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Cell Microbiol. 2019 Jul;21(7):e13026. doi: 10.1111/cmi.13026. Epub 2019 May 7.

TLR9 limits enteric antimicrobial responses and promotes microbiota-based colonisation resistance during Citrobacter rodentium infection.

Author information

1
Department of Pediatrics, BC Children's Hospital Research Institute and the University of British Columbia, Vancouver, British Columbia, Canada.
2
Department of Biology, The Irving K. Barber School of Arts and Sciences, University of British Columbia, Kelowna, British Columbia, Canada.

Abstract

Mammalian cells express an array of toll-like receptors to detect and respond to microbial pathogens, including enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC). These clinically important attaching and effacing (A/E) pathogens infect the apical surface of intestinal epithelial cells, causing inflammation as well as severe diarrheal disease. Because EPEC and EHEC are human-specific, the related murine pathogen Citrobacter rodentium has been widely used to define how hosts defend against A/E pathogens. This study explored the role of TLR9, a receptor that recognises unmethylated CpG dinucleotides present in bacterial DNA, in promoting host defence against C. rodentium. Infected Tlr9-/- mice suffered exaggerated intestinal damage and carried significantly higher (10-100 fold) pathogen burdens in their intestinal tissues as compared with wild type (WT) mice. C. rodentium infection also induced increased antimicrobial responses, as well as hyperactivation of NF-κB signalling in the intestines of Tlr9-/- mice. These changes were associated with accelerated depletion of the intestinal microbiota in Tlr9-/- mice as compared with WT mice. Notably, antibiotic-based depletion of the gut microbiota in WT mice prior to infection increased their susceptibility to the levels seen in Tlr9-/- mice. Our results therefore indicate that TLR9 signalling suppresses intestinal antimicrobial responses, thereby promoting microbiota-mediated colonisation resistance against C. rodentium infection.

PMID:
30893495
DOI:
10.1111/cmi.13026

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