The term "glucan" refers generically to a variety of naturally occurring homopolysaccharides or polyglucoses, including polymers such as cellulose, amylose, glycogen, laminarians, starch, etc. Glucan encompasses branched and unbranched chains of glucose units linked by 1-3, 1-4, and 1-6 glucosidic bonds that may be of either the alpha or beta type.
As defined herein, "particulate glucan" designates a water-insoluble particulate (about 1-3.mu.) polyglucose such as that derived from the cell wall of the yeast Saccharomyces cerevisiae. Particulate glucan is macromolecular and comprises a closed chain of glucopyranose units united by a series of .beta.-1-3 glucosidic linkages. (Hassid et al., 1941, J. Amer. Chem. Soc. 63: 295-298; Di Luzio et al., 1979, Int'l J. Cancer 24: 773-779). X-ray diffraction studies have demonstrated that particulate glucans exist in the form of a triple-stranded helices. (Sarko et al., 1983, Biochem. Soc. Trans. 11: 139-142).