Gregory F. Sonnenberg

Fibroblasts exhibit phenotypic and functional heterogeneity in chronic inflammatory diseases, but how these changes impact immune outcomes remains poorly understood. We identified that a fibroblast population expressing insulin-like growth factor 1 (IGF1) was reduced in patients with inflammatory bowel disease (IBD). Using mouse models of intestinal inflammation, we found cross-talk between IGF1-expressing fibroblasts and group 3 innate lymphoid cells (ILC3s). IGF1 stimulation limited the ability of ILC3s to produce C-X-C motif chemokine ligand 10 (CXCL10) and recruit plasmacytoid dendritic cells (pDCs) to restrain gut inflammation. We propose that this regulatory pathway is conserved in human ILC3s but may become impaired in IBD. Our results define that anti-inflammatory fibroblasts safeguard the gut through regulation of an innate lymphocyte–pDC axis.

Regulatory T (Treg) cells that recognize dietary- or microbiota-derived antigens express RORγt and are essential for immune tolerance in the intestine. A recent paradigm shift found these cells require major histocompatibility complex class II (MHCII) on RORγt+ antigen-presenting cells (APCs) rather than conventional dendritic cells (cDCs) for signal one. Here, we evaluate signal two and unexpectedly find that costimulatory molecules B7-1 (CD80) and B7-2 (CD86) antagonize the generation of microbiota-specific RORγt+ Treg cells. Gain-of-function or loss-of-function therapeutics targeting B7 via CTLA-4 exert reciprocal effects on the generation of microbiota-specific RORγt+ Treg cells. This axis was independent of B7 on RORγt+ APCs but required MHCII on this cell type. Finally, CTLA4-Ig treatment restores microbiota-specific RORγt+ Treg cell generation and protects from experimental intestinal inflammation induced by pathobiont colonization with IL-10R signaling blockade. These results define that RORγt+ Treg cells are uniquely restrained by B7 costimulation, while CTLA4-Ig enhances immune tolerance in the intestine when acting cooperatively with RORγt+ APCs.

Oral tolerance represents a hallmark of intestinal mucosal immunity to prevent inflammatory responses to harmless natural antigens, such as dietary components or commensal organisms. According to recent studies, RORγt⁺ antigen-presenting cell (APC) contributes to intestinal homeostasis, including oral tolerance, through inducing microbiota- and dietary antigen-specific Tregs. Here we identify a cis transcriptional regulatory element that distinguishes RORγt⁺ APCs from other of RORγt⁺ cell types. This sequence within Rorc gene loci, OCR369 governs RORγt expression in ILC3s and other RORγt⁺ APCs, but not T cells, through interaction with RUNX3 and formation of chromatin loops. OCR369 deletion results in a significant reduction of RORγt⁺ APCs in mLN around the weaning period and ILC3s in mLN and intestines of adult mice, accompanied by a decrease in RORγt⁺ Tregs and spontaneous inflammation in the small intestine. Mechanistically, the reduction in RORγt⁺ APCs, including both DC-like cells and MHCII⁺ ILC3s, impairs the development of both dietary antigen-specific and microbiota-specific RORγt⁺ Tregs and results in the loss of oral tolerance, thereby increasing allergy susceptibility. Thus, our findings identify a specific regulatory mechanism for RORγt expression in RORγt⁺ APCs and underscore the pivotal role of these cell types in mediating oral tolerance and maintaining intestinal health.