Carcinoembryonic Antigen-related Cell Adhesion Molecule 1 (CEACAM-1), also known as CD66a and BGP-I, is a 115 kDa type I transmembrane glycoprotein that belongs to the membrane-bound CEA subfamily of the CEA superfamily. On the surface of cells, CEACAM-1 forms non-covalent homo- and heterodimers. The extracellular region contains three C2-type Ig-like domains and one N-terminal V-type Ig-like domain. Multiple splice of CEACAM-1 variants involving regions C-terminal to the second C2-type domain (aa 320 and beyond) exist.