The carcinoembryonic antigen (CEA) gene family, part of the immunoglobulin (Ig) gene superfamily, is a diverse set of highly glycosylated glycoproteins. Two types of membrane anchorage are found in the CEA subgroup of CEACAM proteins. CEACAM1 and CEACAM3 contain a hydrophobic transmembrane domain followed by a cytoplasmic domain, while CEA (also known as CEACAM5) and CEACAM6 are attached to the cell surface via a glycosylphosphatidylinositol (GPI) moiety (Hammarstrom et al. 1999). CEA, CEACAM1, CEACAM3, and CEACAM6 have been shown to serve as receptors for the neisserial phase-variable opacity-associated (Opa) adhesin proteins (Chen & Gotschlich, 1996, Bos et al. 1997, Popp et al. 1999). These adhesin proteins are a major surface component of Neisseria meningitidis and Neisseria gonorrhoeae, and are responsible for bacterial adherence and entry into host cells and interactions with the host immune system. These receptors also bind to DraE adhesin of Escherichia coli (Berger et al. 2004).