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 X 10(9) 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.