Characterization of anti oLH beta-antibodies acting as contraceptives in rhesus monkeys. I. In vitro binding properties.

Female monkeys actively immunized with oLHbeta are infertile when circulation antibody titers become sufficiently high to bind 30% of an iodinated hCG standard. We report here the extensive characterization of the oLHbeta antibodies. Their binding affinity and capacity for human and rhesus gonadotropins were determined. The affinity was high (Ka - 10(9) M-1) and was similar for high, medium and low titer antisera. In contrast, the binding capacity for hCG correlated well with antibody titers (n = 18, r = 0.888, P less than 0.001) and ranged from 0.09 to 8.3 x 10(-7)M. Column chromatographic analysis showed that anti-oLHbeta was mostly IgG. A temporal increase of affinity ('maturation') after booster was absent in the majority of monkeys. Cross-reaction between hCG and hLH as well as rhCG and rhLH was high. The latter, however, did not interfere with regular cycles and ovulation, suggesting that oLHbeta may be a useful antigen for human contraception.