CD63, also known as LAMP-3 or ME491 (melanoma-associated antigen), is a member of the tetraspanin superfamily of protein trafficking proteins. CD63 is ubiquitously expressed and found in late endocytic vesicles, but following cell activation is also present on the plasma membrane. Interaction of CD63 with other membrane proteins or adaptors regulates cell activities such as adhesion, migration and degranulation.