The Role of Complement in Hereditary Angioedema

Abstract

Low levels of C1 inhibitor, the main inhibitor of the classic complement system, result in paroxysmal angioedema attacks that can be incapacitating or even life-threatening in affected individuals. Molecular defects in the gene for C1 inhibitor cause hereditary angioedema. In recent years, new insights in the pathways leading to angioedema due to a deficiency of C1 inhibitor have been gathered. Bradykinin, which is formed upon activation of the kallikrein-kinin system under insufficient regulation by C1 inhibitor, plays a crucial role. Whereas C1 inhibitor also occupies a central mediatory role in other plasma systems, such as the contact activation system of coagulation and the fibrinolytic plasminogen-plasmin system, a C1 inhibitor deficiency may also cause enhanced activation of these pathways. Novel therapeutic modalities for treatment and prevention of hereditary angioedema are now available, such as different forms of C1 inhibitor concentrate and novel agents that interfere in the kallikrein-kinin system.

Keywords: Bradykinin; C1 inhibitor; Coagulation; Complement; Factor XII; Hereditary angioedema; Kallikrein; Kinin; Plasminogen; Serine protease inhibitors.