Monkey antisera with increased specificity to carcinoembryonic antigen (CEA)

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Abstract
Three Macaca irus monkeys were immunized with purified human CEA. One received unmodified CEA and two were immunized with haptenated (4‐hydroxy‐5‐iodo‐3‐nitrophenyl acetyl) CEA. All three monkeys formed precipitating antibodies to CEA. The antisera did not precipitate the CEA‐related normal glycoprotein antigen (NCA). In contrast, CEA‐immunized rabbits, sheep and goats invariably form antibodies against NCA. Radioimmunoassays showed the monkey antisera to contain trace amounts of antibodies to NCA but the titers were about 10‐1,000 times lower than those in rabbit and sheep sera with comparable anti‐CEA titers. These results show that monkeys produce antibodies against CEA, but respond weakly to a normal, CEA‐related antigen. The weak response to NCA suggests that monkeys may possess an NCA‐related antigen. Antisera lacking reactivity to normal CEA‐related antigens may be helpful in establishing a more specific diagnostic test for CEA.