Coagulation factor XII (FXII), a S1A serine protease, is mainly produced in the liver and circulates in plasma as a single chain zymogen. F12 plays a role in initiating the contact activation pathway during clotting. When blood comes into contact with a foreign body, F12 is activated, initiating a series of reactions that eventually lead to the production of thrombin and the formation of fibrin, which promotes blood clotting. In addition, the combination of Plasminogen (Plg) with F12 can promote plasminogen activation and thus increase plasminogen production, which plays an important role in thrombolysis and tissue repair. Thus a functional binding ELISA assay was conducted to detect the interaction of recombinant rat F12 and recombinant chicken Plg. Briefly, biotin-linked F12 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to Plg-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µl stop solution to the wells and read at 450 nm immediately. The binding activity of recombinant rat F12 and recombinant chicken Plg was shown in Figure 1, the EC50 for this effect is 0.56ug/mL.