Antigenic regions on the β chain of human chorionic gonadotropin and development of hormone specific antibodies

Five peptides corresponding to four regions of the β chain of human chorionic gonadotropin (hCG), were synthesized, purified and characterized. The four regions studied were selected on the basis of sequence differences between the β chain of hCG (βhCG) and the β chains of related hormones. The peptides were found to bind rabbit and mouse anti-hCG antibodies as well as rabbit anti-β chain antibodies, but did not bind antibodies against the α chain or against other hormones. All the peptides, even in their free form, were able to elicit high titer antisera in both rabbits and mice. In all cases, anti-peptide antisera bound to the immunizing peptide as well as to the native hCG and the isolated β chain. These anti-peptide antisera did not bind to unrelated peptides, the α chain of hCG or to other hormones with very similar β chains such as human luteotropic hormone (hLH), ovine luteotropic hormone (oLH) and equine chorionic gonadotropin (eCG). Since the areas represented by these peptides elicit antibodies that are specific for human βhCG, they can formulate the basis for the development of discriminatory reagents for the β chain of hCG.