Selectin (SELP), a Ca(2 )-dependent receptor on myeloid cells, belongs to the selectin/LECAM family. SELP binds to neutrophils and monocytes via carbohydrates, it interacts with SELPLG to enable rapid leukocyte rolling over vascular surfaces in early inflammation. It has been reported that that CD24 is a ligand for P-selectin and the CD24/P-selectin binding pathway could be important in the dissemination of tumor cells by facilitating the interaction with platelets or endothelial cells. Thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human SELP and recombinant human CD24. Briefly, biotin-linked SELP were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to CD24-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 human SELP and recombinant human CD24 was shown in Figure 1, the EC50 for this effect is 0.56 ug/mL.