Mapping of dominant B-cell epitopes of a human zona pellucida protein (ZP1)

Zona pellucida (ZP) glycoproteins contain numerous antigenic determinants i ncluding carbohydrate, protein, and conformational epitopes; and the immuno genicity of these complex glycoproteins varies in different mammalian hosts . Studies have now shown that antibodies from primates immunized with a cDN A-expressed recombinant rabbit ZP protein (the homologue of the human ZP1 [ hZP1I] inhibit sperm binding to the ZP without altering ovarian function, u nlike immunization with ZP3 and ZP2 protein families. The ZP1 protein or pe ptides derived from it (recombinant or synthetic) are therefore primary can didates for use in designing safe and reversible human and animal contracep tive vaccines. In order to define peptide epitope(s) that may be critical f or eliciting an immune response sufficient to effect immunological contrace ption without causing any adverse effects on ovarian physiology, studies ha ve been carried out to identify immunodominant B-cell epitopes of the ZP1 p rotein. The amino acid sequence of the hZP1 was used to design a set of 94 (15-mer) biotinylated peptides having an overlap of 9 amino acids. Using th ese peptides in a modified enzyme-linked immunoassay, antibodies in sera fr om rabbits or baboons immunized with native porcine ZP protein were screene d for ZP1 peptide recognition. These studies demonstrate that there are a limited number of peptides recog nized by primate antibodies but that the overlapping peptides sharing the s equence GPLITLELQ1 are recognized by both rabbit and baboon antibodies rega rdless of the adjuvant system used to induce the immune response. This pept ide is 100% conserved in amino acid sequence between the human and pig, alt hough the rabbit protein has two conserved amino acid substitutions (100% s imilar, 77% identical). Because this peptide is immunogenic as well as anti genic in primates, it could play a major role in the development of human c ontraceptive vaccines.