PARTICIPATION OF TARGET FAS PROTEIN IN APOPTOSIS PATHWAY INDUCED BY CD4(-CELLS() TH1 AND CD8(+) CYTOTOXIC T)

The results presented here provide evidence that the presence of Pas p rotein in target cells is essential to permit cytotoxicity (resulting in apoptosis) mediated by cloned CD4(+) Th1 cells. Using mitogen-activ ated B cells as targets, antigen-dependent lysis by CD4(+) Th1 effecte rs was observed with MRL/MpJ+ but not with MRL/MpJ-lpr targets. The co ngenic MRL/MpJ-lpr strain is defective in Pas expression. Target cells from various lymphoid tissues of C3H.MRL-lpr mice were also resistant to the lectin-dependent cytotoxicity of Th1 effecters, whereas C3H/He J targets were sensitive. Moreover, a rapid DNA fragmentation prior to Cr-51 release was induced only in C3H/HeJ targets. Thus, cytotoxicity induced by Th1 effecters correlates with target Fas expression. In co ntrast to Th1 effectors, CD8(+) cytotoxic T lymphocytes (CTLs) killed C3H.MRL-lpr targets. When cytotoxicity was assayed in the presence of EGTA and MgCl2, which chelates extracellular Ca2+ [(Ca2+)(ext)], only C3H.MRL-lpr targets became resistant to CD8(+) CTLs. This (Ca2+)(ext)- independent cytotoxicity of both Th1 and CD8(+) effecters could be inh ibited with unlabeled C3H/HeJ thymocytes or with a transfectoma carryi ng a murine Fas-human mu gene construct. In comparison, C3H.MRL-lpr th ymocytes and the nontransfected parental cell line were poor inhibitor s. Our study demonstrates that CD4(+) Th1 cells and CD8(+) CTLs differ in their (Ca2+)(ext)-dependent cytotoxicity but share a (Ca2+)(ext)-i ndependent cytotoxicity that requires participation of Fas molecules f or cytotoxic signal transduction leading to target apoptosis.