Protective Effect of <i>Bifidobacterium longum</i> subsp. <i>infantis</i> E4 Exopolysaccharide on Intestinal Barrier, Regulation of Gut Microbiota and Metabolite In Vitro, and Immunosuppressed Mice

Exopolysaccharides (EPSs) may play an important role in the function of regulating the intestinal barrier. This study examined the protective effects of EPS-1 and EPS-2 generated by <i>Bifidobacterium longum</i> subsp. <i>infantis</i> E4 (<i>B. infantis</i> E4) on the intestinal barrier. EPS-1 and EPS-2 promoted the survival rates, wound healing rates, transepithelial electrical resistance values, and the mRNA levels of tight junction proteins (TJs), reducing the paracellular permeability of IEC-6 cells. EPS-1 and EPS-2 mitigated intestinal histological lesions, enhanced ileal villus length/crypt depth, and increased the mRNA levels of Muc2 and TJs relative to the model group. Simultaneously, the levels of immune cells IgA and dendritic cells T cells (CD3⁺, CD4⁺, and CD8⁺), and B cells were increased. In addition, EPS-1 and EPS-2 regulate gut microbiota and metabolites in mice. These findings demonstrated that EPS has the potential to regulate organismal health through its immune and intestinal barrier regulatory functions.