A polysaccharide isolated from the cell walls of bacteria, plants, and fungi with immunostimulant and antineoplastic activities. In a solubilized form, beta-glucan binds to a lectin site within complement receptor 3 (CR3) on leukocytes, priming the receptor to trigger cytotoxic degranulation of leukocytes when leukocyte CR3 binds to complement 3 (iC3b)-coated tumors. Thus, the attachment of beta-glucan to CR3 of circulating leukocytes simulates leukocytes to kill iC3b-coated tumor cells in the same way as they kill iC3b-coated yeast. or A small protein normally found on the surface of many cells, including lymphocytes, and in small amounts in the blood and urine. An increased amount in the blood or urine may be a sign of certain diseases, including some types of cancer, such as multiple myeloma or lymphoma.