Inhibition of in vitro gamete adhesion and in vivo fertility in mice by immunization with a synthetic peptide

Problem:To evaluate the contraceptive ability of a synthetic peptide in in vitro and in vivo fertility in the mouse.Method of study:A synthetic peptide segment: GELRERAPGQGTNG (SP) was used to immunize female B6CF1 (C57BL/6 × BALB/c) mice. A peptide with an amino acid sequence QQPLSIQQHERG (p2control) was used as control. Anti-SP and anti-p2control antisera were used to evaluate sperm function inhibition in vitro. Fertility of immunized mice was determined by microscopic evaluation of the number and state of preimplantation embryos (8–16 cell stage).Results:In the mouse, anti-SP antisera recognized surface antigens in the acrosome region of mature and capacitated sperm. Anti-SP antisera inhibited in vitro sperm binding to zona pellucida. In vivo, immune response against SP in Freund's adjuvant resulted in a significant increase (P < 0.01) in the number of dead embryos and eggs (a mean of 66%, in contrast with <25% in control mice). Fertility inhibition in vivo and in vitro was not observed when the p2control peptide was used in the immunizations.Conclusions:These results would suggest that the SP sequence is involved in gamete adhesion, and an antifertility vaccine against the SP peptide segment could be feasible.