Bifidobacterium longum BL300 alleviates DSS-induced Colitis by promoting IgA-mediated Gut Microbiota homeostasis

Inflammatory bowel disease (IBD) is a chronic disease that is related to excessive inflammation and an imbalance in the gut microbiota. In this study, the effect of five Bifidobacterium longum subsp. longum strains on alleviating the colitis induced by dextran sulfate sodium (DSS) was investigated. Disease activity index (DAI) scores combined with hematoxylin and eosin (H&E) analysis showed that only B. longum BL300 could significantly alleviate DSS-induced colitis. Furthermore, immunofluorescence analysis confirmed that the expression of the intestinal barrier-related protein ZO-1, occludin, claudin-1 and MUC2 was significantly up-regulated. Moreover, transcriptome analysis of the colon tissue combined with RT-qPCR analysis revealed that levels of pro-inflammatory cytokines IL-2, IL-6, IL-17, TNF-α and IL-1β were decreased and anti-inflammatory cytokine IL-10 level was increased after B. longum BL300 intervention. Notably, the IgA production immune network was activated by B. longum BL300, which eliminated pathogenic bacteria, such as Escherichia, Shigella, Enterobacter and Prosthecobacter, by forming complexes. Meanwhile, the relative abundance of SCFA-producing bacteria was significantly increased. These results highlight the anti-inflammatory effect of B. longum BL300 on DSS-induced colitis, indicating its use as a probiotic candidate to support recovery from ongoing colitis.