Complement regulators, CD59 and DAF, are both membrane bound glycosyl phosphatidylinositol (GPI)-linked molecules that are involved in inhibiting the MAC complex and causing dissociation of the C3 and C5 convertases, respectively. The paroxysmal nocturnal hemoglobinuria (PNH) mutation in the gene PIG-A results in decreased expression of GPI-linked proteins, including CD59 and DAF. As a result, intense complement-mediated lysis of red blood cells occurs in PNH patients with consequent hemolytic anemia. White blood cells are also susceptible to lysis, and tissue factor release from these damaged cells may contribute to thrombosis often seen in PNH patients (Liebman and Feinstein 2003) .