Mushroom polysaccharide: A review on structural and immunological study

The number of mushrooms on earth is estimated at 140,000, yet maybe only 10% (approximately 14,000 named species) are known. Mushrooms comprise a vast and yet largely untapped source of powerful new pharmaceutical products. In particular, and most importantly for modern medicine, they represent an unlimited source of polysaccharides with antitumor and immunostimulating properties. Many, Basidiomycetes mushrooms (if not all) contain biologically active polysaccharides in fruit bodies, cultured mycelium, culture broth. Data on mushroom polysaccharides have been collected from 651 species and 7 infra specific texa from 182 genera of higher Hetero-and Homo Basidiomycetes. These polysaccharides are of different chemical composition, with most belonging to the group of β-glucans; these have β-(1,3) linkages in the main chain of the glucan and additional β-(1,6) branch points that are needed for their antitumor action. High molecular weight glucans appear to be more effective than those of low molecular weight. Chemical modification is often carried out to improve the antitumor activity of polysaccharides and their clinical qualities (mostly water solubility). Most of the clinical evidence for antitumor activity comes from the commercial polysaccharides lentinan, PSK (krestin), and Schizophyllan, but polysaccharides of some other promising medicinal mushrooms species also show good results. Polysaccharides from mushrooms do not attack cancer cells directly, but produce their antitumor effects by activating different immune responses in the host. The information presented in this review is helpful in exploring and understanding the different mushroom polysaccharides and their biological activities.