Active immunization of female rabbits with purified rabbit acrosin and effect on fertility

Acrosin immunogen was purified from rabbit testes by sequential acid extraction, ammonium sulfate fractionation, cation-exchange, and affinity chromatography. Twelve females received intradermal injections of purified acrosin in Freund's complete adjuvant followed by a booster injection 6 weeks later. A radioimmunoassay for rabbit acrosin was developed and used to monitor the immune response of the recipients. The females were mated at the time when serum titers of acrosin antibodies were maximal. Four of the animals did not become pregnant, and three of these had the highest antibody titers in the total group. The remaining eight rabbits delivered normal litters at term. Of four control females (immunized with bovine serum albumin), one did not become pregnant. The pregnancy rates for the control and acrosin-immunized rabbits were 75% and 67%, respectively. It is concluded that, although active immunization with acrosin had no significant effect on fertility, the antibody titer produced may be a factor.