NCAM (neural cell adhesion molecule, CD56) is an adhesion glycoprotein with five extracellular immunoglobulin-like domains followed by two fibronectin type III repeats. Structural diversity is introduced by alternative splicing resulting in different cytoplasmic domains. NCAM mediates neuronal attachment, neurite extension and cell-cell interactions through homo and heterophilic interactions. PSA (polysialic acid) post-translationally modifies NCAM and increases the metastatic potential of small cell lung carcinoma, Wilms+ tumor, neuroblastoma and rhabdomyosarcoma. CD56 is commonly used along with CD3 and CD16 to identify human NK cells (Mouse NK cells do not express CD56). Human natural killer cells are CD3-CD56+. The large subset with high CD16 expression are mature cytotoxic natural killer cells, while those with low CD16 expression are immature precursors and cytokine producers.
