Coriolus versicolor is thought to be a biological response modifier. PSK induced cytokine expression in human peripheral blood mononuclear cells in vitro. In other studies, PSP as well as a Coriolus extract selectively induced apoptosis of human promyelocytic leukemia HL-60 cells ^(13) (23). PSP also increased apoptotic cell death in cells treated with camptothecin, reduced cellular proliferation, inhibited cell progression through S and G2 phases of DNA replication, reduced 3H-thymidine uptake, and prolonged DNA synthesis time ⁽¹⁴⁾. A medicinal mushroom blend that included Coriolus inhibited cell proliferation and induced cell cycle arrest at the G2/M phase in an invasive human breast cancer cell line  ⁽¹⁵⁾. DNA-microarray analysis indicates the mushroom extract inhibits expression of cell-cycle regulatory genes and suppresses metastatic behavior via inhibition of cell adhesion, migration, and invasion. Inhibition of metastatic behavior was linked to suppression of urokinase plasminogen activator ⁽¹⁵⁾. PSP also inhibits interaction between HIV-1 gp120 and CD4 receptor, HIV-1 transcriptase activity, and glycohydrolase enzyme activity associated with viral glycosylation ⁽¹⁶⁾.

Several animal studies report synergy between PSK and biologic therapies, including a concanavalin A-bound L1210 vaccine and the IgG2a monoclonal antibody against human colon cancer cells ⁽¹⁷⁾. PSP induces cytokine production and T-cell proliferation, and prevents cyclophosphamide-induced immune suppression. Peritoneal macrophages isolated from PSP-fed mice show increased production of reactive nitrogen intermediates, superoxide anions, and tumor necrosis factor ⁽¹⁸⁾. PSP also shows analgesic activity in mouse models ⁽¹⁹⁾.

After consumption of PSP, non-small cell lung cancer patients have increased leukocyte and neutrophil counts, and increased serum IgG and IgM  ⁽⁶⁾. Healthy volunteers as well as breast cancer patients who used a formula containing Coriolus and Salvia were found to have elevated counts of T-helper lymphocytes (CD4+), a high ratio of CD4+/CD8+, and elevated absolute counts of B-lymphocytes ^(7) (8). TNF-alpha and IL-8 gene expression were also found to be significantly induced after PSK administration in healthy volunteers and gastric cancer patients, although individual response varied ⁽²⁰⁾. PSK induced apoptosis in promyelomonocytic leukemia HL-60 cells without inducing differentiation, and p38 MAPK was found to play an important role in this process ⁽²⁴⁾.