Pathways to immunocontraception: biochemical and immunological properties of glycoprotein antigens of the porcine zona pellucida.

The zona pellucida (ZP) is an extracellular coat which surrounds the mammalian oocyte and whose macromolecular composition is unique for each species. Two-dimensional gel electrophoresis of porcine ZP under reducing conditions resolves four major acidic, charge-heterogeneous glycoproteins with apparent molecular weights of 82,000 (ZP1), 61,000 (ZP2), 55,000 (ZP3) and 21,000 (ZP4). Fractionation of heat-solubilized porcine ZP under nondissociative, nonreducing conditions resulted in a preparation, termed purified pig zona antigen (PPZA), substantially enriched in ZP3 and lacking ZP1 and ZP2. PPZA was highly immunogenic in both rabbit and squirrel monkey. Anti-PPZA sera exhibited contraceptive potential as assessed by in vitro inhibition of homologous sperm-zona binding following antibody treatment of human, pig and squirrel monkey oocytes. Alternatively, fractionation of sodium dodecyl sulfate (SDS)-dissociated porcine ZP under nonreducing conditions resulted in isolation of two electrophoretically homogeneous antigens with apparent molecular weights of 82,000 (82K antigen) and 55,000 (55K antigen) as judged by nonreducing SDS-polyacrylamide gel electrophoresis. The 82K antigen exhibited an estimated molecular weight of 345,000 by gel filtration chromatography in nondissociative solvent and was comprised of ZP1 and disulfide-linked heterodimers of ZP2+ZP4 and ZP3+ZP4. The 55K antigen was comprised of ZP3 which was highly aggregated in nondissociative solvent. Each antigen had a characteristic carbohydrate composition and proved to be immunogenic in the rabbit. The effects of active heteroimmunization of squirrel monkeys with 55K antigen on fertility are under investigation.