NK cells in the eye

Tissues within the eye have a limited capacity to regenerate.Consequently, immune-mediated inflammation can have devastating consequences for vision. However, anatomical, physiological and dynamic immunoregulatory processes limit inflammation and immune-mediated responses within the eye-a phenomenon known as immune privilege. Immune privilege limits the activities of both the adaptive and innate immune systems. Cells lining the cornea and within the retina fail to express MHC class I molecules, making them vulnerable to natural killer (NK) cell-mediated lysis. NKT cells are clearly important for the induction of tolerance in the eye and for the survival of corneal allografts. NK cells have divergent roles in microbial infections of the ocular surface and autoimmune diseases of the interior of the eye. The pathogenesis of HSVK is immune-mediated and involves the participation of CD4+ T cells and neutrophils. NK cells indirectly contribute to the pathogenesis of HSVK by promoting the migration of neutrophils into the HSV-infected cornea. By contrast, NK cells and NKT cells participate in the resolution of Pseudomonas keratitis through their coordinated production of IFN, which activates neutrophils and enhances the clearance of bacteria from the infected cornea. The role of NK cells in intraocular inflammation is unclear. Some reports suggest that NK cells are necessary for the full development of EAU, while other studies indicate that NK cells are necessary for the resolution of EIU. Although NK cells can recognize and kill uveal melanoma cells in vitro, the presence of MIF and TGF in the AH and vitreous body silences NK cell-mediated surveillance of intraocular tumor. The eye is indeed an "immunological microcosm" in which a wide array of immunological activities can be observed, including NK cell-mediated processes.