Immunological interference with fertilization

Rabbit antisera against mouse and hamster ovaries and sheep antisera against rabbit ovary have been used to demonstrate ovary specific antigens in these three species of mammals. That one or more of the specific antigens are located in the zona pellucida which surrounds the egg was indicated in immunofluorescence studies and by the effects antibodies have on the zona. After exposure to the antibody a precipitate forms on the zonae of preovulatory, unfertilized and fertilized eggs and all embryonic stages up to the time when the zona is shed. The precipitate was always seen near the outer surface of the zona suggesting that the active sites of the antigen(s) are located in this region. Trypsin and pronase which usually dissolve the zona were ineffective on the precipitated outer portion but did dissolve the inner, unprecipitated region. Species- and tissue-specificity and chemical nature of the zona are discussed. Important roles for the zona antigen(s) in a number of early events in reproduction were indicated by the effects of antizona antibodies have on fertilization and implantation. Pretreatment of unfertilized hamster eggs with zona precipitating antibodies was most effective in blocking sperm attachment to the zona. When the antibody was added subsequent to in vitro insemination, but before the sperm had passed through the outer region of the zona, sperm penetration was blocked. Mouse embryos treated with zona precipitating antibody and cultured in vitro failed to escape from the zonae, implying that implantation could be inhibited by antibody. Passive immunization of female mice with antizona antibodies and precipitattion of the zonae of hamster embryos in transfer experiments reduced the number of implantation sites. The identification of zona antigens and the effects of zona precipitating antibodies on early reproductive events encourage further studies on the zona in reference to immunological control of fertility.