetes; the concomitant defect in antigen presentation may impair the development of self tolerance, which could result in autoimmune disease.

The frequent and conserved DR3-B8-A1 extended haplotype confers less diabetes risk than other DR3 haplotypes.

AIM: The goal of this study was to develop and implement methodology that would aid in the analysis of extended high-density single nucleotide polymorphism (SNP) major histocompatibility complex (MHC) haplotypes combined with human leucocyte antigen (HLA) alleles in relation to type 1 diabetes risk. METHODS: High-density SNP genotype data (2918 SNPs) across the MHC from the Type 1 Diabetes Genetics Consortium (1240 families), in addition to HLA data, were processed into haplotypes using PedCheck and Merlin, and extended DR3 haplotypes were analysed. RESULTS: With this large dense set of SNPs, the conservation of DR3-B8-A1 (8.1) haplotypes spanned the MHC (>/=99% SNP identity). Forty-seven individuals homozygous for the 8.1 haplotype also shared the same homozygous genotype at four 'sentinel' SNPs (rs2157678 'T', rs3130380 'A', rs3094628 'C' and rs3130352 'T'). Conservation extended from HLA-DQB1 to the telomeric end of the SNP panels (3.4 Mb total). In addition, we found that the 8.1 haplotype is associated with lower risk than other DR3 haplotypes by both haplotypic and genotypic analyses [haplotype: p = 0.009, odds ratio (OR) = 0.65; genotype: p = 6.3 x 10(-5), OR = 0.27]. The 8.1 haplotype (from genotypic analyses) is associated with lower risk than the high-risk DR3-B18-A30 haplotype (p = 0.01, OR = 0.23), but the DR3-B18-A30 haplotype did not differ from other non-8.1 DR3 haplotypes relative to diabetes association. CONCLUSION: The 8.1 haplotype demonstrates extreme conservation (>3.4 Mb) and is associated with significantly lower risk for type 1 diabetes than other DR3 haplotypes.