Analysis of the contraceptive potential of antibodies against native and deglycosylated porcine ZP3 in vivo and in vitro

Induction of native protein reactive antibodies by immunization with peptides containing linear B-cell epitopes defined by anti-porcine ZP3 beta monoclonal antibodies

To identify pertinent target epitopes for contraceptive vaccine development, rabbit polyclonal antibodies were raised against four peptides synthesized from the deduced amino acid (aa) sequence of porcine zona pellucida macromolecule ZP3 beta and coupled to diphtheria toxoid (DT). Synthetic peptides consisted of: P1, 23-37 aa; P2, 164-179 aa with an additional C-terminal cysteine; P3, 246-263 aa with an extra C-terminal cysteine; and P4, 310-321 aa residues corresponding to pZP3 beta precursor protein. Selected sequences were based upon B cell epitopes identified previously by monoclonal antibodies. Immune sera reacted with their respective peptides and DT in an ELISA, and also recognized porcine SIZP and pZP3 beta both in ELISA and Western blot and zona pellucida of porcine oocytes in an indirect immunofluorescence assay. None of the four anti-peptide sera recognized pZP3 alpha in Western blot, emphasizing the specificity of these antibodies to pZP3 beta. The anti-peptide sera, individually, failed to inhibit in vitro attachment of boar sperm to antibody treated zona encased porcine oocytes. However, combinations of immune sera against peptides such as P1 + P4, P2 + P4 and P1 + P2 + P4, did significantly inhibit porcine sperm-oocyte interaction. These results identify combinations of peptides that could potentially be used in the design of an immunocontraceptive vaccine based upon synthetic peptides corresponding to pZP3 beta or its homologues in other species.

Expression of bonnet monkey (Macaca radiata) zona pellucida-3 (ZP3) in a prokaryotic system and its immunogenicity

An internal fragment (978 bp) corresponding to the bonnet monkey (Macaca radiata) ZP3, excluding the N-terminus signal sequence and the C-terminus transmembrane-like domain, was amplified by PCR from a full-length cDNA clone. The amplified Bam HI and SacI restricted fragment was cloned in frame downstream of the T5 promoter under lac operator control for expression in the pQE-30 vector. Recombinant ZP3 (r-ZP3) was expressed as a poly-histidine fusion protein in E. coli strains SG13009[pREP4] and BL-21(DE3). Immunoblot with a murine monoclonal antibody, MA-451 (raised against porcine ZP3 beta-a homologue of bonnet ZP3, and cross-reactive with bonnet zona pellucida) revealed a predominant band of 50 kDa besides degraded fragments. Optimum expression of r-ZP3 was observed at 0.5 mM IPTG. Antisera generated in monkeys against synthetic peptides from the N-(23-45 aa residues) and C-(300-322 and 324-347 aa residues) termini of the deduced bonnet monkey precursor ZP3 sequence reacted with the r-ZP3 protein in ELISA. The r-ZP3 expressed in SG13009[pREP4] was purified on Ni-NTA resin under denaturing conditions and conjugated with diphtheria toxoid (DT). Immunization of a female rabbit and six female bonnet monkeys with the r-ZP3-DT conjugate generated antibodies reactive with r-ZP3 in ELISA. Rabbit r-ZP3 antiserum reacted with porcine ZP3 beta and bonnet r-ZP3 but failed to react with porcine ZP3 alpha in a Western blot. Moreover, antisera when tested by indirect immunofluorescence on bonnet monkey ovarian sections, showed positive fluorescence with zona pellucida. The availability of r-ZP3 will further help in evaluating its efficacy for fertility regulation and understanding the autoimmune oophoritis associated with ZP3 immunization in nonhuman primates.

Expression of protamine P2 in the testis of the common marmoset and man visualized using non-radioactive in-situ hybridization

Information on the organization of the spermatogenic cycle of the common marmoset (Callíthrix jacchus), a small New World primate, is limited to a single histological report on the differentiation of spermatids. In the present study we have used non-radioactive in-situ hybridization with a cRNA probe directed against marmoset protamine 2, on fixed sections of marmoset and human testis to elucidate the organization of mature germ cells within the seminiferous epithelium. Specificity of the probe was checked on Northern blots; mP2 hybridized exclusively to mRNA in samples extracted from marmoset and human testis. In sections from human and marmoset testis, positive staining for mRNA was confined to round and elongating spermatids and in the human was reduced in samples from patients with incomplete spermatogenesis. In the human, P2 mRNA was present in groups of cells consistent with the presence of more than one stage of the spermatogenic cycle in transverse sections of individual tubules. In the marmoset, P2-positive cells were detected as a continuous ring of staining in the majority of sections of tubules whilst in others only a group(s) of cells was positive. We conclude that the arrangement of the spermatogenic wave in this New World primate may be intermediate between that seen in rodents (segmental) and in the human (helical).

The potential of the zona pellucida as a target for immunocontraception

PROBLEM

To investigate the contraceptive potential of the zona pellucida.

METHOD

Generation of antibodies against native and recombinant zona glycoproteins which have then been assessed for their capacity to disrupt sperm-zona interaction in vivo and in vitro. The animal model selected for these studies was the common marmoset and the end points examined were antibody titre, ovarian cyclicity and fertility.

RESULTS

The fact that antibodies against the major zona glycoprotein, ZP3, block both the primary and secondary phases of sperm-zona interaction suggests that this molecule might have potential for contraceptive vaccine development. Active immunization of marmoset monkeys with native porcine ZP3 or recombinant human ZP3 produced long term infertility but also precipitated a premature decline in the primordial follicle population.

CONCLUSIONS

Future studies will have to determine whether a safe, effective vaccine can be engineered by coupling unique B-cell epitopes from ZP3 to foreign T-cell antigens.

Response of cynomolgus macaques to immunization against a synthetic peptide from the human zona pellucida

This study tested immunogenicity of a synthetic peptide hZP3(327-341) from a human zona pellucida (ZP) glycoprotein. After antibody response to various peptide-carrier conjugates was assessed in mice, two female cynomolgus macaques were immunized with the peptide conjugated to keyhole limpet hemocyanin (KLH). A control macaque was immunized with KLH. The peptide was immunogenic in both species, and included both B and T cell epitopes since low to moderate titers of peptide-specific antibodies and a T cell proliferative response were measured. Profiles of ovarian steroid metabolites indicated unchanged ovarian function in the macaques, but only the control conceived when bred. Ovarian histology was normal except that immunoglobulin was bound to ZP in follicles of the peptide-immune macaques. ZP from these females bound sperm and induced acrosome reactions at rates equal to those of an untreated control. The results support the feasibility of an immunocontraceptive vaccine based on autologous ZP peptides.

Inhibition of pig oocyte in vitro fertilization by the action of components of the zona pellucida

The aim of the present study was to determine whether the previous addition of porcine zona pellucida (ZP) components to spermatozoa of the same species has an inhibitory effect on in vitro fertilization (IVF). Boar spermatozoa were exposed to whole porcine solubilized zona pellucida (SZP), ZP glycoproteins (55 kDa and 90 kDa) and peptides (37 kDa, 40 kDa and 68kDa). Doses tested were 40, 70 and 100 mug/ml. In vitro fertilization was clearly inhibited by each component when the oocytes were compared with those fertilized with untreated spermatozoa. All the components had an effect in a dose dependent manner.

Immunoregulation of mammalian fertility

Fertility management is a global issue of agricultural, medical, economic, and social consequence. Although many methods have been devised to both inhibit and assist reproduction, more acceptable alternatives are needed. Regulation by immune intervention is a promising technology as applied to livestock, pets, wildlife, and human beings. Outcome is dictated by site within the reproductive axis that is targeted. Fertility is suppressed by immunization against gonadotropin-releasing hormone, gonadotropins, prostaglandin F2 alpha, oxytocin, gonadotropin receptors, and gamete/embryonic antigens. It also is possible to lyse gonadal cells with ligand-antibody hybrid molecules. Ovulation rates are enhanced by vaccination with inhibin. Antibodies to sex steroid hormones have yielded mixed results. Perhaps recombinant viral vectors can be used to deliver reproductive immunogens. A new and simple technique to generate sustained autoimmune reactions to hormones and cellular antigens entails direct gene transfer into somatic cells. Evolving advances in reproductive immunology and biotechnology should furnish us with novel nonsurgical contraceptives and profertility agents that can be efficiently and safely implemented.

Mapping of immunogenic domains on porcine zona pellucida 3 alpha and beta glycoproteins by murine monoclonal antibodies

PROBLEM

Immunization with zona pellucida (ZP) leads to block in fertility with variable degree of ovarian dysfunctions. To design an immunocontraceptive vaccine based on synthetic peptides of zona pellucida, it is imperative to identify and define epitopes involved in sperm binding.

METHOD

Epitopic domains recognized by monoclonal antibodies (MAbs) specific to either porcine ZP3 alpha or ZP3 beta glycoproteins were delineated in an enzyme-linked immunosorbent assay (ELISA) based on the ability of a MAb in solution to inhibit the binding of biotinylated ZP3 to another MAb coated on a microtitration plate. Immunoblot studies were carried out to determine the nature of reactive determinants. Porcine oocytes preincubated with MAbs were tested for sperm binding in vitro.

RESULTS

Out of 23 MAbs generated, 10 had specificity for ZP3 alpha and 13 for ZP3 beta. By using these antibodies, eight epitopic domains on both ZP3 alpha and ZP3 beta were discernible. On ZP3 beta, epitopic domain DI partially overlaps with DII and DV with DVI, whereas on ZP3 alpha domains DI to DV were in close proximity with a partial overlap, suggesting the dominance of this region. All 10 MAbs against ZP3 alpha, and 10 out of 13 against ZP3 beta recognized deglycosylated forms of antigens. Seven antibodies having specificities for ZP3 alpha and ZP3 beta respectively recognized linear epitopes. MA-30, having specificity for ZP3 beta and MA-420 for ZP3 alpha and recognizing linear epitopes significantly inhibit the binding of boar sperm to porcine oocytes in vitro.

CONCLUSIONS

Collectively, these studies indicate the value of utilizing MAbs for identifying and characterizing functionally significant ZP determinants. MAbs recognizing sequential epitopes will help in the elucidation of the amino acid sequence of the epitopes, which will subsequently help in design of synthetic immunocontraceptive vaccines.

Cloning, sequencing and oocyte-specific expression of the marmoset sperm receptor protein, ZP3

The zona pellucida surrounding the mammalian oocyte contains a major glycoprotein species, ZP3, that serves as a cell- and species-specific receptor for spermatozoa. In this study we have determined the primary amino acid structure of marmoset ZP3 (marZP3) and examined the expression of marZP3 mRNA within the ovary. The marZP3 gene possesses an open reading frame of 1272 nucleotides which is expressed specifically by the oocyte and encodes a polypeptide chain of 424 amino acids that exhibits 91% homology with the human ZP3 sequence. The disparity between these molecules was confined to a short domain spanning residues 322-352; otherwise the molecules were very similar, showing conservation of many structural features including the N-linked glycosylation sites, location and number of cysteine and proline residues and hydrophobicity profile. The results of this study have important implications for the use of the marmoset monkey as an animal model for the development of contraceptive vaccines targeting ZP3.