A vision of cell death: insights into immune privilege.

Immune privilege is a term applied to several 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. The most prominent examples of these are the eye, brain and reproductive organs where immune responses either do not proceed, or proceed in a manner different from other areas. Once thought to be a passive process relying on physical barriers, immune privilege can now be viewed as an active process that utilizes multiple mechanisms to maintain organ function. Recently there has been a renewed interest in immune privilege when it was shown that two privileged sites (the eye and testes) constitutively express FasL, which functions by killing lymphoid cells that invade these areas. Here we will examine the role of FasL in immune privilege and discuss how this molecule interacts with other elements of the inflammatory response to maintain organ integrity in the face of potentially damaging immune reactions.