Active immunization of rats with cumulus-free mouse ova: induction of infertility and antibody titers.

Active immunization of rats with cross-reacting zona pellucida antigens derived from cumulus-free mouse ova resulted in the induction in fertility without adverse side effects. Half of the immunized animals never regained their fertility despite repeated matings with fertile males. Two of the remaining animals conceived when antibody titers fell to basal levels and gave birth to litters of normal healthy young. Post mortem examination of immunized animals 24 hours after finding sperm in the vaginal smears resulted in the recovery of tubal ova exhibiting the presence of a precipitate on the outer surface of the zona pellucida. Some of these ova appeared to have been fertilized, suggesting that anti-zona antibodies may also inhibit fertility through a post-fertilization mechanism of action.