Sex difference of antifertility effect by passively immunized monoclonal sperm antibodies

Potential contraceptive use of epididymal proteins: immunization of male rats with epididymal protein DE inhibits sperm fusion ability

Rat epididymal protein DE associates with the sperm surface during maturation and participates in sperm-egg fusion. Immunization of male rats with DE raised specific antibodies and produced a significant reduction in the animals' fertility. The present study focused on determining the in vivo mechanism involved in fertility inhibition. Wistar males were injected with DE, and antibody levels and animal fertility were evaluated. Results revealed an association between the two parameters, since animals with absorbance values lower than 0.5 in ELISA presented high fertility rates (66%, 100%) while those with absorbance values higher than 0.5 exhibited the lowest fertility rates (0%, 33%). Histological studies showed no evidence of orchitis, epididymitis, or vasitis in DE-immunized animals. ELISA results revealed the presence of anti-DE antibodies in epididymal and vas deferential fluids. Indirect immunofluorescence and ELISA experiments indicated that these antibodies would not interfere with the synthesis or secretion of DE or with its association with the sperm surface. Finally, while epididymal sperm recovered from DE-immunized animals presented no changes in motility, viability, or ability to undergo capacitation and acrosome reaction, they exhibited a significant decrease in their ability to fuse with zona-free eggs, with no effect on their ability to bind to the oolemma. Together these results indicate that immunization of male rats with epididymal protein DE specifically interferes with the sperm fertilizing ability, supporting the use of epididymal proteins for contraceptive vaccine development.

Molecular basis of sperm-egg interaction and the prospects for immunocontraception

As the molecular basis of sperm-egg interaction is resolved, so new opportunities are created for the development of immunological approaches to disrupt the process of conception. Thus, realisation that the zona glycoprotein, ZP3, serves as a specific receptor for spermatozoa, has prompted a detailed examination of its contraceptive potential. In primate models, recombinant ZP3 has been shown to suppress fertility very efficiently, however this efficacy is tempered by the appearance of adverse side-effects involving accelerated primordial follicle depletion and a lymphocytic infiltration of the ovarian stroma. Synthetic peptides encoding B-cell epitopes have been found to circumvent the lymphocyte response although the effectiveness of such reagents in preventing the loss of primordial follicles has not yet been determined. The induction of active immunity against sperm-specific antigens has also been shown to generate long term infertility in both males and females. Molecular and immunological techniques are now being used to produce a rapidly expanding list of unique sperm antigens which are currently being evaluated to determine their potential contribution to the development of safe, effective, contraceptive vaccines.

Characterisation of a sperm coating auto-antigen reacting with antisperm antibodies of infertile males using monoclonal antibodies

OBJECTIVE

In a previous study a number of sperm-specific antigens were identified which reacted with antisperm antibodies from both infertile and vasovasostomised males. To investigate the localisation and distribution of these antigens and their role in male fertility, monoclonal antibodies were raised against them; immunoblotting techniques were used to select only those antibodies which competed with human antisperm antibodies for these human auto-antigens.

DESIGN

One antibody, NW21, reacted with an 18 kDa auto-antigen present on epididymal sperm but absent from testicular sperm. Immunohistochemical studies showed that the antigen is produced in small basal cells between the columnar epithelium of the corpus epididymis, passes up into the tubule and then coats sperm passing along the epididymis. Sperm stored in the cauda epididymis and ductus deferens stain strongly for this sperm coating glycoprotein.

CONCLUSIONS

The localisation of this antigen supports the suggestion that auto-immune infertility may represent a response to epididymal rather than testicular sperm. Monoclonal antibodies raised to unique and immunologically accessible sperm coating proteins, produced in the epididymis rather than in the testis, would seem to present an excellent theoretical solution to male contraception.

Potential contraceptive use of epididymal proteins: evidence for the participation of specific antibodies against rat epididymal protein DE in male and female fertility inhibition

Previous studies in our laboratory indicated that immunization of male and female Wistar and Lewis rats with epididymal protein DE, resulted in the development of anti-DE antibodies in over 90% of the animals, with a significant and reversible reduction of fertility. In the present study, ELISA assays performed to analyze the evolution of the immune response indicated that antibody levels in the sera of immunized animals reached a maximum at 8 weeks after the initial injection and then gradually decreased, returning to control values by the end of the sixth month. Western blot experiments demonstrated that the immune sera specifically recognized DE in epididymal sperm extracts and epididymal cytosol, while no reaction was observed with different reproductive and essential organs. The immune sera were also capable of recognizing DE on the surface of both fresh and capacitated sperm as indicated by indirect immunofluorescence experiments. Finally, the exposure of sperm to immune sera prior to uterine insemination resulted in a significant (P < 0.05) reduction in the percentage of fertilized eggs compared to controls, with no effect on sperm motility and viability, nor on their ability to undergo capacitation. Together, these results support the participation of the raised antibodies as mediators of the antifertility effect and suggest a specific interference at the sperm-egg interaction level.

Molecular cloning of an acrosomal sperm antigen gene and the production of its recombinant protein for immunocontraceptive vaccine

A monoclonal antibody, HS-63, which reacts specifically with a highly conserved sperm acrosome antigen, was shown to inhibit in vitro fertilization of mouse and human. The corresponding sperm antigen designated as MSA-63 was purified to homogeneity from mouse testes and used as an immunogen to generate polyclonal antisera in rabbits. The cDNA fragments of MSA-63 gene were cloned from mouse testis cDNA library by an immunoscreening method using polyclonal antisera specific for MSA-63. Using the established cDNA clone as a probe, the gene encoding for MSA-63 protein was found to be conserved among different mammalian species. Only one specific mRNA 1.5 kb in size was identified from the adult mouse testis among different mouse tissues. The recombinant fusion protein containing MSA-63 protein fragment was produced in Escherichia coli and used to immunize female mice. Similar to the original HS-63 monoclonal antibody, the antisera thus produced reacted only with the sperm acrosome and revealed significant inhibition to the in vitro fertilization of mouse oocytes. The results of this preliminary study suggest that it is feasible to mass produce sperm-specific antigens or their antigenic fragments by recombinant DNA technology for the development of sperm antigen-based immunocontraceptive vaccines.

Effect of antibodies to human seminal plasma inhibin on spermatogenesis and sperm agglutination in adult male rats

In vitro incubation of rat epididymal sperm with antiserum to human seminal plasma inhibin (As hSPI) caused agglutination of the sperm. In vivo administration of As hSPI to adult male rats resulted in a significant decrease in testicular as well as epididymal sperm counts. Furthermore, the majority (almost 90%) of the epididymal sperm were agglutinated. When these animals were mated with normal cycling females, significant reduction in fertility was observed.

Purification of an acrosomal antigen recognized by a monoclonal antibody and antifertility effects of isoimmune serum

A highly conserved acrosomal antigen reactive to a monoclonal antibody (HS-63), generated against human sperm, was purified to homogeneity with a combination of conventional procedures and immunoaffinity chromatography using a soluble extract of mouse and rabbit testes. The molecular weight of the purified antigen was 42-50 kD when analysed by sodium dodecylsulphate polyacrylamide gel electrophoresis. The high specificity of the purified antigen to monoclonal antibody HS-63 was shown by indirect immunofluorescent inhibition assay, enzyme-linked immunosorbent assay, Western blot analysis and radioimmunosorbent assay. The purified antigen was used for isoimmunization of mice and rabbits. Following successive immunizations, antisera of high titres were raised and reacted specifically with antigen on the sperm acrosome and in testes of several mammalian species, but not with somatic tissues. These isoimmune sera exhibited strong inhibition on mouse in-vitro fertilization and human sperm penetration of zona-free hamster eggs. The results of this study suggest that the sperm-specific acrosomal antigen reacting with HS-63 could be a good candidate for the development of immunocontraceptive vaccines in humans and in other animals.

Sperm antibodies and human in vitro fertilization

In order to directly evaluate the effects of sperm antibodies in human in vitro fertilization (IVF), the authors preincubated donor sperm in female sera containing sperm antibodies and then inseminated supernumerary human oocytes from a gamete intrafallopian transfer (GIFT) program. The sperm were incubated for 30 minutes in medium containing 20% serum with antisperm activity (Test); or no antisperm activity (Control) as assessed by the immunobead test (IBT). Each oocyte was inseminated with 1 to 2 X 10(5)/ml of the preincubated motile sperm with Control or Test treatments allocated on a random basis. Six positive sera were tested in 17 experiments, resulting in a fertilization rate of 41% (25/61) versus 84% (36/43) for controls (P less than 0.001). When considered individually, three of six positive sera caused significant inhibition. The only serum that gave complete inhibition had the highest titer for IgG (10,000) and lower IgA (100). Absorption with protein A reduced the IgG titer to less than 10 and removed the fertilization inhibitory activity. These results confirm that sperm antibodies from female sera can inhibit human IVF.