[Immunocontraceptive effect of a synthetic chimeric peptide of sperm]

To investigate the immunocontraceptive ability of a new synthetic chimeric peptide with 35 amino acid residues.

A chimeric peptide with 35 amino acid residues was synthesized based on the amino acid sequence of SP17, a protein specific to murine testis/sperm, and cyritestin. The purified product, with keyhole limpet hemocyanin (KLH), was injected subcutaneously into the pad of female and male Balh/C mice. Blood was extracted from the ophthalmic arteries of the mice to identify the corresponding proteins from organs of mice and/or rat and human being by Western blotting. The chimeric peptide was injected into other female mice that were then raised together with male mice in the same cages to observe their status of pregnancy. Freund' adjuvant or normal saline were injected into the controls.

The purity of the new chemiric peptide was 95%. The highest specific IgG titre in mouse serum was 1:6000 and the highest titre of specific IgA in the washing of vaginal mucous membrane of female mice was 1:300. The specific antiserum from the mice immunized by the chimeric peptide and KLH could identify two proteins with the molecular weights of 22 000 and 55 000 from testes of mice, rats, and human being. Western blotting showed no band for the extracts of mouse liver, spleen, and kidney. The pregnancy rate of female immunized mice was 61.11%, significantly lower that those in the controls (P < 0.05). The average number of cubs in a litter was less in the experimental group than in the controls (P < 0.05).

The new chimeric peptide with 35 amino acid residues stimulates powerfully humoral and mucous immunity in mice and obviously decreases the pregnancy rate and the number of cubs in each litter in mice.