Suppression of IL-17 producing type 3 innate lymphoid cells and increased susceptibility to Klebsiella pneumoniae sepsis in neonatal mice exposed to extended empiric antibiotics

Abstract

Background/Objective Over 75% of newborns admitted to the neonatal intensive care unit (NICU) receive antibiotics with no proven infection (empiric) at birth. Empiric antibiotic use in the NICU increases susceptibility to late onset sepsis, but the mechanisms are poorly understood. Methods Neonatal mice were exposed to broad-spectrum antibiotics through their dams from birth for either 3-(short exposure, SE) or 7-days (long exposure, LE). At 14 days, qRT-PCR was used for bacterial 16S rRNA (stool), antimicrobial proteins (AMPs) and cytokines (small intestine, SI). Blood, liver and spleen cultures was utilized to detect bacterial translocation. Histology of SI was performed for Paneth cells. Flow cytometric analysis of lamina propria (LP) cells determined the presence of type 3 innate lymphoid cells (ILC3), neutrophils, macrophages, T- and B-cells. Susceptibility to sepsis was determined by IP injection of K. pneumoniae in 12-day-old pups. Results Mice exposed to SE and LE showed significant expansion of Enterobacteriaceae (2 log difference). LE mice showed baseline translocation of Enterobacteriaceae into the liver and spleen and were more susceptible to sepsis. By flow cytometry, LE mice showed a persistent and significant 50% decrease in IL-17 producing ILC3 in the LP, with other cell types unaffected. Further, the ILC3 present were skewed to the IL-22 producing phenotype. AMPs and Paneth cells were also increased in the SI, likely mediated by the increase in IL-22. Conclusions Extended empiric antibiotic exposure resulted in persistent expansion of Enterobacteriaceae and increased susceptibility to neonatal sepsis, likely mediated by a microbiota-dependent decrease in IL-17-producing ILC3.