Structural characterization of Alpiniae oxyphyllae fructus polysaccharide 2 and its activation effects on RAW264.7 macrophages

•Alpiniae oxyphyllae fructus polysaccharide 2 (AOFP2) activated RAW264.7 cells.•AOFP2 polarized RAW264.7 macrophages toward both the M1 and M2 phenotypes.•The structural characterization of AOFP2 was first reported.•AOFP2 was only composed of glucose with an average molecular weight of 44.3 kDa.•AOFP2 consisted of → 4)-α-D-Glcp-(1→, →4,6)-α-D-Glcp-(1 → and T-α-Glcp. Polysaccharides are important components of Alpiniae oxyphyllae fructus that have been shown to exhibit significant immunomodulatory activity in our previous study. However, whether and how A. oxyphyllae fructus polysaccharides (AOFP) affect macrophages has not been determined. To further study the immunomodulatory activity of AOFP, the effect of AOFP on RAW264.7 cell activation was investigated in the present work. The results showed that AOFP2 significantly increased the phagocytic activity of RAW264.7 macrophages. AOFP2 promoted the secretion of TNF-α, IL-6, IL-10, TGF-β, NO and iNOS and enhanced the Th2-type immune response via its activation effect on macrophages. Additionally, the structure of AOFP2 was characterized in the present study, as the structural features of polysaccharides determine their biological activities. AOFP2 was only composed of glucose, exhibiting an average molecular weight of 44.3 kDa. Furthermore, the infrared spectroscopy, methylation and nuclear magnetic resonance results indicated that AOFP2 consisted of → 4)-α-D-Glcp-(1→, →4,6)-α-D-Glcp-(1 → and T-α-Glcp.