NKp46⁺ ILC3s promote early neutrophil defense against <i>Clostridioides difficile</i> infection through GM-CSF secretion.

Abstract

<i>Clostridioides difficile</i> infection (CDI) is a common cause of antibiotic-associated colitis. <i>C. difficile</i> proliferates and produces toxins that damage the colonic epithelium, leading to symptoms ranging from mild diarrhea to severe pseudomembranous colitis. The host's innate response to CDI occurs in two phases: an early phase in which neutrophils reduce the bacterial load and a late phase involving repair mechanisms to restore epithelial integrity. Group 3 innate lymphoid cells (ILC3s) are crucial in protecting the gut from CDI. Previous studies have shown that ILC3-derived IL-22 is essential in the late phase of CDI for epithelial repair and maintaining an intestinal microbiota that competes with <i>C. difficile</i>, preventing its expansion. Our study finds that ILC3s also protect during the early stages of CDI by sustaining neutrophils through GM-CSF. Less neutrophil production, accumulation, and activation was evident in ILC3-deficient mice than in wild-type (WT) mice, which led to exacerbated symptoms, impaired pathogen clearance, a compromised epithelial barrier, and increased mortality. The adoptive transfer of ILC3s into ILC3-deficient mice restored neutrophil responses and improved disease outcomes. Both in vitro and in vivo experiments revealed that GM-CSF production by ILC3s is crucial for neutrophil production and effective resistance during CDI. Using mice lacking NKp46⁺ ILC3s, we found that this subset significantly contributes to GM-CSF production in CDI. These findings highlight the critical role of the ILC3-neutrophil connection in early innate responses to CDI. Enhancing ILC3 production of GM-CSF could be a promising strategy for improving host defense against CDI and other enteric infections.