Neuroimmunomodulation in immune privilege: role of neuropeptides in ocular immunosuppression

The microenvironments of the eye and brain are physiologically adapted to protect their delicate structures and functions from damaging immunogenic inflammation (delayed-type hypersensitivity). This adaptation is immune privilege. Aqueous humor, the fluid filling the ocular anterior chamber, suppresses antigen-stimulated primed T cells from mediating inflammation by inhibiting the production of the proinflammatory lymphokine interferon gamma. This suppression is mediated by immunosuppressive cytokines and neuropeptides constitutively produced in the eye and released into aqueous humor. Cerebrospinal fluid has similar immunosuppressive activities, cytokines, and neuropeptides as aqueous humor, indicating that similar mechanisms may mediate immune privilege in the eye and brain. The importance of neuropeptides in mediating immunosuppression indicates that immunosuppressive neuroimmunomodulation has a role in preventing induction of immunogenic inflammation within immune-privileged tissues.