Triggering CD 28 molecules synergize with CD 2 (T11.1 and T11,2)-mediated T cell activation

Abstract Pairs of monoclonal antibodies (mAb) defining epitopes T11.1 and T11.2 on the CD 2 molecule are mitogenic for purified human T cells in the presence of a sub‐mitogenic dose of 12‐O‐tetradecanoylphorbol 13‐acetate (TPA). Anti‐CD 28 mAb can substitute for the action of TPA in the anti‐CD 2‐induced proliferative response of resting T cells, whereas each signal alone is unable to mediate this effect. Co‐stimulation by anti‐CD 2 plus anti‐CD 28 mAb is monocyte independent and besides resting T cells also induces strong proliferation of thymocytes and pre‐activated T cells. Modulation of the CD 3‐T cell receptor complex does not inhibit the co‐stimulatory effects of anti‐CD 2 plus anti‐CD 28 mAb. The effect is largely dependent on endogenously produced interleukin 2, since the response is strongly inhibited in the presence of mAb against the 55‐kDa interleukin 2 receptor chain.