Structural characterization and immunomodulatory activity of an acidic polysaccharide from walnut green husk

Acidic walnut green husk polysaccharide with weight average molecular weight of 5.101 kDa was isolated and designated WGHP-2, which was composed of galacturonic acid (69.47 %), galactose (11.18 %), rhamnose (8.67 %), arabinose (3.96 %), glucose (2.21 %), glucuronic acid (2.28 %), xylose (0.83 %), fucose (0.81 %) and mannose (0.59 %). The main glycosidic linkage types of WGHP-2 were -> 4-alpha-D-Glcp-(1 ->, -> 4-alpha-D-GalpA-(1 ->, t-beta-D-GlcpA-(1 ->, -> 2-beta-D-Rhap-(1 ->, t-alpha-D-Galp-(1 ->, -> 4-alpha-D-Galp-(1 -> and -> 2,4)-alpha-D-Manp(1 ->. Immunostimulating assays showed that WGHP-2 could significantly promote the proliferation of RAW264.7 cells, strengthen the phagocytic activity, and up-regulate the production and release of NO, ROS, TNF-alpha, INF-beta and IL -6. Western-blot analysis indicated that MAPK and PI3K/Akt pathways were involved in the activation of macrophages induced by WGHP-2. Overall, our study suggests that WGHP-2 has the potential to be developed as a functional food with good immunostimulatory activity.