Affinity, cross-reactivity and biological effectiveness of rabbit antibodies against a synthetic 37 amino acid C-terminal peptide of human chorionic gonadotrophin.

As a part of a programme to develop a fertility regulating vaccine, antibodies specific for human chorionic gonadotrophin were raised by immunizing rabbits with a synthetic 37 amino acid C-terminal peptide of beta hCG conjugated to tetanus toxoid as carrier, and using Bordetella pertussis or Freund's complete adjuvant as adjuvants. Lack of cross-reactivity of the antibodies with human luteinizing hormone was determined by direct binding in a radioimmunoassay and by immunofluorescence on adult human pituitary sections. Not only did the antibodies bind to native hormone in a radioimmunoassay but they also neutralized the biological activity of hCG as measured by an in vivo bioassay. Rabbits which had been injected with the conjugate with B. pertussis as adjuvant made antibodies of comparable affinity to those animals which had been immunized with the antigen in Freund's complete adjuvant, though the latter group did produce more antibodies.