The glycoprotein hormones CG, LH, FSH, and TSH are composed of two noncovalently linked subunits, α and β. The β-subunit confers hormone specificity, while the α-subunit is homologous within a species. To help in determining the antigenic structure of the common α-subunit, six monoclonal antibodies (mAbs) to the free or heterodimeric α-subunit of human (h) gonadotropic hormones have been prepared and, along with two previously isolated mAbs, have been characterized for binding specificity to α- and β-subunits and the human glycoprotein hormones, CG, LH, FSH, and TSH. Each mAb was derived from hybidomas of FO myeloma cells fused with spleen cells from mice immunized with free α-subunit, hCG or hFSH. mAbs A101, A102, and E512 were specific for the α-subunit but showed the highest affinity for the intact hormone; K2.18, K94.6, E501, E502, and E511 were specific for free α. All of the antibodies inhibited binding of 125I-hCG to luteal membrane receptor, and 125I-labeled mAbs did not recognize hCG/receptor complex. Characterization by two-site binding assays using α, hCG, or hFSH as antigen revealed that all the mAbs bind to unique sites on α which may be overlapping, and which are modified in the intact hormone. The antigenic sites for mAbs E502, E511, and K2.18 are at least partially linear because they bind to reduced, carboxymethylated α.
ASJC Scopus subject areas