CEACAM-1, also known as CD66a, is an immunoglobulin superfamily protein that is expressed on neutrophils, activated NK cells, bile duct and colonic epithelial cells, and endothelial cells. CEACAM-1 is heavily glycosylated and carries high mannose residues and (sialyl) Lewis-x. It is expressed as at least three soluble and seven transmembrane isoforms, with variations occurring in both the ECD and cytoplasmic region. It engages in homotypic adhesion and heterotypic adhesion with CEACAM-3/CD66d and CEACAM-6/CD66c. On neutrophils, CEACAM-1 additionally binds to dendritic cell DC-SIGN via its Lewis-x moiety, inducing dendritic cell maturation and a subsequent Th1-type response.