CD166

CD166, also known as CD166 or activated leukocyte cell adhesion molecule (ALCAM), is a cell adhesion molecule of the immunoglobulin superfamily. It is a transmembrane glycoprotein encoded by the ALCAM gene in humans. The extracellular region contains two immunoglobulin-like domains that mediate adhesive interactions, and the protein can be shed from the cell surface to generate a soluble form found in bodily fluids.

Expression of CD166 is broad, with presence on endothelial and epithelial cells, many other tissue types, and activated leukocytes. Expression levels can be influenced by inflammatory signals, and the protein often appears in tissues undergoing remodeling, immune responses, or development.

CD166 participates in both homophilic and heterophilic adhesion. Its well-described heterophilic interaction with CD6 on T cells supports immune cell contact and contributes to immune synapse formation and lymphocyte activation. CD166 also forms homophilic ALCAM-ALCAM interactions and is involved in processes such as neural development, axon guidance, and possibly angiogenesis and tissue architecture.

In cancer and inflammatory diseases, CD166 has attracted particular attention because its expression can affect cell adhesion, invasion, and metastatic potential in a context-dependent manner. Soluble ALCAM levels in serum have been explored as a potential biomarker in various conditions, though prognostic value varies across diseases and study settings.

Overall, CD166/ALCAM is a multifunctional adhesion molecule that participates in immune cell interactions, development, and tissue remodeling, with relevance to disease biology and potential clinical applications.