CD59 is a GPI-anchored membrane protein that is an inhibitor of the complement membrane attack complex (MAC). CD59 binds to complement components C8 and C9, preventing C9 polymerization and insertion into membranes. Rare cases of CD59 deficiency have been reported to cause paroxysmal nocturnal hemoglobinuria in human patients. Expression of CD59 on tumor cells and viral infected cells makes them resist antibody-dependent complement-mediated lysis. Inhibitors of CD59 expression or activity may suppress tumor cell resistance to complement-mediated attack, and these technologies have been actively pursued for therapeutic applications. In addition, CD59 may regulate insulin secretion by modulating exocytosis, and a glycated form of CD59 with no MAC inhibitory activity is found in diabetic patients.
