HLA-DQB1*0404, a novel DQB1-allele detected in a volunteer blood platelet donor typed for HLA

HLA class II peptide-binding-region analysis reveals funneling of polymorphism in action

BACKGROUND

HLA-class II proteins hold important roles in key physiological processes. The purpose of this study was to compile all class II alleles reported in human population and investigate patterns in pocket variants and their combinations, focusing on the peptide-binding region (PBR).

METHODS

For this purpose, all protein sequences of DPA1, DQA1, DPB1, DQB1 and DRB1 were selected and filtered, in order to have full PBR sequences. Proportional representation was used for pocket variants while population data were also used.

RESULTS

All pocket variants and PBR sequences were retrieved and analyzed based on the preference of amino acids and their properties in all pocket positions. The observed number of pocket variants combinations was much lower than the possible inferred, suggesting that PBR formation is under strict funneling. Also, although class II proteins are very polymorphic, in the majority of the reported alleles in all populations, a significantly less polymorphic pocket core was found.

CONCLUSIONS

Pocket variability of five HLA class II proteins was studied revealing favorable properties of each protein. The actual PBR sequences of HLA class II proteins appear to be governed by restrictions that lead to the establishment of only a fraction of the possible combinations and the polymorphism recorded is the result of intense funneling based on function.

A genome-wide association study of chronic hepatitis B identified novel risk locus in a Japanese population

Hepatitis B virus (HBV) infection is a major health issue worldwide which may lead to hepatic dysfunction, liver cirrhosis and hepatocellular carcinoma. To identify host genetic factors that are associated with chronic hepatitis B (CHB) susceptibility, we previously conducted a two-stage genome-wide association study (GWAS) and identified the association of HLA-DP variants with CHB in Asians; however, only 179 cases and 934 controls were genotyped using genome-wide single nucleotide polymorphism (SNP) arrays. Here, we performed a second GWAS of 519 747 SNPs in 458 Japanese CHB cases and 2056 controls. After adjustment with the previously identified variants in the HLA-DP locus (rs9277535), we detected strong associations at 16 loci with P-value of <5 × 10(-5). We analyzed these loci in three independent Japanese cohorts (2209 CHB cases and 4440 controls) and found significant association of two SNPs (rs2856718 and rs7453920) within the HLA-DQ locus (overall P-value of 5.98 × 10(-28) and 3.99 × 10(-37)). Association of CHB with SNPs rs2856718 and rs7453920 remains significant even after stratification with rs3077 and rs9277535, indicating independent effect of HLA-DQ variants on CHB susceptibility (P-value of 1.52 × 10(-21)- 2.38 × 10(-30)). Subsequent analyses revealed DQA1*0102-DQB1*0604 and DQA1*0101-DQB1*0501 [odds ratios (OR) =0.16, and 0.39, respectively] as protective haplotypes and DQA1*0102-DQB1*0303 and DQA1*0301-DQB1*0601 (OR = 19.03 and 5.02, respectively) as risk haplotypes. These findings indicated that variants in antigen-binding regions of HLA-DP and HLA-DQ contribute to the risk of persistent HBV infection.