Stimulation of the natural immune system in normal mice by polysaccharide from maitake mushroom
Maitake D-Fraction is a polysaccharide extracted from the maitake mushroom (Grifola frondosa S.F. Gray). It is a β-glucan with a β-1,6 main chain with β-1,3 branches. Using normal C3H/Hej mice, its effects on the natural immune system, including macrophages, dendritic cells, and natural killer (NK) cells, were investigated. NK cells attack cells infected with pathogens such as bacteria and virus and produce cytokines, such as interferon-gamma (IFN-γ), that can modulate natural and specific immune responses. D-Fraction was administered to the mice intraperitoneally for 3 consecutive days; spleen cells containing macrophages and dendritic cells were then cultured and the culture supernatants were analyzed for IL-12. At the same time, IFN-γ expression in splenic NK cells was investigated. The levels of these cytokines were increased by D-Fraction. To elucidate NK cell activation by D-Fraction, CD69 expression on the surface of activated NK cells was examined, resulting in an increase in CD69-positive ratio for splenic NK cells. These results indicate that D-Fraction stimulates the natural immunity related to the activation of NK cells indirectly through IL-12 produced by macrophages and dendritic cells. Therefore, administration of D-Fraction to healthy individuals may serve to prevent infection.
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