Origin of the antigens in rabbit semen which induce antifertility antibodies

Summary. Cattle and guinea-pig antisera against rabbit testis, epididy-mal spermatozoa and ejaculated semen had high titres of sperm agglu-tinins and prevented fertilization of ova in rabbits bred with semen treated with these sera. Although cattle antisera produced against seminal plasma from vasectomized rabbits, 9-day-old-rabbit con-ceptuses and rabbit brain and guinea-pig antiserum to seminal plasma containing epididymal secretions exhibited relatively high titres of sperm agglutinins, none of these sera prevented spermatozoa from fertilizing ova. The antifertility antibodies were removed or inactivated in antisera by absorptions with testis material, epididymal spermatozoa and semen supernatant but not by absorption with either type of seminal plasma. Agar-gel diffusion and immuno-electrophoretic techniques revealed that ejaculated rabbit semen contained at least nine antigens. Seven were common to seminal plasma, two to blood serum and two appeared to be spermatozoa-specific originating in the testis. Antisera to the conceptus material reacted with four to six different antigens in semen of which at least one was not common to the antigens in blood serum