CD63 (NKI/C3)

This antibody reacts with a 53 kDa protein which forms a part of the family of tetraspan moieties. The antigen was originally designated as a lysosomal membrane protein characterized as an activation dependent platelet surface antigen. In fact the CD63 antigen has a diverse distribution on the surface and in the cytoplasm of many cell types including lymphoid, myeloid, endothelial cells and melanoma. It has been quite useful in identifying malignant melanoma. Mete et al. found it useful in differentiating renal oncocytomas (RO) from eosinophilic renal cell carcinomas (eRCC). In his series of 35 ROs, 94% demonstrated apical and/or polar CD63 positivity. Of his 77 eRCCs, 96% showed diffuse cytoplasmic staining.