Characterization of human sperm antigens reacting with antisperm antibodies from autologous sera and seminal plasma in a fertile population

Investigation of the stallion sperm proteome by mass spectrometry

Stallion spermatozoa continue to present scientific and clinical challenges with regard to the biological mechanisms responsible for their survival and function. In particular, deeper understanding of sperm energy metabolism, defence against oxidative damage and cell–cell interactions should improve fertility assessment and the application of advanced reproductive technologies in the equine species. In this study, we used highly sensitive LC–MS/MS technology and sequence database analysis to identify and characterise the proteome of Percoll-isolated ejaculated equine spermatozoa, with the aim of furthering our understanding of this cell's complex biological machinery. We were able to identify 9883 peptides comprising 1030 proteins, which were subsequently attributed to 975 gene products. Gene ontology analysis for molecular and cellular processes revealed new information about the metabolism, antioxidant defences and receptors of stallion spermatozoa. Mitochondrial proteins and those involved in catabolic processes constituted dominant categories. Several enzymes specific to β-oxidation of fatty acids were identified, and further experiments were carried out to ascertain their functional significance. Inhibition of carnitine palmitoyl transferase 1, a rate-limiting enzyme of β-oxidation, reduced motility parameters, indicating that β-oxidation contributes to maintenance of motility in stallion spermatozoa.

Molecular identities of human sperm proteins reactive with antibodies in sera of immunoinfertile women

Antisperm antibodies (ASA) can cause infertility in both men and women. It is important to delineate the sperm antigens against which these ASA are directed. Sperm proteins were separated by 2D gel electrophoresis and transferred to nitrocellulose membrane and incubated with sera from fertile women or immunoinfertile women having ASA. The corresponding immunoreactive peptide spots were cored from the gel and analyzed by the two-dimensional (2D) gel electrophoresis/matrix-assisted laser desoprtion ionization-time of flight-mass spectrometry and liquid chromatography-mass spectrometry (MALDI-TOF-MS/LC-MS). A total of 68 spots belonging to 38 different proteins and their isomers were identified. Fourteen of these proteins and their isomers reacted with both the fertile and immunoinfertile sera. Twenty-four of these proteins reacted specifically only with the immunoinfertile sera and not with the fertile sera. Among them was a novel protein designated as a hypothetical protein FLJ32704 (accession # Q96MA6). An immunodominant sequence (amino acid 151-159) of this protein was identified and a nonamer peptide based upon this sequence (IQTLG1TPR) was synthesized and examined for its immunoreactivity. This synthetic peptide reacted with 90% (36/40) of immunoinfertile sera and not with any of the fertile sera (0/40) in the enzyme-linked immnosorbent assay (ELISA). In conclusion, using the 2D gel electrophoresis/MALDI-TOF-MS/LC-MS procedure, we have identified several known and at least one novel antigen against which the antibodies are present in sera of immunoinfertile but not fertile women. Some of these antigens may find applications in specific diagonsis and treatment of infertility/immunoinfertility, and in the development of new generation of contraceptive modalities including contraceptive vaccines.

Are antisperm antibodies indeed sperm-specific?

Antisperm antibodies (ASA) are present in a high percentage of infertile patients. The development of ASA in the male depends on the sequestration of antigens on germ cells, the testis being an immune privileged region. In this study, we investigated the specificity of ASA binding to sperm antigens by exposing a number of organ preparations to ASA. In none of the organ homogenates was a significant difference between the results of the Western blot with ASA-containing fluids, neither serum nor seminal plasma, and those without ASA observed. We conclude from our results that the ASA tested in our study obviously are sperm-specific. ASA as an autoimmune are thus restricted to spermatozoa. The antigens are suitable for trials in immune therapy, they may also serve for the development of antigen-specific diagnosis and treatment in infertility. They also indicate cognate antigens of possible immune contraceptive agents.

Immune response of the tammar wallaby (Macropus eugenii) to sperm antigens

In the present study, male and female tammar wallabies were immunised with whole tammar wallaby sperm in adjuvant. An assay for sperm antibodies using a live sperm ELISA has been developed to detect sperm surface antigens and used to validate an assay using a 3-[(3-cholamidopropyl) dimethylammonio]-1 propanesulfonate (CHAPS) membrane extract of whole tammar wallaby sperm. The tests were used to monitor the immune response to whole sperm in both male and female tammar wallabies. Antisera with a limited array of specificities were generated, with those locating to the midpiece region of the sperm appearing the most likely candidates for targets for fertility perturbation based on immunofluorescence of fixed and non-fixed sperm. These systemically generated antibodies were demonstrated to have access to both the female and male tammar reproductive tracts and were found on ejaculated sperm and antibodies from female sera and follicular fluid-labelled fresh ejaculated sperm from non-immunised males. Preliminary sequencing of these proteins has identified some possibilities for further investigation.

Antibody-binding proteins in human seminal plasma

PROBLEM

The significance of antibody-mediated infertility is unclear and complicated by the finding of that antisperm antibodies are found both in fertile and infertile couples. Seminal plasma contains immunosuppressive factors, one such factor may be antibody-binding proteins (ABP's).

METHOD OF STUDY

Antibody-binding-proteins were purified using human IgG or IgG-Fc affinity chromatography columns. The purified antibody-binding proteins were characterized by their molecular weights, partial amino acid sequences, and immunoreactivities.

RESULTS

Three proteins of molecular weight 74, 70 and 55 kDa and other low molecular weight proteins specifically bound to the IgG or IgG-Fc affinity columns demonstrating Fc-binding specificities. These proteins were not FcgammaRIII, IgG, or fragments of these proteins by their behaviors under reducing conditions, Western blot, and partial amino acid sequence analyses. Amino acid sequence data demonstrated some of these proteins to be novel.

CONCLUSIONS

We have isolated and partially characterized several ABP's from seminal plasma. The IgG-binding proteins we have identified may protect spermatozoa against antibody-mediated damage by conferring protection to antibody-coated spermatozoa. If this hypothesis holds true, differences in the level or function of these ABP's may alter the status of fertility.

N-linked glycan of a sperm CD52 glycoform associated with human infertility

In a benchmark study, Isojima and colleagues established H6-3C4, the first successful heterohybridoma immortalized from the peripheral blood lymphocytes of an infertile woman who exhibited high sperm-immobilizing antibody titers. The present report demonstrates the identity between the glycoprotein antigens recognized by the human H6-3C4 monoclonal antibody (mAb) and the murine S19 mAb, generated in our laboratory to sperm agglutination antigen-1 (SAGA-1). Both mAb's recognize N-linked carbohydrate epitopes on the 15-25 kDa, polymorphic SAGA-1 glycoprotein that is localized to all domains of the human sperm surface. Treatment with phosphatidylinositol-specific phospholipase C demonstrated that SAGA-1 is anchored in the sperm plasmalemma via a GPI-lipid linkage. Immunoaffinity purification and microsequencing indicated that the core peptide of the SAGA-1 glycoprotein is identical to the sequence of CD52, a GPI-anchored lymphocyte differentiation marker implicated in signal transduction. Comparison of anti-SAGA-1 and anti-CD52 immunoreactivities revealed that the sperm form of CD52 exhibits N-linked glycan epitopes, including the epitope recognized by the infertility-associated H6-3C4 mAb, which are not detected on lymphocyte CD52. Thus, the two populations of the CD52 glycoprotein on lymphocytes and spermatozoa represent glycoforms, glycoprotein isoforms with the same core amino acid sequence but different carbohydrate structures. Furthermore, mAb's to the unique carbohydrate epitopes on sperm CD52 have multiple inhibitory effects on sperm function, including a cytotoxic effect on spermatozoa in the presence of complement. These results are the first to implicate unique carbohydrate moieties of a sperm CD52 glycoform as target epitopes in the anti-sperm immune response of an infertile woman. Furthermore, localization of CD52 on all domains of the sperm surface coupled with the multiple sperm-inhibitory effects of antibodies to its unique carbohydrate moieties suggest opportunities for immunocontraceptive development.

Human sperm proteome: immunodominant sperm surface antigens identified with sera from infertile men and women

The objective of this study was to identify those immunodominant sperm antigens recognized by antisperm antibodies (ASA) in the serum samples of infertile men and women. High-resolution two-dimensional gel electrophoresis was employed to separate human sperm proteins using isoelectric focusing or nonequilibrium pH gradient electrophoresis, followed by PAGE. Serum samples from 15 infertile male subjects and 6 infertile female subjects that contained ASA as assayed by the immunobead binding test (IBT) were analyzed by Western blotting followed by enhanced chemiluminescence (ECL). Serum samples from 10 fertile subjects (5 males and 5 females) that were ASA negative by IBT were used as controls. The ECL blots were analyzed by computer scanning to compare the immunoreactivity between serum samples from fertile and infertile subjects and to identify the antigens unique to the sera of the infertile subjects; 98 sperm auto- and iso-antigenic protein spots were recognized by sera from infertile males and females but not from fertile subjects. Based on vectorial labeling with 125I at the sperm surface, a subset of 6 auto- and iso-antigens was identified as possibly relevant to antibody-mediated infertility.

Characterization of a potent sperm-agglutinating monoclonal antibody and its cognate antigens

OBJECTIVE

To identify sperm antigens that are capable of eliciting infertility-related sperm-agglutinating antibodies.

DESIGN

In vitro laboratory experiments.

SETTING

University research laboratory.

PATIENT(S)

Fertile semen donors.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Sperm agglutination, immunofluorescence localization, and flow cytometric analysis of surface expression of A36 antigens. Antigen analysis by Western immunoblotting.

RESULT(S)

Monoclonal antibody A36 induced intensive head-to-head, tail-to-tail, and head-to-tail agglutination of motile human spermatozoa. Antigens recognized by A36 were localized on the acrosomal cap and in the principal tail regions of motile, noncapacitated human sperm. Changes in subcellular levels and localization of the A36-recognized epitope occurred after capacitation and acrosomal loss. A36 reacted with a polymorphic series of proteins in Western blots of sperm extracts from humans and various other animal species, including mouse testis extracts. A common 53-kd antigen was recognized by the antibody in the different antigenic preparations.

CONCLUSION(S)

A mouse antibody to human sperm, monoclonal antibody A36, caused intensive agglutination of noncapacitated human spermatozoa and reacted with antigens on the acrosomal cap and in the principal tail regions. Of the multiple polypeptides that were reactive with the monoclonal antibody in sperm extracts from humans and other animal species, a common 53-kd antigen was recognized.

Expression of the human antigen SPAG2 in the testis and localization to the outer dense fibers in spermatozoa

ABSTRACT Antisperm antibodies (ASAs) have been implicated in some instances of infertility. To characterize sperm antigens relevant to immunologic and immunocontraceptive development, SPAG2 (sperm-associated antigen 2) was identified by screening a human testis cDNA library with human sera positive for ASAs. Subsequently, two isoforms, SPAG2-1 and SPAG2-2, were identified in testis and placenta libraries, respectively. In the current study, Southern analysis of human genomic DNA with a probe common to the two SPAG2 isoforms indicated a single SPAG2 gene; therefore, alternative splicing is a likely mechanism for production of variant mRNAs. In situ hybridization of human testis sections demonstrated the expression of SPAG2 in primary spermatocytes, with decreased or arrested expression in postmeiotic cells. Immunofluorescence of Triton X-100-extracted spermatozoa with an anti-SPAG2 peptide antiserum indicate that SPAG2 is an intracellular component of the sperm flagellum. Electron microscopy refined this localization to the outer dense fibers (ODFs), structural filaments associated with the mammalian sperm axoneme. The ODFs have been reported to be composed of keratin-like intermediate filament proteins. However, SPAG2 does not exhibit the molecular characteristics of such proteins, nor does SPAG2 demonstrate sequence homology with previously characterized ODF proteins. Therefore, SPAG2 represents a novel protein of human sperm ODFs. Characterization of SPAG2 will further our understanding of ODF function in normal sperm motility and of flagellar abnormalities that lead to male infertility.

Sperm-associated and circulating IgA and IgG classes of antibodies recognise different antigens on the human sperm plasma membrane

IgA and IgG antibodies eluted from the surface of spermatozoa obtained from 11 infertile men were used to analyse the antigens defined by each class of sperm-associated antibodies. An enhanced chemiluminescent Western blot technique was developed to detect the low concentrations of immunoglobulins present in the eluted samples. The same analysis was performed with the sperm membrane-specific antibodies isolated from the sera of 8 of the patients included in the study. Sperm-eluted antibodies reacted with a total of 18 protein bands migrating with molecular masses of between 110 and 18 kDa. Individual antibody-binding patterns differed. Furthermore, IgA and IgG antibodies from any one patient recognised different sets of antigens. In spite of the apparent heterogeneity of the antigens defined by sperm-associated antibodies, the majority of these antibodies reacted with three protein zones of 68/64, 37/36 and 20/18 kDa. The antigens defined by the sperm surface-specific antibodies obtained from the sera of eight infertile patients differed from one patient to another and, in the majority of the patients, differed from those defined by the corresponding sperm-associated antibodies. Nevertheless, two protein zones of 68/64 and 20/18 kDa were recognised by both local and systemic antibodies in 6 and 4 patients, respectively.

Autoimmunogenicity of the human sperm protein Sp17 in vasectomized men and identification of linear B cell epitopes

OBJECTIVE

To assess whether human sera positive for antisperm antibodies have detectable levels of Sp17 autoantibodies and to determine the linear B cell epitopes to which these are raised for both native and recombinant Sp17.

DESIGN

Enzyme-linked immunoaborbent assays were performed against recombinant HSp17 on 15 serum samples from prevasovasostomy and postvasovasostomy patients. Positive sera then were used in mimotope analyses to determine HSp17 immunodominant linear B cell epitopes. These were compared with the linear B cell epitopes of recombinant HSp17.

SETTING

University research laboratory.

PATIENT(S)

Fifteen vasectomized or vasovasostomized men.

MAIN OUTCOME MEASURE(S)

Serum antibody reactivity to human Sp17.

RESULT(S)

Sera from vasectomized and vasovasostomized men exhibit Sp17 antibodies raised predominantly to two immunodominant linear B cell epitopes (amino acids 4 to 19 and amino acids 118 to 127), which differed from those of recombinant HSp17 (amino acids 52 to 79 and amino acids 124 to 136).

CONCLUSION(S)

The results show that Sp17 is an antigen to which vasectomized men raise autoantibodies. Two linear B cell epitopes predominate in native Sp17 and these differ from (but overlap with) those of the bacterially expressed recombinant protein.

Characterization of human sperm antigens reacting with antisperm antibodies from autologous sera and seminal plasma: comparison among infertile subpopulations

Immunoblotting techniques were used to characterize the reactivity of human sperm antigens with sperm antibodies from different groups of infertile subjects. Sperm antigens of each subject were tested with autologous sperm antibodies present in serum and seminal plasma in order to assess whether there were qualitative differences in the antigenic structure of spermatozoa among the various infertile groups. Sixty-one infertile males, divided into six groups according to changes in the two main semen parameters (sperm concentration and motility), entered the study. Immunoreactivity to several antigens, in both serum and seminal plasma, was usually demonstrated in infertile subjects. Using a complex statistical package no significant difference was found in the distribution of antigens between groups; this included previously termed "fertility-related antigens' (28, 35, 57 and 62kDa proteins). This suggests that the most relevant sperm antigens involved in reproduction have no particular relationship to sperm concentration and motility.