SERPING1 and angioedema: C1-INH regulates the activation of the contact system by inhibiting the activation of factor XII (FXII) and kallikrein that generate bradykinin (BK), which binds to its specific receptor B2 at the endothelial level to enhance vaso-permeability and vasodilation and cause the formation of angioedema (Fig. 1) [4].