Intraluminal neutrophils limit epithelium damage by reducing pathogen assault on intestinal epithelial cells duringSalmonellagut infection

Abstract

SummaryRecruitment of neutrophils into the gut epithelium is a cardinal feature of intestinal inflammation in response to enteric infections. Previous work using the model pathogenSalmonellaTyphimurium (S. Tm) established that invasion of intestinal epithelial cells byS.Tm leads to recruitment of neutrophils into the gut lumen, where they can reduce pathogen loads transiently. Notably, a fraction of the pathogen population can survive this defense, re-grow to high density, and continue triggering enteropathy. However, the functions of intraluminal neutrophils in the defense against enteric pathogens and their effects on preventing or aggravating epithelial damage are still not fully understood. Here, we address this question via neutrophil depletion in different mouse models ofSalmonellacolitis, which differ in their degree of enteropathy. In an antibiotic pre-treated mouse model, neutrophil depletion by an anti-Ly6G antibody exacerbated epithelial damage. This could be linked to compromised neutrophil-mediated elimination and reduced physical blocking of the gut-luminalS.Tm population such that the pathogen density remained high near the epithelial surface throughout the infection. The removal of luminalS. Tm by gentamicin, an antibiotic restricted to the gut lumen, reversed the effect of neutrophil depletion on epithelial cell loss. Strikingly, when using germ-free mice and anS. TmssaVmutant capable of epithelium invasion, but attenuated for survival and growth within host tissues, neutrophil depletion caused exacerbated immune activation of the gut mucosa and a complete destruction of the epithelial barrier. Together, our data indicate that intraluminal neutrophils are central for maintaining epithelial barrier integrity during acuteSalmonella-induced gut inflammation, by limiting the sustained pathogen assault on the epithelium in a critical window of the infection.Highlights○After the first wave of mucosal invasion (day 1 p.i.),S. Tm maintains the assault from the lumen, triggering the continued expulsion of epithelial cells in antibiotic pre-treated mice.○Neutrophil recruitment into the gut lumen is essential to limit this continuedSalmonellaattack on the epithelium.○In antibiotic pre-treated SPF mice, neutrophil depletion exacerbatesS. Tm invasion, causing excessive epithelial cell loss, which compromises epithelial barrier integrity at later time points (day 2-3 p.i.).○In germ-free mice, neutrophil depletion exacerbates epithelial responses and epithelial barrier destruction even more strongly than in streptomycin pre-treated SPF mice.○Gentamicin treatment andssaVmutant infections indicate that neutrophils prevent epithelial damage by eliminating and physically blocking gut-luminal pathogens.