Ia antigens on alloreactive T cells in man detected by monoclonal antibodies. Evidence for synthesis of HLA-D/DR molecules of the responder type.

A monoclonal antibody (Ab 2.06) directed against a nonpolymorphic determinant of HLA-D/DR molecules was used to study the expression and the biosynthesis of Ia molecules on human T cells before and after allogeneic stimulation. Normal resting peripheral T cells failed to synthesize and/or express Ia antigens. However, at day 7 of a mixed lymphocyte reaction, 40-60% of alloreactive T cells express and synthesize HLA-D/DR molecules of the responder type as assessed by two-dimensional gel electrophoresis genotyping. This Ia+ alloreactive population originates from an Ia - T cell pool and not from an Ia+ T cell population. Moreover, the two-dimensional polyacrylamide gel electrophoresis pattern of Ia on T cells is similar to that obtained with B cells from the same individual.