Synergy between the T3/Ti complex and Tp44 in human T cell activation

Ligands, including antigen, which interact with the T3/T cell antigen receptor (Ti) induce an increase in cytoplasmic free calcium ((Ca/sup + +/)/sub i/). However, such an increase in (Ca/sup + +/)/sub i/ is not sufficient to result in T cell activation. Activation can occur if such ligands, which increase (Ca/sup + +/)/sub i/, are added in the presence of phorbol myristate acetate (PMA). This suggests that interactions involving other T cell surface receptors might function in a manner analogous to PMA and play an important role in T cell activation. Using the human leukemic T cell line Jurkat, they demonstrated that 9.3, a monoclonal antibody specific for a 90 kD homodimer expressed on human T cells (Tp44), synergized with some ligands interacting with T3/Ti on Jurkat in the induction of IL-2 production from Jurkat. Thus, 9.3 synergized with PHA, ConA, or sepharose beads coupled with anti-T3 or anti-Ti but not with calcium ionophores or soluble anti-T3 or anti-Ti. Furthermore, at high concentrations only, 9.3 could also synergize with PMA in the activation of Jurkat and T3/Ti negative mutants of Jurkat. No detectable activation of protein kinase C was induced by 9.3 alone. These studies suggest that T cell activation maymore » result from the simultaneous triggering of several distinct T cell surface molecules.« less