An improved immunogen for anti-human chorionic gonadotropin vaccine eliciting antibodies reactive with a conformation native to the hormone without cross-reaction with human follicle stimulating hormone and human thyroid stimulating hormone.

Beta-subunit of human chorionic gonadotropin (hCG) was associated with alpha-subunit of ovine luteinizing hormone (OLH) to create a heterospecies dimer (HSD) which has a higher steroidogenic potency than the homologous dimer of alpha hCG and beta hCG in the mouse Leydig cell bioassay. The properties and merits of the antibodies induced by this HSD and beta hCG linked to carrier(s) were investigated in rodents and in a subhuman primate species. The antisera had, in both cases, high affinity for binding with hCG (K alpha = 10(9)-10(10) M-1). The mean (+/- S.E.M.) bioneutralization capacity as a percentage of immunoreactivity (determined by radioimmunoassay (RIA)) of the antibodies generated by the HSD-carrier in rats and bonnet monkeys was higher in comparison with those induced by beta hCG linked to carrier (80 +/- 2.3% vs. 63 +/- 1.5% in rats, and 65 +/- 1.9% for HSD vs. 44 +/- 3.7% in monkeys). None of the sera gave any evidence of cross-reactivity with human follicle stimulating hormone (hFSH) and human thyroid stimulating hormone (hTSH).