A comb-like branched β-d-glucan produced by a Cordyceps sinensis fungus and its protective effect against cyclophosphamide-induced immunosuppression in mice

•EPS was isolated from fermentation media of a Cordyceps sinensis fungus (Cs-HK1).•EPS was nearly composed of d-glucose excluding a trace amount of d-mannose.•EPS consisted of (1→3)-β-glucan backbone with single (1→6)-β-glucose as side chain.•EPS showed a comb-like structure with (1→6)-β-glucose branch on every three glucoses.•EPS could improve the levels of TNF-α and INF-γ to enhance immunomodulatory ability.

An exopolysaccharide (EPS) was fractionated from fermentation media of a Cordyceps sinensis fungus (Cs-HK1) by ethanol precipitation at 2/5 volume ratio of ethanol/media. Its structural characteristics were elucidated by FT-IR, GC, GC–MS, 1D and 2D NMR combined with periodate oxidation, Smith degradation, partial acid hydrolysis, and methylation analysis. Furthermore, the immunomodulatory activity of EPS was evaluated by the model of cyclophosphamide-induced immunosuppression. The results from monosaccharide composition and partial acid hydrolysis indicated that EPS almost consisted of glucose excluding a trace amount of mannose. GC–MS and NMR analysis further confirmed EPS had a linear backbone of (1→3)-β-d-glucopyranosyl residues with a single (1→6)-β-d-glucopyranosyl side-branching unit for every three β-d-glucopyranosyl residues, showing a comb-like β-d-glucan with short and intensive branches, which was responsible for high viscosity. Moreover, EPS could significantly enhance immune organs and stimulate the release of major cytokines TNF-α and INF-γ, suggesting that EPS exhibited protective effect in immunocompromised mice.

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