Blocking effect of antisera to recombinant zona pellucida proteins (r-ZPA)on in vitro fertilization

PROBLEM: The zona pellucida is a good target antigen for contraceptive vacc ines due to its strong immunogenicity and high tissue specificity. However, this contraceptive effect is inevitably associated with ovarian failure. T herefore, it is necessary to define an epitope of the zona antigen to which the antibody produced inhibits fertilization without any undesirable side effects. METHOD OF STUDY: The DNA fragment coding for the NH2-terminal region of por cine zona pellucida proteins (ZPA) (1-198 amino acids) and human ZPA (1-206 amino acids) was prepared to produce recombinant porcine ZPA (r-ZPA), r-pZ PA(1-)198 and r-hZPA(1-206). Using Freund's complete adjuvant, antisera aga inst these proteins were raised in rabbits. RESULTS: The resultant antisera to r-pZPA(1-198) and r-hZPA(1-206) were cro ss-reacted with each other on enzyme-linked immunosorbent assay and immunof luorescent staining. The antiserum to r-pZPA(1-198) inhibited in vitro fert ilization in pigs, but not human sperm binding to the zona pellucida, while the antiserum to r-hZPA(1-206) inhibited the human sperm-binding assay. CONCLUSIONS: Antiserum to r-ZPA inhibited fertilization in the animal speci es possessing a homologous amino-acid sequence as an immunogen. The recombi nant protein, r-hZPA(1-206) seems to be a feasible candidate for the develo pment of contraceptive vaccines for humans.