The present study investigated the immunomodulatory activity and associated mechanisms of heat-treated Lactobacillus plantarum LM1004 (HT-LM1004) in a cyclophosphamide (CTX)-induced mouse model of immunosuppression. HT-LM1004 induced phagocytic activity and nitric oxide production in RAW264.7 macrophages and stimulated the release of tumor necrosis factor (TNF)-α, interferon (IFN)-γ, interleukin (IL)-2, and IL-12p70. In mice with CTX-induced immunosuppression, oral HT-LM1004 administration restored thymus and spleen indices, including spleen weight. Consistent with the in vitro results, HT-LM1004 increased TNF-α, IFN-γ, IL-2, and IL-12p70 levels in mice after 14 days of treatment and enhanced the natural killer (NK) cell activity of splenocytes from mice with CTX-induced immunosuppression against YAC-1 lymphoma cells. The method of HT-LM1004 generation influenced this activity: L. plantarum LM1004 grown in a membrane bioreactor, which reduced the size of the cells to <1.0 μm through physical stress (micronization), promoted NK cell cytotoxicity to a greater extent than LM1004 subjected to heat treatment alone. These findings indicate that HT-LM1004 without or with micronization can reverse CTX-induced immunosuppression without adverse side effects by potentiating NK cell function.
Keywords: NK cell activity; cyclophosphamide; cytokine; heat-treated Lactobacillus plantarum LM1004; immune enhancement; macrophage phagocytosis.