Functional Targeting of ILC2s and ILC3s reveals selective roles in intestinal fibrosis and homeostasis.

Innate lymphoid cells (ILCs) are long-lived tissue-resident analogues to T helper cell subsets that lack antigen-specific receptors. Understanding the roles of specific ILC subsets in chronic inflammation and fibrosis has been hampered by a lack of adequate tools for their selective targeting. Here, we used two Cre-deleter strains, Il17rb-CreERT2-eGFP and Rorc-Cre, to selectively delete RORa, a master transcriptional regulator, in ILC2s and ILC3/Th17 cells, respectively. Deletion of RORa in ILC2s led to a significant loss of gastrointestinal ILC2s, a concomitant increase in ILC3s, elevated Th17-type responses, and heightened susceptibility to Crohn's-like fibrosis in a Salmonella infection model. In contrast, RORa deletion in ILC3/Th17 cells reduced IL-17 production, protecting against fibrosis. We further confirmed the role of IL-17 and ILC3 in fibrotic responses using isolithocholic acid (isoLCA), a microbially-derived secondary bile acid and ROR?t inverse agonist. In ROR?t reporter and Th17-deficient Rag1-/- mice, isoLCA reduced IL-17 production by ILC3s. In the context of intestinal fibrosis, we show that isoLCA attenuates collagen deposition and fibrotic pathology by dampening ROR?t-dependent IL-17 production by ILC3s. These findings reveal a novel interplay between ILC2s and ILC3s in gut homeostasis and demonstrate the therapeutic potential of targeting ROR?t in ILC3s as a strategy for preventing fibrosis. Overall design: RNA-seq profiling of primary intestine fibroblasts treated with IL-17A (20 ng/mL or 200 ng/mL) for 24 hours, or untreated control cells.