Structural characterization and immunological activity of polysaccharides from the tuber of Bletilla striata

Two water-soluble polysaccharides, BSP-1 and BSP-2, were extracted and purified from the tuber of Bletilla striata. The molecular weights of BSP-1 and BSP-2 were 83.54 kDa and 12.60 kDa, respectively. The composition and proportion of BSP-1 and BSP-2 were mannose and glucose in molar ratios of 4.0:1.0 and 3.0:1.0 respectively. The two polysaccharides had a linear backbone, consisting mainly of repeating β‑1,4‑linked d‑mannosyl residues and β‑1,4‑linked d‑glucosyl residues. BSP-1 exhibited immunomodulatory effects by increasing the thymus and spleen indices of immunocompromised model mice.