Screening and identification of dominant functional fragments of human epididymal protease inhibitor.

To lay a foundation for the further development of a novel contraceptive vaccine based on epididymal protease inhibitor (Eppin) protein, possible B-cell epitopes were predicted using bioinformatics. Overlapping KLH-coupled peptides corresponding to the 89-133 amino acid domain of Eppin protein were synthesized by the Fmoc method. The male mice were immunized with various peptides resulting in a gradual elevation of specific serum IgG antibodies until they peaked at the seventh week. Treatment with antiserum in immunized mice caused a significant decrease in the sperm-egg binding rate. Eventually, antifertility assays in vivo showed that, the pregnancy rate and the number of births per labor in experimental mice were significantly decreased. The decrease in the F5 and the F4 groups were more outstanding therefore these peptides might be the dominant functional fragments of Eppin protein and provide an experimental basis for the development of effective contraceptive vaccine based on Eppin protein.