Stimulation of human innate immune cells by medicinal mushroom sclerotial polysaccharides

Polysaccharides extracted from the sclerotia of medicinal mushrooms Pleurotus tuberregium (PT) and Polyporus rhinocerus (PR), including two water-soluble polysaccharide-protein complexes (PTW and PRW) and a β-glucan (PRG), were incubated with human innate immune cells, and the extracellular cytokines released by the immune cells to the culture medium were analyzed by using the RayBio® human cytokine antibody array. PRG significantly stimulated the proliferation of NK-92MI cells with a corresponding increase in the expression of cytokines IL-2 and I-309, which belong to the chemokine subfamily and are known to be chemotactic for monocytes. All three sclerotial polysaccharides stimulated the proliferation of CD56+ natural killer (NK) and human normal spleen monocytes/macrophages (MD) cells. Cell surface β-glucan receptors on the immune cells treated with the sclerotial polysaccharides were stained with antibodies of dectin-1 and its isotypes before flow cytometric analysis. Dectin-1 expression on NK-92MI and MD cells, but not on CD56+ NK cells, was upregulated by the three sclerotial polysaccharides. The above results suggest the stimulatory effect of mushroom sclerotial polysaccharides on human innate immune cells. These results provide some insight into the mechanism of immunomodulation of mushroom polysaccharides and their potential development into antitumor agents.