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Sixteen heat-killed bifidobacteria isolated from human intestine and a probiotic strain Lactobacillus GG were tested for their ability to influence IgE-mediated degranulation of rat basophilic leukemia (RBL-2H3) cells in vitro. The bifidobacteria suppressed IgE-mediated degranulation of RBL-2H3 cells by 1.6-56.4% in a strain-dependent manner. Bifidobacteria from healthy infants expressed high inhibitory effects on IgE-mediated degranulation (41-55%), while those from allergic infants varied greatly in their effects against degranulation. Bifidobacteria taxonomically identified as Bifidobacterium bifidum exhibited much stronger inhibitory effects against IgE-mediated degranulation than those taxonomically identified as B. adolescentis (P < 0.05).These results indicate that the intestinal bifidobacteria might be one of factors influencing IgE-mediated allergic responses.

Background: Although much attention has been focused on the anti-allergic effects of probiotics, their mode of action is not fully understood. Mast cells, which play a central role in inducing allergic inflammation, are potential targets of probiotics given the recent discovery that they express Toll-like receptors (TLRs), the pattern recognition receptors for microbial components. In this study, we examined whether allergic reactions of mast cells are modulated by stimulation through TLR2., Methods: The effects on mast cells of the synthetic TLR2 ligand Pam3CSK4 and Bifidobacterium pseudocatenulatum JCM 7041 were evaluated in vitro. Furthermore, the effects of Pam3CSK4 on mast cell-induced increase in vascular permeability in vivo were investigated by employing mast cell-deficient W/W(v) mice into which IgE-sensitized mouse bone marrow-derived mast cells were transferred., Results: Pam3CSK4 and Bifidobacterium pseudocatenulatum JCM 7041 suppressed degranulation of IgE-sensitized mast cells upon antigen stimulation in vitro. Pam3CSK4 also suppressed leukotriene C(4) production triggered by engagement of the high-affinity IgE receptor, FcepsilonRI. Intracellular Ca(2+) mobilization and phosphorylation of Erk were suppressed by pretreatment with Pam3CSK4, suggesting that the TLR2 ligand suppresses activation of mast cells by interrupting FcepsilonRI-mediated intracellular signaling. Pam3CSK4 treatment of bone marrow-derived mast cells reduced the increase in vascular permeability in recipient W/W(v) mice upon intravenous injection of antigen; the decrease was by about half, in a TLR-dependent manner., Conclusion: Collectively, these results demonstrate that the FcepsilonRI-mediated inflammatory responses of mast cells are suppressed by stimulation through TLR2, suggesting that probiotics exert potential anti-allergic effects, at least in part, through direct effects on mast cells., (Copyright 2009 S. Karger AG, Basel.)

Bifidobacterium is a dominant bacterial species among commensals in the human intestine and is thought to have probiotic immunomodulatory effects. In this study, we investigated the effect of the association with Bifidobacterium pseudocatenulatum JCM 7041 (Bp) on dietary ovalbumin (OVA)-specific immune responses using germ-free OVA-specific T cell receptor transgenic mice (OVA23-3 mice). We established germ-free OVA23-3 mice, and then associated with Bp (BIF group) or without (CONT group) and additionally associated with segmented filamentous bacteria (SFB) and clostridia in both groups. BIF and CONT mice were fed an egg-white diet containing OVA for 1 week. Cytokine production in response to OVA by cells of Peyer's patches (PPs) and lamina propria (LP) from the small and large intestine was measured. Interferon (IFN)-gamma and interleukin (IL)-6 production by PP cells from BIF group mice was lower than that of the CONT group. The proportion of PP cells expressing CD4+CD62L(low), an activated/memory T cell phenotype, was higher in BIF group mice than the CONT group. Furthermore, LP cells from the small intestine in Bp-associated mice showed a tendency to produce slightly lower IFN-gamma and IL-6, while the cells from large intestine produced markedly higher IFN-gamma, IL-5 and IL-6 than those in the CONT group. The pattern of cytokine production by PP in BIF animals was similar to those isolated from conventional mice. These results suggest that intestinal association with Bp might down-regulate excessive immune responses to dietary antigens of the small intestine but enhance those of the large intestine.