T‐Cell Proliferation and Expression of MHC Class II Antigens

Two monoclonal antibodies to major histocompatibility complex (MHC) class II antigens, which in combination identify β chains encoded by the SB and DR loci, were used to investigate which of these gene- products were expressed at the cell surface of unstimulated T cells and at various stages of mitogen-induced T-cell maturation. In tests on blood lymphocytes from healthy donors 12% of Tcells expressed class II antigens, but only SB antigens were expressed. During activation of T lymphocytes, SB-coded antigens were expressed before DR antigens, and the kinetics of SB expression correlated with the proliferative response of T cells. These results and consideration of recent reports from other laboratories lead us to suggest that 58-coded class II antigens play a role in T-cell proliferation.