Cell-mediated cytotoxicity (CMC) has traditionally been thought to involve the release of granule components, including perforin and granzymes, from the effector cell (EC) onto the target cell (TC) membrane. Recently, a granule-independent cytolytic mechanism involving the interaction of Fas antigen (CD95) with Fas ligand has been described. We have generated antisense perforin (YT-xP1) and granzyme B (YT-xGrB) transfectants of the human NK-like cell line YT-INDY. These transfectants have greatly reduced cytolytic ability when compared to the vector-transfected control cell line (YT-neo). In this study, however, we demonstrate that the antisense transfectants retain the ability to lyse Fas+ TC. Fas-mediated lysis is Ca2+- independent and is inhibited by a monoclonal anti-Fas blocking Ab, M3. By RT-PCR, we detect message for FasL in unstimulated YT-xP1 and YT-xGrB transfectants, as well as in unstimulated YT-neo. By flow cytometry, we show that YT-neo, YT-xGrB, and YT-xP1 constitutively express surface FasL. These data indicate that in a human NK-like cell line, similar to the murine system, the granule and Fas pathways of cytotoxicity function independently of one another. At least with the TC tested, our data also indicate that the granule and Fas pathways together account for nearly 100% of the cytolytic ability of YT-INDY.
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