CEACAM-3 (carcinoembryonic antigen-related cell adhesion molecule 3; also CD66d and CGM1) is a 31 - 34 kDa member of the CEACAM subfamily of the CEA family of proteins. It is expressed by neutrophils and serves as a microbial receptor for a wide range of microorganisms. Mature human CEACAM-3 is a 218 amino acid (aa) type I transmembrane glycoprotein. Its extracellular domain (aa 35 - 155) shows one V-type Ig-like domain (aa 35 - 142). There are two alternate splice forms of CEACAM-3. One shows a 40 aa substitution for the C-terminal 116 amino acids (aa 137 - 252), while a second shows a 31 aa substitution for the C-terminal 71 amino acids. No definitive rodent CEACAM-3 has been reported.