Purification of soluble beta-glucan with immune-enhancing activity from the cell wall of yeast

Beta-glucan, one of the major cell wall components of Saccharomyces cerevisiae, has been found to enhance immune functions, especially by activating macrophages. However, a major obstacle to the clinical application of beta-(1-->3)-glucan is its low solubility in aqueous media. In this study, soluble beta-glucan, free of mannoprotein, was prepared, and its effects on TNF-alpha secretion and phagocytosis by macrophages were evaluated. Beta-glucan was first rendered soluble from the yeast cell wall by alkaline extraction (glucan-p1). The extract contained 2.8% of protein which was subsequently removed by successive DEAE-cellulose and ConA chromatography. Beta-glucan thus prepared was completely free of mannoprotein and was soluble at neutral pH (glucan-p3). The effects of beta-glucan on phagocytosis and TNF-alpha release activity were investigated. While glucan-p1 moderately induced TNF-alpha secretion at 200 microg/ml (550 pg of TNF-alpha/5 x 10(5) cells), glucan-p3 markedly stimulated macrophages at 200 microg/ml (2,860 pg of TNF-alpha/5 x 10(5) cells). Furthermore, glucan-p3 stimulated phagocytosis about 20% more than glucan-p1 did. In conclusion, we purified water-soluble beta-glucan which was completely devoid of mannoprotein and effectively stimulated the macrophage function, enabling it to be used as an intravenous injection for sepsis.