Ocular Immune Privilege and the Faustian Dilemma

JL he eye and the immune system represent discrete organ systems in vertebrates. Each possesses a unique and vital function that ensures the viability of the host, and loss of either or both brings disease and death. For many years, it has been known that the eye and the immune system are joined in a curious phenomenon called "immune privilege." This phenomenon was first described experimentally more than 100 years ago, and for much of that time, immune privilege has been regarded chiefly as a laboratory curiosity. However, recent evidence strongly supports the view that immune privilege is an important physiologic adaptation that contributes in a significant way to the success of vertebrates. The interaction between the immune system and the eye that leads to immune privilege is best approached by considering the functions and challenges of these two very different organ systems. ognize the body's own molecules (autoantigens). Elimination of these autoreactive lymphocytes avoids the direat of autoimmunity. 3. In addition to antigen-recognizing T-cell receptors and antibodies, the immune system must generate an array of effector mechanisms (immune cells and molecules; see Table 1) that are sufficiendy diverse in functional properties to meet the enormously diverse pathogenic strategies devised by the numerous and diverse pathogenic agents in our environment. 4. With such a wide array of functionally distinct effector modalities, the immune system must then fashion particular immune responses in such a manner that protection is provided for individual organs and tissues without compromising the physiologic functions of these vital tissues.