AIM:to investigate the effect of Bifidobacterium infantis(B.infantis)on the T cell subsets and in attenuating the severity of experimental colitis in mice.METHODS:Normal BALB/c mice were fed different doses of B.infantis for 3 wk,and T cell subsets and related cytokine profiles in mesenteric lymph nodes(MLNs)were detected by flow cytometry and realtime RT-PCR.Colitis was induced by administration of trinitrobenzene sulfonic acid(TNBS)in mice.Before colitis induction,mice were fed high dose B.infantisfor 3 wk.Cytokine profiles in MLNs and histological changes of colonic tissue were examined 6 d after colitis induction.RESULTS:No significant change in cytokine profiles was observed in normal mice fed low dose B.infantis.However,Th1-related cytokines(IL-2,IFN-γ,IL-12p40),Th17-related transcription factor and cytokines(RORγt,IL-21,IL-23),regulatory T cell(Treg)-related transcription factor and cytokines(Foxp3,IL-10)were increased in normal mice fed high dose B.infantis.Furthermore,flow cytometry assay showed B.infantis increased the numbers of CD4+Foxp3+Tregs and Th17cells in MLNs.Colitis was successfully induced by TNBS in mice,characterized by colonic inflammation and aberrant Th1 and Th17 responses.Feeding high dose B.infantis for 3 wk before colitis induction decreased the inflammatory cell infiltration and goblet cell depletion and restored the intestinal epithelium.In addition,B.infantis feeding reduced Th1-related cytokines(T-bet,IL-2 and IFN-γ)and Th17-related cytokines(IL-12p40,RORγt,IL-17A,IL-21 and IL-23),and increased Tregrelated molecules(Foxp3,IL-10 and TGF-β)in colitis mice.CONCLUSION:B.infantis effectively attenuates TNBSinduced colitis by decreasing Th1 and Th17 responses and increasing Foxp3+Treg response in the colonic mucosa. AIM: to investigate the effect of Bifidobacterium infantis (B. infanis) on the T cell subsets and in attenuating the severity of experimental colitis in mice. METHODS: Normal BALB / c mice were fed different doses of B. infanis for 3 wk, and T cell subsets and related cytokine profiles in mesenteric lymph nodes (MLNs) were detected by flow cytometry and realtime RT-PCR. Colitis was induced by administration of trinitrobenzene sulfonic acid (TNBS) in mice. Early colitis induction, mice were fed high dose B . Infantisfor 3 wk. Cytokine profiles in MLNs and histological changes of colonic tissue were examined 6 d after colitis induction .RESULTS: No significant change in cytokine profiles was observed in normal mice fed low dose B. infantis. However, Th1-related cytokines ( IL-2, IFN-γ, IL-12p40), Th17-related transcription factor and cytokines (RORγt, IL- 21, IL- 23), regulatory T cell (Treg) -related transcription factor and cytokines ) were increased in normal mice fed high dose B. infantis. Fluidrther, flow c ytometry assay showed B.infantis increased the numbers of CD4 + Foxp3 + Tregs and Th17cells in MLNs.Colitis was successfully induced by TNBS in mice, characterized by colonic inflammation and aberrant Th1 and Th17 responses. Feeding high dose B. infantis for 3 wk before colitis induction decreased the inflammatory cell infiltration and goblet cell depletion and restored the intestinal epithelium. In addition, B. infanis feeding reduced Th1-related cytokines (T-bet, IL-2 and IFN-γ) and Th17- 12p40, RORγt, IL-17A, IL-21 and IL-23), and increased Tregrelated molecules (Foxp3, IL- 10 and TGF- β) in colitis mice. CONCLUSION: B. attenuant TNBSinduced colitis by decreasing Th1 and Th17 responses and increasing Foxp3 + Treg response in the colonic mucosa.