Immunomodulatory Properties of Plants and Mushrooms

Plants and mushrooms are used for medicinal purposes and the screening of molecules possessing biological activities. A single plant or mushroom may produce both stimulatory and inhibitory effects on immune cells, depending on experimental conditions, but the reason behind this dichotomy remains obscure. We present here a large body of experimental data showing that water extracts of plants and mushrooms usually activate immune cells, whereas ethanol extracts inhibit immune cells. The mode of extraction of plants and mushrooms may thus determine the effects produced on immune cells, possibly due to differential solubility and potency of stimulatory and inhibitory compounds. We also examine the possibility of using such plant and mushroom extracts to treat immune system disorders. Plants and mushrooms contain molecules that modulate immune cell activities, but the factors that determine whether a plant or mushroom may activate or inhibit immune cells remain unclear. Recent studies suggest that the solvent used to prepare a plant or mushroom extract may determine whether the extract produces immunosuppressive or immunostimulant effects. Accordingly, water extracts tend to activate immune cells, while ethanol extracts inhibit immune cell activity. Meta-analyses of randomized clinical trials suggest that many herbal and mushroom-based preparations may reduce immune disorder symptoms in humans. Understanding the effects of solvent extraction may be useful not only to identify new immunomodulatory compounds from plants and mushrooms, but also to facilitate the preparation of extracts producing specific immunological effects on humans.