Structures of (1 → 6)-β-d-glucans from Bulgaria inquinans (Fries) and their immunological activities

In previous study, an unbranched (1 → 6)-β-d-glucan with Mw 2.6 kDa was isolated from fruit bodies of Bulgaria inquinans (Fries). In present paper, three branched (1 → 6)-β-d-glucans were obtained from the water-extracted residues by a sequential KOH-extraction, namely BIK2, BIK10 and BIK30. Their molecular weights were determined to be 37.5 kDa (BIK2), 288.9 kDa (BIK10) and 175.5 kDa (BIK30). Structural analysis indicated that their backbones were substituted by single glucosyls at C-3 positions, the branching ratios were 0.01 (BIK2), 0.17 (BIK10), 0.25 (BIK30). Immunological tests showed that all the four β-d-glucans could significantly increase the ConA or LPS-induced lymphocytes proliferation in vivo. Moreover, branched (1 → 6)-β-d-glucans have more significantly lymphocytes proliferation activities than unbranched (1 → 6)-β-d-glucan, and the effect of (1 → 6)-β-d-glucans on lymphocytes proliferation increases along with molecular weights. The present results well enrich the structure–activity relationships of (1 → 6)-β-d-glucan, and indicate (1 → 6)-β-d-glucans from B. inquinans (Fries) are potential immunostimulating agents.