MONKEY ANTISERA WITH INCREASED SPECIFICITY TO CARCINOEMBRYONIC ANTIGEN (CEA)

Three Macaca irus monkeys were immunized with purified human CEA from liver metastases of colon cancer. One received unmodified CEA and 2 were immunized with haptenated (4-hydroxy-5-iodo-3-nitrophenyl acetyl) CEA. All 3 monkeys formed precipitating antibodies to CEA. The antisera did not precipitate the CEA-related normal glycoprotein antigen (NCA). CEA-immunized rabbits, sheep and goats invariably formed antibodies against NCA. Radioimmunoassays showed the monkey antisera to contain trace amounts of antibodies to NCA but the titers were about 10-1000 times lower than those in rabbit and sheep sera with comparable anti-CEA titers. 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.