TNFα suppresses IFNγ-induced MHC class II expression on retinal pigmented epithelial cells cultures

Purpose: One major consequence of retinal pigment epithelium (RPE) cell activation during autoimmune uveitis is the induction of MHC II molecules expression at their surface. IFN gamma is regarded as the main cytokine involved in this induction. As TNF alpha plays a central role in autoimmune uveitis, we investigated its effects on IFN gamma-mediated MHC II induction on RPE cells. Methods: Retinal pigment epithelium cells (ARPE-19) were stimulated with IFN gamma, TNF alpha and the anti-TNF alpha antibody infliximab. The expression of MHCII and ICAM-1 was analysed by flow cytometry. The activation and expression of IRF-1 and STAT-1, two proteins involved in IFN gamma-signalling pathway, were analysed by WB. Class II transactivator (CIITA) expression was monitored by qRT-PCR and immunoprecipitation. Results: TNF alpha inhibits IFN gamma-induced MHC II expression on ARPE cells in a dose-dependent manner. Infliximab completely reverses the inhibitory effect of TNF alpha. We did not observe an inhibitory effect of TNF alpha on the expression of ICAM-1 induced by IFN gamma. Similarly, IFN gamma-induced STAT1 phosphorylation and IRF1 expression were not affected by TNF alpha. On the contrary, we found that TNF alpha suppresses IFN gamma-induced CIITA mRNA accumulation and protein expression. Conclusion: TNF alpha inhibits IFN gamma-induced MHC II expression in RPE cells. This inhibitory effect was reversed by infliximab and was not because of a global inhibition of IFN gamma -mediated RPE cell activation but rather to a specific down-regulation of CIITA expression. Those findings are consistent with the role of TNF alpha in the resolution of inflammation and might help to elucidate the complex development of autoimmune uveitis.