Surface antigens specifically expressed by activated T cells in humans

By immunizing BALB/c mice with human T cells derived from a secondary mixed lymphocyte reaction (MLR) and successive fusion of the spleen cells with P3 X63Ag8U1 myeloma cells, several monoclonal antibodies to activated T cells were obtained. Four of them (MLR1-4) were shown to be specific for activated T cells only, showing no reactivity with peripheral blood cells. The antigens recognized by these antibodies are differently distributed and appear on T cells at different times after stimulation. Thus, MLR2 stains nearly all the responder T cells present in a secondary MLR, while MLR1, 3 and 4 stain only a fraction. MLR2 and 3 are also present on mitogen-stimulated cells. At least 3 of these MLR antigens may define different sets of activated T cells, and are likely to become useful in monitoring T cell activation also in the course of diseases involving the immune system.