C1r, C1s, MASP2, Factor XIIa, plasma kallikrein (C1r, C1s, MASP2, FXIIa, KLKB1)

C1r, C1s, MASP2, Factor XIIa, and plasma kallikrein are a group of serine proteases involved in the regulation and activation of the complement classical and lectin pathways (C1r, C1s, MASP2), and the contact/kallikrein-kinin and intrinsic coagulation pathways (Factor XIIa, plasma kallikrein)[1][2][3][4][6]. These enzymes are regulated by the serpin C1-inhibitor (C1-INH) and are pivotal in controlling processes such as inflammation, vascular permeability, immune complex clearance, and blood clotting. Dysfunction or dysregulation of these proteases, or their inhibition/regulation (for instance, in hereditary angioedema), leads to a range of clinical consequences including swelling, bleeding, or thrombosis. Therapeutically, inhibitors of these enzymes (chiefly C1-INH, but also small-molecule or antibody inhibitors) are used or in development for diseases such as hereditary angioedema and inflammatory or thrombotic disorders[3][4][5][6].

Other names

C1r proteaseComplement component 1, r subcomponentC1s proteaseComplement component 1, s subcomponentMannan-binding lectin serine protease 2MASP-2Hageman factorF12KLKB1Prekallikrein (inactive precursor)Kininogenase

Protease inhibitors (block active site of targeted enzymes, e.g., C1-INH inhibits all five proteins listed) Monoclonal antibodies or peptides that block enzyme activation or substrate binding Downregulation of bradykinin production (for kallikrein-related therapies)