Nitric oxide-induced regulatory T cells inhibit Th17 but not Th1 cell differentiation and function.

NO is a free radical with pleiotropic functions. We have shown earlier that NO induces a population of CD4(+)CD25(+)Foxp3(-) regulatory T cells (NO-Tregs) that suppress the functions of CD4(+)CD25(-) effector T cells in vitro and in vivo. We report in this study an unexpected finding that NO-Tregs suppressed Th17 but not Th1 cell differentiation and function. In contrast, natural Tregs (nTregs), which suppressed Th1 cells, failed to suppress Th17 cells. Consistent with this observation, NO-Tregs inhibited the expression of retinoic acid-related orphan receptor γt but not T-bet, whereas nTregs suppressed T-bet but not retinoic acid-related orphan receptor γt expression. The NO-Treg-mediated suppression of Th17 was partially cell contact-dependent and was associated with IL-10. In vivo, adoptively transferred NO-Tregs potently attenuated experimental autoimmune encephalomyelitis. The disease suppression was accompanied by a reduction of Th17, but not Th1 cells in the draining lymph nodes, and a decrease in the production of IL-17, but an increase in IL-10 synthesis. Our results therefore demonstrate the differential suppressive function between NO-Tregs and nTregs and indicate specialization of the regulatory mechanism of the immune system.

Limited peripheral T cell anergy predisposes to retinal autoimmunity.

Autoimmune uveoretinitis accounts for at least 10% of worldwide blindness, yet it is unclear why tolerance to retinal Ags is so fragile and, particularly, to what extent this might be due to defects in peripheral tolerance. To address this issue, we generated double-transgenic mice expressing hen egg lysozyme, under the retinal interphotoreceptor retinoid-binding promoter, and a hen egg lysozyme-specific CD4(+) TCR transgene. In this manner, we have tracked autoreactive CD4(+) T cells from their development in the thymus to their involvement in uveoretinitis and compared tolerogenic mechanisms induced in a variety of organs to the same self-Ag. Our findings show that central tolerance to retinal and pancreatic Ags is qualitatively similar and equally dependent on the transcriptional regulator protein AIRE. However, the lack of Ag presentation in the eye-draining lymph nodes results in a failure to induce high levels of T cell anergy. Under these circumstances, despite considerable central deletion, low levels of retinal-specific autoreactive CD4(+) T cells can induce severe autoimmune disease. The relative lack of anergy induction by retinal Ags, in contrast to the same Ag in other organs, helps to explain the unique susceptibility of the eye to spontaneous and experimentally induced autoimmune disease.