<unk>  <unk> ,<unk>  esterase<unk>  is a protease<unk>  belonging to the serpin superfamily. Its main function is the inhibition of the complement system to prevent spontaneous activation but also as the major regulator of the contact system.<unk>  is an acute-phase protein that circulates in blood at levels of around 0.25 g/L. The levels rise ~2-fold during inflammation.<unk>  irreversibly binds to and inactivates<unk> r and<unk> s proteases in the<unk>  complex of classical pathway of complement. MASP-1 and MASP-2 proteases in MBL complexes of the lectin pathway are also inactivated. This way,<unk>  prevents the proteolytic cleavage of later complement components C4 and C2 by<unk>  and MBL. Although named after its complement<unk> y activity,<unk>  also inhibits proteases of the fibrinolytic, clotting, and kinin pathways. Note that<unk>  is the most important physiological<unk>  of plasma kallikrein, fXIa, and fXIIa.
C1-inhibitor
Complement component 3
C3a 
Complement component 4
Complement component 5a
Β-Thromboglobulin
Antileukotriene
Α-Hederin