Gnotobiotic Mouse Immune Response Induced byBifidobacteriumsp. Strains Isolated from Infants

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Abstract
Bifidobacterium, which is a dominant genus in infants’ fecal flora and can be used as a probiotic, has shown beneficial effects in various pathologies, including allergic diseases, but its role in immunity has so far been little known. Numerous studies have shown the crucial role of the initial intestinal colonization in the development of the intestinal immune system, and bifidobacteria could play a major role in this process. For a better understanding of the effect ofBifidobacteriumon the immune system, we aimed at determining the impact ofBifidobacteriumon the T-helper 1 (TH1)/TH2 balance by using gnotobiotic mice. Germfree mice were inoculated withBifidobacterium longumNCC2705, whose genome is sequenced, and with nineBifidobacteriumstrains isolated from infants’ fecal flora. Five days after inoculation, mice were killed. Transforming growth factor β1 (TGF-β1), interleukin-4 (IL-4), IL-10, and gamma interferon (IFN-γ) gene expressions in the ileum and IFN-γ, tumor necrosis factor alpha (TNF-α), IL-10, IL-4, and IL-5 secretions by splenocytes cultivated for 48 h with concanavalin A were quantified. TwoBifidobacteriumspecies had no effect (B. adolescentis) or little effect (B. breve) on the immune system.Bifidobacterium bifidum,Bifidobacterium dentium, and oneB. longumstrain induced TH1 and TH2 cytokines at the systemic and intestinal levels. OneB. longumstrain induced a TH2 orientation with high levels of IL-4 and IL-10, both secreted by splenocytes, and of TGF-β gene expression in the ileum. The other two strains induced TH1 orientations with high levels of IFN-γ and TNF-α splenocyte secretions.Bifidobacterium's capacity to stimulate immunity is species specific, but its influence on the orientation of the immune system is strain specific.