<i>Bifidobacterium longum</i> 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 <i>Bifidobacterium longum</i> subsp. <i>longum</i> 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 <i>B. longum</i> 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 <i>B. longum</i> BL300 intervention. Notably, the IgA production immune network was activated by <i>B. longum</i> BL300, which eliminated pathogenic bacteria, such as <i>Escherichia, Shigella</i>, <i>Enterobacter</i> and <i>Prosthecobacter</i>, by forming complexes. Meanwhile, the relative abundance of SCFA-producing bacteria was significantly increased. These results highlight the anti-inflammatory effect of <i>B. longum</i> BL300 on DSS-induced colitis, indicating its use as a probiotic candidate to support recovery from ongoing colitis.