Flagellin-Dependent and -Independent Inflammatory Responses following Infection by EnteropathogenicEscherichia coliandCitrobacter 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 ⌬fliC EPEC, a rapid activation of several proinflammatory genes, including those encoding IL-8, monocyte chemoattractant protein 1, macrophage inflammatory protein 3␣ (MIP3␣), and ␤-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-B. At later infection time points, a subset of these proinflammatory genes (IL-8 and MIP3␣) was also induced in cells infected with ⌬fliC EPEC. The nonmotile A/E pathogen C. rodentium also triggered similar innate responses through a TLR5-independent but partially NF-B-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.

Inhibition of NF-κB Signaling in Human Dendritic Cells by the Enteropathogenic Escherichia coli Effector Protein NleE

“…We were also able to show that EPEC inhibits proinflammatory cytokine expression by human PP cells. These results support data obtained on rabbit enterocytes (6) and human epithelial cell lines cells (9)(10)(11), which showed a type III secretion dependent reduction of IL-8 production. Similar results were recently reported for EHEC, which can downregulate the proinflammatory cytokine production by intestinal epithelial cells in response to its own Shiga toxin (20) and uses the effector NleH1 to subvert NF-kB-dependent transcription by binding to the ribosomal protein s3 (21).…”

“…However, other work suggests that the situation is more complex, and that EPEC can also reduce cytokine production (8)(9)(10)(11). Because inhibition of cytokine production is dependent on a functional T3SS (8)(9)(10)(11), EPEC may also inject inhibitory effector proteins into epithelial cells.…”

Associations between Mucosal Innate and Adaptive Immune Responses and Resolution of Diarrheal Pathogen Infections

“…CI, confidence interval. inflammation and pathology following neutrophil infiltration (24,28,43,44). This inconsistency may reflect the innate immune system's ability to provide a protective response but also produce negative consequences, including exacerbated tissue destruction, following the hyperactivation of this system (28).…”

Fecal Leukocytes in Children Infected with Diarrheagenic Escherichia coli

“…Although EPEC strains are not invasive pathogens, they induce an inflammatory response in the gut epithelium in vivo by triggering production of cytokines and chemokines, including IL-8, which recruits polymorphonuclear leukocytes to the infection site (24). In vitro studies have shown that intestinal epithelial cells infected with EPEC trigger IL-8 release through Toll-like receptor 5 (TLR-5) and activation of NF-B, mediated by flagellin, the secreted protein of the EPEC fliC gene (16). In addition, NleE, a type 3 secretory system (T3SS) effector, is required for EPEC-induced polymorphonuclear leukocyte migration (28).…”