CD59 (also known as HRF20, protectin) is a 20 kDa glycoprotein attached to the plasma membrane by a glycosylphosphatidylinositol (GPI) anchor. It blocks MAC formation in the complement pathway by interfering with C9 membrane insertion and polymerization, but it does not affect the generation of C3 and C5 activation products. CD59 is expressed on several cell types, including leukocytes, endothelial and epithelial cells, erythrocytes, and cells of the central nervous system. CD59 belongs to the Ly6 superfamily of proteins. This product is suitable for use in flow cytometry.