THE NONPOLYMORPHIC MHC CLASS-II ISOTYPE, HLA-DQA2, IS EXPRESSED ON THE SURFACE OF B-LYMPHOBLASTOID-CELLS

The more centromeric of the two human MHC class II DQA genes, DQA2, ha s not previously been shown to express a protein product, However, its high degree of sequence similarity to DQA1, the fact that it is highl y evolutionarily conserved, and the recent demonstration of its transc ription in some cell lines suggest that a DQA2 alpha-chain may be expr essed, Polyclonal antipeptide antisera were generated and shown to be specific for DQA2 in Western blotting of Triton X-114 preparations of B lymphoblastoid cell lines, DQA2 expression is variable, although alw ays at least threefold less than that of DQA1, and is found in all hap lotypes examined, Immunoprecipitations of biotin-labeled cell surface proteins reveal that DQA2 appears at the cell surface, In keeping with others' findings, no evidence for an expressed DQB2 beta-chain was fo und, prompting investigation of the means by which DQA2 gains access t o the cell surface, Antisera specific for allotypic and isotypic MHC c lass II P-chains were used in sequential immunoprecipitation experimen ts to search for a beta-chain partner for DQA2, and a transfectant sys tem was established in an attempt to promote pairing of DQA2 with a se lected DQB1 (0501) chain, In neither case was DQA2 found to dimerize with an MHC class II beta-chain, Despite this, DQA2 is capable of form ing a complex with invariant chain.