Purification and Properties of a Monoclonal Antibody Specific to the Freeβ-Subunit of Human Chorionic Gonadotropin (hCGβ) and Its Use in the Isolation of Free hCGβProduced by Choriocarcinoma Cells*

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Abstract
The free .beta.-subunit of hCG is secreted by several tumors and is reported to be different from native hCG.beta.. We have developed a monoclonal antibody, B158, specific for free hCG.beta. to facilitate the detection and isolation of tumor-derived free hCG.beta. in the presence of intact hCG and hCG.alpha.. B158 belongs to the immunoglobulin G1 subclass, has high affinity for hCG.beta. (Ka, 1.05 .times. 109 M-1), and can be obtained in large quantities. The sensitivity of this antibody to detect free hCG.beta. in a RIA is less than 1 ng. B158 has negligible cross-reactivity with hCG, human LH, and other intact glycoprotein hormones and reacts with the free .beta.-subunits of deglycosylated hCG, human LH, and ovine LH. The antibody completely inhibits the recombination of hCG.beta. with hCG.alpha. indicating the antigenic site to be in the subunit interaction region or its vicinity. Comparison of the amino acid sequences of the various cross-reacting and noncross-reacting hormones indicates that the antigenic site may be discontinuous and conformational. B158 was purified to homogeneity from ascites fluid by DEAE-Affi-Gel blue and hCG.beta. affinity chromatography. Immobilized pure B158 antibody was used to isolate free hCG.beta. in a homogeneous form and high yield from BeWo choriocarcinoma cell culture supernatants. This free hCG.beta. has a slightly higher mol wt than standard hCG.beta. and recombines normally with hCG.alpha.. BeWo cells appear to produce only one species of free hCG.beta.

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