IRE1α-XBP1 sustains cytokine responses of group 3 innate lymphoid cells in inflammatory bowel disease

Group 3 innate lymphoid cells (ILC3s) are key players in intestinal homeostasis. Endoplasmic reticulum (ER) stress is linked to inflammatory bowel disease (IBD). Herein, we used cell culture, novel mouse models, and human specimens to examine if ER stress in ILC3s impacts IBD pathophysiology. We show that mouse intestinal ILC3s exhibited a 24h-rhythmic expression pattern of the master ER stress response regulator, IRE1α-XBP1. Proinflammatory cytokine IL-23 selectively stimulated IRE1α-XBP1 in mouse ILC3s through mitochondrial reactive oxygen species (mtROS). IRE1α-XBP1 was activated in ILC3s of mice exposed to experimental colitis and in inflamed human IBD specimens. Mice with Ire1α deletion in ILC3s (Ire1αΔRorc) showed reduced expression of ER stress response and cytokine genes including Il22 in ILC3s and were highly vulnerable to infections and colitis. Administration of IL-22 counteracted their colitis susceptibility. In human ILC3s, IRE1 inhibitors suppressed cytokine production, which was upregulated by an IRE1 activator. Moreover, the frequencies of intestinal XBP1s+ ILC3s in Crohn’s disease patients before administration of ustekinumab, an anti-IL-12/IL-23 antibody, positively correlated with response to treatment. We demonstrate that a non-canonical mtROS-IRE1α-XBP1 pathway augments cytokine production by ILC3s and identify XBP1+ ILC3s as a potential biomarker for predicting response to anti-IL-23 therapies in IBD. Group 3 innate lymphoid cells (ILC3s) have recently emerged as important regulators and potential drug targets for IBD. However, the response of ILC3s to environmental stimuli during intestinal inflammation remains elusive. IRE1a-XBP1 serves as the regulatory hub of the unfolded protein response (UPR) that plays a vital role in intestinal inflammation.