FAS-BASED LYMPHOCYTE-MEDIATED CYTOTOXICITY AGAINST SYNGENEIC ACTIVATED LYMPHOCYTES - A REGULATORY PATHWAY

To investigate the possibility that Fas-based immune regulation and Fa s-based T cell-mediated cytotoxicity (F-CMC) are causally related, we explored the latter in activated lymphocyte populations. These were sh own to contain effector cells exerting cytotoxicity via an F-CMC mecha nism which could be differentially triggered by PMA and ionomycin. F-C MC operated in trans, requiring an lpr (Fas) product on target cells a nd a gld product on effector cells. Activated lymphocyte populations w ere also shown to contain F-CMC target cells. Activated lymphocyte pop ulations thus contained both effector and target F-CMC cells,which cou ld lyse each other. Fas-based cytotoxicity can thus lead to the lysis of syngeneic activated lymphocytes, consistent with the possibility of its participation in the down-regulation of immune responses, and mor e generally offering a model of socially controlled, direct membrane-m ediated cell death.