Immunological and electrophoretic studies on human chorionic gonadotropin antigen 2 with special reference to subunits of human chorionic gonadotropin and quantitative analysis of antigen 2 in the urine of normal pregnant women and patients with tropho blastic disease by radio immunoassay
Shikoku Acta Medica 36(6): 491-502
The immunochemistry of hCG(human chorionic gonadotropin)-Antigen 2(Ag2) was characterized by polyacrylamide gel electrophoresis, SDS (sodium dodecyl sulfate) disc electrophoresis and immunoelectrophoresis using anti-hCG .beta. serum and anti-crude hCG serum (absorbed anti-hCG serum), and was compared with that of hCG subunits. Ag2 levels in the urine of pregnant women and trophoblastic tumor patients were determined by a newly developed radioimmunoassay for Ag2. The ratios of immunoreactive Ag2 to hCG in urine were examined. Using polyacrylamide gel electrophoresis, hCG and its subunits migrated toward the anode but Ag2 displaced toward the cathode. By immunoelectrophoresis, precipitin arcs of hCG.alpha. and hCG.beta. fused to that of Ag2 with a single spur. When subjected to SDS disc electrophoresis, Ag2 showed a single migrating band and its MW was estimated as .apprx. 30,000 daltons. The cross-reactivity of hCG with anti-Ag2 antibody was 5% at a 50% inhibition dose, but hCG subunits did not reveal any cross-reactivity. The ratio of immunoreactive Ag2 to hCG in urine was significantly higher in 6 patients with choriocarcinoma (10.47 .+-. 4.47) than that in 10 patients with hydatidiform and destructive mole (0.67 .+-. 0.31). In normal pregnant women, the Ag2/hCG ratio was 0.54 .+-. 0.10 (n = 17) in the 1st trimester, 0.63 .+-. 0.09 (n = 23) in the 2nd trimester and 0.24 .+-. 0.04 (n = 16) in the 3rd trimester. Apparently Ag2 is not identical with hCG subunits but possesses a partial structure of their antigenic determinants. A significant increase in urinary Ag2 levels in patients with choriocarcinoma may reflect an imbalance in the synthetic or metabolic pathway of hCG in malignant cells.