Structural characterization and macrophage immunomodulatory activity of a novel polysaccharide from Smilax glabra Roxb

•A novel heteropolysaccharide (SGRP1) with notable immunomudulatory activity is obtained from Smilax glabra Roxb.•Structure of SGRP1 is characterized by HPGPC, GC, GC–MS, FT-IR and NMR.•Immunomodulatory effects of SGRP1 are evaluated with RAW264.7 cells.•SGRP1 promote the phagocytosis and increase the secretion of NO, IL-6, TNF-α and IL-1β.•The immunomodularoty mechanism of SGRP1 is elucidated for the first time. A novel heteropolysaccharide (SGRP1) with great immunomodulatory activity was isolated from the root of Smilax glabra Roxb. by hot water extraction. Physical and chemical analyses showed that SGRP1 had an average molecular weight of 1.26×104Da and was composed of mannose, fucose and glucose in molar ratio of 1.00:3.09:39.41. The glycosidic linkage types of SGRP1 were proven to be (1→3)-linked −α-l-Fuc, (1→3)-linked-α-l-Man, (1→)-linked-α-d-Glc, and (1→6)-linked-α-d-Glc. The in vitro immunomodulatory assays demonstrated that SGRP1 could evidently promote the phagocytosis and increase macrophage-derived biological factors including nitric oxide (NO), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) secretion via JNK and ERK signaling pathways and NLRP3 inflammasome signaling pathway. The data supported that SGRP1 had immunomodulatory potential through activating macrophages and enhancing host immune system function, which enabled it to be a novel immunomodulator for application in immunological diseases or functional food.