TL1A is a central regulator of group 3 innate lymphoid cell function in colitis

Inflammatory bowel disease (IBD) results from a dysregulated interaction between the microbiota and a genetically susceptible host. Genetic studies have linked TNFSF15 polymorphisms and its protein TNF-like ligand 1A (TL1A) with IBD, but the functional role of TL1A in linking tissue homeostasis and intestinal inflammation is not known. Here, using cell-specific genetic deletion models, we report an essential role for CX3CR1+ mononuclear phagocyte (MNP)-derived TL1A, which is induced by adherent IBD-associated microbiota, in regulating group 3 innate lymphoid cell (ILC3) production of IL-22 and mucosal healing in acute colitis. However, in contrast to this protective role in acute colitis, TL1A-dependent expression of OX40L in MHCII+ ILC3 during colitis leads to co-stimulation of antigen-specific T cells and is required for chronic T cell colitis. These results identify a new role for ILC3 in regulating intestinal T cells and reveal a central role for TL1A in regulating ILC3 barrier immunity during colitis.