The intestinal mucosa is exposed to a myriad of infectious and food antigens, and a unique barrier mechanism by the mucosal immune system handles them on the mucosal surface. Such mucosal defense mechanisms maintain homeostasis of intestinal functions and structure. Anatomic associations exist between nerve fibers and cellular components of the immune system, which is also regulated in part by the central nervous and endocrine systems acting principally via the hypothalamic-pituitary-adrenal axis. Leptin, the product of the ob gene regulates food intake as well as metabolic and endocrine functions, and also plays a regulatory role in immune-inflammatory responses, suggesting that these regulatory systems interplay one another in human body. Abrogation of these mucosal defense and regulatory mechanisms may alter mucosa defense mechanisms in the intestinal tract and be involved in the pathogenesis of inflammatory bowel disease.

View full abstract

Recent epidemiological findings concerning the relation between intestinal microflora and allergic disorder support an idea that lactic bacteria, bifidobacteria and lactobacilli, colonized in the human intestinal lumen, would contribute to prevention of allergy. Furthermore, some studies reported that lactic bacteria suppressed Th2 type immune response associated with development of allergy through enhancement of Th1 response. It is well known that intake of indigestible oligosaccharides is able to increase indigenous lactic bacteria, especially bifidobacteria. We investigated effects of raffinose, a kind of oligosaccharide, on Th1/Th2 immune response using ovalbumin specific T-cell receptor transgenic mice. Feeding raffinose to the transgenic mice significantly reduced IL-4 production from mesenteric lymph nodes cells and serum IgE response, which were induced by ingestion of ovalbumin. These results suggest that intake of raffinose suppresses unfavorable Th2 response induced by oral antigens, although types of intestinal bacteria linked to the change of rodent immune response remain unknown because feeding raffinose did not influence bacterial counts of cultivable bacteria in the ceca of the mice.

View full abstract

To elucidate the effect of fermented milk containing Lactobacillus johnsonii La1 on the intestinal microflora and fecal characteristics, a double-blind placebo control cross-over trial was conducted. Twenty-four healthy Japanese young women were randomly divided into two groups, and either of fermented milk containing L. johnsonii La1 (1×10⁹ cfu/120 g, test fermented milk) or placebo fermented milk without L. johnsonii La1 was administered daily for 21 days at the test period and placebo period, respectively. Compared to non-intake period, the number of bifidobacteria and lactobacilli were significantly increased and the number of lecithinase positive Clostridium was significantly decreased in the feces during the test period. Fecal pH was significantly decreased and concentration of short chain fatty acids showed tendency to increase. L. johnsonii La1 was identified by colony PCR technique in all subjects after the administration of the test fermented milk during the test period, neither non-intake period nor placebo period. Defecation frequency in the subjects with mild constipation significantly increased during the test period. These results suggest that fermented milk containing L. johnsonii La1 has an efficacy to improve the intestinal microflora and fecal characteristics by reaching the viable strain.

View full abstract

We prepared new transgalactosylated oligosaccharides mixture (N-GOS) and investigated effects of the four different oligosaccharides species (disaccharides, trioligosaccharides, tetraoligosaccharides, 4'-galactosyllactose) purified from N-GOS on the growth of 62 different established enterobacterial strains belonging to 22 bacterial genera in vitro. All of the bifidobacteria and the lactobacilli species tested, Bacteroides vulgatus, Clostridium perfringens, Enterococcus faecium, Streptococcus salivarius, and Escherichia coli utilized the transgalactosylated disaccharides for their growth in vitro. All of the bifidobacterial species tested, 3 Lactobacillus species, B. vulgatus, C. clostridiiforme, B. fragilis, Eubacterium rectale, and C. perfringens were able to utilize trioligosaccharides, which showed the similar utilization pattern to that of 4'-galactosyllactose. The bacterial species which could utilize the tetraoligosaccharides fraction of N-GOS were only 5 bifidobacterial species, B. vulgatus, L. reuteri, E. rectale, and C. perfringens. Then we examined the effect of N-GOS administration on human fecal flora, organic acid concentration, pH, water content, ammonia, phenols, β-glucuronidase activity and bile acid concentrations in the feces of 22 healthy volunteers (mean age : 39±10 years). The volunteers were divided into 2 groups of 11 subjects, and the two experimental groups were given 2.5 g or 5 g of N-GOS a day for 2 weeks. In both groups, significant increases in the total anaerobes, both the viable number and population level of indigenous bifidobacteria were shown at 1 and 2 weeks of administration of N-GOS when compared to those at the week before administration. The number of bacteroidaceae was also increased during N-GOS administration, but there were no significant increases in the rate of Bacteroides population to the total anaerobe population. The total organic acid content and bile acid concentration were significantly decreased during administration of high-dose N-GOS, suggesting that N-GOS administration affected the intestinal metabolic activity. There were no significant changes in fecal pH, water content, ammonia, phenols and β-glucuronidase activity by N-GOS administration. These results suggested that N-GOS stimulates anaerobic bacterial growth, especially indigenous bifidobacteria, which might influence organic acids and bile acid metabolisms.

View full abstract