Treg-specific IL-6R signaling: a novel role in the regulation of the intestinal epithelium.

Mucosal homeostasis requires coordinated immune regulation and epithelial repair. Inflammatory bowel disease (IBD) arises from disrupted coordination between the immune system and intestinal epithelium, where resolution and repair must occur in parallel. Interleukin-6 (IL-6) plays a dual role: it promotes epithelial regeneration but destabilizes regulatory T cells (Tregs). We aimed to determine the contribution of Treg IL-6 receptor (IL-6R) signaling to intestinal inflammation and epithelial integrity. We developed a conditional knockout mouse model in which IL-6R was deleted from Tregs (Treg IL-6R knockout). These mice were subjected to dextran sodium sulfate (DSS)-induced colitis and a T cell transfer model of colitis. Soluble IL-6R production by Tregs was assessed in vitro, and transcriptional changes in epithelial cells were analyzed by RNA-seq. Human colonic organoids from IBD patients were treated with IL-6 or hyper-IL-6 (IL-6/sIL-6R fusion protein) to test downstream signaling effects. Tregs lacking IL-6R improved colitis to a similar extent as control Tregs in the adoptive transfer model, indicating intact suppressive function. However, Treg IL-6R knockout mice were more susceptible to DSS colitis than controls, suggesting a physiologic role for Treg IL-6R signaling in epithelial protection. In vitro, Tregs shed soluble IL-6R, enabling IL-6 trans-signaling to epithelial cells. Intestinal epithelial cells from Treg IL-6R knockout mice compared to WTcre controls revealed widespread transcriptional downregulation of genes related to survival and repair pathways at baseline, and impaired transcriptional responses following DSS treatment. In human organoids, IL-6 trans-signaling elicited stronger STAT3 activation than IL-6 alone. These findings reveal a previously unrecognized role for Treg-derived IL-6R in promoting epithelial resilience and maintaining mucosal homeostasis.