Characterization of monoclonal antibodies against human sperm antigens by immunoassays including sperm function assays and epitope evaluation

Molecular nature of a sperm acrosomal antigen recognized by HS-13 monoclonal antibody

Among the numerous monoclonal antibodies generated against human sperm antigens, HS-13 monoclonal antibody was shown to react with an intra-acrosomal antigen from human, mouse and rat. In this study, HS-13 was used as the affinity ligand for the purification of the cognate antigen from human sperm by immunoaffinity chromatography. The purified cognate antigen from human sperm, designated as HSAg-13, was found to be a protein with a molecular weight of approximately 80 kDa on SDS-PAGE in the presence of reducing reagents. This monoclonal antibody was used as the probe to study the tissue distributions and developmental expression of the cognate antigen from human, mouse and rat by immunohistochemical assays. It was concluded that the antigen recognized by HS-13 antibody is highly sperm specific and found only in sperm and mature testis, but not in any other somatic tissues examined in human and mouse. The antigen was shown to be expressed at the postmeiotic stages of spermatogenesis in mouse and rat. By using indirect immunofluorescent staining assay, HS-13 was shown to react only with the methanol-fixed acrosome-intact sperm but not with the live sperm. Following calcium ionophore A23187 treatment, acrosome-reacted sperm showed either negative staining or residual staining in the equatorial region, suggesting the intra-acrosomal location of HSAg-13. The spontaneous acrosome reaction following overnight incubation in BWW medium resulted in a statistically significant decrease of antibody-stained human sperm. In view of excellent correlations for the scoring of acrosome-intact sperm with that of fluorescence-labeled Pisum sativum agglutinin (PSA) probe, HS-13 monoclonal antibody can be routinely used for monitoring sperm capacitation and acrosome reaction.

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.

The monoclonal antibody GZS-1 detects a maturation-associated antigen of human spermatozoa that is also present on the surface of human mononuclear blood cells

A monoclonal antibody (GZS-1) has been generated by fusion of mouse myeloma cells with spleen cells from BALB/c mice immunised with human sperm cells. The antibody was determined to be an IgG1. The corresponding antigen is present on the whole surface of ejaculated human spermatozoa. It is not detectable on spermatozoa of other mammalian species (rabbit, cat, dog, sheep, boar, bull, horse). In human male genital organs, immunostaining with GZS-1 is observed on sperm cells in the epididymis and the ductus deferens together with the lining epithelium of those organs. No reactivity of sperm cells or germ cell precursors in the testis has been detected. Functional tests using the antibody show a strong inhibitory effect of human sperm in the hamster egg penetration assay. Furthermore, the GZS-1 antigen is detectable on the surface of human lymphocytes and monocytes by immunogold electron microscopy and FACS analysis. By Western blotting of human sperm and seminal plasma performed under reducing conditions immunostaining was detected at 21-25, 31, 51-54, and 62 kDa. The reaction with human lymphocytes shows one major band at 62 kDa and additional bands at 31 and 54 kDa. The results suggest that the monoclonal antibody GZS-1 may recognise an antigen which is secreted from the epithelial cells of the epididymis and binds to ejaculated spermatozoa as a sperm coating antigen. This component may be involved in the capacitation of the sperm and the acrosome reaction. Molecules that are expressed both on sperm and on immunocompetent cells may be relevant for the regulation of immunological processes or for the development of the related immunological tolerance of sperm in the female reproductive tract.

Binding of the anti-human sperm monoclonal antibody HS-11 to bull spermatozoa is correlated with fertility in vitro

The present study aimed to determine if there is bull to bull variation in the binding of the anti-human sperm monoclonal antibody (MAb) HS-11 to bull spermatozoa, and to investigate if there is any correlation between HS-11 binding to spermatozoa and in vitro fertility of the bulls tested. Semen samples of a single collection (split frozen in 0.5-ml straws) from 8 dairy bulls were used. Swim-up separated motile spermatozoa were incubated in 90-microl drops of capacitation medium (TALP+10 microg/ml heparin) at 39 degrees C, 5% CO2, 95% air. At 0, 2, 4 and 6 h of incubation HS-11 was added (1:1000 final concentration), and the MAb binding was assessed by indirect immunofluorescence assay (IIFA). The HS-11 binding was indicated by a bright green fluorescence of the sperm acrosome region. In vitro-matured, good quality bovine oocytes were randomly allocated to spermatozoa of each bull for in vitro fertilization. Sperm samples of 2 to 3 bulls were used in each trial until 4 replicates per bull were attained for IVF (n approximately 100 oocytes/bull) and IIFA experiments. Sperm capacitation status was assessed simultaneously using an egg yolk lysophosphatidylcholine- (LC) induced acrosome reaction assay. The binding of HS-11 to spermatozoa was maximum at 4 h of incubation in most (6/8) of the bull semen samples. Significant (P < 0.01) differences were observed between bulls in the binding of HS-11 to their spermatozoa (range 22 +/- 8 to 52 +/- 5%) at 4 h, but not within replicates. Similarly, variations (P < 0.05) in the cleavage rate were also seen (range 22 +/- 9 to 58 +/- 7%) between bulls. The HS-11 binding and cleavage were significantly correlated (r = 0.43; n = 32; P < 0.05). The highest percentage of spermatozoa underwent acrosome reaction in response to LC treatment at the 4-h incubation period. This and the linear relationship between HS-11 binding and the cleavage rate observed in the present study together strengthen our earlier suggestion that the binding of the monoclonal antibody HS-11 to bull spermatozoa on a time-dependent manner, may indicate capacitation changes. We conclude that 1) between-bull differences exist in HS-11 binding to spermatozoa, and in the cleavage rate, and 2) HS-11 binding to spermatozoa is correlated with fertility, as determined by the cleavage of bovine oocytes matured and fertilized in vitro.

Inhibition by anti-sperm monoclonal antibodies of the penetration of zona-free hamster oocytes by human spermatozoa

Fourteen mAb specific for human sperm membrane antigens were selected to investigate their inhibitory effect on fertilization. The antigens were not expressed in other human somatic tissues but were present in sperm from other species. The antibodies were purified from ascites fluid produced in mice. The zona-free hamster egg penetration assay was used for the evaluation of the blocking ability of these antibodies. The inhibition rate was generally related to a decrease in the number of adherent sperm. Three groups of antibodies were distinguished: (i) four mAb that have high inhibition at any concentration; (ii) four mAb with an intermediate inhibitory effect, that is more dependent on the antibody concentration tested; and (iii) six mAb with little or no effect at any concentration. The presence of antibodies leads to a lower penetration index, or number of penetrating sperm per oocyte. MAb specific for head antigens promote high inhibition of fertilization; these antibodies show a patchy staining on the sperm head. The antibodies localized in the midpiece have an intermediate inhibitory effect. No inhibition is detected with the equatorial region binding pattern. Sperm agglutination does not play any role in the inhibition caused by the antibodies described here.

Studies of a sperm/placenta cross-reacting antigen, STX-10

A monoclonal antibody, HSA-10 initially produced against acrosome-reacted human sperm was also shown to cross-react with human placenta/trophoblast. Transmission electron microscopy, as well as indirect immunofluorescent assay, demonstrated that HSA-10 was found to react with antigen on the inner acrosome of human sperm. The cognate antigen, designated as STX-10, was found to exist as an aggregate in the native form when analyzed by Sephacryl S-300 gel filtration chromatography. When purified by HSA-10-immunoaffinity chromatography from human placenta extract, STX-10 was found to be predominantly a group of glycoproteins with a subunit molecular mass in the range of 75 +/- 5 kDa, whereas an additional group of three proteins with subunit molecular mass less than 20 kDa were copurified from human sperm extract. A sandwich enzyme immunoassay was designed to quantitatively determine the immunoactivity of STX-10 in solution, using HSA-10 monoclonal antibody for coating and for signal detection via enzyme conjugation. Based on this assay, it was found that STX-10 could be detected only in human sperm and placenta extract, but not in any other human somatic tissues, such as serum, brain, heart, muscle, kidney and liver. The immunoactivity of STX-10 was found to be sensitive to proteolytic digestion, low pH, in the presence of reducing agent, but resistant to treatment with sodium periodate. This observation suggests that HSA-10 specific epitope is a peptide in nature and not a carbohydrate moiety. Results of antifertility studies revealed that HSA-10 significantly inhibited human sperm penetration to zona-free hamster ova. Thus, the results of this study are consistent with those of WHO Workshop evaluations that seem to suggest that STX-10 is a highly gamete-specific antigen localized on the inner acrosome of human sperm and in human trophoblast/placenta. Therefore, it may play an important role during human fertilization and embryo development.

Molecular identity of a sperm acrosome antigen recognized by HS-63 monoclonal antibody

The molecular identity of mouse sperm acrosome antigen recognized by HS-63 monoclonal antibody was analyzed by various biochemical, immunological and molecular biological methods. When its cognate antigen, MSA-63 was isolated from mouse testis by immunoaffinity chromatography, a group of protein spots with wide range of molecular sizes and isoelectric points were identified. Through previous studies, it was established that most of these protein spots were actin-like molecules co-purified with MSA-63 protein from mouse testis. To analyze the molecular size heterogeneity of the isolated MSA-63 proteins, rabbit antisera against a computer-predicted antigenic synthetic peptide (amino acid residue No. 160-171) and a recombinant glutathione S-transferase (GST) fusion protein (GST-63) were raised. These two antisera and those raised against the isolated MSA-63 protein were used as the probes in comparative Western blot assay, indirect immunofluorescent assay and enzyme-linked immunosorbent assay (ELISA). Using ELISA, antisera against GST-63 and computer-predicted antigenic synthetic peptides were shown to cross-react with affinity-isolated MSA-63 protein coated on microwells. However, little immunological cross-reactivity was observed between GST-63 fusion protein and the synthetic peptide. By using a Western blot assay, two major protein bands of 22 and 32 kDa, respectively were commonly detected on mouse testis homogenate strips by both anti-MSA-63 and anti-GST-63. In addition, anti-MSA-63 also recognized several protein bands with molecular masses greater than 35 kDa. The results of this study suggested that the molecular heterogeneity of MSA-63 protein isolated from mouse testis and sperm, is due to a series of post-translational modifications on a single gene product. These modifications may include glycosylations, proteolytic digestions and tight non-covalent associations with other testicular cytoskeletal proteins, such as actins.

Electron microscopic immunolocalization of a conserved sperm acrosomal antigen recognized by HS-63 monoclonal antibody

HS-63 monoclonal antibody was shown to react with a sperm-specific acrosomal antigen from spermatozoa of a variety of mammalian species. Indirect immunofluorescence showed that HS-63 was associated with acrosome-intact sperm after sperm had been fixed with methanol. Electron microscopy (EM) was employed to determine the ultrastructural localization of this sperm antigen. When the immunogold labelled goat anti-mouse IgG was used as a probe, we demonstrated that HS-63 monoclonal antibody did not bind to the freshly prepared human spermatozoa. However, gold particles were observed in the intra-acrosomal region, when the spermatozoa had been pre-treated with 0.5% Triton X-100 prior to incubation with HS-63. We further observed that the immunogold did not stain the inner acrosome membrane when the spermatozoa became acrosome-reacted. A good correlation was obtained between the percentage of spermatozoa which did not react with HS-63 as determined by indirect immunofluorescence assay and that of acrosome-reacted spermatozoa as quantitated by electron microscopy. The results of this EM study were consistent with those obtained by indirect immunofluorescence assay and both indicated that HS-63 reacts only with the capacitated and acrosome-intact spermatozoa. Therefore, HS-63 monoclonal antibody is a useful probe for rapid evaluation of acrosomal status in human spermatozoa.

The glycosylphosphatidylinositol-anchored lymphocyte antigen CDw52 is associated with the epididymal maturation of human spermatozoa

The CAMPATH-1 (CDw52) antigen is a small glycosylphosphatidylinositol (GPI) anchored glycoprotein with a mature peptide comprising only 12 amino acids. It is abundantly expressed on human lymphocytes and is an unusually good target for complement-mediated cell lysis. The immunosuppressive and lymphocyte-depleting effects of CAMPATH-1 antibodies are being tested in a variety of diseases. Here we show that the antigen is also expressed at a high level in the male reproductive system, being found in the epididymis, seminal vesicle, seminal plasma and on the surface of mature (but not testicular) spermatozoa. Its possible transfer from epithelial cells in the epididymis to maturing sperm may represent a novel method of acquisition of cell surface antigens. In the presence of human complement, CAMPATH-1 antibodies inhibited the motility of washed sperm. However, seminal plasma blocks antibody binding and can protect sperm from this cytotoxic effect.

Human sperm proteins from testicular and epididymal origin that participate in fertilization: modulation of sperm binding to zona-free hamster oocytes, using monoclonal antibodies

In order to identify human sperm surface proteins involved in the gamete recognition process, mouse monoclonal antibodies were directed against human spermatozoa and screened with live spermatozoa by enzyme-linked immunosorbent assay (ELISA). Immunoperoxidase staining of human testis showed the early presence of four corresponding proteins on germinal cells, while six were detected primarily in testis fluid. The presence of 17 proteins was evidenced in the epididymis. Eight were detected with a decreasing gradient from the beginning to the end of the organ, including vasa efferentia for three of them. The other nine were observed in only one defined segment, usually the caput epididymis, which was found to be the most active region. Comparison of spermatozoa patterns from testis, vasa efferentia, and the three regions of epididymis pointed out a progressive coating. By contrast, three antibodies displayed a migration of spermatozoa surface domains in the course of epididymal transit. Six antibodies were found to inhibit human spermatozoa adherence to zona-free hamster oocytes, while nine promoted it. Molecular weights of antigens corresponding to nine of the antibodies ranged from 11 to 215 kDa. No correlation could be established with previously described human proteins. These observations emphasize the role of epididymis in human sperm maturation.

Monoclonal antibodies affecting sperm-zona binding and/or zona-induced acrosome reaction

The majority of anti-sperm monoclonal antibodies which were shown to inhibit in vitro fertilization in our laboratory react with antigens in the acrosomal region of spermatozoa. To elucidate the mechanism of human and/or mouse fertilization inhibition, the effects of these antibodies on mouse sperm-zona binding and mouse zona-induced acrosome reaction in vitro were studied. Among these antibodies, MS-4 and MS-7 were shown to react partially with uncapacitated mouse sperm, and to react more with capacitated mouse sperm, whereas HS-9, HS-11 and HS-63 react only with capacitated and acrosome-intact human or mouse sperm. HS-63 and MS-4 were shown to inhibit zona-induced acrosome reaction significantly, but not the sperm-zona binding. On the other hand, HS-9, HS-11 and MS-7 were shown to inhibit both sperm-zona binding and zona-induced acrosome reaction. The results of this study suggest that fertilization inhibition caused by these antibodies could result from that of the initial sperm-zona binding and/or zona-induced acrosome reaction.

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.

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.

Application of an immunological method to detect trace amounts of dried human semen

An immunological assay based on a monoclonal antibody was used for identification of trace amounts of dried human semen in forensic science evidence. The monoclonal antibody (Mab 4E6) produced recognizes a human sperm-coating antigen which is specific to human seminal plasma. This antigen seems to be a protein secreted by the epithelial cells of the ejaculatory duct, which is stable indefinitely at room temperature. Mab 4E6 reacts positively with semen samples from individuals independently to their ABO group or secretory status, but does not react with semen from bull, ram, boar, horse, rabbit and dog. In the assay system developed, Mab 4E6 can detect human seminal plasma at concentrations of 0.5 micrograms/ml total protein. A similar sensitivity is found when human semen stains are eluted from forensic science samples and tested by the same assay. This method shows a good correlation with the microscopic methods routinely used. The method described is very sensitive and reproducible, it is time saving and special laboratory equipment is not needed.