Poster Session I - A45 0HOST RESPONSE TO BACTERIA INDUCES A SHIFT TOWARDS THE ENTEROENDOCRINE CELL LINEAGE IN MURINE ENTEROIDS

Abstract Background Shigella flexneri is a leading cause of bacterial dysentery, disproportionately affecting low-resource settings. While its interaction with host cells has been extensively studied in immortalized cell lines, responses in primary intestinal epithelial systems remain poorly understood. Mice deficient in the innate immune sensor NLRC4 are highly susceptible to S. flexneri, offering a physiologically relevant model to examine host-pathogen dynamics in the gut. Aims To investigate how primary intestinal epithelial cells respond to S. flexneri infection and to determine the role of NLRC4 in shaping these responses, particularly in the context of bacterial sensing, inflammation, and epithelial cell lineage dynamics. Methods Ileal organoids were derived from wild-type (WT) and NLRC4-deficient (Nlrc4-/-) C57 BL/6 mice. Organoids were exposed to either invasive or non-invasive strains of S. flexneri, including bacterial supernatants. Intracellular bacterial growth, epithelial uptake, and transcriptional responses were assessed, including lineage-specific gene expression analysis. Results NLRC4 was necessary to restrict intracellular growth of S. flexneri in organoids. Unexpectedly, WT organoids also responded to cell-free S. flexneri supernatants, suggesting NLRC4-dependent detection of type III secretion system components even in the absence of bacterial invasion. In Nlrc4-/- organoids, both invasive and non-invasive S. flexneri were internalized, indicating a potential for intestinal epithelial cell-mediated bacterial uptake. Transcriptomic analysis revealed suppression of inflammatory pathways in infected Nlrc4-/- organoids, coupled with increased expression of enteroendocrine cell markers. Similar transcriptional shifts were observed upon exposure to a non-pathogenic S. flexneri strain, but not bacterial supernatants, indicating that enteroendocrine cell expansion may be driven by bacterial contact or uptake. Conclusions Primary murine intestinal epithelial cells exhibit distinct mechanisms of pathogen detection and response, including NLRC4-mediated sensing of bacterial effectors prior to invasion. The expansion of enteroendocrine cells during infection suggests a novel role for this cell lineage in host-pathogen interactions. These findings highlight the importance of studying gut immunity in physiologically relevant epithelial systems to better understand host responses to commensal and pathogenic microbes. Funding Agencies CCC, CIHR