Anti-inflammatory effect of retinoic acid on experimental autoimmune uveoretinitis

Aims To determine whether an active metabolite of vitamin A, all-trans retinoic acid (ATRA), reduces inflammation in experimental autoimmune uveoretinitis (EAU). Methods Naive CD4(+) T cells were activated with anti-CD3, anti-CD28 and transforming growth factor (TGF)-beta, in the presence or absence of ATRA. Intracellular expression of transcription factor forkhead box P3 (Foxp3) and interleukin (IL)-17 in the activated CD4(+) T cells was assessed by flow cytometry. C57BL/6 mice were immunised with human interphotoreceptor retinoid binding protein peptide 1-20 (IRBP(1-20)). ATRA was administered intraperitoneally every other day (0.2 mg/mouse per day) from day 0 to day 21. In vivo-primed draining lymph node cells from vehicle-treated or ATRA-treated mice were stimulated with IRBP(1-20) and the culture supernatant fraction was harvested for assay of interferon (IFN)-gamma and IL-17 by ELISA. Results ATRA synergised with TGF-beta to induce Foxp3(+) T regulatory cells (Treg) and reciprocally inhibited development of IL-17-producing T helper cells (Th17) induced by TGF-beta and IL-6. ATRA treatment reduced the severity of EAU clinically, and IFN-gamma and IL-17 production were significantly reduced in ATRA-treated mice. Conclusion These findings demonstrate that ATRA treatment ameliorates severity of EAU and reduces the Th1/Th17 responses. ATRA may represent a new therapeutic modality for human refractory uveitis.