Analysis of carcinoembryonic antigen determinants by monoclonal antibodies and lectins

Two out of five determinants recognized by monoclonal antibodies (MoAbs) on carcinoembryonic antigen (CEA) were analyzed by blocking the CEA-MoAb interaction with 9 different lectins in a solid phase radioimmunoassay. Two batches of CEA were first studied for their binding to lectins at the solid phase. Lotus, soybean and wheat germ lectins were most active, but the reaction pattern was different with the two CEA batches. The corresponding sugars were capable of inhibiting the lectin-CEA binding. MoAbs were fixed to the solid phase, and their reaction with CEA was tried to be blocked by preincubating the antigen with lectins. Lotus lectin and wheat germ agglutinin were clearly blocking the MoAb-CEA interaction, but this was strikingly dependent on the CEA batch used and the particular CEA determinant investigated. These reactions could not be blocked by sugars. The data provide evidence for a role of sugars in the sterical configuration of CEA determinants. In view of the heterogeneity of the findings, however, the conclusion is drawn that the protein moiety plays the more important role in the configuration of the CEA determinants studied.