IL-17A controls CNS autoimmunity by regulating gut microbiota and inducing regulatory T cells

A disrupted equilibrium among gut microbiota, IL-17A-producing CD4 T-cells (Th17), and regulatory CD4 T-cells (Treg) have been linked with the pathobiology of multiple sclerosis (MS). While gut microbiota can regulate both Treg and Th17 cells, the impact of IL-17A on this gut-immune connection remains unclear. Utilizing HLA-DR3 transgenic mouse model of MS, we show that IL-17A deficiency (HLA-DR3.IL17A-/-) resulted in milder disease characterized by increased Tregs and expansion of Treg-promoting gut microbes, including Prevotella. Cohousing HLA-DR3 mice with HLA-DR3.IL17A-/- transferred the milder disease phenotype and associated microbiota changes to DR3 mice, highlighting the dominant role of gut microbiota in Treg induction and disease amelioration. DR3.IL17A-/- mice also showed a higher abundance of functional pathways linked with short-chain fatty acid synthesis and elevated IL-10 in dendritic cells. Enrichment of the Treg-promoting PPAR signaling pathway expression in the colon of HLA-DR3.IL17A-/- mice and following Prevotella administration in HLA-DR3 mice underscores the importance of gut microbiota in IL-17A-mediated immune regulation. Thus, our study uncovers a previously unappreciated role for IL-17A in shaping gut microbiota and immune regulation, with far-reaching implications for MS treatment. One-Sentence SummaryIL-17A modulates Treg and gut microbiota to control EAE