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

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Abstract
We investigated the cytotoxicity mechanisms of alloantigen-specific human CD4+ and CD8+ cytotoxic T lymphocytes (CTLs) using cells from family members 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+/− cell lines that were established from B-lymphocytes of a patient with Fas deficiency and her mother, respectively. Both CD4+ and CD8+CTL bulk lines and clones directed against allogeneic HLA antigens exerted cytotoxicity against Fas−/− and Fas+/− cells to almost the same degree. The cytotoxicity of CD4+ and CD8+ CTLs appeared to be Ca2+-dependent and was completely inhibited by concanamycin A, an inhibitor of perforin-mediated cytotoxicity. 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 TH0, 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.