Contact Activation System (CAS)

The contact activation system (CAS), also known as the plasma contact system, is a group of plasma proteins that play a central role in initiating blood coagulation and inflammation when blood comes into contact with certain surfaces. The CAS is crucial for the intrinsic pathway of coagulation and for mediating inflammatory responses. Key components include Factor XII (FXII), Prekallikrein (PK), High Molecular Weight Kininogen (HK), and Factor XI (FXI). Upon contact with activating surfaces, FXII is activated, leading to the activation of PK and FXI, and the release of bradykinin from HK, amplifying both coagulation and inflammatory signals. Dysregulation or overactivation contributes to various pathologies including hereditary angioedema and thrombosis risk.

Other names

Plasma Contact System