A dominant interfering mutant of FADD/MORT1 enhances deletion of autoreactive thymocytes and inhibits proliferation of mature T lymphocytes.

Members of the tumour necrosis factor receptor family that contain a death domain have pleiotropic activities. They induce apoptosis via interaction with intracellular FADD/MORT1 and trigger cell growth or differentiation via TRADD and TRAF molecules. The impact of FADD/MORT1-transduced signals on T lymphocyte development was investigated in transgenic mice expressing a dominant negative mutant protein, FADD-DN. Unexpectedly, FADD-DN enhanced negative selection of self-reactive thymic lymphocytes and inhibited T cell activation by increasing apoptosis. Thus signalling through FADD/MORT1 does not lead exclusively to cell death, but under certain circumstances can promote cell survival and proliferation.