NaM172-2B5 also known as membrane attack complex inhibition factor (MACIF), membrane inhibitor of reactive lysis (MIRL) is widely distributed on cells in all tissues. CD59 is expressed, like CD55, in erythrocytes, lymphocytes, monocytes, polymorphonuclear cells and platelets. CD59 inhibits formation of the complement membrane attack (MAC); thus protecting cells from complement mediated lysis. The expression of CD59 on erythrocytes is important for their survival. CD59 is a Glycosyl-phosphatidylinositol (GPI) anchored cell surface glycoprotein involved in protecting cells from host-mediated complement attack.