EspO-mediated neutrophil accumulation drives lethality during Citrobacter rodentium infection in interleukin-22-deficient mice.

Citrobacter rodentium (CR) is a murine-specific enteric pathogen widely used to model infections of the attaching and effacing pathogens enteropathogenic and enterohaemorrhagic Escherichia coli. Infection induces colonic epithelial damage and inflammation that are resolved in resistant mice but result in severe disease and mortality in mice lacking interleukin-22 (IL-22). While IL-22-deficient (Il22-/-) mice succumb to CR infection due to dehydration, in part mediated by disruption of the barrier integrity by the type III secretion system (T3SS) effector EspF, the contribution of immunopathology to infection outcomes is not known. Here, using CR we tested whether dysregulated neutrophil responses drive disease progression in Il22-/- mice. We show that IL-22 deficiency is associated with progressive colonic pathology and increased neutrophil accumulation and activity in the colonic mucosa. Infection of mice with CR lacking the T3SS effector EspO, which is implicated in neutrophil recruitment, resulted in markedly reduced neutrophil accumulation and activity in Il22-/- mice without altering bacterial burden. Notably, CRΔespO infection led to reduced colonic inflammation and complete survival of Il22-/- mice. Consistent with these findings, CXCR2 antagonist treated Il22-/- mice displayed attenuated disease severity and delayed mortality. Together, we identified EspO as the second effector, alongside EspF, whose deletion results in survival of CR-infected Il22-/- mice. Moreover, these findings suggest that excessive neutrophil accumulation and activity are key drivers of lethality during CR infection in Il22-/- mice and that EspO amplifies neutrophil-dependent pathology within a vulnerable epithelial environment.