Abstract: Objective: To investigate the effect of Bifidobacterium animalis subsp. lactis XLTG11 (XLTG11) on immune function and intestinal flora in cyclophosphamide (CTX)-immunosuppressed mice. Methods: Altogether 60 mice were randomly divided into five groups: blank, model, low-dose, medium-dose and high-dose XLTG11 groups. The blank group was injected intraperitoneally with normal saline from day 1 to 3, and the other groups 100 μL of CTX solution (40 mg/kg) to establish an immunocompromised mouse model. From day 4 to 30, the low-, medium- and high-dose XLTG11 groups were given 0.2 mL of XLTG11 suspensions at doses of 2.5 × 106, 2.5 × 107 and 2.5 × 108 CFU/animal, respectively, and both blank and model groups 0.2 mL of normal saline/animal. Body mass, immune organ index, delayed-type metamorphosis, proliferation of splenic lymphocytes, T-lymphocyte subpopulation, natural killer (NK) cell activity, phagocytic activity of peritoneal macrophages, cytokine levels, intestinal flora structure, and short-chain fatty acids (SCFA) were detected in each group of mice. Results: XLTG11 increased the immune organ index, foot-plantar thickness, splenic lymphocyte proliferation, T lymphocyte subsets CD4+ and CD8+, NK cell activity and macrophage phagocytosis activity, and cellular immune factors (interleukin (IL)-6, IL-10, IL-1β and interferon (IFN)-γ) in immunosuppressed mice. In addition, XLTG11 alleviated intestinal tissue damage caused by CTX, regulated the intestinal flora and increased intestinal SCFA (acetic, propionic and butyric acid) levels. Conclusion: XLTG11 could significantly enhance the immune function and regulate the intestinal flora of mice.

Key words: Bifidobacterium animalis subsp. lactis XLTG11; immunomodulation; intestinal flora; short chain fatty acid