Cross-talk between ROR_γt⁺ innate lymphoid cells and intestinal macrophages induces mucosal IL-22 production In Crohn's disease

Background: Interleukin (IL)-22-producing ROR_γt ⁺ innate lymphoid cells (ILCs) play a pivotal role in intestinal immunity. Recent reports demonstrated that ILCs contribute to mucosal protection and intestinal inflammation in mice. In humans, numbers of ROR _γt⁺ ILCs are significantly increased in the intestine of patients with Crohn's disease (CD), suggesting that ILCs may be associated with intestinal inflammation in CD. However, the mechanism by which ILCs are regulated in the intestine of patients with CD is poorly understood. This study aimed to determine the activation mechanism of intestinal ILCs in patients with CD. Methods: CD45+ lineage marker-ILCs were isolated from intestinal lamina propria of patients with CD. ILCs were then subdivided into 4 distinct populations based on the expression of CD56 and CD127. Purified ILC subsets were cocultured with intestinal CD14+ macrophages, and IL-22 production was evaluated. Results: CD127⁺CD56^- and CD127 ⁺CD56⁺ ILC, but not CD127^-CD56⁺ or CD127^-CD56^- ILC, subsets expressed ROR_γt and produced IL-22. IL-22 production by these ILC subsets was enhanced when ILCs were cocultured with intestinal macrophages. IL-23 or cell-to-cell contact was required for macrophage-mediated activation of ILCs. IL-22 production by ILCs was perturbed in inflamed mucosa compared with noninflamed mucosa. IL-22 induced the expression of Reg1_α and Claudin-1 in human intestinal epithelial organoids. Conclusions: ROR_γt⁺ ILCs might enhance mucosal barrier function through the upregulation of Reg1 _α through production of IL-22. Although CD14⁺ macrophages augment intestinal inflammation in patients with CD, macrophages also promote a negative feedback pathway through the activation of IL-22 production by ROR_γt⁺ ILCs.