Structural characterization and innate immunomodulatory effect of glucomannan from Bletilla striata

The crude polysaccharide of Bletilla striata in this study was extracted by water extraction and alcohol precipitation and further purified by gel column to yield the purified component Bletilla striata polysaccharide (BSP). Its structure and innate immune regulation activity were studied. BSP mainly comprises mannose and glucose, with a monosaccharide molar ratio of 2.9:1 and a weight-average molecular weight of 28,365 Da. It is a new low-molecular-weight water-soluble neutral glucomannan. BSP contains a → 6)-β-Manp-(1→, →4)-β-Glcp-(1→, →4)-β-Manp-(1 → and →3)-α-Manp-(1 → linear main chain, containing β-Glcp-(1 → and β-Manp-(1 → two branched chain fragments were connected to the Man residue at position 4. BSP can enhance the anti-infection ability of Caenorhabditis elegans against Pseudomonas aeruginosa, significantly improve the phagocytic ability of RAW264.7 macrophages, stimulate the secretion of NO and TNF-α, and have good innate immune regulation activity. These findings guide the use of Bletilla striata polysaccharides with immunomodulatory action.