Search for peptide immunogens of the beta-subunit of human chorionic gonadotropin (hCG) capable of eliciting hormone specific and neutralizing antisera. Identification of an undecapeptide eliciting hCG-specific antisera.

The work reported herein describes our attempts to identify peptide immunogens of the beta-subunit of the pregnancy-specific placental hormone, human chorionic gonadotropin (hCG), capable of eliciting hormone specific and neutralizing antisera. Hydrophilicity profiles of the beta-subunits of hCG and the homologous pituitary hormone, human luteinizing hormone (hLH) were compared and two sequences which are hydrophilic but unique to hCG-beta were identified. They are 6-12 and 109-119 of hCG-beta. Results of the studies with the undecapeptide 109-119 of hCG-beta are reported in this paper. The undecapeptide amide was synthesized using the p-(acyloxy) benzhydrylamine resin and antisera to the peptide were elicited in rabbits using the peptide-diphtheria toxoid conjugate. The peptide is highly immunogenic as both the rabbits responded with high titers of antibodies to the peptide. The antipeptide antibodies bound to hCG but not to hLH showing thereby that the region 109-119 of hCG-beta is a unique determinant of hCG. However, the antibodies were found not to neutralize the biological activity of hCG.