Ann Mathew

Neutrophils are key first responders in the host response to Clostridioides difficile infection (CDI). Although a high number of tissue and blood neutrophils clearly correlates with adverse outcomes in CDI patients, their functional role remains poorly defined. Using murine (CMT-93) and human (Caco-2) intestinal epithelial cell (IEC) lines co-cultured with neutrophils and a pre-clinical mouse model of CDI, we show that activated neutrophils exacerbate C. difficile-induced IEC injury. To identify neutrophil subtypes and biological pathways that contribute to CDI-associated IEC damage, we utilized single-cell RNAseq (scRNAseq) to generate the first transcriptomic atlas of murine bone marrow, blood, and colonic neutrophils in acute CDI. Our analyses identified a novel neutrophil population in the colonic lamina propria, "cNeu3," which exhibited high expression of genes associated with neutrophil activation and degranulation. Informed by cNeu3 signature genes from the scRNAseq dataset, we validated the presence of these neutrophils in mouse colon using flow cytometry (CD11b^hiCD63^hiIL-1β^hiMIP-1α^hiMALT1^hi cells). We found that their abundance correlated with increased epithelial damage. Tumor Necrosis Factor (TNF) was sufficient to polarize mouse bone marrow neutrophils to a cNeu3 phenotype in vitro. Finally, TNF-primed human neutrophils worsened C. difficile toxin-induced IEC damage, which was improved when neutrophil degranulation was blocked. Collectively, our data provide novel insights into neutrophil-mediated pathology during CDI.

Neutrophils are key first responders to Clostridioides difficile infection (CDI). Excessive tissue and blood neutrophils are associated with worse histopathology and adverse outcomes, however their functional role during CDI remains poorly defined. Utilizing intestinal epithelial cell (IEC)-neutrophil co-cultures and a pre-clinical animal model of CDI, we show that neutrophils exacerbate C. difficile -induced IEC injury. We utilized cutting-edge single-cell transcriptomics to illuminate neutrophil subtypes and biological pathways that could exacerbate CDI-associated IEC damage. As such, we have established the first transcriptomics atlas of bone marrow (BM), blood, and colonic neutrophils after CDI. We found that CDI altered the developmental trajectory of BM and blood neutrophils towards populations that exhibit gene signatures associated with pro-inflammatory responses and neutrophil-mediated tissue damage. Similarly, the transcriptomic signature of colonic neutrophils was consistent with hyper-inflammatory and highly differentiated cells that had amplified expression of cytokine-mediated signaling and degranulation priming genes. One of the top 10 variable features in colonic neutrophils was the gene for neutrophil glycoprotein, Olfactomedin 4 (OLFM4). CDI enhanced OLFM4 mRNA and protein expression in neutrophils, and OLFM4 ⁺ cells aggregated to areas of severe IEC damage. Compared to uninfected controls, both humans and mice with CDI had higher concentrations of circulating OLFM4; and in mice, OLFM4 deficiency resulted in faster recovery and better survival after infection. Collectively, these studies provide novel insights into neutrophil-mediated pathology after CDI and highlight the pathogenic role of OLFM4 ⁺ neutrophils in regulating CDI-induced IEC damage. One Sentence Summary: Utilizing single-cell transcriptomics, IEC-epithelial co-cultures, and pre-clinical models of CDI, we have identified a subset of neutrophils that are marked by OLFM4 expression as pathogenic determinants of IEC barrier damage after CDI.