Structural characteristics of two polysaccharides from L. fumosum (Pers.) P.D. Orton. and their immunomodulatory effects on RAW264.7 macrophages.

Two polysaccharides, LFP-I and LFP-II, were isolated from L. Fumosum mushroom, and their structures and immunostimulatory effects were investigated. Structural analysis revealed that LFP-I had a molecular weight of 13,288 Da and consisted of fucose (13.12 %), mannose (15.75 %), glucose (46.46 %) and galactose (24.67 %). LFP-II, with a molecular weight of 13,288 Da, was primarily composed of glucose. Bond structure analysis and nuclear magnetic resonance (NMR) characterization confirmed that LFP-I possessed an α-D-(1 → 6)-linked galactan backbone with double substitutions at the O-2 and O-3 positions with mannan and glucofuranosyl units, including β-D-(1 → 6)-linked short glucan side chains and terminal fucose. LFP-II featured a backbone of β-D-(1 → 3)-linked glucan with monosubstitution at the O-6 positions with glucose. In cellular experiments, LFP-I and LFP-II were found to enhance phagocytosis and the secretion of immune cytokines (NO, TNF-α, and IL-6) by up-regulating their mRNA expression in macrophages, with LFP-II being particularly effective. From the perspective of structure-activity relationships, LFP-II exhibited a stronger immunomodulatory effect on macrophages, which was attributed to its higher β-glucan content in the backbone. Overall, our findings provide a theoretical basis for the application of L. Fumosum polysaccharides as functional foods or immunomodulatory agents in food health.