Ig superfamily members are known to mediate cell adhesion, as:
 NCAM1 (MIM.116930)
 ICAM1 (MIM.147840)
 VCAM1 (vascular cell adhesion molecule-1) (MIM.192225)

They also mediate antigen recognition:
 immunoglobulins (IGH, IGL, IGK)
 T-cell receptors (TCRA, TCRB, TCRD, TCRG)
 MHC molecules.

In addition, a subgroup comprising 30 members characterized by the presence of one or more immunoreceptor tyrosine-based inhibitory motifs (ITIMs) within their cytoplasmic domain has also been recognized. PECAM1, which has 6 ITIMs within its cytoplasmic domain, is a member of this subfamily;

Another subfamily is the carcinoembryonic antigen gene family (CEA gene family).

Functions

 N-CAM regulates homophilic (like-like) interactions between neurons and between neurons and muscle.

 CD56 also associates with fibroblast growth factor receptor (FGFR) and stimulates tyrosine kinase activity of receptor to induce neurite outgrowth.

 When neural crest cells stop making N-CAM and N-cadherin and start displaying integrin receptors, cells separate and migrate.

 CD56 contributes to cell-cell or cell-matrix adhesion during development

 Lymphocyte activated killer phenomenon mediated by IL-2 activated CD56+, CD3-, NK cells

Expression in normal cells

 NK cells (80-90%)
 activated T cells
 cerebellum and brain at neuromuscular junctions
 normal neuroendocrine tissues
 bile ducts and biliary ductules (#14576479#)

Expression in tumors

 myeloma
 myeloid leukemias
 neuroendocrine tumors
 Wilm tumor
 adult neuroblastoma
 NK/T cell lymphomas
 pancreatic acinar cell carcinoma
 pheochromocytoma
 small cell lung carcinoma