Beta-glucan is a complex polysaccharide composed of glucose molecules extracted and purified from the cell wall of common baker"s yeast, Saccharomyces cerevisiae. Beta-glucan is used to maintain or stimulate the effectiveness of the immune system. Animal and human cell culture studies have shown that beta-glucan can stimulate several aspects of immune function, such as phagocytosis and interleukin production. Source Naturals Beta-Glucan uses a purification process that removes the mannoproteins and yeast residues that may reduce the effectiveness of beta-glucan.