Many polysaccharides isolated from mushroom are considered to be biological response modifiers and have been shown to enhance various immune responses in vivo and in vitro. We demonstrate that a novel polysaccharide–protein complex (PPC) extracted from Phellinus linteus was a potent immunomodulator. PPC had a molecular weight of approximately 73 kDa. It was composed of five different monosaccharides, predominantly D-glucose and D-mannose, in the molar ratio of 3:2, the main amino acid being aspartic acid. PPC had a unique mode of immunostimulation with regard to its cell-type specificity. PPC was found to markedly increase the proliferation of B cells, but not T cells. Although PPC and lipopolysaccharide (LPS) had a similar mode of action in B cells, they were differentiated by the fact that PPC-induced cellular activation was not inhibited by polymyxin B (PB), a specific inhibitor of LPS. PPC increased the cytokine production and nitric oxide (NO) from macrophages. PPC also enhanced the lytic death of NO-sensitive tumor cells, B16 melanoma, through the production of NO. In addition, PPC up-regulated the natural killer (NK) cell-mediated killing of tumor cells, YAC-1 lymphoma in vitro. These results suggest that PPC stimulated the tumoricidal activities of macrophages and NK cells, and induced the proliferation of B cells in vitro. This process may be the mechanism by which PPC produced its therapeutic effects.
2006 by Japan Society for Bioscience, Biotechnology, and Agrochemistry