An extract of Lentinula edodes mycelia (L.E.M.) was obtained with hot water after culturing in medium comprising bagasse and rice bran. It has been reported that L.E.M. exhibits physiological effects such as anticancer activity and immunoregulatory activity, and that such effects involve macrophage activation. We examined the active components in L.E.M. by fractionation using an anion exchange carrier and gel chromatography, and determined whether they stimulate production of the cytokine tumor necrosis factor-α (TNF-α) in RAW264.7 cells. We obtained 2 polysaccharide fractions, IA-a and IA-b, which potently stimulated cytokine production. We also confirmed that IA-a and IA-b significantly stimulate phagocytosis in RAW264.7 cells. To determine the structures of these fractions, we performed sugar component analysis, methylation analysis, FT-IR, 13C-NMR analysis, and molecular weight analysis. The results showed that the major component of IA-a is a 1,4-α-glucan exhibiting 1,6-branching and having a molecular weight of approximately 250,000. This branching structure suggests that IA-a has a glycogen-like structure. In addition, the major component of IA-b appears to be an arabinoxylan-like polysaccharide, mainly consisting of arabinose and xylose, with a molecular weight of approximately 8,500.
