Saccharomyces cerevisiae mutant displaying β-glucans on cell surface

The deletion of MCD4 leads to an increase in β-1,6-glucan level and a decrease in glycosylphosphatidylinositol-anchored protein and mannan levels in the cell wall of Saccharomyces cerevisiae, suggesting that mcd4 deletion mutant (mcd4Δ) displays β-glucans on the cell surface without a mannan cover. An observation of the cell surface of mcd4Δ cells and an examination of the effect of contact between mcd4Δ cells and mouse macrophages indicated that macrophages were activated by contact with mcd4Δ cells displaying β-glucans on the cell surface. We further examined the effect of intraperitoneal ethanol-fixed mcd4Δ cells on the survival period of mice infected with Candida albicans. mcd4Δ cells prolonged the survival period, implying that mcd4Δ cells may enhance the immune function of mice via macrophage activation. Moreover, we examined the structures of β-glucans (i.e., alkali- and acetic acid-insoluble β-glucans) extracted from mcd4Δ with 13C-NMR and the effect of extracted β-glucans on TNF-α secretion from macrophages. The structures of the β-glucans from mcd4Δ differed from those of wild type (WT); however, there was no difference in tumor necrosis factor-α (TNF-α) secretion level between β-glucans from mcd4Δ and those from WT. The yield of purified β-glucans obtained from dry cells of mcd4Δ was higher than that obtained from dry cells of WT. mcd4Δ may be a superior strain for the preparation of β-glucans.