Requirements for the triggering of lysis by cloned murine cytolytic T lymphocytes (CTL)

Cloned murine cytolytic T lymphocytes (CTL) having defined specificity were triggered by the phorbol ester PMA + a calcium ionophore (either A23187 or Ionomycin) to lyse syngeneic or third party target cells efficiently. Neither PMA nor calcium ionophore alone induced efficient lysis. The characteristics of the lytic process induced by these signals are similar to those of antigen specific or lectin facilitated lysis by CTL: lysis is calcium and temperature dependent, and shows directionality and kinetics similar to lysis mediated via the antigen receptor. Helper T lymphocytes were not induced by these agents to lyse target cells efficiently. Activation of L3 CTL clone lysis by PMA + ionophore differed from antigen-mediated activation in specificity and in susceptibility to inhibition by cytochalasin B, an inhibitor of antigen mediated conjugate formation. Anti-LFA-1 monoclonal antibodies inhibited antigen-mediated, lectin-facilitated, or PMA + ionophore induced lysis. Anti-Lyt-2 and anti-receptor antibodies had little if any effect on lysis induced by PMA + ionophore. The triggering of lysis with PMA + ionophore appears to involve intracellular signals similar to those involved in lysis mediated by the antigen receptor.