Triggering CD 28 molecules synergize with CD 2 (T 11.1 and T 11.2)-mediated T cell activation.

Pairs of monoclonal antibodies (mAb) defining epitopes T 11.1 and T 11.2 on the CD 2 molecule are mitogenic for purified human T cells in the presence of a submitogenic 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.