Relationship of enhanced butyrate production by colonic butyrate-producing bacteria and immunomodulatory effects in normal mice fed insoluble fraction of Brassica rapa L

22 This study was performed to determine the effects of feeding a fiber-rich fraction of 23 Brassica vegetables on immune response through changes in enteric bacteria and short 24 chain fatty acid (SCFA) production in normal mice. The boiled water-insoluble fraction 25 of Brassica rapa L. (nozawana), which consisted mainly of dietary fiber, was chosen as 26 a test material. A total of 31 male C57BL/6J mice were divided into two groups and 27 housed in a specific pathogen-free facility. The animals were fed either a control diet or 28 the control diet plus insoluble B. rapa L. fraction for 2 weeks and sacrificed for 29 determination of microbiological and SCFA profiles in lower gut samples and of 30 immunological molecules. rRNA-based quantification indicated that the relative 31 population of Bacteroidetes was markedly lower in the colon samples of the insoluble B. 32 rapa L. fraction-fed group than the controls. Populations of the Eubacterium rectale 33 group and Faecalibacterium prausnitzii, both of which are representative 34 butyrate-producing bacteria, doubled after 2 weeks of the fraction intake accompanying 35 a marginal increase in colonic butyrate proportion. In addition, feeding with the fraction 36 significantly increased levels of the antiinflammatory cytokine, interleukin (IL)-10, and 37 tended to increase splenic regulatory T cell numbers, but significantly reduced the 38 population of cells expressing activation markers. We demonstrated that inclusion of the 39 boiled water-insoluble fraction of B. rapa L. can alter the composition of the gut 40 microbiota to decrease Bacteroidetes and to increase butyrate-producing bacteria, either 41 of which may be involved in the observed shift in production of splenic IL-10. 42