Commensal-derived OMVs elicit a mild proinflammatory response in intestinal epithelial cells

Under normal physiological conditions, the intestinal immunity remains largely hyporesponsive to the commensal microbiota, yet also retains the inherent ability to rapidly respond to pathogenic antigens. However, immunomodulatory activities of extracellular products from commensal bacteria have been little studied, with previous investigations generally utilising the live bacterium to study microbiota-epithelial interactions. In this study, we demonstrate that extracellular products of a commensal bacterium, Escherichia coli C25, elicit a moderate release of proinflammatory IL-8 and stimulate transcriptional up-regulation of Toll-like receptors (TLRs) in intestinal epithelial cell lines, HT29-19A and Caco-2. Additionally, we show that removal of outer membrane vesicles (OMVs) diminishes the proinflammatory effect of secreted products from E. coli C25. Furthermore, we show that isolated OMVs have a dose-dependent proinflammatory effect on IECs. Interestingly, a relatively high concentration (10x culture concentration) of OMVs had no significant regulatory effects on TLR mRNA expression in both cell lines. Finally, we also demonstrate a that pre-incubation with E. coli C25-derived OMVs subsequently inhibited the internalisation of the bacterium itself in both cell lines. Taken together, our results suggest that commensal-derived extracellular products, in particular OMVs, could significantly contribute to intestinal homeostasis. We also demonstrate a unique interaction between commensal-derived OMVs and host cells.