Synbiotic Effects of the Dietary Fiber Long‐Chain Inulin and Probiotic Lactobacillus acidophilus W37 Can be Caused by Direct, Synergistic Stimulation of Immune Toll‐Like Receptors and Dendritic Cells

SCOPE: Synbiotic effects of dietary fibers and lactobacilli are usually explained by synergistic modulation of gut microbiota. New insight, however, has demonstrated that both dietary fibers and lactobacilli can directly stimulate immune cells and benefit consumer immunity. Here, the synergistic effects of immune active long‐chain inulin (lcITF) and Lactobacillus acidophilus W37 (LaW37) on dendritic cells (DCs) are investigated. METHODS AND RESULTS: Effects of lcITF and LaW37 alone or combined were studied on Toll‐like receptor (TLRs) signaling and cytokine secretion by DCs in the presence and absence of media of intestinal epithelial cell (IEC) exposed to the ingredients. Also, the effects of DC responses against Salmonella Typhimurium (STM) were investigated. Synergistic effects were observed on TLR2 and 3. Synergistic effects were not always pro‐inflammatory. LaW37 was strongly pro‐inflammatory, while cytokine responses were regulatory when combined with lcITF. Exposure of DCs to IECs medium changed the DCs’ response, which revealed synergistic enhancing effects of lcITF/LaW37 on production of IL‐6 and IL‐8. DCs’ response in the presence of STM and LaW37 were so strong that lcITF had no additional effect. CONCLUSION: It is demonstrated that synbiotic effects of dietary fibers and bacteria are not limited to the effects on gut microbiota but can also occur by synergistically directly stimulating IECs and/or immune cells.