Sperm Fractions Responsible for Immunologic Induction of Pre- and Postfertilization Infertility in Rabbits

Female rabbits were isoimmunized against 0.3 M lithium diiodosalicylate (LIS) soluble extracts of washed rabbit sperm and homogenized rabbit testis. The rates of fertility, measured as percentage of corpora lutea represented by viable embryo implants at 9–13 days after breeding, for the 2 groups were 45% (P<0.05) and 56%, respectively, compared with 71% for control rabbits. Antisera from rabbits immunized against the sperm-LIS extract possessed intermediate titers of sperm immobilizing and agglutinating antibodies and significantly reduced fertility of sperm used in artificial insemination of nonimmunized does. In the second phase of the study, groups of rabbits were immunized against increased amounts of LIS solubilized extracts of sperm and testis, the LIS-extracted sperm pellet and also detergent (Nonidet NP.40) extracts of sperm pellet and of homogenized testis. Does immunized with the LIS extract of sperm exhibited low fertility (3%) and produced antisera that had high titers of sperm antibodies that blocked sperm attachment to rat ova in vitro and inhibited sperm from in vivo fertilization of nonimmune does. Rabbits immunized with the LIS-extracted sperm pellet and the NP.40 extract of the pellet experienced significantly low incidencs of implantation, 15 and 28%, respectively. Fertilization rate in 3 does immunized against the LIS-extracted sperm pellet was normal (91%), but the implantation rate (19%) was reduced. Antisera from these 2 groups of rabbits possessed low titers of sperm antibodies and did not inhibit sperm attachment to rat ova or fertilization in nonimmune rabbits. A significant reduction in implantation of transferred-fertilized ova occurred in rabbits immunized against the NP.40 soluble fraction of the LIS-extracted sperm pellet (19.5%) compared with rabbits immunized against the LIS-soluble fraction (39.8%) and against saline (41.3%). It is concluded that immunization of female rabbits either with immunogens in the LIS-soluble fraction of sperm or the sperm pellet after LIS extraction resulted in prefertilization and postfertilization antifertility effects, respectively.