In this study, we investigated the influence of a fiber-free diet on the intestinal secretory immune system in young animals. Four-week-old rats were fed either a purified diet containing sucrose as the only carbohydrate source (fiber(-) diet) or a diet supplemented with 15% natural crude fiber from sugar beets (fiber(+) diet). After 14 days of feeding, we measured total IgA content in 24-hr fecal samples and in intestinal tissues and the expression of intestinal polymeric immunoglobulin receptors (pIgRs), which are essential for IgA secretion. The excretion of total IgA in the feces was significantly lower in rats fed the fiber(-) diet than in those fed the fiber(+) diet (27% vs. 100%; p < 0.05). However, the total IgA content in the intestinal tissue extracts did not differ between the groups. The pIgR signal intensities observed by immunohistochemistry were somewhat lower in the colon of the rats fed the fiber(-) diet. Western blot analysis showed that pIgR protein expression in the distal colon of rats fed the fiber(-) diet was significantly lower than that in rats fed the fiber(+) diet (38% vs. 100%, p < 0.05). Conversely, colonic pIgR mRNA expression did not differ between the groups. Thus, we conclude that a fiber-free diet decreases colonic pIgR protein expression by a posttranscriptional mechanism, resulting in decreased luminal secretory immune system activity and thus, suboptimal protection of the colonic mucosa.

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This study examined the effects of L-arabinose on mouse intestinal microbiota and urinary isoflavonoids. Male mice were randomly divided into two groups: those fed a 0.05% daidzein-2.5% L-arabinose diet (AR group) and those fed a 0.05% daidzein control diet (CO group) for 28 days. The amounts of daidzein detected in urine were significantly lower in the AR group than in the CO group. The ratio of equol/daidzein was significantly higher in the AR group (p<0.01) than in the CO group. The composition of caecal flora differed between the AR and CO groups. The occupation ratios of Prevotella and Lactobacillales were significantly lower in the AR group. This study suggests that dietary L-arabinose has the potential to affect the metabolism of equol from daidzein by altering the metabolic activity of intestinal microbiota.

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We investigated Candida albicans-induced mast cell degranulation in vitro and in vivo. Cell wall fraction but not culture supernatant and cell membrane fraction prepared from hyphally grown C. albicans induced β-hexosaminidase release in RBL-2H3 cells. Cell wall mannan and soluble β-glucan fractions also induced β-hexosaminidase release. Histological examination of mouse forestomach showed that C. albicans gut colonization induces mast cell degranulation. However, intragastric administration of cell wall fraction failed to induce mast cell degranulation. We propose that cell wall polysaccharides are responsible for mast cell degranulation in the C. albicans-colonized gut.

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There is a growing interest in the study of the human gut microbiota, as correlations between changes in bacterial profiles and diseases are increasingly discovered. Studies in this field generally use fecal samples, but it is often easier to obtain colon content aspirates during colonoscopy. This study used automated ribosomal internal spacer analysis (ARISA) to examine the extent to which the microbiota of colon aspirate samples obtained after bowel cleansing can reflect interindividual differences and serve as a proxy for fecal samples. Pre-bowel preparation fecal samples as well as colonoscopy aspirate samples from the cecum and rectum were obtained from 19 subjects. DNA was extracted from all samples, and comparative analysis was performed, including analysis of similarity (ANOSIM) and nonmetric multidimensional scaling. ANOSIM confirmed that samples from the same individual were well separated from samples from different individuals. Significantly larger differences were found between samples from different individuals than between samples of the same individual (R = 0.7605, p < 0.0001). These findings show that post-bowel preparation aspirates maintain a strong individual signature. Colonoscopy aspirates can therefore serve as a substitute for fecal samples in studies comparing the microbiota of different clinical study groups, especially when fecal samples are unavailable.

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