Here we report that ILC s sensed oxysterols through GPR
Here, we report that ILC3s sensed oxysterols through GPR183, which was highly expressed by LTi-like ILC3s. 7α,25-OHC-synthesizing enzymes were produced by fibroblastic stromal tyrosine kinase found in intestinal lymphoid structures, and the GPR183 ligand 7α,25-OHC acted as a chemoattractant for ILC3s. GPR183 and 7α,25-OHC were required for ILC3 localization to lymphoid structures in the colon, and ablation of Gpr183 in ILC3s caused a defect in the formation of colonic CPs and ILFs. The same phenotype was observed in mice lacking Ch25h, demonstrating a requirement for oxysterols in lymphoid tissue organogenesis. Furthermore, 7α,25-OHC was increased by inflammatory signals, and GPR183 controlled inflammatory cell recruitment during colitis. Consequently, Gpr183-deficient mice were less susceptible to colitis in an innate model of intestinal inflammation. Our results establish a role for a lipid ligand and its cell-surface receptor in controlling ILC3 migration, lymphoid tissue development, and inflammatory responses in the intestine.
Discussion Little is known regarding how ILCs directly sense signals from their environment and which signaling pathways enable ILCs to perform tissue remodeling. Our work demonstrates that LTi-like ILC3s were controlled by oxysterols that signal through the receptor GPR183. This instructs ILC3 positioning and lymphoid tissue formation in the colon. We propose a model where local generation of 7α,25-OHC by fibroblastic stromal cells attracts GPR183-expressing LTi-like ILC3s to sites of CP formation. This process positions LTα1β2+ ILC3s for crosstalk with LTβR+ stromal cells, which promotes the recruitment of GPR183-expressing B cells, to complete ILF formation. Moreover, our study provides information on the mechanisms that control the spatial and functional compartmentalization of ILC3s in the intestine. After homing to the intestine, ILC3s segregate into two distinct locations. Localization of NKp46+ ILC3s to the villi of the lamina propria occurs in a CXCL16-CXCR6-dependent manner, which supports epithelial defense through the production of IL-22 (Satoh-Takayama et al., 2014). We have shown that GPR183 and its ligand 7α,25-OHC position LTi-like ILC3s to colonic CPs, where these cells promote lymphoid tissue formation. Previous studies have established an essential function for GPR183 and its ligand 7α,25-OHC in lymphoid organs and humoral immunity (Gatto et al., 2009, Gatto et al., 2013, Hannedouche et al., 2011, Li et al., 2016, Liu et al., 2011, Pereira et al., 2009, Yi and Cyster, 2013, Yi et al., 2012). We have now demonstrated a role for GPR183 and oxysterols in lymphoid tissue development in the large intestine. Thus, our study has established a broader function of the oxysterol-GPR183-ligand-receptor system by linking GPR183-mediated cell positioning to tissue reorganization during steady-state homeostasis and inflammation. Whereas the signals regulating the formation of SILTs in the small intestine are well known, those in the colon have remained poorly understood. As in the small intestine, LTi-like ILC3s and LTα1β2 are required for colonic lymphoid organogenesis. However, the microbiota and receptor activator of NF-κB ligand (RANKL)-RANK, CXCL13-CXCR5, and CCL20-CCR6 are required for ILF development only in the small intestine (Buettner and Lochner, 2016, Randall and Mebius, 2014). Accordingly, we have described a colon-specific pathway governing the postnatal development of lymphoid tissues. One question relates to our finding that oxysterol-GPR183 signaling is critical for CP and ILF formation in the colon but dispensable in the small intestine. GPR183 and its ligand were expressed in both the small and large intestines. Moreover, 7α,25-OHC was required for ILC3 migration to CPs not only in the colon but also in the small intestine. Despite this, lymphoid tissue development in the small intestine was normal in mice lacking 7α,25-OHC. Together, our observations indicate that, as a compensatory response, B cells form lymphoid follicles when ILC3s are unable to migrate to CPs as a result of a lack of GPR183 ligand. This notion is supported by previous studies demonstrating lymphoid-tissue-inducing activity of B cells and compensatory lymphoid tissue formation when ILC3s are absent or when LTβR signaling is blocked in utero (Buettner and Lochner, 2016). This process must be driven by factors that operate specifically in the small intestine, because we observed compensatory B cell cluster formation only in the small intestine, but not in the colon. Such factors are the microbiota, CCL20, and CXCL13, which are all dispensable for ILC3 recruitment and CP formation but essential for B cell recruitment and ILF formation in the small intestine (Buettner and Lochner, 2016). In conclusion, we favor the concept that the 7α,25-OHC-GPR183 pathway is active, but not absolutely required for lymphoid tissue formation, in the small intestine because other redundant factors are sufficient in the absence of GPR183 ligand.