The blood group A-like site on the carcinoembryonic antigen.

For quantitation of the apparent interaction between hu man anti-blood group A (anti-A) antibodies and radioiodinated purified carcinoembryonic antigen (CEA), a radioimmunoassay utilizing molecular sieve chromatography was devised. By the use of this procedure the following observations were made: (a) the majority of human sera that contain anti-A antibodies are capable of binding to radioiodinated purified CEA; (¿>) this binding is due pre dominantly to immunoglobulin M moieties in the sera and thus confirms observations made by radioimmunoelectrophoresis; (c) inhibition studies demonstrated that immu noglobulin M anti-A antibodies are capable of binding to a site, or sites, present on purified CEA. On the basis of these findings it is concluded that there exists a blood group A-like site on the CEA molecule cap able of being recognized by anti-A antibodies.