Khan Mohammed A, Bouzari Saeid, Ma Caixia, Rosenberger Carrie M, Bergstrom Kirk S B, Gibson Deanna L, Steiner Theodore S, Vallance Bruce A
Division of Gastroenterology, BC Children's Hospital, Vancouver, British Columbia, Canada.
Infect Immun. 2008 Apr;76(4):1410-22. doi: 10.1128/IAI.01141-07. Epub 2008 Jan 28.
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.
肠道致病性大肠杆菌（EPEC）和鼠病原体啮齿柠檬酸杆菌属于细菌病原体的紧密黏附性（A/E）家族。这些非侵袭性细菌利用III型分泌系统（T3SS）感染肠道肠上皮细胞，导致腹泻病和肠道炎症。虽然EPEC fliC基因的分泌产物鞭毛蛋白可促使上皮细胞释放白细胞介素8（IL-8），但尚不清楚A/E细菌是否也会引发不依赖FliC的上皮炎症反应。本研究的目的是确定上皮炎症反应对EPEC或啮齿柠檬酸杆菌直接感染的FliC依赖性或非依赖性。野生型和缺失fliC的EPEC感染Caco-2肠道上皮细胞后，包括编码IL-8、单核细胞趋化蛋白1、巨噬细胞炎性蛋白3α（MIP3α）和β-防御素2的基因在内的几种促炎基因以FliC依赖性方式迅速激活。这些反应伴随着丝裂原活化蛋白激酶的激活以及Toll样受体5（TLR5）依赖性的核因子κB激活。在感染后期，缺失fliC的EPEC感染的细胞中也诱导了这些促炎基因的一个子集（IL-8和MIP3α）。非运动性的A/E病原体啮齿柠檬酸杆菌也通过不依赖TLR5但部分依赖核因子κB的机制引发了类似的先天反应。此外，在缺乏肠上皮细胞损伤位点编码的T3SS的情况下，EPEC不依赖FliC的反应增强，这表明转位的细菌效应器抑制而非引发不依赖FliC的炎症反应。因此，我们证明A/E病原体感染肠道上皮细胞可通过依赖FliC和不依赖FliC的途径引发上皮细胞一系列促炎反应，扩展了我们对这些病原体感染后先天上皮反应的理解。
