CD63 (CD63 antigen, LAMP-3, NKI-C3, ME491, melanoma associated antigen CD63) is a member of the tetraspanin integral membrane glycoprotein family that plays a role in intracellular vesicular transport and is involved in cell morphology, motility, and proliferation. CD63 is mainly associated with intracellular vesicles (eg, lysosomes and endosomes) but can be expressed at the cell surface and secreted as exosomes through fusion of endosomes with the plasma membrane. It is broadly expressed in the body, including within gastric parietal cells, platelets, endothelial cells, fibroblasts, mast cells, brain white matter, renal tubules, macrophages, dendritic cells, T-lymphocytes, neutrophils, and many epithelial cells. CD63 is also associated with tumor progression, where the protein is overexpressed during the early stages and reduced as invasion and malignancy progresses (melanomas, ovarian cancers, lung, breast and colon carcinomas). Antibodies to CD63 can be used to identify melanoma and melanocytic tumors and other tumors. References: Exp Cell Res 2009: 1484-1592; Thromb Res. 2010;125(2):152-158. doi: 10.1016/j.thromres.2009.07.005; Cytometry A. 2004;61(1):62-68. doi: 10.1002/cyto.a.20068; Dev Cell. 2011;21(4):708-721. doi: 10.1016/j.devcel.2011.08.019; Cancer Res. 1988;48(11):2955-2962. PMID: 3365686; Am J Pathol. 1998;153(3):973-983. PMID: 9736046; Arch Pathol Lab Med. 2001;125(6):751-758. doi: 10.1043/0003-9985(2001)125<0751:RA>2.0.CO;2.