ILC2s navigate tissue redistribution during infection using stage-specific S1P receptors

Lymphocytes can circulate as well as take residence within tissues. The mechanisms by which circulating populations are recruited to infected tissue sites have been characterized, but the extent and molecular basis of tissue-resident cell recirculation is enigmatic. Here, we show that helminth infection- or IL-25-induced redistribution of intestinal tissue-localized group 2 innate lymphoid cells (ILC2s) requires access to the lymphatic vessel network even though secondary lymphoid structures, which are essential signal hubs for adaptive lymphocyte differentiation and dispatch, are dispensable for tissue ILC2 mobilization. IL-25 signals induce a dramatic change in epigenetic landscape of intestinal ILC2s, enabling the expression of sphingosine-1-phosphate (S1P) receptors. S1PR5 is critical for ILC2 exit from intestinal tissue to lymph, whereas S1PR1 plays a dominant role in ILC2 egress from mesenteric lymph nodes to blood circulation and then to lung, where redistributed ILC2s contribute to tissue repair. The requirement of two S1PRs is largely due to the dynamic expression of the tissue-retention marker CD69, which mediates S1PR1 internalization. This stage-specific requirement of different S1P receptors for ILC2 redistribution during infection illustrates that innate and adaptive lymphocytes share a circulatory network frame but employ specialized navigation cues for their distinct migratory requirements. iILC2s were sort-purified from the gut, mesenteric lymph node, and the lung of C57BL/6 mice (iILC2: Lin- CD45+ KLRG1+ ST2-) on day 4 after IL-25 injection. ILC2 were sort-purified from the gut of C57BL/6 mice ((ILC2: Lin- CD45+ KLRG1+ ST2+).