TH17 cells contribute to uveitis and scleritis and are expanded by IL-2 and inhibited by IL-27/STAT1

T-helper type 17 cells (T(H)17) are implicated in rodent models of immune-mediated diseases. Here we report their involvement in human uveitis and scleritis, and validate our findings in experimental autoimmune uveoretinitis (EAU), a model of uveitis. T(H)17 cells were present in human peripheral blood mononuclear cells (PBMC), and were expanded by interleukin (IL)-2 and inhibited by interferon (IFN)-gamma. Their numbers increased during active uveitis and scleritis and decreased following treatment. IL-17 was elevated in EAU and upregulated tumor necrosis factor (TNF)-alpha in retinal cells, suggesting a mechanism by which T(H)17 may contribute to ocular pathology. Furthermore, IL-27 was constitutively expressed in retinal ganglion and photoreceptor cells, was upregulated by IFN-gamma and inhibited proliferation of T(H)17. These findings suggest that T(H)1 cells may mitigate uveitis by antagonizing the T(H)17 phenotype through the IFN-gamma-mediated induction of IL-27 in target tissue. The finding that IL-2 promotes T(H)17 expansion provides explanations for the efficacy of IL-2R antibody therapy in uveitis, and suggests that antagonism of T(H)17 by IFN-gamma and/or IL-27 could be used for the treatment of chronic inflammation.     

Interleukin 27 Induces the Expression of Complement Factor H (CFH) in the Retina

Complement factor H (CFH) is a central regulator of the complement system and has been implicated in the etiology of age-related macular degeneration (AMD), a leading cause of blindness in the elderly. In view of previous studies showing that reduced expression of CFH in the retina is a risk factor for developing AMD, there is significant interest in understanding how CFH expression is regulated in the retina. In this study, we have shown that the anti-inflammatory cytokine, IL-27, induced CFH expression in mouse retinal cells and human retinal pigmented epithelial cells (RPE) through STAT1-mediated up-regulation of Interferon Regulatory Factor-1 (IRF-1) and IRF-8. We further show that cells in the ganglion and inner-nuclear layers of the retina constitutively express IRF-1 and IRF-8 and enhanced CFH expression in the retina during ocular inflammation correlated with significant increase in the expression of IRF-1, IRF-8 and IL-27 (IL-27p28 and Ebi3). Our data thus reveal a novel role of IL-27 in regulating complement activation through up-regulation of CFH and suggest that defects in IL-27 signaling or expression may contribute to the reduction of CFH expression in the retina of patients with AMD.