Structural characterisation and immunomodulatory effects of polysaccharides isolated fromDendrobium aphyllum

Summary A crude polysaccharide extract ofDendrobium aphyllum(cDAP, yield 38.15 ± 0.20%) was generated. TheD. aphyllumpolysaccharide (DAP, Mw471.586kDa), purified byDEAE‐Sepharose and Sephadex‐G200 Fast Flow, was composed of mannose (71.3%) and glucose (28.7%), according toGC–MSanalysis. Its backbone was composed of β‐d‐mannopyranose and β‐d‐glucopyranose residues, as revealed by infrared spectroscopic analysis. Its glycosidic bond was mainly 1, 4‐linked, and theO‐acetyl groups were mainly linked to mannose residues, according to periodate oxidation and Smith degradation analysis. TheDAPunits polymerised into a filiform‐shaped spatial pattern, as characterised by atomic force microscopy and scanning electron microscopy.DAPtreatment enhanced cytokine secretion (nitric oxide, interleukin‐6 and tumour necrosis factor‐α) and pinocytic and phagocytic capacities ofRAW264.7 mouse macrophages. The complement receptor 3 and mannose receptor were identified to be the receptors ofDAPonRAW264.7 cells, indicating that the Akt/mTOR/MAPKandIKK/nuclear factor‐ĸBpathways could be involved inDAP‐activated immunomodulation.