A Radioimmunoassay for the Core Fragment of the Human Chorionic Gonadotropinβ-Subunit

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Abstract
We developed a RIA for the β-core fragment of hCG that is excreted in the urine of pregnant women and some patients with cancer. We purified β-core from crude commercial preparations of hCG (of which β-core is a major constituent) derived from pregnancy urine and used this purified β-core material to immunize rabbits. One antiserum (RW25) was particularly useful in that a RIA with purified β-core as both radioligand and reference preparation had high sensitivity for β-core detection and low cross-reactivity with other hCG-related molecules and glycoprotein hormones. The cross-reactivities of purified hCG (CR125), hCGβ (CR125), and hCGα (CR125) preparations were in each instance less than 3 × 10−3 (wt/wt). The cross-reactivities of purified pituitary glycoprotein hormones were in each instance less than 2 × 10−4 (wt/wt). Using the RW25 RIA, virtually all β-core immunoreactivity in pregnancy urine eluted from Sephadex G-100 in a position coincident with that of purified β-core. Urine from men and nonpregnant women contained very low levels of β-core immunoreactivity (μg/L). while urine from pregnant women and patients with testicular cancer or other neoplasms had levels of β-core immunoreactivity ranging as high as 26,000 μg/L. We conclude that the improved specificity of our β-core RIA will facilitate studies of the physiology and cancer biology of β-core molecules.