title: Flagellin-dependent and -independent inflammatory responses following infection by enteropathogenic Escherichia coli and Citrobacter rodentium.
abstract: Enteropathogenic Escherichia coli (EPEC) and the murine pathogen Citrobacter rodentium belong to the attaching and effacing (A/E) family of bacterial pathogens. These noninvasive bacteria infect intestinal enterocytes using a type 3 secretion system (T3SS), leading to diarrheal disease and intestinal inflammation. While flagellin, the secreted product of the EPEC fliC gene, causes the release of interleukin 8 (IL-8) from epithelial cells, it is unclear whether A/E bacteria also trigger epithelial inflammatory responses that are FliC independent. The aims of this study were to characterize the FliC dependence or independence of epithelial inflammatory responses to direct infection by EPEC or C. rodentium. Following infection of Caco-2 intestinal epithelial cells by wild-type and DeltafliC EPEC, a rapid activation of several proinflammatory genes, including those encoding IL-8, monocyte chemoattractant protein 1, macrophage inflammatory protein 3alpha (MIP3alpha), and beta-defensin 2, occurred in a FliC-dependent manner. These responses were accompanied by mitogen-activated protein kinase activation, as well as the Toll-like receptor 5 (TLR5)-dependent activation of NF-kappaB. At later infection time points, a subset of these proinflammatory genes (IL-8 and MIP3alpha) was also induced in cells infected with DeltafliC EPEC. The nonmotile A/E pathogen C. rodentium also triggered similar innate responses through a TLR5-independent but partially NF-kappaB-dependent mechanism. Moreover, the EPEC FliC-independent responses were increased in the absence of the locus of enterocyte effacement-encoded T3SS, suggesting that translocated bacterial effectors suppress rather than cause the FliC-independent inflammatory response. Thus, we demonstrate that infection of intestinal epithelial cells by A/E pathogens can trigger an array of proinflammatory responses from epithelial cells through both FliC-dependent and -independent pathways, expanding our understanding of the innate epithelial response to infection by these pathogens.
authors.affiliation: Division of Gastroenterology, BC Children's Hospital, Vancouver, British Columbia, Canada.
authors.forename: Mohammed A
authors.initials: MA
authors.lastname: Khan
authors.forename: Saeid
authors.initials: S
authors.lastname: Bouzari
authors.forename: Caixia
authors.initials: C
authors.lastname: Ma
authors.forename: Carrie M
authors.initials: CM
authors.lastname: Rosenberger
authors.forename: Kirk S B
authors.initials: KS
authors.lastname: Bergstrom
authors.forename: Deanna L
authors.initials: DL
authors.lastname: Gibson
authors.forename: Theodore S
authors.initials: TS
authors.lastname: Steiner
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Vallance
mesh_terms: D000818:Animals; D018938:Caco-2 Cells; D054418:Chemokine CCL20 / Q000378:metabolism; D044082:Citrobacter rodentium / Q000502:physiology*; D003713:Dendritic Cells / Q000166:cytology / Q000502:physiology; D004756:Enterobacteriaceae Infections / Q000378:metabolism* / Q000382:microbiology; D054308:Enteropathogenic Escherichia coli / Q000502:physiology*; D004847:Epithelial Cells / Q000378:metabolism* / Q000382:microbiology; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D005408:Flagellin / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007249:Inflammation / Q000378:metabolism*; D016209:Interleukin-8 / Q000378:metabolism; D051379:Mice; D008809:Mice, Inbred C3H; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism; D013997:Time Factors; D051198:Toll-Like Receptor 5 / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D054418:Chemokine CCL20; D029968:Escherichia coli Proteins; C516095:FliC protein, E coli; D016209:Interleukin-8; D016328:NF-kappa B; D051198:Toll-Like Receptor 5; D005408:Flagellin; D048051:p38 Mitogen-Activated Protein Kinases