Granule exocytosis, and not the Fas/Fas ligand system, is the main pathwayof cytotoxicity mediated by alloantigen-specific CD4(+) as well as CD8(+) cytotoxic T lymphocytes in humans

We investigated the cytotoxicity mechanisms of alloantigen-specific human C D4(+) and CD8(+) cytotoxic T lymphocytes (CTLs) using cells from family mem bers with the Fas gene mutation. Alloantigen-specific CD4(+) and CD8(+) CTL bulk lines and clones were generated from 2 individuals by stimulation of their peripheral blood lymphocytes with allogeneic Fas(-/-) or Fas(+/-) cel l lines that were established from B-lymphocytes of a patient with Fas defi ciency and her mother, respectively. Both CD4(+) and CD8(+) CTL bulk lines and clones directed against allogeneic HLA antigens exerted cytotoxicity ag ainst Fas(-/-) and Fas(+/-) cells to almost the same degree, The cytotoxici ty of CD4(+) and CD8(+) CTLs appeared to be Ca2+-dependent and was complete ly inhibited by concanamycin A, an inhibitor of perforin-mediated cytotoxic ity. Messenger RNAs for the major mediators of CTL cytotoxicity, Fas ligand , perforin, and granzyme B were all detected in these CD4(+) CTLs with the use of the reverse transcriptase polymerase chain reaction. The majority of CD4(+) CTL clones that showed Fas-independent cytotoxicity were T(H)0, as determined by their cytokine production profile. These data, obtained with the use of a novel experimental system, clearly show that the main pathway of cytotoxicity mediated by alloantigen-specific human CD4(+) as well as by CD8(+) CTLs is granule exocytosis, and not the Fas/Fas ligand system. (Blo od, 2000; 95:2352-2355) (C) 2000 by The American Society of Hematology.