PECAM-1 (platelet-endothelial cell adhesion molecule-1; also known as CD31) is a 130 kDa type I transmembrane glycoprotein adhesion molecule in the immunoglobulin superfamily. Expression is restricted to cells involved in circulation, especially endothelial cells, platelets, monocytes, neutrophils and lymphocyte subsets. PECAM-1 is concentrated at cell-cell junctions and is required for transendothelial migration (TEM). Besides, Cadherin 5 (CDH5) has been identified as an interactor of PECAM-1, thus a binding ELISA assay was conducted to detect the interaction of recombinant human PECAM-1 and recombinant human CDH5. Briefly, PECAM-1 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100μl were then transferred to CDH5-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-PECAM-1 pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50µL stop solution to the wells and read at 450/630nm immediately. The binding activity of PECAM-1 and CDH5 was shown in Figure 1, the ED50 for this effect is 126.6 ng/mL.