AbstractThe gut wall houses mast cells that are anatomically situated near enteric neuronal fibers. Roles of specific neuropeptides in modulating function of immune components like mast cells in response to challenge with bacterial components are relatively unknown. Investigating such interactions requires models that include diverse cellular elements in native anatomic arrangements. Using an organotypic slice model that maintains gut wall cellular diversity ex vivo, the present study compared responses between tissues derived from male and female mice to examine neural‐immune signaling in the gut wall after selected treatments. Ileum slices were treated with pharmacological reagents that block neuronal function (e.g., tetrodotoxin) or vasoactive intestinal peptide (VIP) receptors prior to challenge with lipopolysaccharide (LPS) to assess their influence on anatomic plasticity of VIP fibers and activation of mast cells. Sex differences were observed in the number of mucosal mast cells (c‐kit/ACK2 immunoreactive) at baseline, regardless of treatment, with female ileum tissue having 46% more ACK2‐IR mast cells than males. After challenge with LPS, male mast cell counts rose to female levels. Furthermore, sex differences were observed in the percentage of ACK2‐IR cells within 1 µm of a VIP+ neuronal fiber, and mast cell size, a metric previously tied to activation, with females having larger cells at baseline. Male mast cell sizes reached female levels after LPS challenge. This study suggests sex differences in neural‐immune plasticity and in mast cell activation both basally and in response to challenge with LPS. These sex differences could potentially impact functional neuroimmune response to pathogens.