Characterization of human sperm surface antigens with monoclonal antibodies

Monoclonal antibodies against antigens expressed by human sperm

The production and characterization of 21 mouse monoclonal antibodies (TüS1-TüS21) with specificity predominantly for human spermatozoa antigens is described. Reactivity of cells from human ejaculates, peripheral blood and several organs was determined using the alkaline phosphatase-anti-alkaline phosphatase (APAAP)-technique as well as the indirect immunofluorescence test. 15 of the monoclonal antibodies reacted with various regions of human sperm and often also with their precursor cells in the testis. Cross-reactivity with animal spermatozoa was frequently observed.

The abundant 19-kilodalton protein associated with human sperm nuclei that is related to seminal plasma alpha-inhibins

A basic protein with a relative molecular mass of 19 kDa has been identified and isolated to purity from sonication-resistant, partially demembranized human sperm nuclei. Several criteria prove that this is the unique sperm-specific protein, which was previously thought to be a sperm/testis histone. Partial primary structure sequencing demonstrates homologies with human seminal alpha-inhibins and semenogelin. From the sequence and Western-blotting data with antibodies against basic seminal inhibin-like peptide, we propose that this 19-kD protein is a product of 52-kDa semenogelin processing. The 19-kDa protein was not found among seminal plasma proteins and may be protected from further cleavage into inhibin-like peptides by its association with the sperm head. Immunofluorescence data indicate its localization in the nuclear periphery, with preferential concentration at the acrosome calyx boundary.

Purification and characterization of sperm-coating antigen, identified by a monoclonal antibody

A procedure was designed for purification of a human seminal plasma-specific antigen (HSP-antigen) identified by a monoclonal antibody produced in this laboratory (mAb 4E6). Pooled human seminal plasma was fractionated by consecutively applied methods: affinity chromatography on Lentil lectin sepharose, gel chromatography on Ultrogel AcA 34 and immunoaffinity on mAb 4E6 coupled CNBr-Sepharose 4B. The antigen-containing fraction obtained after this procedure was proved to be homogeneous when analysed by electrophoresis in polyacrylamide gel. After the consecutive purification procedures the degree of purification was 128 times as compared to the starting material. Electrophoretic analysis of the purified 4E6 antigen under reducing conditions showed that it consisted of 3 polypeptide subunits with molecular weight 70 kDa, 64 kDa and 60 kDa respectively. On the basis of the data obtained from competitive ELISA testing of sera from infertile patients it has been suggested that the identified antigen may be involved in pathogenesis of immunologic infertility.

Sperm immobilizing and fertilization-blocking monoclonal antibody 2C6 to human seminal plasma antigen and characterization of the antigen epitope corresponding to the monoclonal antibody

A monoclonal antibody (Mab 2C6) with strong sperm immobilizing and agglutinating activities was generated by cell fusion between spleen cells from a mouse immunized with human seminal plasma (HSP) and mouse myeloma cells. It also showed a strong inhibitory effect on human sperm-egg interaction. The corresponding antigen was present on the whole surface of ejaculated spermatozoa. In male genital organs, immunostaining with Mab 2C6 was observed in epididymis and seminal vesicle but not in testis. By Western blotting, immunostaining with Mab 2C6 was detected around the 15-25 kDa region under both reducing and non-reducing conditions. The antigen corresponding to Mab 2C6 was susceptible to treatment with periodate or trifluoromethanesulfonic acid. The antigenic activities were slightly increased by treatment with neuraminidase but reduced by further treatment with glycosidases. Enzymatic digestions with pronase and papain also reduced the antigenic activities. The antigen molecules exhibited a strong binding affinity to RCA lectin. These results indicated that Mab 2C6 recognized one of the components which might be secreted from epididymis or seminal vesicle and bind to ejaculated spermatozoa as a sperm coating antigen. The corresponding antigen seems to be a glycoprotein and its carbohydrate moiety has an important role in the conformation of the antigen epitope.

Protein synthesis and secretion in the human epididymis and immunoreactivity with sperm antibodies

The synthesis and secretion of proteins in the different regions of the human epididymis were studied in vitro. Epididymal tissues obtained from patients undergoing castration for prostatic carcinoma or from cadavers were incubated in the presence of [35S]methionine, and the resulting radiolabeled proteins were analysed on SDS-PAGE. The corpus region was found to be the most active segment in total protein synthesis. Significant qualitative and quantitative changes were observed in the pattern of proteins secreted from the different epididymal regions. To establish those epididymal proteins that interact with maturing sperm, the secreted products were immunoreacted with antibodies raised against a Triton X-100 extract of ejaculated human sperm heads. The antibodies react mainly with the head region of ejaculated spermatozoa as judged by indirect immunofluorescence. Protein A-gold labeling of freeze-fracture images showed gold particle distribution on the sperm plasma membrane. Western blot analysis of the secreted proteins revealed four bands (66, 37, 32, and 29 kDa) in the proximal regions and six additional bands (80, 76, 48, 27, 22, and 17 kDa) in the distal part of the epididymis. Immunoprecipitation of the secreted proteins with these antibodies revealed six radioactive bands of 170, 80, 76, 60, 48, and 37 kDa, which indicates that certain proteins of epididymal origin bind to the sperm plasma membrane.

Partial purification of a boar sperm membrane protein inducing sperm agglutinating antibody

For the development of immunological contraception, attention is being concentrated on the possibility of using a sperm membrane antigen. Boar sperm membrane was extracted with triton-X 100 and fractionated by Sephadex G-150 column chromatography. The glycosylated and nonglycosylated portions of protein peaks from the gel filtration were obtained by fractionating on concanavalin A-Sepharose and eluting the bound protein with 0.3 M methyl mannoside. A glycosylated fraction was found to induce sperm agglutinating antibodies in rabbit. The partially purified protein has a molecular weight of 30 kilodaltons, as determined by sodium dodecyl polyacrylamide gel electrophoresis. Further work is planned on the histochemical determination of the origin of this protein and species cross-activity of the antibody.

Analyses of epididymal sperm surface antigens by monoclonal antibodies against hamster spermatozoa

BALB/c mice were immunized with spermatozoa from cauda epididymides of hamsters and the immune spleen cells were fused with mouse myeloma cells (P3U1). Seven hybridomas (GHS-1,-2,-3,-4,-5,-6, and -7) that produced monoclonal antibodies (Mabs) binding to the epididymal spermatozoa were established. Three Mabs (GHS-3,-4, and -6) were IgM and the other four were IgG1. All Mabs reacted to hamster spermatozoa from cauda epididymides but none of the Mabs except GHS-5 and -7 reacted to spermatozoa in testis. GHS-5 and -7 Mabs bound to the acrosome region of spermatozoa in both testis and epididymis. The antigens corresponding to GHS-2, -4, and -6 Mabs appeared to be excreted from epithelial cells of caput epididymis, while those to GHS-1 and -3 Mabs seemed to be produced in cauda epididymis. Both groups of the antigens bound to the surface of spermatozoa during their epididymal transit. Immunoblotting analyses of epididymal fluid showed that the antigen epitopes corresponding to GHS-1,-2,-3,-4, and -6 Mabs were distributed to multiple components with different molecular weights ranging from over 100 to 25 kd. The distribution patterns of the epitopes corresponding to GHS-1 and -3 Mabs and GHS-2,-4, and -6 Mabs were very similar, respectively, but each group pattern was quite different from each other. GHS-5 Mab reacted to a component of sperm extract with a molecular weight of around 94 kd, while GHS-7 Mab failed to recognize any components transblotted.

Monoclonal antibody against human sperm acrosome inhibits sperm penetration of zona-free hamster eggs

Human spermatozoa were exposed to a monoclonal antibody (C11H), which recognizes sperm acrosin. The antibody was presented to the sperm during capacitation and/or insemination, and its effect on penetration was tested using zona-free hamster eggs. An inhibitory effect on penetration was observed when the antibody was present during insemination but not when it was included only in the capacitation medium. As judged by immunofluorescence microscopy, most of the sperm bound to the egg surface were devoid of acrosomal staining. Some of the bound sperm were stained at their equatorial segments. Sperm that had penetrated the ooplasm did not exhibit immunofluorescence.

Molecular dissection of human testicular germ cell differentiation with monoclonal antibodies

Monoclonal antibodies (MoAbs) were raised by immunising mice with nucleated cells other than sperm (NCOS) obtained from semen of an oligospermic donor. These MoAbs recognised different germ cell differentiation antigens (GDA) which appear at various stages of spermatogenesis and/or spermiogenesis. The GDA were found to be differentially expressed on spermatocytes, spermatids and on the various sub-regions of human spermatozoe. Some of the MoAbs also recognised changes in the antigenic structure of the sperm during their post-testicular maturation. Using solubilised sperm products, MoAb GDA-J/F1 reacted with a 92 kDa band in Western immunoblotting. The importance of these antibodies in the study of germ cell differentiation together with their potential clinical uses in the investigation of infertility, autoimmunity and immunological contraception are discussed.

Capacitation-related changes in antigen distribution on mouse sperm heads and its relation to fertilization rate in vitro

The anti-mouse sperm monoclonal antibody OBF13 did not react with fresh epididymal sperm. However, when sperm were incubated in a culture medium capable of inducing capacitation, the entire head of the sperm began to react with this antibody. This change of reactivity was not observed when sperm were incubated in a Ca2+-free medium. The change of the reactivity to the antibody was studied in relation to the fertilizing ability of sperm as measured in an in vitro fertilization system; a significant correlation was observed between the appearance of head-stained sperm and fertilization rate.

Intermediate filament proteins in human sperm heads

Monoclonal antibodies made against human sperm cells have been characterized with regard to binding patterns and molecular coordinates of the recognized antigens. Antibodies T5 and T6 gave uniform binding to the acrosomal cap in an intact cell, and decreased to equatorial segment binding in an 'acrosome-reacted' cell. Monoclonal antibody T15 gave the reverse: equatorial segment binding in intact cells and uniform acrosomal cap binding in reacted cells. From staining patterns on cultured cell lines, determination of molecular coordinates, immunoblots, and partial peptide analysis, we have determined that T15 is directed against the cytoskeletal protein, vimentin, while T5 and T6 recognize a keratin-like protein which may be unique to sperm cells. This is the first immunological and biochemical study to analyse both types of intermediate filament proteins in human sperm cells.

Inconsistent reactivity of an anti-sperm monoclonal antibody and its relationship to sperm capacitation

An anti-sperm monoclonal antibody was developed from female C57BL/6 mice immunized with epididymal sperm from a syngeneic male mouse. Immunofluorescence staining revealed that the antibody did not react to fresh epididymal sperm but attached to the capacitated sperm found in the peri-vitelline spaces of the ova. When the antibody was applied to sperm incubated in vitro, variously stained sperm were observed. It was presumed that the antigenic site detected by the antibody was hidden in the fresh epididymal sperm and was spread from the acrosomal cap region to the entire head during the capacitation process.

Immunodissection of sperm surface modifications during epididymal maturation

Mammalian spermatozoa undergo changes in morphology, composition, and function during transit through the epididymis. These changes correlate with acquisition by sperm of the ability to fertilize ova. It has been found that sperm from the cauda epididymidis, but not those from the caput epididymidis, are able to bind to the zona pellucida. This would imply a modification in sperm surface characteristics. Biochemical and immunological studies have demonstrated changes in sperm surface composition during epididymal maturation. These changes involve addition of epididymal secretory products to the sperm surface, loss or alteration of existing sperm surface molecules, and possibly the unmasking of preexisting molecules or epitopes. Several laboratories have studied the epididymal secretory proteins in the rat, but a consensus has not been reached on the identification, characterization, source, and sperm surface association of these proteins. Monoclonal antibodies are beginning to be used to characterize sperm surface components and sperm maturation antigens. They are proving to be valuable tools for the dissection of epididymal maturation when used in conjunction with biochemical and physiological approaches.

Detection of anti-sperm activities of monoclonal antibodies to human sperm

The anti-sperm activities of a series of monoclonal antibodies to human sperm have been compared using agglutination, immunofluorescence, ELISA and 'panning' assays. The antibodies fell into two categories, those that could be detected by agglutination but not immunofluorescence assays and those that could be detected by immunofluorescence but not agglutination. Antibodies positive in the agglutination assays were also positive in the 'panning' assay. None of the antibodies tested was positive in the ELISA assays. These results, and others, are discussed in relation to the problems associated with the detection of anti-sperm antibodies in sub-fertile human populations.

Sialoglycoproteins of ejaculated human spermatozoa and seminal plasma

Ejaculated human sperm were found to possess three major sialoglycoproteins with molecular weights of 30 000, 14 000 and 12 000 and one minor species of 18 000. Liquefied seminal plasma from normal donors contain two major sialoglycoproteins with molecular weights of 17 000 and 15 000 and two minor species of 70 000 and 54 000. In contrast, the liquefied sperm-free semen of vasectomized men had two major species of sialoglycoproteins of 20 000 and 18 000 daltons plus two minor species of 54 000 and 40 000.

An acrosomal antigen of human spermatozoa and spermatogenic cells characterized with a monoclonal antibody

Monoclonal antibodies were raised against acrosomal antigens of human sperm by immunizing BALB/CA mice with purified ejaculated human spermatozoa. An ELISA-assay, employing glutaraldehyde-fixed spermatozoa as antigen, was used to screen the hybridomas producing anti-human sperm antibodies. Two hybridoma cell-lines produced antibodies which bound to the acrosomal region of spermatozoa. Both gave identical results in preliminary tests and therefore only one was chosen for further experiments. This antibody stained the acrosomal region of fixed but not living spermatozoa by indirect immunofluorescence, indicating an intra-acrosomal localization of the antigen. In acetone-fixed frozen sections of human testis this antigen was expressed only in germ cells in the adluminal compartment of seminiferous tubules. The antigen was clearly visible in round spermatids from the beginning of the cap phase of acrosome development and was also present in premature germ cells which were present in ejaculates and which were in the early stages of acrosome development. By immunochemical analysis this antibody recognized a molecule of 50 K MW as well as other components of 24 to 34 K. The pattern of staining for the antigen was similar in the presence or absence of beta-mercaptoethanol in the sample buffer. The species specificity of the antigen was studied by indirect immunofluorescence using acetone-fixed spermatozoa and the antigen was found to be present in mouse, bovine, ram and boar spermatozoa. This antibody may be useful as an acrosomal marker.