# Olfactomedin-4+ neutrophils exacerbate intestinal epithelial damage in Clostridioides difficile infection

## TL;DR

This paper shows that a specific type of neutrophil, marked by Olfactomedin-4, worsens intestinal damage in Clostridioides difficile infection.

## Contribution

The study identifies OLFM4+ neutrophils as a novel subset that exacerbates intestinal epithelial damage during CDI.

## Key findings

- OLFM4+ neutrophils accumulate in areas of severe intestinal epithelial damage in C. difficile-infected mice.
- Recombinant OLFM4 protein and OLFM4+ neutrophils increase toxin-induced intestinal epithelial cell damage in vitro.
- Plasma OLFM4 levels are elevated in both infected mice and CDI patients.

## Abstract

Neutrophils are dominant cells during acute immune response to Clostridioides difficile infection (CDI). A higher number of infiltrating colonic neutrophils is clearly linked to greater tissue damage and severe CDI (3, 4). However, the mechanism(s) by which neutrophils exacerbate tissue damage in CDI remain unknown. We investigated the role of a neutrophil subset marked by Olfactomedin-4 expression (OLFM4+ neutrophils) during CDI. Single-cell transcriptomics reveal that Olfm4 is increased in blood neutrophils of infected mice, and these cells exhibit gene signatures characterized by high expression of degranulation genes. In C. difficile-infected mice, OLFM4+ neutrophils aggregate to areas of severe intestinal epithelial cell (IEC) damage, and plasma OLFM4 was significantly increased in both C. difficile-infected mice and patients. In vitro, OLFM4+ neutrophils and recombinant OLFM4 protein exacerbated C. difficile toxin-induced IEC damage. In sum, our studies provide novel insights into neutrophil-mediated pathology and highlight the role of OLFM4+ neutrophils in worsening CDI-induced IEC damage.