Cluster Of Differentiation 42b (CD42b) also known as CD42b GP Ib is a platelet activation marker involved in the process of coagulation as an aggregating factor. It is composed of a heterodimer, an alpha chain and a beta chain, that is linked by disulfide bonds. The binding of the CD42b-IX-V complex to VWF facilitates initial platelet adhesion to vascular subendothelium after vascular injury and also initiates signaling events within the platelet that lead to enhanced platelet activation, thrombosis and hemostasis. Besides, ITGaM has been identified as an interactor of CD42b, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human CD42b and recombinant human ITGaM. Briefly, CD42b was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to ITGaM-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-CD42b 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 50 µL stop solution to the wells and read at 450/630 nm immediately. The binding activity of recombinant human CD42b and recombinant human ITGaM was shown in Figure 1, the EC50 for this effect is1.16 ug/mL.