[Molecular morphology of placental and pituitary hormones: epitope mapping with monoclonal antibodies]

Abstract

The immunologically and biologically active molecular characteristics of human glycoprotein hormones were studied with the aid of previously produced and characterized monoclonal antibodies (MCA). Placentally derived human chorionic gonadotropin (hCG) and pituitary human follicle stimulating hormone (hFSH) were taken as examples for the use of MCA in the elucidation of molecular morphological and functional correlations and the diagnostic application of these findings. The immunological surface of hCG and of hFSH was probed by 26 MCA to these hormones and bovine luteinizing hormone. In 2-site immunoassays--resembling immunoradiometric assays (IRMA)--pairs of MCA were applied to simultaneous scanning of the molecules. Nine different recognition patterns were distinguished in the case of hCG and 5 for hFSH, reflecting the same number of immunological epitopes. These were either located on the alpha- or beta-subunit or expressed only by the conformationally intact molecule (c-epitopes). The construction of an immunological map revealed an equatorial cluster of alpha-, beta- and c-epitopes, with distinct epitopes on each subunit. This suggests a similar immunological arrangement of epitopes on all human glycoprotein hormones. Antigenic determinants of all 3 main specificities (alpha, beta, c) are involved in the expression of the biological activity of hCG. Surprisingly, hCG is not functionally neutralizable by means of MCA to one of the epitopes (beta 3)--although located on the hormone-specific beta-subunit which is evolutionary highly conserved throughout a large number of mammalian species. On the basis of the epitope map it was possible to establish IRMAs with predictable specificities for selective measurement of hFSH and hCG and its subunit.(ABSTRACT TRUNCATED AT 250 WORDS)