Extraction, structural characterization, and immunomodulatory activity of a high-molecular-weight polysaccharide from cultured ophiocordyceps.

Ophiocordyceps (Ophiocordyceps sinensis) is a precious medicinal and edible fungus widely utilized in nutraceuticals and functional foods. However, the structural intricacies and biological potential of its high-molecular-weight polysaccharides remain largely unknown. In the present study, a novel high-molecular-weight neutral polysaccharide, designated as CSP1b, was isolated and purified from cultured ophiocordyceps via water extraction, ethanol precipitation, and sequential column chromatography. Characterization revealed that CSP1b possesses an extraordinary molecular weight of 2.65 × 107 Da and consists predominantly of glucose (73.98%), mannose (13.35%), and galactose (12.67%). Structural elucidation identified CSP1b as a galactomannoglucan with a backbone of →4)-α-D-Glcp-(1 → 6)-α-D-Glcp-(1→, branched at the O-6 position by side chains containing →6)-α-D-Glcp-(1→, α-D-Manp-(1→, and various galactose residues, resulting in a branching degree of 32.06%. The polysaccharide exhibited a filamentous and ribbon-like intertwined surface morphology. In vitro immunomodulatory assays demonstrated that CSP1b significantly enhanced the proliferation and phagocytic capacity of RAW 264.7 (mouse macrophage cell line), as well as induced the secretion of nitric oxide (NO) and cytokines (TNF-α, IL-6) in a dose-dependent manner. In summary, a novel high-molecular-weight galactomannoglucan (CSP1b) was isolated for the first time from cultured ophiocordyceps and exhibited potent immunostimulatory activity. These findings enrich the polysaccharide library of ophiocordyceps and support its application in immunoregulatory products.