Colon epithelial cells exposed to probiotic bacteria modify macrophage activation and chemotaxis in response to a bacterial pathogen

Bacteria may influence toll-like receptor (TLR)-dependent colonic epithelial cell (CEC) production of inflammatory mediators and subsequently activate immune cells implicated in carcinogenesis. We hypothesized that probiotic bacteria would decrease Escherichia coli O157: H7 ( O157: H7) induced production of NO and IL-6 as well as macrophage activation and chemotaxis in a genus- and species-specific manner.;O157: H7 induced production of NO and IL-6 compared to untreated YAMC and IMCE epithelial cells (p-value <0.001). CECs co-treated with O157: H7 and probiotics showed a genus- and species-specific decrease in NO and IL-6 compared to O157: H7 (p-value <0.001). Neutralizing antibodies against TLR-2 and -4 reduced NO and IL-6 compared to O157: H7 (p-value <0.05).;Supernatants collected from CECs treated with O157: H7 exposed to macrophages induced IL-6 (p<0.001) but not macrophage NO. Supernatants from CECs co-treated with O157: H7 and probiotics exposed to macrophages caused a decrease in macrophage IL-6 compared to O157: H7 in a genus- and species-specific manner (p-value <0.001). Supernatants from O157: H7-treated IMCE cells resulted in macrophage chemotaxis (p <0.01). These results suggest that O157: H7-induced NO and IL-6 occurs, in part, by activating TLR-2 and 4. The mechanisms by which probiotic bacteria ameliorate these TLR-mediated events require further research.