Antigen/mitogen induced cytolytic activity and IL-2 secretion in memory-like CTL-hybridomas

Memory-like monoclonal CTL hybridomas, derived from fusion of the AKR thymoma BW5147 with secondary CTL generated in vivo or in MLC cultures, have been used to study the mechanism whereby antigen/mitogen induces anamnestic CTL responses. Specifically, we have asked whether induction of cytolytic activity can be promoted by an antigenic/mitogenic signal without involvement of IL-2 receptors, IL-2, or other extrinsic factors. We have found that antigen/lectin alone can trigger the cytolytic potential of the hybridomas and induce IL-2 secretion. Pure IL-2 and conditioned medium were ineffective inducers of cytotoxicity. Moreover, IL-2 receptors were not detected on the hybrid cells before and after antigenic stimulation, demonstrating that expression of IL-2 receptors and induction of specific killing activity are not genetically linked. Non-activated and activated cells conjugated with target cells equally well, suggesting that induction of cytolytic activity involves a post target cell binding step. Close linkage between cytotoxicity and IL-2 secretion has been observed: induction of killing was consistently associated with IL-2 secretion and stimulation of both activities could be blocked by Cyclosporin A. IL-2 was secreted by the CTL hybrids as early as 3 h following stimulation. We propose that the immediate supply of IL-2 by such memory CTL enhances antigenic response of other, IL-2-dependent T cells.