CD53 is a member of the transmembrane 4 superfamily, also called the tetraspanin family. Most of these members are cell-surface proteins that are characterized by the presence of four hydrophobic domains. These 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. Familial deficiency of CD53 gene has been linked to an immunodeficiency associated with recurrent infectious diseases caused by bacteria, fungi and viruses. CD53 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.