part of positively regulates plasma kallikrein-kinin cascade activation of plasma proteins involved in acute inflammatory response Factor XII activation Any process that activates Factor XII (Hageman factor). Factor XII is a protein synthesized by the liver that circulates in an inactive form until it encounters collagen or basement membrane or activated platelets (as occurs at the site of endothelial injury). Factor XII then undergoes a conformational change (becoming factor XIIa), exposing an active serine center that can subsequently cleave protein substrates and activate a variety of mediator systems. Factor XII is a participant in the clotting cascade as well as the kinin cascade. GO:0002542 biological_process Hageman factor activation regulation of acute inflammatory response positive regulation of protein processing