The G10F5 antibody reacts with CD66b (previously denoted CD67), an ~95 kDa single-chain glycosylphosphatidylinositol (GPI)-linked glycoprotein expressed by neutrophilic and eosinophilic granulocytes. CD66b is a member of the carcinoembryonic antigen (CEA)-like subfamily of proteins within the immunoglobulin superfamily and possesses two Ig-like C2-type domains and one Ig-like V-type domain. In neutrophils, CD66b is localized within granules in the cytoplasm as well as being expressed on the plasma membrane. Surface expression levels increase upon granulocyte activation, an effect induced by stimulators such as phorbol myristate acetate (PMA), calcium ionophore, and N-formylmethionyl-leucyl-phenylalanine (FMLP). CD66b appears to play a role as a signaling receptor involved in cell adhesion, phagocytosis, and chemotaxis by regulating granulocyte activation and adhesion to several proteins, including CD66c, galectin-3, fibronectin, and E-selectin.