FAS INVOLVEMENT IN CYTOTOXICITY MEDIATED BY HUMAN NK CELLS

Lysis of target cells (TC) by cytolytic lymphocytes involves the secre tion of cytoplasmic granules containing perforin and serine esterases by the effector cell (EC). Recently, a granule-independent cytolytic m echanism involving the interaction of the apoptosis-triggering Fas ant igen (CD95) with Fas Ligand (Fast) has been revealed in T cells. Howev er, whether the Fas lytic pathway also functions in NH cells has not b een established. We purified human peripheral NK cells (>98% CD56(+)) and found that PMA and ionomycin treatment upregulated Fas(+) message and stimulated the NK cells to lyse a Fast TC. This lysis was partiall y inhibited by the anti-Fas-blocking antibody M3 or by Fas . Fc fusion protein. We also found that Fast is constitutively expressed on the h uman NK-like leukemia cell line YT-INDY and that YT-INDY utilizes a Ca 2+-independent Pas lytic pathway, as well as the granule pathway. We h ave previously shown that CD28/B7 interactions are involved in TC reco gnition by YT-INDY. K562 cotransfected with Fas and B7-1 (K562/Fas/B7) was lysed by YT-INDY at a higher level than a vector-transfected K562 line, whereas K562 transfected with Fas alone was not. Lysis of K562/ Fas/B7 cotransfectants was partially Fas-mediated, as indicated by the presence of Ca2+-independent, M3-inhibitable lysis, Ca2+-independent, Fas-mediated lysis of several TC by YT-INDY was inhibited by anti-CD2 8 antibody. Anti-LFA-1 also inhibited Fas-mediated cytotoxicity in YT- INDY. Thus, fresh human NK cells and the human NK-like cell line YT-IN DY are capable of using the Fas lytic pathway, In YT-INDY, CD28/B7 and LFA-1/ICAM interactions appear to influence the Fas lytic pathway. (C ) 1995 Academic Press, Inc.