Intimate Adherence by Enteropathogenic Escherichia coli Modulates TLR5 Localization and Proinflammatory Host Response in Intestinal Epithelial Cells

Enteropathogenic Escherichia coli (EPEC) causes diarrhoeal disease by altering enterocyte physiology and producing mucosal inflammation. Many details concerning the host response against EPEC remain unknown. We evaluated the role of EPEC virulence factors on the inflammatory response through an analysis of bacterial recognition, cell signalling, and cytokine production using an in vitro epithelial cell infection model. Interestingly, we found that EPEC infection recruits Toll-like receptor 5 (TLR5) to the cell surface. We confirmed that type 3 secretion system (T3SS) and flagellin (FliC) are necessary for efficient extracellular regulated kinases 1 and 2 (ERK1/2) activation and found that intimin could down-regulate this pathway. Besides flagellin, intimin was required to keep nuclear factor kappa B (NF-kappa B) activated during infection. EPEC infection activated tumour necrosis factor alpha (TNF-alpha) production and induced interleukin (IL)-1 beta and IL-8 release. Virulence factors such as intimin, T3SS, EspA and fliC were required for IL-1 beta secretion, whereas intimin and T3SS participated in IL-8 release. Flagellin was essential for late secretion of TNF-alpha and IL-8 and intimin stimulated cytokine secretion. Initial adherence limited TNF-alpha release, whereas late attachment sustained TNF-alpha secretion. We conclude that intimin modulates TLR5 activation and intimate adherence alters the proinflammatory response.