Effect of Alloimmunization and Heteroimmunization with Zonae Pellucidae on Fertility in Rabbits

The effect of active immunization with porcine or rabbit zonae pellucidae on the fertility of rabbits was studied. A total of 28 rabbits in groups of four were immunized with 1) intact, 2) heat-solubilized or 3) detergent-dissociated (SDS-sodium sulfite-solubilized) porcine or rabbit zonae, or 4) complete Freund’s adjuvant. Serum antibodies to zona antigens were monitored by immunoelectrophoresis and by radioimmunoassay methods. All of the animals in the groups which were heteroimmunized with intact or with heat-solubilized porcine zonae were infertile in both term pregnancy studies or in 4–8-cell embryo recovery studies. Normal ovarian function was interrupted in these animals, since normal ova were not ovulated after hCG treatment. Ovulation appeared normal in animals immunized with detergent-dissociated porcine zonae or with rabbit zonae in any form. Although fertility was reduced in these latter groups, some animals had normal offspring or normal cleaving embryos even though antibodies to zonae were present in their serum. These studies demonstrate that 1) heteroimmunization of rabbits with porcine zonae is more effective in reducing fertility than alloimmunization with rabbit zonae; 2) the reduction of fertility by immunization with zonae is dependent on the state of solubilization of zonae prior to immunization; 3) serum antibodies to some zona antigens can be present which do not inhibit fertilization; and 4) the reason(s) for infertility by active immunization with zona antigens may be other than (or in addition to) the blockage of sperm binding to the zonae or penetration of the zonae. We conclude that the rabbit is an excellent model for the comparison of the effects on fertility of alloimmunization and heteroimmunization with zona antigens.