Endoscopic photoconversion reveals unexpectedly broad leukocyte trafficking to and from the gut.

Gut-microbiota/immune-cell interactions play important roles in immune system homeostasis and responsiveness, but surprisingly little is known about the movement of immune cells into and, particularly, out of the gut. We used a minimally invasive system to monitor immigration of diverse innate and adaptive immune-cell types to the intestine from a distant lymph node, and a novel endoscopic adaptation of the system to follow their emigration from the distal colon to nearby and distal lymphoid organs. We uncovered an unexpectedly broad movement of leukocytes to and from the gut at steady state, as well as subset-specific migration proclivities. Moreover, we evidenced a critical cellular link between an intestinal microbe, segmented filamentous bacteria, and an extraintestinal autoinflammatory disease, the K/BxN model of arthritis.