FAS and autoimmune lymphoproliferative syndrome: Initially, based on the discovery that defects in Fas signaling led to the accumulation of T cells in autoimmune lymphoproliferative syndrome (ALPS) patients and lpr/gld mice, and the requirement for Fas in an in vitro model of activated T cell death it was assumed that Fas signaling was required for the contraction of T cell responses (Watanabe-Fukunaga et al., 1992; Takahashi et al., 1994; Brunner et al., 1995; Dhein et al., 1995; Fisher et al., 1995; Rieux-Laucat et al., 1995).