TLR7 Engagement on Dendritic Cells Enhances Autoreactive Th17 Responses via Activation of ERK

In this study, we showed that TLR7 activation significantly promoted interphotoreceptor retinoid-binding protein (IRBP)-specific Th17 responses by upregulating RORγt, IL-17, GM-CSF, and IL-23R expression in experimental autoimmune uveitis mice. In vivo administration of CL097 activated dendritic cells (DCs) and endowed them with an increased ability to activate IRBP-specific Th17 cells. CL097-treated DCs (CL097-DCs) formed a cytokine milieu that favored the generation and maintenance of Th17 cells by stimulating IL-1β, IL-6, and IL-23 expression. Furthermore, IRBP-specific T cells from immunized mice injected with CL097-DCs produced more IL-17 and transferred more severe experimental autoimmune uveitis than did those from mice injected with DCs. The enhanced immunostimulatory activities of CL097-DCs depended on JNK, ERK, and p38 activation. Blockade of ERK, but not p38 or JNK, completely abolished the Th17 responses induced by CL097-DCs. Collectively, our findings suggest that CL097 treatment significantly promotes autoreactive IL-17⁺ T cell responses through enhancing DC activation, which is mediated, at least in part, via the activation of ERK signaling.