HLA-DMA alleles are possible new markers of rheumatoid arthritis: study of a Corsican group

Human leukocyte Antigen-DM polymorphisms in autoimmune diseases

Classical MHC class II (MHCII) proteins present peptides for CD4⁺ T-cell surveillance and are by far the most prominent risk factor for a number of autoimmune disorders. To date, many studies have shown that this link between particular MHCII alleles and disease depends on the MHCII's particular ability to bind and present certain peptides in specific physiological contexts. However, less attention has been paid to the non-classical MHCII molecule human leucocyte antigen-DM, which catalyses peptide exchange on classical MHCII proteins acting as a peptide editor. DM function impacts the presentation of both antigenic peptides in the periphery and key self-peptides during T-cell development in the thymus. In this way, DM activity directly influences the response to pathogens, as well as mechanisms of self-tolerance acquisition. While decreased DM editing of particular MHCII proteins has been proposed to be related to autoimmune disorders, no experimental evidence for different DM catalytic properties had been reported until recently. Biochemical and structural investigations, together with new animal models of loss of DM activity, have provided an attractive foundation for identifying different catalytic efficiencies for DM allotypes. Here, we revisit the current knowledge of DM function and discuss how DM function may impart autoimmunity at the organism level.

Cholesteryl ester transfer protein gene polymorphisms are associated with coronary artery disease in Corsican population (France)

The aim of the present study was to investigate the association between coronary artery disease (CAD) and Cholesterol Ester Transfer Protein (CETP) (gaaa)n polymorphisms of the CETP gene in Central Corsica island (France). The study group was composed by 300 unrelated Corsican patients with angiographically documented CAD and 300 unrelated healthy blood donors. Significant differences were observed in the distribution of CETP (gaaa)n alleles between the groups under study (p=0.03; chi(2): 16.8, df: 8). The occurrence of a long allele (408 bp) was higher in cases (12%) than in control group (2%), showing a 6.75-fold increased risk for CAD in Corsica patients (p=0.0055; OR=6.750; 95% CIs=1.47-31.00). The correlation of this polymorphism with the lipid profile (cholesterol, low density lipoprotein-cholesterol, high density lipoprotein-cholesterol and triglycerides) in the patients group was determined. There was a significant association of the long alleles of CETP (gaaa)n with HDL-C levels. In the patient and in the control groups the LL genotypes had lower HDL-C compared with the SS and SL genotypes (p<0.0001). In summary our results suggest that the genetic variation at the CETP gene may play an important role in determining CAD in Corsican population.

The complexity of HLA class II (DRB1, DQB1, DM) associations with disseminated Mycobacterium avium complex infection among HIV-1-seropositive whites

Earlier associations of polymorphism in classic HLA class II (DRB1 and DQB1) genes have been extended to include the accessory genes DMA and DMB as determinants of disseminated Mycobacterium avium complex (DMAC) infection among HIV-1-seropositive whites. From the Multicenter AIDS Cohort study, 176 DMAC cases were matched with 176 controls in a nested case-control study. PCR-based HLA genotyping techniques were used to resolve variants of DRB1 and DQB1 to their four-digit or five-digit alleles, and single-strand conformation polymorphism was used to resolve sequences in exon 3 at each DM locus. The DMA*0102 allele occurred less frequently among DMAC cases than among controls (OR = 0.46, p =.02). Combinations of DRB1 alleles with or without specific DMA and DMB variants showed significant differences in distributions between the cases and controls, but both of the previously associated class II alleles (DRB1*1501 and DRB1*0701) showed stronger positive associations with DMAC in the absence than in the presence of DMA*0102. Apparent joint effects of DRB1 and DM allelic combinations on occurrence and timing of DMAC suggest that class II disease relationships may be better predicted by biologically plausible interactive combinations than by polymorphisms in individual genes.

HLA DMA and DMB show no association with rheumatoid arthritis in US Caucasians

HLA DM is a heterodimeric molecule functioning in normal antigen presentation; it is encoded by adjacent HLA-region loci, HLA DMA and DMB, located between DP and DQ. Some previous studies have suggested that HLA susceptibility to rheumatoid arthritis (RA) is associated with certain DMA and DMB alleles. Our aim was to examine whether this association is also present in US Caucasians. We studied 288 US Caucasian subjects with rheumatoid arthritis and 263 US Caucasian control subjects. DMA and DMB typing was achieved by PCR amplification followed by sequence-specific oligonucleotide hybridization and by PCR-restriction fragment length polymorphism. There was no frequency difference for DMA alleles or DMB alleles between RA and control subjects, indicating no association. Neither was a difference apparent when data were analysed in subgroups based on shared-epitope DRB1, on the rheumatoid factor test, on radiographic changes of RA, or on sex. DRB1-DQB1-DMB analyses for linkage disequilibrium showed that the DRB1*0401-DQB1*0301 haplotype had the DMB*0103 allele more often than DMB*0101 (estimated haplotype frequencies 0.08 and 0.039 in RA, respectively). In contrast, the DRB1 *0401-DQB1 *0302 haplotype usually had the DMB*0101 allele (haplotype frequency 0.084 compared to 0.01 for DMB*0103). Thus, neither HLA DMA nor DMB was associated with RA in this population, and not all shared-epitope-bearing haplotypes had the same DMB allele distribution.