Complement-mediated hemolytic anemia and platelet activation in mCd59a and mCd59b double knockout mice (53.4)

Abstract

The complement regulatory protein CD59 inhibits formation of the complement membrane attack complex (MAC). Humans express only one while mice express two Cd59 genes; each mCd59 gene contains two promoters that control its expression in a tissue specific manner. Thus, total deficiency of mCd59 activity is required to study unambiguously the role of MAC and CD59 in mouse models of human diseases including paroxysmal nocturnal hemoglobinuria (PNH), a complement mediated hemolytic anemia with thrombosis due to the lack of GPI-linked membrane proteins, especially CD59. Here we report the targeted deletion of both mCd59 genes in mCd59ab−/− mice, their PNH-like phenotype, and the use of these mice in complement sufficient and complement (C3) deficient background to establish the role of complement in the activation of PNH-like platelets in vivo. Low NO bioavailability in the vasculature due to increased NO-scavenging free hemoglobin in their blood has long been suspected to contribute to the thrombotic diathesis and smooth muscle dystonias of PNH-patients. Using an NO-synthase inhibitor in vivo and an NO donor in vitro, we established a novel balancing effect of nitric oxide (NO) in the complement-mediated activation of mCd59ab−/− (CD59 deficient, PNH-like). These results unmask a hitherto unrecognized role for NO in balancing complement-mediated platelet activation.