Structural characterization of an active polysaccharide of longan and evaluation of immunological activity

An active polysaccharide (LPD2) was isolated from longan pulp by comparing the effects of polysaccharides on the phagocytosis of macrophages. LPD2 was composed of arabinose, mannose, glucose, and galactose in a molar ratio of 0.25:0.49:1:0.5 with average molecular weight of 9.64 × 106 Da. The main linkages of the sugar residues of LPD2 were (1→4)-β-Glc and (1→6)-β-Man. LPD2 significantly enhanced the lymphocytes proliferation, phagocytosis and NO and IL-6 secretion by macrophage. The anti-TLR2 and anti-TLR4 mAbs markedly suppressed LPD2-mediated NO and IL-6 production. Furthermore, anti-TLR4 or anti-TLR2 plus anti-TLR4 treatment significantly decreased LPD2-induced increase of MyD88, IRAK4, TRAF6 and INOS mRNA expression. Moreover, western blotting analysis showed that LPD2 enhanced the expression of target proteins in MyD88/IRAK4-TRAF6- INOS pathways. These results suggested that LPD2 induced macrophage activation partly via the TLR2- and TLR4-mediated MyD88/IRAK4-TRAF6 signaling pathways. Knowing the structural features and activities of active polysaccharide of longan gives the insights into longan polysaccharide application as an immunomodulatory agent.