Modulatory Effect of the Alfalfa Polysaccharide Fraction II on Cyclophosphamide-Induced Immunosuppression in Mice

This study investigated the protective effects of alfalfa polysaccharide fraction II (APS-II) on immunosuppression induced by cyclophosphamide (CTX) in mice. APS-II was extracted using ultrasound-assisted enzymatic extraction method and purified by DEAE-52 cellulose chromatography. Its structural characteristics, including molecular weight (Mw), monosaccharide composition, and thermal stability, were analyzed. A CTX-induced immunosuppressed mouse model was established to evaluate the effects of APS-II on immune organ indices, serum cytokines, antioxidant indicators in liver and spleen tissues, and intestinal microbiota. Results showed that APS-II, with main Mw of 28.05 kDa, consisted of glucose, galactose, mannose, arabinose, glucuronic acid, and rhamnose in the molar ratio of 8.04:1.22:1.18:0.92:1:0.06. Treatment with medium and high doses of APS-II significantly restored thymus and spleen indices (p < 0.05), increased serum cytokine levels of interleukin-2 (IL-2), interleukin-1 beta (IL-1β), and interferon-gamma (IFN-γ) (p < 0.05), and ameliorated spleen and thymus histopathology. Antioxidant parameters of total antioxidant capacity (T-AOC), catalase (CAT), and glutathione (GSH) were elevated, and malondialdehyde (MDA) was reduced, reaching significance at the high dose (p < 0.05). Additionally, APS-II reshaped the gut microbiota by increasing Bacteroidota abundance and reducing the Firmicutes/Bacteroidota ratio (p < 0.05), enriching Muribaculaceae and Lactobacillus (p < 0.01), while decreasing potentially pathogenic Rikenellaceae. In conclusion, APS-II provides significant protection against CTX-induced immunosuppression and holds promise as a functional food ingredient for immune health. PRACTICAL APPLICATIONS: Alfalfa polysaccharide fraction II (APS-II) exerts a protective effect on mice with CTX-induced immunosuppression, laying the scientific foundation for its development as an immunomodulatory ingredient in functional foods and dietary supplements.