C1 esterase inhibitor (C1-INH)

C1 esterase inhibitor (C1-INH) is a serine protease inhibitor (serpin) that plays a critical role in regulating the complement system, contact system, and coagulation/fibrinolytic pathways. It inhibits the activation of the classical complement pathway by binding to and inactivating proteases such as C1r and C1s. C1-INH also regulates the contact system by inhibiting plasma kallikrein, factor XIIa, and factor XIa. Deficiency or dysfunction of C1-INH leads to unchecked complement activation and increased bradykinin levels, resulting in conditions like hereditary angioedema (HAE).

Other names

C1-inhibitor

Irreversibly binds to and inhibits target proteases (C1s, kallikrein, factor XIIa/XIa), preventing their enzymatic activity and downstream effects like bradykinin production and complement activation.