Delineation of three classes of CEA antigenic determinants: identification of membrane-associated CEA as an independent species of CEA
Leung, J.P.; Plow, E.F.; Eshdat, Y.; Marchesi, V.T.; Edgington, T.S.
Journal of Immunology 119(1): 271-276
1977
ISSN/ISBN: 0022-1767 PMID: 68974 Document Number: 121785
The immunochemical relationship between membrane-associated CEA (CEA-M) and isolated conventional whole CEA and the species CEA-S was investigated. These glycoproteins gave precipitin reactions of apparent identity by using antisera to CEA-M and CEA-S; the binding of each of these glycoproteins relative to one another by anti-tumor glycoprotein, anti-CEA-S and anti-CEA-M antisera differed to a significant degree, indicative of some degree of nonidentity. Competitive inhibition radioimmunoassay with a 125I CEA-S ligand and a broadly reactive anti-CEA-S antiserum demonstrated that all 3 glycoproteins possessed in common antigenic determinants of the CEA group of glycoproteins but at apparent different concentration. These appeared to reflect the presence of CEA group-specific determinants. When 125I CEA-M and an anti-CEA-M antiserum were used in competitive inhibition assays, CEA and CEA-S were antigenically deficient relative to CEA-M. After absorption of the anti-CEA-M with CEA, CEA-M produced complete inhibition, SDS-unfolded CEA produced 60% inhibition and CEA was unreactive. This antiserum was further absorbed with SDS-unfolded CEA and used in assay with 125I CEA-M. Although CEA-M remained reactive, CEA or CEA subjected to denaturants such as SDS, 2-mercaptoethanol and SDS with 2-mercaptoethanol did not inhibit this assay system, indicating the absence of the remaining determinants present on CEA-M. The existence was proposed not only of CEA group-specific determinants but of CEA cryptic determinants that may be generated from soluble forms of CEA and CEA-S by unfolding the exposure of cryptic sites. The existence of CEA species-specific determinants, which appear to be unique to a particular species of CEA, were demonstrated. In a CEA-M-specific radioimmunoassay system with CEA-M absorbed antiserum, the CEA-M species-specific determinants can be directly demonstrated in microsome-rich homogenates of colonic adenocarcinomas. Molecules bearing CEA-M species-specific determinants are produced by cells and are not an artifact of isolation of CEA-M. Demonstration of this 3rd class of determinants on CEA-M in this study establishes that it is an independent species of CEA.