Polymorphism of human B-cell alloantigens: evidence for three loci within the HLA system

The B-cell alloantigens of an HLA-DR3-homozygous, MB2-homozygous, MT2-positive lymphoblastoid cell line were studied by two-dimensional gel electrophoresis. Analysis of gel patterns suggested assignment of the HLA-DR3 determinant to the larger (35,000-dalton) subunit (alpha) of the B-cell alloantigen. MB2 was found to be either a determinant on the small (27,000 dalton) subunit (beta) or a crossreactive determinant(s) on the HLA-DR3 alpha subunit and an additional alpha subunit. MT2 was found to be a determinant on Ia antigen-like molecules distinct from those carrying the MB and HLA-DR determinants. The results are consistent with the existence in the major histocompatibility complex of at least three loci encoding B-cell alloantigens.