Purification and characterization of a novel mixed-linkage α,β-d-glucan from Arca subcrenata and its immunoregulatory activity

Arca subcrenata Lischke is a seafood with high nutritional value. In this study, we purified and characterized a novel water-soluble polysaccharide (ASPG-2) from Arca subcrenata with significant immunoregulatory effects and no apparent cell toxicity. ASPG-2 is a class of mixed-linkage α,β-d-glucan backbones with α-linked side chains with a molecular weight of 4.39 × 105 Da. Its structure was characterized as a repeating unit consisting of (1 → 3)-β-d-Glcp, (1 → 4)-α-d-Glcp, (1 → 4,6)-α-d-Glcp and (1 → 6)-α-d-Glcp. Using mouse RAW264.7 macrophages, we demonstrated that ASPG-2 exerted marked immunoregulatory effects by promoting the secretion of NO and increasing the phagocytosis of RAW264.7 cells in vitro. Moreover, flow cytometry analysis of the expression of the cell surface molecule CD86 revealed that ASPG-2 could polarize RAW264.7 cells into the M1 type. The immunomodulatory mechanism of ASPG-2 in macrophages was associated with the activation of the TLR4-MAPK/Akt-NF-κB signalling pathways. These results indicated that ASPG-2 might be researched and developed as a potential immunomodulatory agent or health product from marine organisms. [Display omitted] •A new novel water-soluble mixed-linkage α,β-d-glucan (ASPG-2) was purified from Arca subcrenata.•The structure of ASPG-2 was identified by HPGPC, methylation analysis, and NMR.•ASPG-2 enhanced phagocytosis and induced secretion of NO in RAW 264.7 cells.•ASPG-2 polarized macrophages to the M1 type of tumour-killing macrophages.•ASPG-2 exerted an immunomodulatory effect by the TLR4-MAPKs/Akt-NF-κB signalling pathway in RAW 264.7 cells.