Keith Summa remembers the moment his team saw the data: in the inflamed colon tissue of mice, a quiet but powerful immune conversation was unfolding between two unlikely cellular partners—eosinophils and type 3 innate lymphoid cells (ILC3s). This dialogue, mediated by the enzyme COX-2, was not fueling inflammation, as so many immune responses do in inflammatory bowel disease (IBD), but calming it. For the 3 million Americans living with IBD, this discovery offers a new hope—not just for understanding the disease, but for redefining how it might be treated.
IBD, which includes Crohn’s disease and ulcerative colitis, is marked by a breakdown in the intestinal barrier and unchecked immune activation. For years, eosinophils—white blood cells often associated with allergic responses—have been observed in inflamed gut tissue, but their role has been a mystery. Are they attackers or protectors? The new study, published in the Proceedings of the National Academy of Sciences, provides a compelling answer: under the right conditions, they’re peacekeepers.
Using RNA sequencing and genetically modified mouse models, researchers found that eosinophils in inflamed colon tissue ramp up production of COX-2, the enzyme encoded by the PTGS2 gene. COX-2 in turn generates prostaglandin E2 (PGE2), a signaling molecule that activates ILC3s to release IL-22, a cytokine known to strengthen the gut lining and reduce inflammation. When the scientists deleted COX-2 specifically in eosinophils, the mice developed earlier and more severe colitis—proof that this pathway is not just present, but protective.
The discovery reveals a previously unknown immune circuit: eosinophils sense inflammation, produce COX-2, and through PGE2, signal ILC3s to restore balance. "This protective circuit might provide a counterbalance to the chronically disrupted immune activity present in IBD," said Summa, assistant professor of Medicine at Northwestern University and co-author of the study. Yingzi Cong, Ph.D., the Stanley Gradowski Professor of Gastroenterology and another co-author, added that boosting this pathway could lead to treatments that strengthen the intestinal barrier—not by suppressing immunity, but by enhancing the body’s own regulatory systems.
Current IBD therapies often focus on broadly dampening the immune response, which can leave patients vulnerable to infections. A treatment that amplifies this natural protective circuit—perhaps with targeted biologics or small molecules—could offer a more precise, restorative approach. The team now aims to uncover what triggers this circuit in the first place: what signals turn it on during inflammation, and what might disrupt it in chronic disease.
As research shifts from suppression to restoration, this tiny cellular conversation may one day help millions keep the peace in their guts.