Ocular immunosuppressive microenvironment.

Over the past 30 years, it has become evident that within the ocular microenvironment there are active mechanisms of immunoregulation and immunosuppression. The immunoregulation and immunosuppression are mediated by the constitutive presence of neuropeptides found in aqueous humor. Each of these immunosuppressive neuropeptides contributes in its own way to suppress induction of delayed-type hypersensitivity and to induce regulatory immunity. Collectively, the neuropeptides in aqueous humor suppress the activation of Th1 cells while promoting the induction of CD25+ CD4+ regulatory T cells. The central mediator of aqueous humor regulation of immunity is the neuropeptide alpha-melanocyte stimulating hormone (alpha-MSH). This ocular system of immunoregulation and immunosuppression through alpha-MSH not only suppresses immunogenic inflammation, but also actively manipulates immunity to make the immune response itself immunosuppressive.