This antibody reacts with the CD63- antigen, which is expressed in platelet lysosomes that is translocated to the platelet surface upon activation with strong agonists. The antigen is also present in most peripheral blood cells (not in erythrocytes) and in many tissues; both surface and cytoplasmatic locations are reported. It has been reported a cellular expression of CD63 in intracellular lysosomal, endosomal and granulate protein, in Weibel Palade bodies of vascular endothelium, in degranulated neutrophils, monocytes, macrophages and endothelium.
It has been showed an Immunohistochemistry staining of fibroblasts, osteoclasts, smooth muscle, neural tissue (brain white matter and peripheral nerves) and synovial lining cells.