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 vaccines due to its strong immunogenicity and high tissue specificity. However, this contraceptive effect is inevitably associated with ovarian failure. Therefore, 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 porcine 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-pZPA1-198 and r-hZPA1-206. Using Freund's complete adjuvant. antisera against these proteins were raised in rabbits. RESULTS: The resultant antisera to r-pZPA1-198 and r-hZPA1-206 were cross-reacted with each other on enzyme-linked immunosorbent assay and immunofluorescent staining. The antiserum to r-pZPA1-198 inhibited in vitro fertilization in pigs, but not human sperm binding to the zona pellucida, while the antiserum to r-hZPA1-206 inhibited the human sperm-binding assay. CONCLUSIONS: Antiserum to r-ZPA inhibited fertilization in the animal species possessing a homologous amino-acid sequence as an immunogen. The recombinant protein, r-hZPA1-206 seems to be a feasible candidate for the development of contraceptive vaccines for humans.