Immune-enhancing alkali-soluble glucans produced by wild-type and mutant Saccharomyces cerevisiae

The alkali-soluble glucan of the yeast cell wall contains β-(1,3)- and (1,6)-D-linkages and is known to systemically enhance the immune system. In the previous study [6], in order to isolate cell wall mutants, a wild-type strain was mutagenized by exposure to ultraviolet light, and the mutants were then selected via treatment with laminarinase (endo-β-(1,3)-D-glucanase). The mass of alkali- and water-soluble glucans produced by the mutant was measured to be 33.8 mg/g of the dry mass of the yeast cell. Our results showed that the mutants generated the amount of alkali-soluble glucan 10-fold higher than that generated by the wild-type. Structural analysis showed that the alkali-soluble glucan from the mutants was associated with a higher degree of β-(1,6)-D-linkage than was observed in conjunction with the wild-type. Yeast cell wall β-glucan was shown to interact with macrophages via receptors, thereby inducing the release of tumor necrosis factor alpha (TNF-α) and nitric oxide. Alkali-soluble β-glucans, both from water-soluble and water-insoluble glucan, exhibited a higher degree of macrophage activity with regard to both the secretion of tumor necrosis factor alpha (TNF-α) and nitric oxide and direct phagocytosis, than did the positive control (1 μg of lipopolysaccharide).