Novel HLA-DRB1 alleles discovered during routine sequencing based typing, DRB1*03052, DRB1*04032, DRB1*1139 and DRB1*1346

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.

Detection of a rare Caucasoid HLA-DRB1*0337 in a Taiwanese bone marrow donor using sequence-based typing method

We here describe the identification of HLA-DRB1*0337, using sequence-based typing (SBT) method, in a Taiwanese bone marrow donor intrigued by a casual curiosity on the donor's racial background. On high-resolution sequence-specific primer (SSP) typing we observed misleading reaction patterns due to similarity of DNA sequences in the exon 2 of DRB1*0301, *0317, *0337 and *1139. When encountering rare alleles in HLA typing, it is important to pay extra attentions to avoid pitfalls and shortcomings of SSP typing kits routinely used and bear in mind that constant up-dating of high-resolution SSP typing kits to be able to distinguish newly reported alleles. SBT may be considered as a back-up HLA typing method to confirm rare alleles.