Sandwich assay for carcinoembryonic antigen with immobilized lectins and a monoclonal antibody

A lectin-linked immunoradiometric assay (L-IRMA) using 7 different lectins and a monoclonal antibody (MoAb) directed against the protein moiety-specific epitope was developed to detect carcinoembryonic antigen (CEA). The method used for L-IRMA was as follows: certain CEAs that reacted with lectin agarose beads were allowed to bind further to an 125I-labeled anti-CEA MoAb, and the resulting trapped 125I-MoAb was counted in a gamma counter. From the results, CEAs which interacted with Phaseolus vulgaris erythroagglutinin and leukoagglutinin were presumed to contain the complex type of sugar chains. Furthermore, CEAs interacting specifically with wheat germ agglutinin lectin were found in the tested samples, suggesting that the CEA had a hybrid or a complex type of sugar chain as the core structure of the sugar chain, except for that in seminal plasma. These results obtained by L-IRMA were in good accord with the data obtained from serial lectin affinity chromatography. L-IRMA may therefore be a simple method to study the glycoprotein heterogeneities in tumors and in normal subjects.