Stimulation of human peripheral blood polymorphonuclear cell iodination by PSK subfractions

A protein-bound polysaccharide, PSK, extracted from the mycelium of Coriolus versicolor (Fr.) Quel, stimulated the iodination (incorporation of radioactive iodine into an acid-insoluble fraction) of human peripheral blood polymorphonuclear cells (PMN), human promyelocytic leukemic HL-60 cells and human myeloblastic leukemic ML-1 cells. In contrast, PSK did not significantly increase the iodination of other cultured cell lines (U-937, THP-1, L-929, T98G, BALB 3T3). The PSK stimulation of iodination of both PMN and HL-60 cells depended on incubation time and temperature, and was significantly suppressed by the presence of myeloperoxidase inhibitors. Among various PSK subfractions, the highest molecular weight fraction (MW greater than 200 kD), or the fraction precipitated at pH 4.0-4.5, stimulated the iodination most. In contrast, natural and chemically modified glucans had little or no stimulation activity. The active PSK subfractions synergistically enhanced TNF stimulation of PMN iodination. The data suggest the presence of some unique components in PSK which directly stimulate the iodination of myeloperoxidase-positive cells.