Structural elucidation and immunomodulatory activity of a β-D-glucan prepared by freeze-thawing from Hericium erinaceus

H6PC20, a water-soluble beta-D-glucan, with a molecular mass of 2390 kDa (HPSEC-MALLS-RI), was obtained by extracting the fresh fruiting bodies of Hericium erinaceus at mature stage with hot water, freeze-thawing, precipitating and further rinsing with 20% (v/v) of ethanol. The primary structure of H6PC20 was proposed as a beta-(1 -> 3)-linked-D-glucan with a (1 -> 6)-beta-linked-D-glucopyranosyl side-branching unit on every third residue by using methylation analysis, H-1 and C-13 NMR spectroscopy, including COSY, TOCSY, HSQC and HMBC. The rho value (R-g/R-h) and the exponent (alpha) of [eta] = k M-w(alpha) of H6PC20 were calculated as 1.86 and 0.54, respectively, indicating flexible random coil conformation of H6PC20 in aqueous solution. H6PC20 could induce the proliferation of lymphocytes and enhance the expression of inflammatory cytokines IL-6, TNF-alpha and IL-1 beta secreted by THP-1 macrophages. The present study indicated that the macromolecular beta-glucan H6PC20 possessed potent immune-enhancing bioactivities and could be a potential ingredient for healthy food or medicine development.