Prostaglandin E2 and SOCS1 have a role in intestinal immune tolerance

Interleukin 10 (IL-10) and regulatory T cells (Tregs) maintain tolerance to intestinal microorganisms. However, Il10^-/- Rag2^-/- mice, which lack IL-10 and Tregs, remain healthy, suggesting the existence of other mechanisms of tolerance. Here, we identify suppressor of cytokine signalling 1 (SOCS1) as an essential mediator of immune tolerance in the intestine. Socs1^-/- Rag2^-/- mice develop severe colitis, which can be prevented by the reduction of microbiota and the transfer of IL-10-sufficient Tregs. Additionally, we find an essential role for prostaglandin E2 (PGE2) in the maintenance of tolerance within the intestine in the absence of Tregs. Socs1^-/- dendritic cells are resistant to PGE2-mediated immunosuppression because of dysregulated cytokine signalling. Thus, we propose that SOCS1 and PGE2, potentially interacting together, act as an alternative intestinal tolerance mechanism distinct from IL-10 and Tregs.