Vascular cell adhesion protein 1 (VCAM-1) is a cell adhesion molecule and a member of the immunoglobulin superfamily. Alternatively spliced forms are known to occur, but the most common form is a type I transmembrane protein with a 674 amino acid extracellular segment that includes seven C2-type immunoglobulin domains. VCAM-1 is expressed by activated endothelial cells and certain other cell types including macrophages, dendritic cells, neurons, smooth muscle cells, fibroblasts, and oocytes. Besides, Integrin Alpha 4 (ITGa4) has been identified as an interactor of VCAM-1, thus a binding ELISA assay was conducted to detect the interaction of recombinant human VCAM-1 and recombinant human ITGa4. Briefly, biotin-linked VCAM-1 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to ITGa4-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 450nm immediately. The binding activity of recombinant human VCAM-1 and recombinant human ITGa4 was shown in Figure 1, the EC50 for this effect is 0.261 ug/mL.