MOLECULAR-BIOLOGY APPROACHES TO EVALUATE SPECIES VARIATION IN IMMUNOGENICITY AND ANTIGENICITY OF ZONA-PELLUCIDA PROTEINS

Immunocontraception using the glycoproteins of the mammalian zona pell ucida (ZP) has held great promise because antibodies specific to ZP an tigens would inhibit fertility and not be abortive. It has been shown, however, that some ZP proteins will elicit adverse effects since immu nization may affect ovarian follicular development. These effects vary among different mammalian species as well as on the source of the ZP immunogen. Therefore, the use of molecular biology has been essential in identifying specific ZP protein(s) that inhibit fertility without a ltering ovarian follicular development and in defining the relationshi ps of ZP proteins among different species. Use of recombinant ZP prote ins has allowed us to begin to dissect antigenic domains of ZP protein s and to evaluate their potential roles in the fertilization process. Recent studies using recombinant rabbit ZP proteins to immunize cynomo lgus monkeys (Maraca fascicularis) have shown that the 55 kDa ZP prote in will elicit antibodies that inhibit sperm binding while not alterin g ovarian function, in contrast to immunization with a recombinant tru ncated protein of the 75 kDa ZP protein which causes ovarian dysgenesi s. The rabbit 55 kDa protein is the homologue of the pig ZP3 alpha spe rm receptor and the human ZPB protein but is distinct from the mouse Z P3 sperm receptor. Expression of this protein using the baculovirus ex pression system has further shown that the 55 kDa protein binds to cap acitated rabbit spermatozoa over the acrosomal region and induces the acrosome reaction. Antibodies against this recombinant form of the ZP also inhibit rabbit spermatozoa from binding to rabbit egg in vitro. T hese studies demonstrate the need to determine the structure and funct ion of ZP proteins of different mammalian species to evaluate their po tential for contraceptive vaccines.