A CHIMERIC SPERM PEPTIDE INDUCES ANTIBODIES AND STRAIN-SPECIFIC REVERSIBLE INFERTILITY IN MICE

The development of a contraceptive vaccine based on a gamete-specific antigen requires knowledge of the ability of the antigen to elicit an immune response that inhibits fertilization. A well-defined immune res ponse, as elicited by a synthetic peptide comprising a dominant B-cell epitope coupled to a common promiscuous T-cell epitope, might be pref erable. In this study, the immunodominant B-cell epitope of sperm anti gen Sp17 has been identified and synthesized as a chimeric peptide wit h the promiscuous T-cell epitope bovine RNase[94-104] at the N termina l. Immunization of female BALB/c mice with this peptide induced a dose -dependent reduction in fertility. Although antibodies to recombinant and native Sp17 were elicited in these mice, there was no strict corre lation between the level of these antibodies and the reduction in fert ility. Moreover, the induction of infertility was strain-specific sinc e no effect on fertility could be induced in B6AF1 mice. To understand the mechanism behind this apparent strain-specific infertility induct ion, a more extended study on both the humoral and the cellular immune response to the chimeric peptide was performed. The antigen-specific T-cell response and the levels of antigen-specific cytokines are the m ajor factors that affect fertility outcome.