Mitogenic activity of particulate yeast beta-(1->3)-D-glucan and its water-soluble derivatives

Particulate beta-D-glucan was isolated from baker's yeast using autolysis and delipidization of the cells, followed by alkaline and acid treatment. The residual water-insoluble glucan termed cerevan has a beta-(1-->3)-linked backbone with beta-(1-->6)-linked short side chains. In order to achieve water solubility of the glucan, various derivatives were prepared (carboxymethyl-, carboxyethyl-, hydroxyethyl-, sulfoethyl-), and the beta-glucan was oxidized to glucuronoglucan. Their solubility, degree of substitution (DS), and molecular weight distribution (M(w)) were compared. The immunomodulatory activity of these preparations was investigated in mitogenic and co-mitogenic tests on rat thymocytes. Cerevan showed higher stimulation indices compared with the known immunomodulator zymosan. Of the water-soluble derivatives, sulfoethylglucan was found to be the most active. Of the carboxymethyl derivatives of various DS, the preparation with DS=0.75 exhibited the highest activity. Water-soluble carboxymethyl preparations with DS > 1.0 and low-molecular-weight glucuronoglucan were inactive.