A Soluble Fiber Diet Increases Bacteroides fragilis Group Abundance and Immunoglobulin A Production in the Gut.

Immunoglobulin A (IgA) is essential for defense of the intestinal mucosa against harmful pathogens. Previous studies have shown that , the major phylum of gut microbiota together with , impact IgA production. However, the relative abundances of species of responsible for IgA production were not well understood. In the present study, we identified some specific species that were associated with gut IgA induction by -based profiling of species distribution among The levels of IgA and the expression of the gene encoding activation-induced cytidine deaminase (AID) in the large intestine lamina propria, which is crucial for class switch recombination from IgM to IgA, were increased in soluble high-fiber diet (sHFD)-fed mice. We found that was the most abundant species in both sHFD- and normal diet-fed mice. In addition, the gut IgA levels were associated with the relative abundance of group species such as , , and Conversely, the ratio of to other species was reduced in insoluble high-fiber diet fed- and no-fiber diet-fed mice. To investigate whether increases IgA production, we generated monoassociated mice and found increased gut IgA production and AID expression. Collectively, soluble dietary fiber increases the ratio of gut group, such as , and IgA production. This might improve gut immune function, thereby protecting against bowel pathogens and reducing the incidence of inflammatory bowel diseases. Immunoglobulin A (IgA) is essential for defense of the intestinal mucosa against harmful pathogens. Gut microbiota impact IgA production, but the specific species responsible for IgA production remain largely elusive. Previous studies have shown that IgA and , the major phyla of gut microbiota, were increased in soluble high-fiber diet-fed mice. We show here that the levels of IgA in the gut and the expression of activation-induced cytidine deaminase (AID) in the large intestine lamina propria, which is crucial for class switch recombination from IgM to IgA, were correlated with the abundance of group species such as , , and monoassociated mice increased gut IgA production and AID expression. Soluble dietary fiber may improve gut immune function, thereby protecting against bowel pathogens and reducing inflammatory bowel diseases.