Relationship between solubility of grifolan, a fungal 1,3-β-D-glucan, and production of tumor necrosis factor by macrophages in vitro

Grifolan, GRN, is a fungal antitumor fl-glucan isolated from Grifola frondosa. Various studies suggested that the underlying mechanism of the antitumor activity of GRN is strongly related to immune modulation. In the previous publication (Adachi et al., 1994; Okazaki et al., 1995), we have shown that GRN activates macrophages to produce tumor necrosis factor (TNF) in vitro. In this study, the structural unit essential to produce TNF was examined by chemical modifications of GRN. GRN suspended in distilled water was treated at 150 degreesC for up to 3 h. Addition of the resulting turbid solution to the RAW 264.7 macrophage-like cell line produced TNF, and the relative activity was diminished in relation to the heat treatment period. The fractions with a heating period longer than 15 min did not show any activity. After centrifugation of the resulting solution, significant activity was shown by precipitate fractions, suggesting that the insoluble form of GRN is important for TNF production. Interestingly, the precipitate fraction obtained from 9 min of treatment also had significant activity. In addition, admixing the soluble fraction with the particles significantly inhibited the TNF production. In contrast to these observations, the high-molecular-mass subfraction of the soluble fraction prepared by ultrafiltration produced significant amounts of TNF. Similar phenomena were shown with sodium hydroxide treatment and dimethylsulfoxide treatment. These facts strongly suggested that insoluble as well as a high molecular mass soluble form of GRN are required for TNF production by macrophages.