In this study, the effects of dietary nucleotides on the immune response balance between T helper cells type 1 (Th1) and type 2, and on the mucosal immune response in weanling mice were investigated. It was demonstrated that dietary nucleotides up-regulate the Th1 immune response and suppress the antigen-specific IgE antibody response in weanling mice. Thus, the results suggest that dietary nucleotides may be beneficial for the prevention of allergic diseases in early infancy. In addition, it was shown that dietary nucleotides increased the proportion of a γδT-cell receptor (TCR) -bearing intestinal intraepithelial lymphocyte (IEL) subset, IL-7 production by intestinal epithelial cells and the antigen-specific IgA response. Therefore, the present study indicates that dietary nucleotides may have an effect on the mucosal intranet in the intestinal mucosal immune system.

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Pulsed-field gel electrophoresis and lectin blotting were performed on a total of 41 B. longum strains isolated from 27 human fecal samples and 14 probiotic products in order to characterize their clonality and variation in expression of exopolysacchrides (EPSs; cell-bound polysaccharides). The probiotic isolates formed several distinct clonal clusters, and most of them shared the same lectin blotting profile. Almost all human fecal isolates were distinct from the probiotic isolates not only clonally but also in terms of EPS expression. Most of the fecal isolates within each clonal cluster presented different lectin blotting profiles, suggesting that the structures of EPSs from B. longum were of a labile nature independent of their clonality. Lectin blotting was also performed on a total 38 B. longum strains that had been isolated periodically (at the 1st, 23 rd, and 68th weeks) from fecal samples of 12 human subjects in order to evaluate whether EPS expression was host-specific. B. longum strains that had been isolated from fecal samples of the same individual at different times presented identical or almost identical lectin blotting profiles in 9 out of 12 subjects despite being clonally distant from each other. These findings suggest that variations in EPS expression are related to the hosts but not to the strains' clonality. This in turn suggests that human hosts can discriminate indigenous strains from exogenous ones based on EPS expression profiles.

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