Serological Identification of Five HLA-D Associated (Ia-like) Determinants*

Five antisera raised within HLA-A and -B compatible, HLA-D disparate combinations were reactive in a modified NIH microcytotoxicity test with B lymphocytes, but not with T lymphocytes from the immunizing donor, as well as with B lymphocytes from most or all donors sharing his immunizing HLA-D phenotype. Four antisera recognized structures closely associated with the HLA-D determinants Dw2, Dw3, Dw4 and LD 108. One serum had a broad reactivity pattern including Dw3, Dw6 and some unknown specificity(ies). In population and family studies, these B lymphocyte antigens behaved as if they were governed by one genetic locus in the B-D region of the HLA complex. We conclude that the antisera produced by this method recognize Ia-like antigens identical to or very closely associated with the HLA-D determinants.