Arid5a Mediates an IL-17–Dependent Pathway That Drives Autoimmunity but Not Antifungal Host Defense

IL-17 contributes to the pathogenesis of certain autoimmune diseases, but conversely is essential for host defense against fungi. Ab-based biologic drugs that neutralize IL-17 are effective in autoimmunity but can be accompanied by adverse side effects. Candida albicans is a commensal fungus that is the primary causative agent of oropharyngeal and disseminated candidiasis. Defects in IL-17 signaling cause susceptibility to candidiasis in mice and humans. A key facet of IL-17 receptor signaling involves RNA-binding proteins, which orchestrate the fate of target mRNA transcripts. In tissue culture models we showed that the RNA-binding protein AT-rich interaction domain 5A (Arid5a) promotes the stability and/or translation of multiple IL-17–dependent mRNAs. Moreover, during oropharyngeal candidiasis, Arid5a is elevated within the oral mucosa in an IL-17–dependent manner. However, the contribution of Arid5a to IL-17–driven events in vivo is poorly defined. In this study, we used CRISPR-Cas9 to generate mice lacking Arid5a. Arid5a−/− mice were fully resistant to experimental autoimmune encephalomyelitis, an autoimmune setting in which IL-17 signaling drives pathology. Surprisingly, Arid5a−/− mice were resistant to oropharyngeal candidiasis and systemic candidiasis, similar to immunocompetent wild-type mice and contrasting with mice defective in IL-17 signaling. Therefore, Arid5a-dependent signals mediate pathology in autoimmunity and yet are not required for immunity to candidiasis, indicating that selective targeting of IL-17 signaling pathway components may be a viable strategy for development of therapeutics that spare IL-17–driven host defense.