Regulation of ocular immune responses.

The existence of immune privilege in numerous tissues and organs, including the eye, has been re-emphasised during the past few years, and experimental studies have begun to unravel the multiple mechanisms, both passive and active, that make privilege possible. In this review, recent evidence bearing on the factors responsible for immune privilege in the anterior chamber of the eye is described. One dimension of ocular immune privilege depends upon local factors that limit and modify the expression of immunity. As a consequence, the local expression of immunogenic inflammation is largely curtailed within the eye. Another dimension of ocular immune privilege concerns the modification of induction of systemic immunity to antigens placed within, or arising from, the eye. Systemic responses to ocular antigens are devoid of delayed hypersensitivity T cells and complement-fixing antibodies, and the stage for these stereotypic responses is set by factors within the ocular microenvironment acting on indigenous antigen presenting cells. Overall, regulation of immune responses directed at ocular antigens appears to be designed to prevent inflammation from disrupting the visual axis and thereby causing blindness.