Balance of bacterial pro- and anti-inflammatory mediators dictates net effect of enteropathogenicEscherichia colion intestinal epithelial cells

Abstract

Enteropathogenic Escherichia coli (EPEC) virulence requires a type III secretion system (TTSS) to deliver effector molecules in host cells. Although the TTSS is crucial to EPEC pathogenesis, its function in EPEC-induced inflammation is not known. The aim of this study was to investigate the role of the TTSS in EPEC-induced inflammation. HT-29 intestinal epithelial cells were infected with wild-type (WT) EPEC or select mutant strains or exposed to corresponding filter-sterilized supernatants (SN), and interleukin-8 (IL-8) secretion was determined by ELISA. EPEC SN stimulated significantly greater IL-8 production than EPEC organisms. Flagellin, as well as a TTSS-independent >50-kDa nonflagellin protein, was found to significantly contribute to this response. Dose-response studies showed that increasing concentrations of WT SN proportionally increased IL-8, whereas increasing multiplicity of infection of EPEC inversely correlated with IL-8 secretion, suggesting that EPEC dampens this host response. Infection with DeltaescN (nonfunctional TTSS) markedly increased IL-8 compared with WT, indicating that a functional TTSS is required for this anti-inflammatory property; complementation of escN restored the attenuated response. Mutation of espB also enhanced the IL-8 response, and complementation returned IL-8 to near WT levels, suggesting involvement of this effector. The anti-inflammatory effect extends to both bacterial and host-derived proinflammatory stimuli, since prior infection with EPEC suppressed the IL-8 response to tumor necrosis factor-alpha, IL-1beta, and enterohemorrhagic E. coli flagellin. These findings indicate that EPEC-induced inflammation is a balance between pro- and anti-inflammatory proteins; extracellular factors, including flagellin and an unidentified TTSS-independent, >50-kDa protein, trigger inflammation while intracellular TTSS-dependent factors, including EspB, attenuate this response.

Flagellin-Dependent and -Independent Inflammatory Responses following Infection by EnteropathogenicEscherichia coliandCitrobacter rodentium

“…Dissecting what will undoubtedly be a complex mixture of bacterial and host factors involved in this FliC-independent response will be the focus of future studies. Our data also support findings by Sharma et al (37) that the presence of the T3SS inhibits rather than induces epithelial inflammatory responses. Thus, A/E pathogens not only trigger epithelial inflammatory responses, they may also be able to locally limit these responses, creating protected niches that permit the growth and survival of these bacteria in the face of the host response.…”

“…Previous studies had implicated the LEE-encoded T3SS (and the bacterial effector proteins that are dependent on its function to translocate into host cells) in causing (13,35), as well as suppressing (37), the inflammatory response by EPEC-infected epithelial cells. Interestingly, the loss of the LEE-encoded T3SS (⌬escN) did not attenuate IL-8 levels (Fig.…”

Contribution of FliC to Epithelial Cell Invasion by Enterohemorrhagic Escherichia coli O113:H21

“…Serovar Typhimurium can also translocate FliC across the intestinal epithelium in SPI-1-induced vesicles, where it stimulates a potent inflammatory response via Toll-like receptor 5 (TLR5) signaling (15). Proinflammatory chemokine production is also upregulated by FliC through TLR5 signaling during EHEC O157:H7 and EPEC O127:H6 infection of intestinal tissue (22,31,35). In addition to its involvement in inflammation, EPEC O127:H6 flagellin contributes to the adherence of bacteria to epithelial cells (16).…”

The role of epithelial malfunction in the pathogenesis of enteropathogenic E. coli-induced diarrhea

“…Indeed, it was shown that EPEC-secreted components exert a proinflammatory effect, whereas its attachment to IECs and the translocation of effector molecules by the T3SS attenuate this response. 60 The outcome of this balance is the induction of an inflammatory response, mostly driven by the activation of NF-kB, MAPK-ERK1/2, and protein kinase Cz, all leading to the expression and release of interleukin (IL)-8, a potent neutrophil chemoattractant. 58,61,62 This results in an important neutrophilic infiltration into the lamina propria, epithelial crypts, and intestinal lumen.…”

“…66 The inflammatory response associated with EPEC is associated with an increase in proinflammatory cytokines, such as TNFa, interferon (IFN) g, and IL-1b, in the infected mucosa. 58,60 Several studies have shown the role of these cytokines in epithelial barrier disruption. Indeed, IFNg, alone or in synergy with TNFa, is known to induce epithelial barrier dysfunction, independently of its proapoptotic properties.…”