CEACAM-8, also known as CD66b and CD67, is a GPI-linked protein belonging to the immunoglobulin superfamily, carcinoembryonic antigen (CEA)-like subfamily. A homolog of CEACAM-8 has not been identified in rodents. CEACAM-8 is exclusively expressed on human granulocytes, including neutrophils and eosinophils, and is characterized as a granulocyte activation marker. CEACAM-8 is mainly found in secondary granules with low amounts on cell the surface. Upon activation of granulocytes with various stimuli, CEACAM-8 is rapidly upregulated and released from intracellular granules, leading to a high level of expression on the plasma membrane. CEACAM-8 has been reported to be involved in immune response, leukocyte migration, cell adhesion and degranulation. Engagement of CEACAM-8 with Galectin-3 activates a Src kinase, Hck, inducing cell adhesion and degranulation. In addition, CEACAM-8 constitutively associates integrin β2 and CD11b in lipid rafts, regulating cell adhesion and activation of eosinophils. CEACAM-8 can specifically bind CEACAM-6 (CD66c) through their Ig-like V-type domain in calcium-independent manner. The interaction of CEACAM-8 and CEACAM-6 mediates heterophilic cell adhesion.