A Novel Polysaccharide Isolated From Fresh Longan (Dimocarpus longan Lour.) Activates Macrophage via TLR2/4-Mediated PI3/AKT and MyD88/TRAF6 Pathways

Abstract

A novel immunomodulatory polysaccharide (LP4) with a molecular weight 6.31 × 104 g/mol was purified from fresh longan pulp. It was composed of mannose, glucose, glucuronic acid, galactose, xylose, arabinose, galacturonic acid, fucose, and rhamnose in a molar percentage of 36:31:10:7:4:4:3:2:2, and mainly linked by (1→6)-β-Man, (1→4)-β-Glc and (1→6)-α-Glc. LP4 can obviously enhance the phagocytosis of macrophages and promote the proliferation of lymphocytes. After treating macrophages with LP4 (12.5–50 μg/ml), the production of IL-1β and TNF-α was significantly increased. These increases of cytokines were suppressed when the TLR2/TLR4 receptors were inhibited by anti-TLR2 and/or anti-TLR4 antibodies. Moreover, the mRNA expression of INOS, AKT, PI3K, TRAF6 and MyD88 was significantly suppressed by TLR2/TLR4 antibodies. These results indicated that LP4 induced macrophage activation mainly via the TLR2 and TLR4-induced PI3K/AKT and MyD88/TRAF6 pathways.

Comparative Study on the Mechanism of Macrophage Activation Induced by Polysaccharides from Fresh and Dried Longan

“…Specifically, dried longan-derived polysaccharides engage Toll-like receptors (TLRs) 2/4 and the Ca 2+ /CR3 receptor, whereas fresh longan-derived polysaccharides primarily act through TLR2/4 receptors. Both dried and fresh longan-derived polysaccharides have been reported to exert immunomodulatory effects via the MyD88/TRAF6 -mediated MAPK and PI3K/AKT signaling pathways [ 15 , 16 , 17 ]. However, due to the fragmented results of previous research, it remains unclear whether other receptors and signaling pathways are involved in the immunomodulatory activities of polysaccharides from dried and fresh longan.…”