Antitumor mechanisms of orally administered shiitake fruit bodies.

When tumor-bearing mice were given diet containing fruit bodies of shiitake (L-feed), the tumor growth was apparently inhibited. To elucidate the mechanisms of this action, the effects of the L-feed on the production superoxide anion (SOA) by macrophages and the cytotoxicity of natural killer T cells were studied. When MM-46 carcinoma-bearing C3H mice were maintained on L-feed (containing 20% shiitake powder), SOA production by macrophages was increased about 2.0 to 2.3 times. Furthermore, the cytotoxic activities of natural killer cells and killer T cells were increased 1.9 times and 1.4 times, compared with their counterparts from normal C3H mice fed on shiitake-free diet. These results suggest that shiitake powder given orally activates various effector cells to attack tumor cells. It appears to potentiate cellular functions and at the same time to prevent a decrease of immune function of the tumor-bearing host. Keywordsshiitake; antitumor activity; macrophage; natural killer cell; superoxide anion; cytotoxic T cell