Structure and anti-tumor activity of a polysaccharide from Bletilla ochracea Schltr

The polysaccharide fraction of Bletilla ochracea (BOP) was isolated from its tubers, and purified by DEAE-52 Cellulose and Sephadex G-200 column chromatography. The structural features of BOP were analyzed by GC-MS, HPLP, FT-IR, methylation and NMR. The average molecular weight of BOP was approximately 4.9 × 10⁵ Da, and the monosaccharide composition was 7.88:2.12 mix of mannose and glucose. The FT-IR and NMR analyses revealed the following linkage: [→(4-β-D-Man-1)₄ → (4-β-D-Glc-1)₂ → 4-2-O-acetyl-β-D-Man-1 → 4-β-D-Man-1 → 4-3-O-acetyl-β-D-Man-1 → 4-2-O-acetyl-β-D-Man-1→]. Although BOP had no effect on the proliferation rate of CT26 colon carcinoma cells, it significantly inhibited tumor xenograft growth in vivo by stimulating CD4⁺ T cell expansion in the spleen of the tumor-bearing mice. Taken together, BOP is a potent immunomodulatory agent that can be considered for anti-tumor therapy.