A new radioimmunoassay for human chorionic gonadotropin using monoclonal antibody

A new radioimmunoassay (RIA) for human Chorionic Gonadotropin (hCG) was developed using murine monoclonal antibody to the beta-subunit of hCG (beta-hCG). The IgG fraction of the monoclonal antibody which did not react with 125I-beta-hCG was purified from hybridoma ascites, and covalently coupled to Sepharose 4B. This solid-phase antibody was incubated with standard hCG or serum sampled for 48 hours. The reaction medium was then removed by centrifugation and 125I-beta-hCG and anti-beta-hCG rabbit polyclonal antibody were added to the precipitate. The alcohol precipitation method was used for separating "bound" and "free" forms in the second reaction. The sensitivity for hCG in this assay system was 0.5 mIU/ml serum and the cross-reactivity with human Luteinizing Hormone (hLH) was 0.4%. This assay system was shown to be clinically applicable. Serial serum samples from two patients with trophoblastic disease were assayed and minute amounts of hCG, which could not be determined by conventional assay methods, could be assayed by this new RIA.