Ocular immune privilege and CTL tolerance

The introduction of antigens into the anterior chamber (AC) of the eye, an immune-privileged site, induces immune responses that effectively eliminate ocular pathogens while minimizing tissue damage that can cause blindness. This specialized immune response, termed AC associated immune deviation (ACAID) is thought to be an evolutionary compromise to preserve the delicate microanatomy of the eye while maintaining ocular immune responses. The injection of soluble antigen in the AC of mice results in systemic tolerance characterized by reduced priming for antigen-specific delayed-type hypersensitivity (DTH) and cytotoxic T lymphocyte (CTL) responses. Similarly, the injection of histo incompatible tumors into the AC of mice reduces priming for DTH responses specific to minor antigens. However, robust tumor-specific CTL responses are induced systemically following this treatment that are capable of eliminating a subsequent injection of the same tumors in the skin or the opposite eye. Interestingly, CTL responses induced by administration of tumors in the AC fail to eliminate the primary ocular tumor. In this review, we compare and contrast CTL responses generated by the injection of soluble or tumor-associated antigens in the AC and discuss mechanisms employed to induce ocular CTL tolerance.