Bifidobacterium breve MN15965 Improved Bacterial Diversity, Short-Chain Fatty Acid Production, and Immune Activation...

The gut microbiota serves as a critical interface for host immunity, making it a promising target for probiotic intervention. In this study, we investigated the immunomodulatory potential of the strain Bifidobacterium breve (B. breve) MN15965 and the underlying role of gut bacterial communities in this process. We first assessed its in vitro immunomodulatory activity by measuring nitric oxide and cytokine secretion in THP-1 macrophages. Subsequently, an immunosuppressed mouse model was established by treating BALB/c mice with cyclophosphamide (CTX), a chemotherapeutic agent known to cause immune dysfunction and mucosal damage. In this model, we performed a series of analyses, including H&E staining, measurement of hematological parameters and serum cytokines/immunoglobulins, quantification of fecal short-chain fatty acids (SCFAs) by gas chromatography, and profiling of gut microbiota composition via 16S rRNA gene amplicon sequencing. The results showed that MN15965 supernatant enhanced TNF-α, IL-1β, and GM-CSF secretion in THP-1 cells, promoting M1 macrophage activation in vitro. In the in vivo model, MN15965 administration restored spleen and thymus tissue integrity and improved physiological indices, hematological parameters, and immunoglobulin levels. Furthermore, MN15965 increased fecal SCFAs, particularly butyric and valeric acid, increased gut bacterial diversity, and enriched potentially beneficial SCFA-producing taxa, including Lachnospiraceae and Eubacterium. These findings demonstrate that B. breve MN15965 alleviated CTX-induced immunosuppression by activating immune responses, regulating gut bacterial communities, and boosting SCFA production.