Antigenic Determinants of Carcinoembryonic Antigen

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Abstract
Radioimmunoassays for carcinoembryonic antigen (CEA) have been established using a variety of different antisera raised in goat, monkey, rabbit, guinea pig and rat. The extent to which different antigens compete for antibodies in the sera has been estimated. The antigens used were: CEA, asialo CEA, Smith‐degraded CEA (50% carbohydrate removed), CEA treated with an extract of Trichomonas foetus (70% carbohydrate removed), reduced‐alkylated CEA (disulphide bonds ruptured), a peptic digest of CEA and CEX. The results demonstrated that there are at least five chemically distinct antigenic determinants: three are on protein—one, sensitive to conformation, a second, sensitive to conformation and to periodate, a third, insensitive to conformation—and two on carbohydrate, one common to CEA and CEX and another on CEA alone.