Abstract: Objective: To investigate the percentages of lymphocyte subsets, the transformation and proliferation activities of T lymphocytes, the expression levels of serum immunoglobulin and cytokines in the immunosuppressive model rats after given Bifidobacterium lactis M8, and to elucidate the effect of Bifidobacterium lactis M8 on the immune function of the immunosuppressive model rats. Methods: Fifty Wistar rats were randomly divided into blank control group, model control group, low dose of Bifidobacterium lactis M8 group, middle dose of Bifidobacterium lactis M8 group, and high dose of Bifidobacterium lactis M8 group, and there were 10 rats in each group.The rats in each group were administrated with probiotic bifidobacterium lactis M8 for 6 d.From the 7th day, except for blank control group, the rats in the other groups were given cyclophosphamide (CTX) for 3 d to construct the immunosuppressive models; the rats in low, middle, and high doses of Bifidobacterium lactis M8 groups were given 0.01, 0.10 and 1.00 g bifidobacterium lactis M8, and the rats in blank control group and model control group were given sterile saline with the same volume. The percentages of lymphocyte subsets (CD3+ T lymphocytes, CD4+ T lymphocytes, CD8+ T lymphocytes, B lymphocytes and NK cells) in whole blood of the rats in various groups were detected by flow cytometry, the transformation and proliferation activities of T lymphocytes of the rats in various groups were detected by CCK-8 method, the levels of serum immunoglobulin A (IGA), immunoglobulin G (IgG), interleukin-2(IL-2), interleukin-6(IL-6), interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) of the rats in various groups were detected by ELISA method. Results: Compared with blank control group, the percentages of CD3+ T lymphocytes, CD4+ T lymphocytes, CD8+ T lymphocytes, B lymphocytes and NK cells in whole blood of the rats inmodel control group were decreased significantly (P<0.05); compared with model control group, the percentages of CD3+ T lymphocytes, CD4+ T lymphocytes and CD8+ T lymphocytes in whole blood of the rats in high dose of Bifidobacterium lactis M8 group were increased significantly (P<0.05 or P<0.01),and the percentages of B lymphocytes and NK cells were increased significantly (P<0.01).Compared with blank control group, the transformation and proliferation activities of T lymphocytes of the rats in model control group was decreased (P<0.01); compared with model control group, the transformation and proliferation activities of T lymphocytes of the rats in middle and high doses of Bifidobacterium lactis M8 group were increased (P<0.01). Compared with blank control group, the levels of serum IgA, IgG, IL-2, IL-6, IFN-γ and TNF -α of the rats in model control group were decreased (P<0.01); compared with model control group, the levels of serum IgA, IgG, IL-2, IL-6, IFN-γ and TNF-α of the rats in middle and high doses of Bifidobacterium lactis M8 group were increased (P<0.05 or P<0.01). Conclusion: Perfusion of Bifidobacterium lactis M8 can improve the specific and non-specific immune response regulation ability of the immunosuppressed model rats. Bifidobacterium lactis M8 has a promotion effect on the immune regulation of the immunosuppressed rats.

Key words: Bifidobacterium lactis M8, cyclophosphamide, lymphocyte, transformation and proliferation, lymphocyte subset, cytokine