A neutral polysaccharide with a triple helix structure from ginger: Characterization and immunomodulatory activity

•Neutral ginger polysaccharide (NGP) had a lower molecular weight of 6305 Da.•The proposed repeating unit of NGP was obtained.•NGP significantly enhanced the RAW264.7 cell viability and phagocytic activity.•NGP had remarkable promoting effect on cytokines production of RAW264.7 macrophages. A neutral ginger polysaccharide fraction (NGP) was isolated from ginger, and its primary structures and immunomodulatory activity were investigated. The results showed that NGP had a low molecular weight of 6305 Da. NGP principally consisted of glucose (93.88%) together with minor levels of galactose (3.27%) and arabinose (1.67%). Besides, results of methylation analysis and 1D/2D NMR spectroscopy demonstrated that NGP was α-glucan which had the main chain of 1,4-linked α-d-Glcp and α-d-Glcp residues branched at C-6 position which was different from the common triple helical β-glucans. NGP also displayed a remarkable immunological activity on the RAW264.7 cells in vitro. It could significantly enhance the proliferation of macrophages without cytotoxicity and increase the production of immune substances (NO, TNF-α, IL-1β and IL-6). The secretion at the concentration of 200 μg/mL was 29.41 μM, 1496.71, 44.30 and 1889.83 pg/mL for each substance, respectively. The results indicated that NGP could be a potential immune agent and might provide meaningful information for further chain conformation and immune mechanism research.