Primate chorionic gonadotropins: antigenic similarities to the unique carboxyl-terminal peptide of HCGbeta subunit

Antigenic similarities of chorionic gonadotropin from human (hCG), chimpanzee (chCG), gorilla (gCG), orangutan (orCG), baboon (paCG), macaque (mCG), and marmoset (maCG) were investigated in a radioimmunoassay system using an antiserum (rabbit H93) with antigenic determinants known to reside in the terminal 15 amino acid residues of the unique carboxyl-terminal peptide of hCGbeta, which makes it highly specific for hCG without crossreactivity to hLH. Our findings indicate that the extreme antigenic similarity between chCG and hCG at the unique carboxyl-terminal region of hCGbeta, as well as the availability of these apes for laboratory research, make the chimpanzee the optimal nonhuman primate model for assessing potential risks of fertility control in women by immunization against hCGbeta.