Apolipoprotein A1 (APOA1) is the major protein component of HDL particles in plasma. It is a cofactor for lecithin cholesterolacyltransferase (LCAT) which is responsible for the formation of most plasma cholesteryl esters. ApoA1 was also isolated as a prostacyclin (PGI2) stabilizing factor, and thus may have an anticlotting effect. ApoA1 is often used as a biomarker for prediction of cardiovascular diseases. Besides, Plasminogen Activator, Urokinase (uPA) has been identified as an interactor of APOA1, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human APOA1 and recombinant human uPA. Briefly, biotin-linked APOA1 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to uPA-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 450/630 nm immediately. The binding activity of recombinant human uPA and recombinant human APOA1 was shown in Figure 1, the EC50 for this effect is 0.08 ug/mL.