Development of a rapid human chorionic gonadotropin beta subunit radio immunoassay using nylon balls coupled with antibodies to human chorionic gonadotropin and its clinical application
Minamisawa, Y.
Shikoku Acta Medica 38(2): 82-94
1982
Accession: 005131933
A rapid, specific and centrifugation-free heterologous hCG[human chorionic gonadotropin]-.beta. RIA [radioimmunoassay] with sufficient sensitivity, precision and reproducibility was developed by employing nylon balls as solid phase for coupling with antibodies to hCG-.beta. of 7 antiserum samples from 7 different rabbits which were immunized with an identical hCG-.beta. preparation, one showing a minimum cross-reactivity with human LH [lutropin] (8.8%) was selected for the source of antibodies to hCG-.beta. A purified IgG fraction was isolated from this antiserum and was conjugated to nylon balls, glass beads or to polystyrene balls to test binding capacities for 125I-hCG. Nylon balls showed the greatest binding capability for 125I-hCG (35.0 .+-. 0.5%) among the 3 kinds of solid phase, and incubation for 3 h at 37.degree. C under gentle shaking was found most appropriate to attain a maximum binding when the ball was used. Use of nylon balls permitted omission of centrifugation for separation of bound and free hormones and the entire assay could be completed within 3 h. The standard curve was linear on log-logit transform in the region of 0.25-250 ng/ml hCG. Serum LH level under physiological conditions was below 1 ng hCG (equivalent to 6.4 mIU)/ml. The intra- and interassay coefficients of variation were 3.0-5.9% and 3.3-6.9%, respectively. In addition, the hCG levels of 85 serum samples determined by this assay were well correlated with those measured by the double antibody hCG-.beta. RIA (r = 0.956, P < 0.001). Using this assay system the presence of circulating hCG (9-16.5 ng/ml) was detected in 5 out of 70 patients with malignant nontrophoblastic tumors, and in 4 of the 5 patients serum hCG decreased in concentration or disappeared after radical surgery or chemotherapy. The present method also would provide the basis for the development of similar rapid and convenient assays of other peptide hormones.