Active immunization of mice with porcine zonae pellucidae: immune response and effect on fertility

Female mice were heteroimmunized with varying dosages of intact and heat-solubilized porcine zonae. Mouse immune response was monitored by radioimmunoassay and the effect on mouse fertility of circulating antibodies to pig zonae was observed. Porcine zonae were a potent heteroimmunogen in the mouse and, for all dosages studied, the immune response was characterized by a rapid rise in titer, culminating in a peak which was followed by a plateau period of extended duration and of significantly high anti-zona activity. Maximum immune response was achieved using a dosage of 4000 heat-solubilized zonae per mouse. Studies involving alteration of immunization regimes, but use of a constant zonae dosage, indicated that maximal response to this antigenic target was obtained intact zonae applied over a series of injections rather than in a single application. In vitro studies involving proteolytic lysis or of sperm attachment to mouse zonae pretreated with either antibodies to mouse zonae (homologous system) or pig zonae (heterologous system) demonstrated that zona antibodies are considerably more biologically effective in the homologous system. Immunization of mice with pig zonae had no significant effect upon altering mouse fertility. The significance of these fertility results is discussed with respect to the information obtained from the in vitro studies and in respect to the continued consideration of the zona as an immunocontraceptive antigenic target.