PSK belongs to a class of immunomodulators known as biological response modifiers capable of immunostimulatory and anticancer activities. It induces IL-8 and TNF-a cytokine gene expression in human peripheral blood mononuclear cells from normal healthy subjects and gastric cancer patients given PSK orally6. Peripheral blood CD4+/CD8+ ratio and IL-2 production which were suppressed by chemotherapy were found to increase after oral administration of PSK in patients with ovarian cancer7. Oral administration of PSK in older people without disease and patients with malignancy resulted in the restoration of the depressed cellular immunity as determined by the positive Mantoux skin test and skin test reactivity to PHA and endotoxin as well as T cell transformation test in vitro8. Furthermore, neutrophil functions as determined by chemotaxis and chemiluminescence also increased significantly in patients treated with PSK9. Circulating natural killer cells were found to significantly increase after administration of PSK in subjects with chronic fatigue syndrome10.
In patients undergoing radical surgery for cancer, oral administration of PSK prevented surgical stress-induced immunosuppression with a restoration of depressed levels of circulating CD4+ helper T cells, CD8+CD11- cytotoxic T cells and NK cells, and an accompanying reduction in the level of suppressor CD8+CD11+ T cells11,12. PSK also activates NK cells and enhances cytotoxic T cell activity in cancer patients13,14.
Maintaining the correct balance between cellular (mediated by Th1 helper cells) and humoral (mediated by Th2 helper cells) immunity is critical to the body’s ability to mount an effective immune response to infection and human diseases based on the patterns of cytokines secreted15. In cancer-bearing state, the balance between Th1 and Th2 immune responses is shifted towards Th2 dominance resulting in poor prognosis. PSK therapy causes a shift of the Th1/Th2 balance towards Th1 dominance in patients with gastric or colorectal cancer16, a condition promoting better outcome for cancer therapy.