Immunomodulatory Mechanism of Bangia fusco-purpurea Polysaccharides in Cyclophosphamide-Induced Immunosuppressed Mice

The immunomodulatory effects of Bangia fusco-purpurea polysaccharides (BFP) in a mouse model of cyclophosphamide (CTX)-induced immunosuppression were investigated. As a result, BFP intervention significantly improved natural killer (NK) cell viability, macrophage phagocytosis and carbon clearance capacity, enhanced T-lymphocyte proliferation, up-regulated the proportions of CD4⁺, down-regulated the proportions of CD8⁺ T cells, increased the ratio of CD4⁺/CD8⁺ cells, reduced the proportion of Th17 cells and the ratio of CD3^-CD19⁺ B cells, and increased the levels of serum hemolysin, immunoglobulin (Ig) A, IgG and immune-related cytokines such as interleukin (IL)-2, IL-6, tumor necrosis factor-α (TNF-α), and interferon-γ (INF-γ), which demonstrated its potent regulatory effects on nonspecific immunity, cellular immunity and humoral immunity in immunosuppressed mice. Furthermore, the effects of BFP on the surface receptors of intestinal immune cells in immunosuppressed mice were analyzed. It was found that BFP significantly downregulated the mRNA (P < 0.05) and protein (P < 0.01) expression of Toll-like receptor 2 (TLR2), TLR4, IL-6 and TNF-α. Based on this, we speculated that BFP can enhance the immunity through the regulation axis of the TLR2/TLR4 downstream signaling pathway. This study provides scientific support for in-depth understanding of the nutritional value of sea foods and promoting the incorporation of sea foods into residents' diets.