Radioimmunological characterization of carcinoembryonic antigen (CEA) preparations

A multi-step radioimmunological test system was applied to the characterization of carcinoembryonic antigen (CEA) preparations obtained by column chromatography including ion exchange procedure. CEA contents were estimated by means of a sequential inhibition radioimmunoassay using Protein A-bearing Staphylococci for coprecipitation. Data were expressed as "units CEA" and compared with results obtained from commercial CEA-RIA kits. In addition, attempts were made to evaluate the presence of normal cross-reacting antigens in CEA preparations by the application of an antiserum to perchloric acid extract from normal lung tissue. Data from these tests were expressed as "units NLA" (NLA stands for "normal cross-reacting lung antigen"). The factor "units CEA/units NLA" proved useful as an indication of the tumour specificity of those antigenic components measured in the inhibition assay. Moreover, radioimmunoprecipitation tests with subsequent SDS polyacrylamide gel electrophoretic analysis were performed in order to get information on the molecular weight of the molecule(s) involved in the radioimmunological CEA determination procedure. The test system displayed 1) highly specific CEA reagibility in the standard inhibition assay, 2) test sensitivity of about 200 pg CEA (when related to the Hoffman/La Roche test) and 1 ng CEA (when related to CEA-IRE-SORIN), 3) low reagibility to normal cross-reacting antigens, also when compared to the commercial tests, 4) a molecular weight of about 200,000 daltons for the component(s) measured, and 5) evidence of inhomogeneity of the CEA batches investigated and those international references available. The latter might in part be attributed to so-called species-specific CEA-related determinants. The test system proved also useful for CEA estimations in crude tissue extracts.