Wen, Yankai

Inflammatory bowel disease (IBD) is driven by a breakdown in immune regulation and epithelial barrier function, yet the contribution of eosinophils to this process has remained poorly defined and controversial. While eosinophils infiltrate the intestinal mucosa during both flares and remission, their role in shaping disease outcomes is unclear. Our RNA-seq analyses of colonic eosinophils isolated from dextran sulfate sodium (DSS)-treated mice revealed a significant upregulation of cyclooxygenase (COX)-2 (gene name, Ptgs2 ). Eosinophil-specific deletion of COX-2 (Ptgs2 fl/fl eoCre +/− ) reduced IL-22 production and exacerbated DSS- and trinitrobenzene sulfonic acid (TNBS)-induced colitis, characterized by greater weight loss, higher disease activity, colon shortening, and epithelial injury. Administration of recombinant IL-22 reversed these phenotypes. Mechanistically, eosinophil-derived COX-2 enhanced IL-22 production by type 3 Innate lymphoid cells (ILC3s) through prostaglandin E2 (PGE 2 ) signaling. Consistently, Ptgs2 fl/fl eoCre +/− mice exhibited reduced colonic PGE 2 levels, while PGE 2 analog treatment restored IL-22 production and mucosal protection. Our findings identify eosinophil-derived COX-2 and PGE 2 as a critical regulator of IL-22 production during colitis, uncovering a eosinophil–ILC3 cross talk that safeguards the intestinal barrier and represents a promising therapeutic target in IBD.

Background and Aims: A better understanding of the underlying mechanism of acetaminophen (APAP)‐induced liver injury (AILI) remains an important endeavor to develop therapeutic approaches. Eosinophils have been detected in liver biopsies of patients with APAP overdose. We recently demonstrated a profound protective role of eosinophils against AILI; however, the molecular mechanism had not been elucidated. Approach and Results: In agreement with our previous data from experiments using genetic deletion of eosinophils, we found that depletion of eosinophils in wild‐type (WT) mice by an anti‐IL‐15 antibody resulted in exacerbated AILI. Moreover, adoptive transfer of eosinophils significantly reduced liver injury and mortality rate in WT mice. Mechanistic studies using eosinophil‐specific IL‐4/IL‐13 knockout mice demonstrated that these cytokines, through inhibiting interferon‐γ, mediated the hepatoprotective function of eosinophils. Reverse phase protein array analyses and in vitro experiments using various inhibitors demonstrated that IL‐33 stimulation of eosinophils activated p38 mitogen‐activated protein kinase (MAPK), and in turn, cyclooxygenases (COX), which triggered NF‐κB–mediated IL‐4/IL‐13 production. In vivo adoptive transfer experiments showed that in contrast to naive eosinophils, those pretreated with COX inhibitors failed to attenuate AILI. Conclusions: The current study revealed that eosinophil‐derived IL‐4/IL‐13 accounted for the hepatoprotective effect of eosinophils during AILI. The data demonstrated that the p38 MAPK/COX/NF‐κB signaling cascade played a critical role in inducing IL‐4/IL‐13 production by eosinophils in response to IL‐33.

Eosinophils protect against liver injury during orthotopic liver transplantation and other conditions of hepatic ischemia-reperfusion injury in mice.