CD53 is a member of the tetraspan family of molecules, and is expressed by all leucocytes, but is absent from red cells and platelets. Most of the tetraspan family of molecules are cell surface proteins that are characterized by the presence of four hydrophobic domains. The proteins mediate signal transduction events that play a role in the regulation of cell development, activation, growth and motility. CD53 is a cell surface glycoprotein that is known to complex with integrins. It contributes to the transduction of CD2 generated signals in T cells and natural killer cells and has been suggested to play a role in growth regulation. Familial deficiency of this gene has been linked to an immunodeficiency associated with recurrent infectious diseases caused by bacteria, fungi and viruses. CD53 is a glycoprotein of 32-40 kDa belonging to the tetraspans family (TM4SF). CD53 antigen is exclusivelly expressed on leucocytes (not present on platelets, red blood cells and non-hematopoietic cells). CD53 is important for signal transduction. CD53 cross-linking promotes activation of human B cells and rat macrophages.Synonyms: Cell surface glycoprotein CD53, Leukocyte surface antigen CD53, MOX44, TSPAN25, Tetraspanin-25