Structure-Activity Relationship of (1→3)-β-D-Glucans in the Induction of Cytokine Production from Macrophages, in Vitro

抄録

In a previous study, we reported that one of the gel-forming (1→3)-β-D-glucans, grifolan (from Grifola frondosa, GRN), stimulated cytokine production from macrophages in vitro. However, several other gel-forming (1→3)-β-D-glucans, such as sonifilan (SPG) and SSG, did not induce cytokine production from macrophages. The ultrastructure of gel-forming (1→3)-β-D-glucans, especially the triple-and single-helix, does not affect the cytokine-inducing activity. The action on tumor necrosis factor α (TNFα) release was correlated with the molecular weight of GRN, since the highest molecular weight fraction of GRN, Mr≥450000, exhibited the strongest activity. Although, native SSG (Mr≥2000000) did not induce cytokine production, chemical modification involving debranching of the side chain glucosyl residues of SSG resulted in TNFα inducing activity. These results suggest that the branching ratio and molecular weight of (1→3)-β-D-glucans are important factors for the production of cytokines from macrophages. GRN-inducible TNFα release was reduced by co-culturing with SPG, SSG, or the soluble β-glucan, laminarin (LAM). Pretreatment alone with SPG or LAM was not sufficient for significant inhibition of GRN-inducible TNFα release. TNFα production induced with 50μg/ml of zymosan (ZyM) was also reduced by addition of SPG, but TNFα production, stimulated with a higher concentration (100μg/ml) of ZyM or with lipopolysaccharide (LPS), was not reduced significantly. The inhibitory effect of LAM on the uptake of GRN by RAW264.7 cells was not completely correlated with TNFα release. These results suggest that macrophages may incorporate β-glucans through certain (1→3)-β-D-glucan-specific mechanisms and/or other endocytosis pathways, and that the β-glucan-specific route is partially associated with cytokine production. In conclusion, TNFα release by macrophages is induced only by β-glucans with high molecular weights and lower branching ratios, and the mechanism for the recognition of β-glucans is multiple and assumed to be divided into several parts involving various cellular functions.