Beneficial effect of immunobiotic strains on attenuation of Salmonella induced inflammatory response in human intestinal epithelial cells

Probiotic bacteria have the ability to modulate host immune responses and have potent therapeutic functional effects against several diseases, including inflammatory diseases. However, beneficial effects of probiotics are strain specific and their interactions with host immune cells to modulate inflammatory response are largely unknown. Intestinal epithelial cells (IECs), which are the first line of defense against invading pathogens, and connects between commensals/probiotics and immune system; therefore, in this study, we used human IECs to assess the probiotic effects of three selected Lactobacillus strains in vitro. An HT-29 colonic epithelial cell and HT-29/blood mononuclear cells co-culture system were stimulated with Lactobacillus followed by Salmonella for different hours, after which the mRNA level of cytokines, β-defensin-2 and negative regulators for TLR signaling and protein levels of ZO-1 and IκB-α were analyzed by real-time polymerase chain reaction and western blot analysis. L. brevis decreased Salmonella induced IL-6, IL-8, MCP-1 and IL-1β levels, whereas L. pentosus suppressed IL-6 and MCP-1 in HT-29 cells. Moreover, L. brevis was able to increase the mRNA levels of A20, Tollip, SIGIRR and IRAKM, while L. pentosus reduced the levels of A20, and IRAKM in response to Salmonella. In addition, decrease in protein level of TNF-α and increase in mRNA level of IL-10 was observed in L. brevis and L. pentosus treated HT-29 cells. Lactobacillus strains were differentially modulated ZO-1 and p-IκB-α in HT-29 cells treated with Salmonella. Overall, the results of this study indicate that Lactobacillus strains attenuate Salmonella induced inflammatory responses through beneficial modulation of TLR negative regulators and the NF-κB pathway.