SYNERGY BETWEEN T-CELL RECEPTOR AND FAS (CD95 APO-1) SIGNALING IN MOUSE THYMOCYTE DEATH/

Administration of anti-TCR/CD3 epsilon antibody in vivo or in thymic o rgan culture results in the apoptotic death of CD4(+)/CD8(+) thymocyte s. In contrast, purified thymocytes in suspension culture are resistan t to TCR/CD3 epsilon-induced apoptotic death. We show that induction o f thymocyte death, in suspension culture, can be induced by the combin ation of TCR/CD3 epsilon and Fas (CD95/Apo-1) signaling. No significan t thymocyte death was observed after in vitro Fas cross-linking unless TCR/CD3 epsilon was simultaneously co-cross-linked or metabolic inhib itors such as actinomycin D were added. Furthermore, TCR/CD3 epsilon a nd Fas synergy did not operate through upregulation of Fas but by faci litation of the Fas-mediated death signal. Both TCR(mid/lo)/HSA(hi)/CD 4(+)/CD8(+) (double positive) and TCR(hi)/HSA(lo)/CD4(+)/CD8(-) or CD4 (-)/CD8(+) (single positive) thymocytes were susceptible to death indu ced by co-cross-linking of TCR/CD3 epsilon and Fas. Our results reveal a signaling synergy between the Fas and TCR/CD3 epsilon complex that has important implications for our understanding of in vivo vs in vitr o models of thymocyte deletion. (C) 1996 Academic Press, Inc.