Binding Studies on Two Different Monoclonal Antibodies Raised Against CEA

Binding characteristics of two mouse monoclonal antibodies MA/1 and MA/200 raised to carcinoembryonic antigen (CEA) are presented. Double antibody radioimmunoassay and a solid phase assay confirmed that MA/1 binds weakly to CEA extracted from tumour tissue but strongly to CEA in patients' serum. Antibody MA/200 binds with high affinity to both 'tumour' and 'serum' CEA. Ligand-receptor relationship for MA/1 and MA/200 binding to both tumour CEA and CEA isolated from serum are presented from equilibrium binding data analysed by the method of Scatchard. Co-titration experiments also indicated that MA/1 and MA/200 and an established polyclonal anti-CEA bind to a similar subpopulation of CEA or CEA-like molecules, but the binding data demonstrate that their respective binding sites are chemically different.