Identification of a new lymphocyte subset surface antigen, the expression of which disappears after in vitro and in vivo stimulation. Distribution, biochemistry, and functional studies.

Two monoclonal antibodies (MoAbs) are described (MD 2.6, IgG1 and MD 4.3, IgG2a) that react with a nonlineage specific lymphocyte subset surface antigen. This antigen is expressed on B cells, a subset of both T8+ and T4+ cells, cells that exert killer and natural killer cell activity in vitro, B cells in lymph nodes, and a small percentage of thymocytes. Expression of the antigen was found to be variable on T cells but not on B cells among individuals. Following polyclonal activation, expression of the determinant detected was lost from the cell surface. Both MD+ and MD+ cells responded to PHA and in MLC. MLC resulted in the generation of cytotoxic T lymphocytes and primed T lymphocytes in both the MD+ and MD+ subpopulations. In contrast, the response to soluble antigens was found to reside almost exclusively in the MD-subset. Immunoprecipitation indicates that the MoAbs react with an antigen that has a molecular weight of 220-240 KD which can be cleaved into subunits of 70-80 kD by beta-mercaptoethanol.