Abstract: This study explored the regulatory effects of Bifidobacterium animalis J12 and its postbiotics on immunosuppression induced by cyclophosphamide (CTX) in mice and the impact on the structure of gut microbiota. The results indicated that the live cells of B. animalis J12 regulated the number and overexpression of T, natural killer (NK), natural killer T (NKT), cytotoxic T (CTL), and T helper (Th) lymphocytes in the spleen of CTX immunosuppressed mice. The fermentation supernatant significantly alleviated the impact of CTX on Th cells, but the heat-inactivated cells of J12 did not show significant effects on CTX-induced immunosuppression. Both the live cells and fermentation supernatant rescued gut microbiota imbalance induced by CTX, significantly increasing the abundance of Alloprevotella in the gut, and reducing the abundance of Lachnospiraceae_NK4A136_group, thereby regulating the metabolism and immune system, and restoring the disordered immune state. In summary, J12 live cells can effectively accelerate recovery from immunosuppression induced by CTX, indicating its potential as an immunomodulator.

Key words: heat-inactivated cells; live cells; Bifidobacterium; immunity; cyclophosphamide