The most recent development in shiitake medical research involves the use of shiitake extract to inhibit the reproduction of human immunodeficiency virus (HIV) in tissue culture. Researchers working at Japan's Yamaguchi University School of Medicine have reported that shiitake extract has a "protective effect" that inhibits the usual cell-destroying effects of the HIV virus. Researchers have noted that substances such as shiitake, which both enhance the immune response and have anti-viral effects, should be further evaluated for the treatment of AIDS.

In addition to fighting cancer, inhibiting the growth of viruses, and lowering cholesterol, shiitake have potent antibiotic effects against other organisms. A substance called cortinelin, a broad-spectrum antibacterial agent, which has been isolated from shiitake, kills a wide range of pathogenic bacteria. A sulfide compound extracted from shiitake has been found to have an effect against the fungus that causes ringworm and other skin diseases.