Functional maturation of monocytes/macrophages induced by PSK subfractions.

When mouse resident peritoneal macrophages were cultured with PSK (Krestin), a protein-bound polysaccharide extracted from Coriolus versicolor, they became enlarged and elongated and expressed higher NBT-reducing activity. PSK stimulated the production of differentiation-inducing factor and cytotoxic factor by the mouse macrophage-like cell line J774.1, and iodination (incorporation of radioactive iodine into an acid-insoluble fraction) and interleukin-1-like factor production by human peripheral blood monocytes. Among four different PSK subfractions, the highest molecular weight fraction (MW greater than 200 kD) was the most potent. Natural and chemically modified glucans had little or no activity. The data suggest that some unique structure of the highest molecular weight fraction of PSK directly stimulates the monocytes/macrophages.