Description:
<jats:title>Abstract</jats:title><jats:p><jats:italic>Bacteroides</jats:italic>, a predominant commensal bacteria in the gut, are thought to be responsible for the development of inflammatory bowel disease (IBD). In the present study, we examined whether or not bifidobacteria suppress <jats:italic>B. vulgatus</jats:italic>, a representative pathogenic <jats:italic>Bacteroides</jats:italic> species, in both the coculture system and the gnotobiotic murine model. As a result, <jats:italic>Bifidobacterium infantis</jats:italic> 1222 highly inhibited the growth of <jats:italic>B. vulgatus</jats:italic> in the coculture and also significantly suppressed the systemic antibody response raised by <jats:italic>B. vulgatus</jats:italic> colonizing the gut in gnotobiotic mice. Colonization of the mice by <jats:italic>B. vulgatus</jats:italic> increased the number of Peyer's patch (PP) cells bearing PNA (peanut agglutinin)<jats:sup>+</jats:sup>/anti‐κ<jats:sup>+</jats:sup> phenotype, which represents plasma cell‐like B cells. Moreover, treatment of those <jats:italic>B. vulgatus</jats:italic>‐implanted mice with <jats:italic>B. infantis</jats:italic> 1222 abrogated such increase in the number of PNA<jats:sup>+</jats:sup>/anti‐κ<jats:sup>+</jats:sup> cells. These results thus suggested that <jats:italic>B. infantis</jats:italic> 1222 protected the gut epithelial layer including the PP from being invaded by <jats:italic>Bacteroides</jats:italic>, thereby suppressing the systemic antibody response raised by <jats:italic>Bacteroides</jats:italic>.</jats:p>