A vision of cell death: Fas ligand and immune privilege 10 years later

Immune privilege is a term applied to organs that have a unique relationship with the immune response. These sites prohibit the spread of inflammation, since even minor episodes can threaten organ integrity and function. Once thought to be a passive process relying on physical barriers, immune privilege is now viewed as an active process, which uses multiple mechanisms to maintain organ function. The prototypic organ of immune privilege has been the eye, where the spread of inflammation can threaten vision. Nearly 10 years ago, we discussed the finding that Fas ligand (FasL) was constitutively expressed in the eye and played a major role in immune privilege by inducing apoptosis in inflammatory cells that enter the eye. In this review, we reexamine the original evidence for the role of FasL in immune privilege, update progress on some of the concepts, and discuss some of the issues that remain unresolved.