Fas-independent cytotoxicity mediated by human CD4(+) CTL directed againstherpes simplex virus-infected cells

The present study was undertaken to clarify the mechanisms of cytotoxicity mediated by virus-specific human CD4(+) CTLs using the lymphocytes of famil y members with a Fas gene mutation. CD4(+) CTL bulk lines and clones direct ed against HSV-infected cells were established from lymphocytes of a patien t with a homozygous Fas gene mutation and of the patient's mother. HSV-spec ific CD4(+) CTLs generated from lymphocytes of the patient and her mother e xerted cytotoxicity against HSV-infected cells from the patient (Fas(-/-)) and from her mother (Fas(+/-)) to almost the same degree in an HLA class II -restricted manner. mRNAs for the major mediators of CTL cytotoxicity, Fas ligand, perforin, and granzyme B, were detected in these CD4(+) CTLs using the RT-PCR and flow cytometry, The cytotoxicity of the HSV-specific CD4(+) CTLs appeared to be Ca2+-dependent and was almost completely inhibited by c oncanamycin A, a potent inhibitor of the perforin-based cytotoxic pathway. Although the Fas/Fas ligand system has been reported to be the most importa nt mechanism for CD4(+) CTL-mediated cytotoxicity in the murine system, the present findings strongly suggest that granule exocytosis, not the Fas/Fas Ligand system, is the main pathway for the cytotoxicity mediated by HSV-sp ecific human CD4(+) CTLs.