Long-term effects of immunization with porcine zona pellucida on rabbit ovaries

Groups of rabbits were immunized with 4 doses of porcine zona pellucida antigen along with different adjuvants. The presence of antibody after immunization was checked periodically using different assay systems. The impact of immunization on ovaries was evaluated at different time intervals up to 2 years. Results of the study showed generation of high titre antibodies which could be detected until the end of the period of observation. The antibodies specifically bound to zona pellucida in situ were demonstrated by immunoperoxidase staining, and in vitro by inhibition of enzymatic digestion of zonae. Histologically, antibodies had numerous pathological effects on ovaries including thinning of the cortex, aberrant cell clusters, stromal cell hyperplasia, perifollicular fibrosis, irregular zona formation and arrest of follicle development. These changes could be correlated with the length of exposure to antibodies. It is concluded that heat-solubilized porcine zona (HSPZ) protein is a very strong immunogen and causes infertility by arresting the maturation of developing follicles. There is a need to identify the sperm receptor so that immunization could selectively impair sperm-egg interaction.