Intestinal infection results in impaired lung innate immunity to secondary respiratory infection.

BackgroundPneumonia and diarrhea are among the leading causes of death worldwide, and epidemiological studies have demonstrated that diarrhea is associated with an increased risk of subsequent pneumonia. Our aim was to determine the impact of intestinal infection on innate immune responses in the lung. MethodsUsing a mouse model of intestinal infection by Salmonella enterica serovar Typhimurium (S. Typhimurium (ST)), we investigated how infection in the gut compartment can modulate immunity in the lungs and impact susceptibility to bacterial (Klebsiella pneumoniae (KP)) challenge. ResultsWe found alterations in frequencies of innate immune cells in lungs of intestinally-infected mice compared to uninfected mice. On subsequent challenge with K. pneumoniae we found that mice with prior intestinal infection have higher lung bacterial burden and inflammation, increased neutrophil margination, and neutrophil extracellular traps (NETs), but lower overall numbers of neutrophils, compared to mice without prior intestinal infection. Total numbers of dendritic cells, innate-like T cells, and natural killer cells were not different between mice with and without prior intestinal infection. ConclusionsTogether, these results suggest that intestinal infection impacts lung innate immune responses, most notably neutrophil characteristics, potentially resulting in increased susceptibility to secondary pneumonia. Article summaryWe show, in a mouse model, that prior intestinal infection with Salmonella Typhimurium leads to increased susceptibility to respiratory Klebsiella pneumoniae infection, which is associated with altered neutrophil responses.