Bifidobacterium infantis modulates human intestinal epithelial cell function by attenuating the secretion of CCL20

Background and aims: Enteropathogenic bacteria elicit mucosal immune responses that can lead to the secretion of pro-inflammatory mediators including CCL20. Bacterial flagellin is a key inducer of CCL20 secretion by intestinal epithelial cells. CCL20 is chemotactic for immature dendritic cells, and T and B lymphocytes. Previous studies have demonstrated that probiotic bacteria may limit intestinal inflammation by attenuating pathogen-induced interleukin (IL)-8 secretion. In this study, we investigated whether the probiotic bacterium Bifidobacterium infantis modulates CCL20 induction by flagellated pathogens.Methods: HT-29 human intestinal epithelial cells were incubated with increasing doses of B. infantis, or with Clostridium difficile (ribotype 001), Salmonella typhimurium, or 0.5 mg/ml of its flagellin for varying times. In some studies, HT-29 cells were pre-treated with B. infantis for 2 It prior to infection or flagellin stimulation. CCL20 protein levels in cell culture supernatants were measured by ELISA.Results: Compared to untreated cells (106 +/- 23 pg/ml), C. difficile (1044 233 pg/ml), S. typhimurium (6167 1700 pg/ml), and flagellin (2620 690 pg/ml) stimulated a significant secretion of CCL20 by HT-29 cells. B. infantis did not augment CCL20 production (123 35 pg/ml). In contrast, B. infantis dose-dependently reduced the baseline secretion of CCL20, and at a concentration of 1x10(7)/ml this inhibition was significant (22% reduction). In cells pre-treated with the probiotic bacteria, C. difficile-, S. typhimurium, and flagellin-induced CCL20 secretion were attenuated by 15%, 22%, or 28%, respectively.Conclusion: Flagellin and flagellated pathogens, but not B. infantis, stimulate CCL20 secretion by intestinal epithelial cells, This study is the first to demonstrate that a commensal strain can attenuate CCL20 secretion at baseline and in response to pro-inflammatory stimuli. Collectively, the study suggests that by mediating CCL20 secretion, B. infantis can exert immunomodulatory effects on intestinal epithelial cells that mediate host responses to flagellin and enteric pathogens.