Update on zona pellucida glycoproteins based contraceptive vaccine

Immunogenicity and contraceptive efficacy of plant-produced putative mouse-specific contraceptive peptides

Rodent population control through contraception requires species-specific oral contraceptive vaccines. Therefore, in this study, we produced putative mouse-specific contraceptive peptides, mZP2 (from oocyte) and mIzumo1 (from sperm), in plants using Agrobacterium-mediated transient expression. Peptides were produced separately in Nicotiana benthamiana using constructs encoding antigens containing three copies of each peptide. We also determined the immunogenicity and contraceptive effects of the plant-produced antigens in female BALB/c mice. Mice immunized subcutaneously with a relatively low amount of antigen (5 µg/dose of each peptide in a mixture) showed systemic immune responses against mZP2-3 and mIzumo1-3 antigens. Moreover, the mean litter size of mice treated with the plant-produced antigens was reduced by 39% compared to that of the control mice. Notably, there was a significant negative correlation between the number of pups born and individual antibody levels against both antigens. Immunofluorescence assays demonstrated the binding of induced antibodies to the oocytes of BALB/c and wild-type mice in vivo and in vitro, respectively. Our study demonstrate the feasibility of producing small contraceptive peptides in plants that can be further used to develop oral contraceptive vaccines against mouse populations.

Oral and Subcutaneous Immunization with a Plant-Produced Mouse-Specific Zona Pellucida 3 Peptide Presented on Hepatitis B Core Antigen Virus-like Particles

A short mouse-specific peptide from zona pellucida 3 (mZP3, amino acids 328-342) has been shown to be associated with antibody-mediated contraception. In this study, we investigated the production of mZP3 in the plant, as an orally applicable host, and examined the immunogenicity of this small peptide in the BALB/c mouse model. The mZP3 peptide was inserted into the major immunodominant region of the hepatitis B core antigen and was produced in Nicotiana benthamiana plants via Agrobacterium-mediated transient expression. Soluble HBcAg-mZP3 accumulated at levels up to 2.63 mg/g leaf dry weight (LDW) containing ~172 µg/mg LDW mZP3 peptide. Sucrose gradient analysis and electron microscopy indicated the assembly of the HBcAg-mZP3 virus-like particles (VLPs) in the soluble protein fraction. Subcutaneously administered mZP3 peptide displayed on HBcAg VLPs was immunogenic in BALB/c mice at a relatively low dosage (5.5 µg mZP3 per dose) and led to the generation of mZP3-specific antibodies that bound to the native zona pellucida of wild mice. Oral delivery of dried leaves expressing HBcAg-mZP3 also elicited mZP3-specific serum IgG and mucosal IgA that cross-reacted with the zona pellucida of wild mice. According to these results, it is worthwhile to investigate the efficiency of plants producing HBcAg-mZP3 VLPs as immunogenic edible baits in reducing the fertility of wild mice through inducing antibodies that cross-react to the zona pellucida.

Plant-Produced Mouse-Specific Zona Pellucida 3 Peptide Induces Immune Responses in Mice

Contraceptive vaccines are designed to stimulate autoimmune responses to molecules involved in the reproductive process. A mouse-specific peptide from zona pellucida 3 (mZP3) has been proposed as a target epitope. Here, we employed a plant expression system for the production of glycosylated mZP3 and evaluated the immunogenicity of plant-produced mZP3-based antigens in a female BALB/c mouse model. In the mZP3-1 antigen, mZP3 fused with a T-cell epitope of tetanus toxoid, a histidine tag, and a SEKDEL sequence. A fusion antigen (GFP-mZP3-1) and a polypeptide antigen containing three repeats of mZP3 (mZP3-3) were also examined. Glycosylation of mZP3 should be achieved by targeting proteins to the endoplasmic reticulum. Agrobacterium-mediated transient expression of antigens resulted in successful production of mZP3 in Nicotiana benthamiana. Compared with mZP3-1, GFP-mZP3-1 and mZP3-3 increased the production of the mZP3 peptide by more than 20 and 25 times, respectively. The glycosylation of the proteins was indicated by their size and their binding to a carbohydrate-binding protein. Both plant-produced GFP-mZP3-1 and mZP3-3 antigens were immunogenic in mice; however, mZP3-3 generated significantly higher levels of serum antibodies against mZP3. Induced antibodies recognized native zona pellucida of wild mouse, and specific binding of antibodies to the oocytes was observed in immunohistochemical studies. Therefore, these preliminary results indicated that the plants can be an efficient system for the production of immunogenic mZP3 peptide, which may affect the fertility of wild mice.

The status of fertility control for rodents-recent achievements and future directions

Management of overabundant rodents at a landscape scale is complex but often required to sustainably reduce rodent abundance below damage thresholds. Current conventional techniques such as poisoning are not species specific, with some approaches becoming increasingly unacceptable to the general public. Fertility control, first proposed for vertebrate pest management over 5 decades ago, has gained public acceptance because it is perceived as a potentially more species-specific and humane approach compared with many lethal methods. An ideal fertility control agent needs to induce infertility across one or more breeding seasons, be easily delivered to an appropriate proportion of the population, be species specific with minimal side-effects (behavioral or social structure changes), and be environmentally benign and cost effective. To date, effective fertility control of rodents has not been demonstrated at landscape scales and very few products have achieved registration. Reproductive targets for fertility control include disrupting the hormonal feedback associated with the hypothalamic-pituitary-gonadal axis, gonad function, fertilization, and/or early implantation. We review progress on the oral delivery of various agents for which laboratory studies have demonstrated efficacy in females and/or males and synthesize progress with the development and/or use of synthetic steroids, plant extracts, ovarian specific peptides, and immunocontraceptive vaccines. There are promising results for field application of synthetic steroids (levonorgestrel, quinestrol), chemosterilants (4-vinylcyclohexene diepoxide), and some plant extracts (triptolide). For most fertility control agents, more research is essential to enable their efficient and cost-effective delivery such that rodent impacts at a population level are mitigated and food security is improved.

Latheef S, Sharun K, Khurana SK, K. A, Tiwari R, Bhatt P, K. V, Chaicumpa W. Role of Antisperm Antibodies in Infertility, Pregnancy, and Potential forContraceptive and Antifertility Vaccine Designs: Research Progress and Pioneering Vision

Sperm of humans, non-human primates, and other mammalian subjects is considered to be antigenic. The effect of changes in autoimmunity on reproductive cells such as spermatozoa and oocytes play a critical but indistinct role in fertility. Antisperm antibodies (ASAs) are invariably present in both females and males. However, the degree of ASA occurrence may vary according to individual and gender. Although the extent of infertility due to ASAs alone is yet to be determined, it has been found in almost 9-12% of patients who are infertile due to different causes. Postcoital presence of spermatozoa in the reproductive tract of women is not a contributory factor in ASA generation. However, ASA generation may be induced by trauma to the vaginal mucosa, or by anal or oral sex resulting in the deposition of sperm inside the digestive tract. It is strongly believed that, in humans and other species, at least some antibodies may bind to sperm antigens, causing infertility. This form of infertility is termed as immunological infertility, which may be accompanied by impairment of fertility, even in individuals with normozoospermia. Researchers target ASAs for two major reasons: (i) to elucidate the association between ASAs and infertility, the reason ASAs causes infertility, and the mechanism underlying ASA-mediated infertility; and (ii) to assess the potential of ASAs as a contraceptive in humans in case ASAs influences infertility. Therefore, this review explores the potential application of ASAs in the development of anti-spermatozoa vaccines for contraceptive purposes. The usefulness of ASAs for diagnosing obstructive azoospermia, salpingitis, and oligoasthenoteratozoospermia has been reviewed extensively. Important patents pertaining to potential candidates for spermatozoa-derived vaccines that may be utilized as contraceptives are discussed in depth. Antifertility vaccines, as well as treatments for ASA-related infertility, are also highlighted. This review will address many unresolved issues regarding mechanisms involving ASAs in the diagnosis, as well as prognoses, of male infertility. More documented scientific reports are cited to support the mechanisms underlying the potential role of ASA in infertility. The usefulness of sperm antigens or ASAs (recombinant) in human and wild or captive animal contraceptive vaccines has been revealed through research but is yet to be validated via clinical testing.

Vaccination with an Epitope Peptide of IZUMO1 to Induce Contraception in Female Mice

PROBLEM

The development of a new and suitable contraceptive methods, as well as in-depth and systematic research into underlying contraceptive mechanisms, is crucial. IZUMO1 plays an important role in the fusion of the sperm and ovum during fertilization. Izumo(-/-) mice are infertile. Therefore, IZUMO1 may be a potential target for the development of a contraceptive vaccine.

METHOD OF STUDY

Linear B-cell epitopes (BCE) were identified in IZUMO using biosynthetic peptides and used to immunize female mice.

RESULTS

Five IZUMO BCE were identified: DLVLDCL177-183, YSFYRV196-201 (named BCE-2), YLT217-219, SMVGPED221-227, and DAGNY228-232. Active immunization with the BCE-2 vaccine sharply decreased the fertility rate in female mice in a safe and reversible manner. In vitro fertilization showed that the BCE-2 vaccine interferes with and blocks the fusion of the sperm and the ovum.

CONCLUSIONS

B-cell epitopes-2 may be a new candidate for the development of contraceptive vaccine due to its effectiveness, safety, and reversibility.

Immunocontraceptives: How far from reality?

Despite high expectations of safer, effective, economical, longer acting contraceptives, to date, there are no licensed contraceptive vaccines available in the market. Nevertheless, a role for vaccines undoubtedly exists as an aid to birth spacing and as a nonsurgical means of generating sterility. The research concerned in the area so far has been successful on the feline population, with room still for exhaustive studies on humans. The future of contraceptive vaccines holds great promise in terms of comfort, price, efficacy, rare complications, and possibly nonselective action on animal populations as well as on humans. This brief review deals with the basic aspects of immunocontraceptives along with the efforts done so far. There is a need for further research in aspects involving the rate of evolution of contraception resistance based on genetics, resistance phenotypes, or cross generation effects. Gonadotropin-releasing hormone and luteinizing-hormone have not been investigated in humans, as both reported impotency in animals; the follicle-stimulating hormone has been shown to cause oligospermia; zona pellucida has also not been studied in humans as it causes irreversible oophoritis, while the sperm has the potential for success in humans based on the data from immunoreproductive studies. Even as the position of the human chorionic gonadotropin vaccine looks hopeful, research on other possible targets continue with an eventual aim of discovering a vaccine that is more immunogenically effective.

Evidence for the inhibition of fertilization in vitro by anti-ZP3 antisera derived from DNA vaccine

Previously we have found that DNA vaccine, pCMV4-rZPC' can generate specific antibodies against rabbit ZPC (amino acid 263-415, rZPC'), which binds to ovarian ZP and leads to a significant reduction of fertility in vivo. The purpose of this study was to evaluate the effect of antisera from pCMV4-rZPC(')-immunized mice on sperm-oocyte interaction in vitro. The effect of antisera from DNA vaccine-immunized mice on fertilization and early embryonic development was studied using an in vitro fertilization system. The results showed that the antisera supplemented in fertilization medium (10%, v/v) significantly decreased the rate of fertilization compared to that of control groups (P<0.05); whereas the antisera showed no significant effect on the rate of fertilization when ZP-free eggs were used. Moreover, the antisera pre-neutralized with mouse soluble zona pellucida lost the capacity to inhibit fertilization when compared with that of control groups. In addition, the antisera showed no detrimental effect on early developmental potential of mouse embryos in vitro. Taken together, our study provided herein direct evidence showing that antisera generated by DNA vaccine can block sperm-egg recognition during fertilization via targeting the oocyte ZP proteins.

DNA vaccine encoding chimeric protein encompassing epitopes of human ZP3 and ZP4: immunogenicity and characterization of antibodies

Immunization with zona pellucida (ZP) glycoproteins leads to curtailment of fertility often associated with ovarian dysfunction. To avoid ovarian dysfunction, synthetic peptides corresponding to ZP glycoproteins have been proposed as candidate immunogens. In the present study, plasmid DNA encoding a human ZP glycoprotein-3 (ZP3) epitope corresponding to amino acid (aa) residues 334-343 and a human ZP glycoprotein-4 (ZP4) epitope corresponding to aa residues 251-273 separated by a triglycine spacer was constructed using the mammalian expression vector, VR1020. The plasmid DNA construct expressed both human ZP3 and ZP4 epitopes, as revealed by transient transfection of COS-1 (African green monkey, kidney) mammalian cells. Active immunization of female BALB/cJ mice with the DNA vaccine led to generation of antibodies reactive with baculovirus-expressed recombinant human ZP3, ZP4 and ZP3((334-343aa))-GGG-ZP4((251-273aa)) synthetic peptide in an ELISA as well as T cell responses. Antibodies generated by the DNA vaccine also recognized native ZP. The immune sera significantly inhibited (p<0.005) the binding of FITC-labeled ZP3 to capacitated human sperm, whereas no inhibition in the binding of FITC-labeled ZP4 was observed. However, a significant decrease in acrosomal exocytosis mediated by both recombinant human ZP3 (p<0.005) and ZP4 (p<0.005) was observed in presence of the immune sera. These studies demonstrate that a DNA vaccine can be designed to elicit antibodies against small epitopes of ZP glycoproteins.

Immunization with recombinant murine cytomegalovirus expressing murine zona pellucida 3 causes permanent infertility in BALB/c mice due to follicle depletion and ovulation failure

Zona pellucida (ZP) glycoproteins are promising candidate antigens for use in immunocontraceptive vaccines because of their crucial role in mammalian fertilization. A single intraperitoneal immunization with recombinant murine cytomegalovirus engineered to express murine ZP3 (rMCMV-mZP3) induces permanent infertility with no evident systemic illness in female BALB/c mice. To investigate the mechanisms underpinning reproductive failure elicited by rMCMV-mZP3, ovarian parameters and reproductive function were evaluated at time points spanning 10 days to 5 wk after virus inoculation. Fertility was substantially impaired by 14 days after inoculation with rMCMV-mZP3 and was fully ablated by 21 days. Pregnancies established after inoculation but before complete infertility showed no adverse effects on fetal viability assessed at Day 17.5 post coitum (pc). Infertile mice retained estrous cycling activity and remained receptive to mating; however, at Day 3.5 pc there were fewer developing embryos and corpora lutea, plasma progesterone content was reduced, and there was no evidence of excess unfertilized oocytes. Consistent with this, profound ovarian pathology was evident from 10 days after rMCMV-mZP3 inoculation, with a decline first in mature ovarian follicles and then in immature ovarian follicles and with diminished expression of genes regulating follicle development, including Nobox, Gdf9, and Gja1 (connexin43). Follicle loss was associated with mild focal oophoritis and with recruitment of inflammatory leukocytes, predominantly CD4(+) and CD8(+) T cells evident from 10 days after virus inoculation. These data indicate that vaccination with rMCMV-mZP3 causes permanent infertility in BALB/c mice principally due to induction of ovarian autoimmune pathology leading to progressive oocyte depletion and eventual ovulation failure.

Polypeptide backbone derived from carboxyl terminal of mouse ZP3 inhibits sperm-zona binding

For mammalian organism, fertilization begins with species-specific recognition between sperm and egg, a process depending upon egg zona pellucida glycoproteins and putative sperm interacting protein(s). In mouse, zona pellucida glycoprotein ZP3 is believed to be the primary receptor for sperm and inducer of sperm acrosomal reaction, and its function has been attributed to the specific O-linked oligosaccharides attached to polypeptide backbone. While lots of reports have focused on the role of ZP3's oligosaccharides in fertilization, there are few concerning its polypeptide backbone. To investigate whether mZP3 polypeptide backbone is involved in sperm-egg recognition, three partially overlapping cDNA fragments, together covering entire mouse ZP3, were cloned, expressed and purified under denaturing condition. Although all three refolded proteins possess native conformation, only one derived from the carboxyl terminal showed inhibitory effect to the sperm-zona binding during in vitro fertilization. This phenomenon could not be explained by enhanced acrosomal exocytosis rate, in that the acrosomal reaction assay demonstrated its inability to induce the acrosomal reaction. Our results suggest that the carboxyl terminal of mZP3 polypeptide backbone interacts with sperm and such interaction plays a significant role in sperm-zona binding, ultimately successful fertilization.

Antisperm antibodies and conception

Sperm have been known to be antigenic for more than a century. There is a strong body of evidence that in humans and in other species at least some antibodies that bind to sperm antigens can cause infertility. Therefore, these antibodies are of interest today for two practical reasons. Firstly, the association of the antibodies with infertility means that they must be detected and then the couples treated appropriately. Secondly, because these antibodies can induce infertility they have the potential to be developed for contraceptive purposes in humans and also for the control of feral animal populations.

Contraception today

Modern contraceptive methods represent more than a technical advance: they are the instrument of a true social revolution-the "first reproductive revolution" in the history of humanity, an achievement of the second part of the 20th century, when modern, effective methods became available. Today a great diversity of techniques have been made available and-thanks to them, fertility rates have decreased from 5.1 in 1950 to 3.7 in 1990. As a consequence, the growth of human population that had more than tripled, from 1.8 to more than 6 billion in just one century, is today being brought under control. At the turn of the millennium, all over the world, more than 600 million married women are using contraception, with nearly 500 million in developing countries. Among married women, contraceptive use rose in all but two developing countries surveyed more than once since 1990. Among unmarried, sexually active women, it grew in 21 of 25 countries recently surveyed. Hormonal contraception, the best known method, first made available as a daily pill, can today be administered through seven different routes: intramuscularly, intranasally, intrauterus, intravaginally, orally, subcutaneously, and transdermally. In the field of oral contraception, new strategies include further dose reduction, the synthesis of new active molecules, and new administration schedules. A new minipill (progestin-only preparation) containing desogestrel has been recently marketed in a number of countries and is capable of consistently inhibiting ovulation in most women. New contraceptive rings to be inserted in the vagina offer a novel approach by providing a sustained release of steroids and low failure rates. The transdermal route for delivering contraceptive steroids is now established via a contraceptive patch, a spray, or a gel. The intramuscular route has also seen new products with the marketing of improved monthly injectable preparations containing an estrogen and a progestin. After the first device capable of delivering progesterone directly into the uterus was withdrawn, a new system releasing locally 20 microg evonorgestrel is today marketed in a majority of countries with excellent contraceptive and therapeutic performance. Finally, several subcutaneously implanted systems have been developed: contraceptive "rods," where the polymeric matrix is mixed with the steroid and "capsules" made of a hollow polymer tube filled with free steroid crystals. New advances have also been made in nonhormonal intrauterine contraception with the development of "frameless" devices. The HIV/AIDS pandemic forced policy makers to look for ways to protect young people from sexually transmitted diseases as well as from untimely pregnancies. This led to the development of the so-called dual protection method, involving the use of a physical barrier (condom) as well as that of a second, highly effective contraceptive method. More complex is the situation with antifertility vaccines, still at a preliminary stage of development and unlikely to be in widespread use for years to come. Last, but not least, work is in progress to provide effective emergency contraception after an unprotected intercourse. Very promising in this area is the use of selective progesterone receptor modulators (antiprogestins).

Immunocontraception in mice using repeated, multi-antigen peptides: immunization with purified recombinant antigens

Two immunocontraceptive antigens (AgE and AgF) were constructed that included different combinations of highly species-specific peptides from the mouse reproductive antigens SP56, ZP3, ZP2, and ZP1 in the form of multi-antigen peptides (MAPs). Both AgE and AgF contained three tandem repeats each of ZP2 and ZP3 peptide epitopes and a single copy of a ZP1 peptide sequence all of which had previously been demonstrated to individually have immunodominant or contraceptive effects. In addition, AgF contained a single contraceptive peptide derived from SP56, the putative ZP3 receptor protein on sperm. The antigens were expressed and affinity purified as recombinant repeated multi-antigen (polyepitope) peptides using an Escherichia coli maltose binding protein (MBP) expression system. Female BALB/c mice actively immunized with these antigens in Freund's adjuvants produced variable serum antibody responses to the component peptides. Fertility rates for animals immunized with AgE (40%) and AgF (20%) were significantly reduced compared to MBP immunized mice (90%), but the reduction in fertility did not correlate with peptide-specific serum antibody levels. Ovaries from all immunized mice appeared histologically normal with no evidence of oophoritis. These results demonstrate that high levels of immunocontraception can be achieved in mice, without apparent side-effects, using species-specific immunogens that include repeated peptides from proteins involved in fertilization.

Prospects for fertility control in the European rabbit (Oryctolagus cuniculus) using myxoma virus-vectored immunocontraception

Research over the last 15 years has examined whether fertility control can reduce overabundant rabbit populations and whether an effective immunocontraceptive agent can be developed and delivered. The results of this research indicate that for fertility control to have an environmental impact at least 80% of females will need to be infertile and that this infertility will need to be permanent. Epidemiological studies suggest that this level of infertility may be very difficult to obtain with a recombinant myxoma virus because of competition with field strains of virus. Research with laboratory rabbits using recombinant myxoma virus to deliver an immunocontraceptive antigen demonstrated that it was possible to obtain the required level of infertility using rabbit zona pellucida C as an antigen. However, only ~50% of animals remained infertile in the medium term. Further research on delivery vector and antigen selection would be needed to produce a practical immunocontraceptive virus for laboratory testing. Such a virus would then need to be optimised for transmissibility before it would be suitable for field testing.

Immunogenicity and contraceptive potential of three infertility-relevant zona pellucida 2 epitopes in the marsupial brushtail possum (Trichosurus vulpecula)

In a previous study, three infertility-relevant epitopes of possum ZP2 (Pep12 (amino acids 111–125), Pep31 (amino acids 301–315), and Pep44 (amino acids 431–445)) were identified using sera from possums (Trichosurus vulpecula) immunized with recombinant possum zona pellucida 2 (ZP2) constructs, and a synthetic peptide library of possum ZP2 protein. In this study, the three peptides were conjugated to keyhole limpet hemocyanin and 300 μg of each conjugated peptide were administered subcutaneously to female possums (n = 20 per peptide) in complete Freund’s adjuvant. Immunogen doses were repeated 3 and 6 weeks later using incomplete Freund’s adjuvant. Control animals were immunized with either phosphate-buffered saline only (n = 10) or 300 μg keyhole limpet hemocyanin (n = 10), administered with the same adjuvants. Serum antibodies from animals immunized against these three epitopes bound to the corresponding possum ZP2 peptides, recombinant possum ZP2 protein constructs, and native zona. Possum fertility was assessed following superovulation and artificial insemination. Peptides Pep12 and Pep31 had no significant effects on fertility parameters (P > 0.05). However, animals immunized with Pep44 had lower egg fertilization rates (immunized 19.5% versus control 60.5%, P < 0.05) and produced significantly fewer embryos than control animals (immunized 0.5 embryos versus control 2.4 embryos, P < 0.05). The number of Pep44-immunized females that produced embryos was reduced by 64%. Identification and characterization of possum infertility-relevant epitopes on possum ZP2 protein will assist development of safe, humane, and possum-specific immunocontraceptive vaccines for controlling the introduced possums in New Zealand.

Biological control of vertebrate pests using virally vectored immunocontraception

Species-specific viruses are being genetically engineered to produce contraceptive biological controls for pest animals such as mice, rabbits and foxes. The virus vaccines are intended to trigger an autoimmune response in the target animals that interferes with their fertility in a process termed virally vectored immunocontraception. Laboratory experiments have shown that high levels of infertility can be induced in mice infected with recombinant murine cytomegalovirus and ectromelia virus expressing reproductive antigens as well as in rabbits using myxoma virus vectors. The strategies used to produce and deliver species-specific immunocontraceptive vaccines to free-living wildlife are presented in this review. Discussion includes coverage of the likely safety of the proposed vaccines as well as the implications of the approach for fertility control in other species.

Epitope topology and removal of mouse acrosomal plasma membrane by P12-targeted immunoaggregation

P12 is a Kazal-type trypsin inhibitor that has been purified from mouse seminal vesicle secretion. We observed a slight impact of P12 on sperm capacitation, and demonstrated the removal of plasma membrane overlaying the acrosome region by immunoaggregation of P12 on mouse sperm. Further, we compared the immunoreactivity of P12 antibody to ten P12 variants, including six single-site mutated mutants (R19L, Y21V, D22G, R43G, K44S, and R45T), two multisite mutated mutants (R43G/K44S/R45T and L50H/R52G/K53A), and two deletion mutants (Nd10 and Cd8) in which 10 and 8 residues were deleted from the N- and C-terminals, respectively. We found that the N-terminal region, 43RKR45, and the C-terminal region, but not R19, Y21, and D22, are involved in the three epitopes that reside on one side and are three-dimensionally distant from R19, Y21, and D22 on the P12 molecule. Based on the epitope topology, we elucidated the structural basis by which P12 antibody immunoaggregated P12 on sperm head.

Sperm-zona pellucida interaction and immunological infertility

Immune reactions against gametes appear to be physiologically important for the maintenance of homeostasis in reproduction. In contrast, aberration of the immune homeostasis might give rise to 'immunological infertility'. Antisperm antibodies cause infertility by blocking fertilization. The mechanism can be explained as inhibiting the acrosome reaction of sperm by their blocking effect on capacitation through inhibiting an increase of fluidity of the sperm membrane. Autoantibodies against zona pellucida also cause infertility by blocking sperm-zona pellucida interaction, though the definitive mechanism has not been elucidated. Pretreatment of spermatozoa with D-mannnose completely inhibited sperm penetration through, but not binding to, the zona pellucida. Furthermore, very rapid kinetics between sperm extracts and D-mannnose by a BIAcore apparatus suggest that a D-mannose ligand of the sperm surface is easy to bind to and dissociate from a D-mannose residue in the sperm receptor site on the zona pellucida. Thus, D-mannnose on the human zona pellucida might be an essential molecule acting as a second sperm receptor, through which sperm penetrate into the zona pellucida. Because these antibodies appear to not cause any deleterious clinical symptoms, sperm and zona pellucida antigens are promising candidates in the development of an immunocontraceptive. (Reprod Med Biol 2006; 5: 95-104).

Sperm-zona pellucida interaction and immunological infertility

Immune reactions against gametes appear to be physiologically important for the maintenance of homeostasis in reproduction. In contrast, aberration of the immune homeostasis might give rise to 'immunological infertility'. Antisperm antibodies cause infertility by blocking fertilization. The mechanism can be explained as inhibiting the acrosome reaction of sperm by their blocking effect on capacitation through inhibiting an increase of fluidity of the sperm membrane. Autoantibodies against zona pellucida also cause infertility by blocking sperm-zona pellucida interaction, though the definitive mechanism has not been elucidated. Pretreatment of spermatozoa with D-mannnose completely inhibited sperm penetration through, but not binding to, the zona pellucida. Furthermore, very rapid kinetics between sperm extracts and D-mannnose by a BIAcore apparatus suggest that a D-mannose ligand of the sperm surface is easy to bind to and dissociate from a D-mannose residue in the sperm receptor site on the zona pellucida. Thus, D-mannnose on the human zona pellucida might be an essential molecule acting as a second sperm receptor, through which sperm penetrate into the zona pellucida. Because these antibodies appear to not cause any deleterious clinical symptoms, sperm and zona pellucida antigens are promising candidates in the development of an immunocontraceptive. (Reprod Med Biol 2006; 5: 95-104).