CD56 is a member of the Ig super family and comprises five Ig-like domains and two extracellular fibronectin-type III domains. It is expressed as three major isoforms within the nervous system, on NK cells, and a specific set of T-cells. CD56+ NK and T-cells are unique in their ability to mediate cell-mediated cytotoxicity against certain tumor cell targets without MHC restriction. Other CD56 physiological functions include: mediating cell adhesion, triggering neurite extension and migration, and brain synapse formation.
