HLA class II polymorphism and genetic susceptibility to insulin-dependent diabetes mellitus

Non-classical MHC I-E negatively regulates macrophage activation and Th17 cell development in NOD mice

Transgenic expression of I-E molecules prevents diabetes in NOD mice. So far, the precise role of these non-classical MHC II molecules remains elusive. Here, we showed that transgenic expression of I-E^k alpha 16 molecule in NOD mice selectively reduced Th17 cells in the thymus and pancreatic draining lymph nodes. The reduction in Th17 cells was associated with both attenuated IL-6 production and decreased activation of macrophages. Mechanistically, transgenic expression of the I-E molecule diminished expression of intracellular classical MHC II molecule and led to impaired TLR4-mediated signaling. In contrast to classical MHC II molecule, this non-classical MHC II molecule negatively regulates the inflammatory responses of macrophages. Altogether, our study reveals a novel regulatory role of I-E molecules in modulating inflammatory immune responses.

Analysis of tumor necrosis factor-alpha promoter polymorphism in type 1 diabetes: HLA-B and -DRB1 alleles are primarily associated with the disease in Japanese

Polymorphisms in the 5'-flanking region of the tumor necrosis factor (TNF)-alpha gene were examined to study the genetic background of type 1 diabetes in Japanese. Five different biallelic polymorphisms were examined in 136 type 1 diabetic patients and 300 control subjects. The frequencies of individuals carrying TNF-alpha-857T allele (designated as TNFP-D allele) or -863A/-1,031C allele (designated as TNFP-B allele) were significantly increased in the patients as compared with the controls. Since these TNF-alpha alleles are in linkage disequilibria with certain DRB1 and HLA-B alleles, two-locus analyses were carried out. The TNFP-D allele did not increase the risk in either the presence or absence of the DRB1*0405 or HLA-B54 allele, while the DRB1*0405 and HLA-B54 alleles per se could confer susceptibility in both the TNFP-D allele-positive and -negative populations. Moreover, an odds ratio was remarkably elevated in the population carrying both DRB1*0405 and HLA-B54. Similarly, the TNFP-B allele did not show significant association with the disease in either the HLA-B61-positive or -negative population, while the HLA-B61 allele could significantly increase the risk in the TNFP-B allele-positive population. These data suggest that the associations of TNFP-D and -B alleles may be secondary to their linkage disequilibria with the susceptible HLA class I and class II alleles. Because HLA-B and DRB1 genes were independently associated, both of these genes may be contributed primarily to the pathogenesis of type 1 diabetes in Japanese.

Genetic control of diabetes mellitus

Genetic inheritance predisposing individuals to diabetes mellitus was discussed in this work group. The two forms of the disease, Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) were discussed separately since the pattern of inheritance and genes involved appear to be distinctly different. Within these subtypes there is considerable genetic heterogeneity, and superimposed environmental factors confound the analysis. New technologies that will allow finer molecular analysis, as well as new candidates genes, were presented.

HLA class II sequences and genetic susceptibility to insulin dependent diabetes mellitus

The analysis of HLA class II sequence variation in IDDM patients and controls, made possible by the PCR, has revealed that specific alleles are associated with IDDM. The HLA-DQ beta chain appears to play a role in determining genetic susceptibility and resistance, although polymorphisms in the DRB1, the DQ alpha, and the DP beta chain may also contribute. Although there is a correlation between susceptibility and the charge of DQ beta residue 57, the complex genetic epidemiology of IDDM cannot be accounted for by polymorphism at this position. As we have discussed previously (Horn et al, 1988a, 1988b; Erlich et al, 1990b), there are no unique class II sequences associated with IDDM, consistent with the view that 'normal' class II alleles confer susceptibility. Given the estimates of concordance of under 50% for monozygotic twins and approximately 15% (Tattersall and Pyke, 1972; Thomson, 1988) for HLA-identical sibs--it is not surprising that some unaffected individuals contain putative susceptibility alleles. Perhaps some environmental 'triggering' agent, such as viral infection, is required for the disease to develop in susceptible individuals. Other non-MHC-linked genes which contribute to susceptibility may account for the difference in concordance rates for monozygotic twins and for HLA-identical sibs. In the NOD (non-obese diabetic) mouse and the BB rat models for IDDM, non-MHC susceptibility loci have been identified and mapped (Colle et al, 1981; Hattori et al, 1986) but, in humans, the analysis of non-MHC candidate loci (i.e. the T cell receptor) has, thus far, failed to reveal any other susceptibility loci. In general, the HLA-linked genetic susceptibility to IDDM, as well as to other autoimmune diseases, appears to be associated with specific combinations of class II epitopes (e.g. alleles, haplotypes or genotypes) rather than with specific individual residues or epitopes. Understanding the role of these predisposing sequences will require structural analysis of the class II molecules as well as in vitro and in vivo functional studies of interactions with putative autoantigens and T cell receptors. In the meantime, DNA typing offers the potential for identifying individuals at high risk. These susceptible individuals could be monitored by immunological (e.g. anti-islet cell antibody) or by metabolic tests to detect the preclinical phase of IDDM.