Regulatory T cells with superior immunosuppressive capacity emigrate from the inflamed colon to draining lymph nodes.

Foxp3+ Regulatory T cells (Tregs) play a critical role in the maintenance of colon homeostasis. Here we utilized photoconvertible KikGR mice to track immune cells from the caecum and ascending (proximal) colon in the steady state and DSS-induced colitis. We found that Tregs from the proximal colon (colonic migratory Tregs) migrated exclusively to the distal part of mesenteric lymph nodes (dMLN) in an S1PR1-dependent process. In the steady state, colonic migratory CD25+ Tregs expressed higher levels of CD103, ICOS, LAG3 and CTLA-4 in comparison with pre-existing LN Tregs. Intestinal inflammation led to accelerated Treg replacement in the colon, bidirectional Treg migration from the colon to dMLN and vice versa, as well as increases in Treg number, proliferation and expression of immunosuppressive molecules. This was especially apparent for CD25 very high Tregs induced in colitis. Furthermore, colonic migratory Tregs from the inflamed colon included more interleukin (IL)-10 producing cells, and demonstrated greater inhibition of T-cell proliferation in comparison with pre-existing LN Tregs. Thus, our results suggest that Tregs with superior immunosuppressive capacity are increased both in the colon and dMLN upon inflammation. These Tregs recirculate between the colon and dMLN, and are likely to contribute to the downregulation of intestinal inflammation.