Fas and other cell death signaling pathways.

The Fas system ensures, within the immune system, one of the two main pathways of T-cell mediated cytotoxicity, and, importantly, at least part of the downregulation of immune responses. Recently, Fas has been increasingly implicated in other functions, such as protection of immune privileged tissues and disposal of cells undergoing genomic alterations. The Fas system can be viewed as a cell death signal, linking extracellular information to the cell death execution stage. In this review, the Fas pathway will be described, compared to the other known T-cell mediated cytotoxicity mechanism, and then more generally to other cell death signals. The general features of cell death signaling will be emphasized as well as the peculiarities of the Fas system.