Degradation Products of Complex Arabinoxylans by Bacteroides intestinalis Enhance the Host Immune Response

Bacteroides spp. of the human colonic microbiome degrade complex arabinoxylans from dietary fiber and release ferulic acid. Several studies have demonstrated the beneficial effects of ferulic acid. Here, we hypothesized that ferulic acid or the ferulic acid-rich culture supernatant of Bacteroides intestinalis, cultured in the presence of complex arabinoxylans, enhances the immune response. Ferulic acid and the culture supernatant of bacteria cultured in the presence of insoluble arabinoxylans significantly decreased the expression of tumor necrosis factor-α and increased the expression of interleukin-10 and transforming growth factor β1 from activated dendritic cells compared to controls. The number of granulocytes in mesenteric lymph nodes, the number of spleen monocytes/granulocytes, and interleukin-2 and interleukin-12 plasma levels were significantly increased in mice treated with ferulic acid or the culture supernatant of bacteria cultured with insoluble arabinoxylans. Ferulic acid or the culture supernatant of bacteria cultured with insoluble arabinoxylans increased the expression of interleukin-12, interferon-α, and interferon-β in intestinal epithelial cell lines. This study shows that ferulic acid or the ferulic acid-rich culture supernatant of the colonic bacterium Bacteroides intestinalis, cultured with insoluble arabinoxylans, exerts anti-inflammatory activity in dendritic cells under inflammatory conditions and enhances the Th1-type immune response under physiological conditions in mice.