Evidence for extrathymic generation of regulatory T cells specific for a retinal antigen.

Background: Thymic expression of a photoreceptor cell antigen, interphotoreceptor retinoid-binding protein, is known to generate regulatory T cells (T(reg)) that prevent spontaneous autoimmune disease of the retina. However, the contribution of other endogenous, tissue-specific antigens (Ags) expressed in the retina to the generation of T(reg) is uncertain.

Methods: Transgenic mice that express beta-galactosidase (beta-gal) in photoreceptor cells, together with beta-gal-specific T cell receptor transgenic mice, were used to study the induction of T(reg) in vivo.

Results: Transgenic expression of beta-gal on the arrestin promoter led to a spontaneous immunoregulatory response that inhibited the development of immune responses to beta-gal. The regulation was transferred by CD3+4+25+ T(reg). Several strategies were then used to show that beta-gal expressed in the retina supported spontaneous, thymus-independent T(reg) development. The endogenous T(reg) also differed from the T(reg) induced by Ag inoculation into the anterior chamber of the eye.

Conclusion: These results demonstrate that retinal expression of very small amounts of a tissue-specific Ag can generate T(reg) in the periphery.