Commensal bacteria exert immunomodulatory activities on human intestinal immune cells

Aims: Intestinal epithelial cells (IEC) and dendritic cells (DC) play a crucial role in antigen sampling and maintaining gut homeostasis. Here we investigated the responses of these gut cells to commensal and pathogenic bacteria.

Methods: HT-29 IEC were incubated with Bifidobacterium infantis, Lactobacillus salivarius, or Salmonella typhimurium, or were pre-treated with a probiotic for 2h prior to S. typhimurium infection. Gene arrays were used to examine inflammatory gene expression. Nuclear factor (NF)-kB activation, interleukin (IL)-8 secretion, and S. typhimurium adherence to IEC were assessed using TransAM assay, ELISA, and fluorescence, respectively. IL-10 and IL-12 secretion by bacteria-treated mesenteric lymph node-derived DC were measured using ELISA.

Results: S. typhimurium increased expression of 36 of 847 immune-related genes assayed, whereas the probiotic bacteria did not stimulate these genes. S. typhimurium increased NF-kB activation and IL-8 secretion, and these S. typhimurium-induced pro-inflammatory responses were attenuated by pre-treatment with B. infantis or L. salivarius. The probiotics did not interfere with pathogen binding to the IEC. S. typhimurium-induced IL-12, whereas the probiotic bacteria stimulated IL-10, not IL-12, secretion by DC.

Conclusions: B. infantis or L. salivarius functionally modulate the epithelium by attenuating S. typhimurium-induced pro-inflammatory responses and inducing regulatory cytokine secretion by DC.