Infertility due to antisperm antibodies

Antisperm antibodies associated with infertility: properties and encoding genes of target antigens

Infertility among couples of reproductive age is a perplexing condition when the cause is indeterminate. These cases are classified as unexplained infertility. In a subset of subjects, antisperm antibodies with sperm agglutinating and/or immobilizing activities have been detected in the blood or fluids of the reproductive tract. These cases are designated as immunologic infertility although a cause and effect relationship of the antibodies to infertility has not been established. In this review, seven target sperm antigens to antibodies associated with infertility and their encoding genes are described. The antisperm antibodies (ASAs) examined were obtained from infertile women or were monoclonal antibodies (mAb) raised against human sperm proteins. All the ASAs studied possessed potent sperm agglutinating and/or immobilizing activities. The target antigens were isolated from human and other mammalian sperm, and the encoding genes identified. The seven antigens are YWK-II, BE-20, rSMP-B, BS-63 (nucleoporin-related), BS-17 (calpastatin), HED-2 (zyxin), and 75- kDa. Each antigen is a distinct and separate entity and is produced by different cells of the reproductive tract, (e.g., germ cells, epididymal epithelial cells, and Sertoli cells). No single predominant target component has been found to interact with the ASAs. It is proposed that immunologic infertility is the consequence of the combined actions of multiple ASAs in immobilizing and/or agglutinating spermatozoa, blocking spermegg interaction, preventing implantation, and/or arresting embryo development.

Cloning of a glucose phosphate isomerase/neuroleukin-like sperm antigen involved in sperm agglutination

The mouse monoclonal antibody (mAb) A36 produced by us and shown to induce extensive, "tangled" sperm agglutination was used to isolate cDNAs encoding its cognate antigen. Three overlapping cDNA clones specifically recognized by the mAb were isolated from a human testis cDNA expression library in lambdagt11. Sequencing of these cDNAs yielded the complete nucleotide sequence of a 3-kilobase cDNA that encodes the mAb-related polypeptide, designated sperm antigen-36 (SA-36), composed of 558 deduced amino acids. SA-36 cDNA contained a 5' untranslated region of 234 nucleotides (nt), an open reading frame of 1674 nt, and a 3' untranslated region of 1138 nt. SA-36 cDNA displayed > 99% homology to glucose phosphate isomerase (GPI)/neuroleukin (NLK) mRNA. This surprising homology was confirmed in Western blots demonstrating that mAb A36 reacted specifically with GPI obtained from rabbit muscle and from baker's yeast. Moreover, polyclonal, monospecific antibodies produced against beta-galactosidase/SA-36-3 fusion protein stained human spermatozoa and caused intensive agglutination of these cells in a manner similar to that with the mAb. Taken together, the data presented here demonstrated that mAb A36 cognate sperm surface antigen, encoded by SA-36 cDNA, is a GPI/NLK-like protein involved in sperm agglutination.

Identification of human sperm peptide sequence involved in egg binding for immunocontraception

Development of a vaccine based on sperm antigens represents a promising approach to contraception. The sperm-zona pellucida (ZP) interaction constitutes the most important event in the fertilization process, and the molecular sequences involved at this site may provide the most attractive candidates for immunocontraception. In the present study, using the phase peptide display technique, a novel dodecamer sequence, designated as YLP(12), was identified that is involved in sperm-ZP recognition/binding. The synthetic 12-mer peptide based on this sequence and its monovalent Fab' antibodies specifically and significantly (P < 0.05) inhibited human sperm-ZP binding. In Western blot and immunoprecipitation procedures, the YLP(12) peptide recognized the ZP3 component of solubilized human ZP proteins. In the Western blot procedure involving 10 different human tissue extracts, the anti-YLP(12) Fab' antibodies recognized a protein band of approximately 72 +/- 2 kDa only in the testis lane. The peptide sequence was localized on the acrosomal region of the human sperm cell. These findings indicate that the novel testis-specific 12-mer YLP(12) that is present in the acrosomal region and is involved in human sperm-ZP interaction may find applications in contraceptive vaccine development, as well as in diagnosis and treatment of male infertility mediated through sperm dysfunction.

FSP95, a testis-specific 95-kilodalton fibrous sheath antigen that undergoes tyrosine phosphorylation in capacitated human spermatozoa

Protein tyrosine phosphorylation has been associated with both capacitation and motility of mammalian sperm. During capacitation, human spermatozoa undergo tyrosine phosphorylation of a characteristic set of proteins, only one of which has thus far been cloned and localized. We report here the sequence of a fibrous sheath protein of 95 kDa (FSP95) that undergoes tyrosine phosphorylation during capacitation of human spermatozoa and has similarity to sperm A-kinase anchor proteins (AKAPs). FSP95 is both auto- and iso-antigenic in humans as it is recognized by sera containing antisperm antibodies from infertile men and women. The 853-residue protein has a calculated molecular weight of 94.6 kDa and an isoelectric point (pI) of 6.0, and it contains multiple potential phosphorylation sites for protein kinase C and casein kinase II as well as one potential tyrosine kinase phosphorylation site at amino acid 435. The sequence has amino acid homology to mouse sperm fibrous sheath AKAP82 (pro-mAKAP82, 34% identity) and to human sperm fibrous sheath AKAP82 (pro-hAKAP82, 32% identity). The gene encoding FSP95 has 5 exons separated by 4 introns and is located on chromosome 12 at locus p13.3. Northern analysis detected a single transcript of approximately 3.0 kilobases, and Northern dot blot analysis of 50 human tissues revealed FSP95 mRNA expression only in testis. By employing sperm immobilization, indirect immunofluorescence, and immunoelectron microscopy with antisera to purified recombinant FSP95, the protein was localized to the ribs of the fibrous sheath in the principal piece of the sperm tail. FSP95 is the second fibrous sheath protein to be cloned, sequenced and localized in human spermatozoa.

A comparison of the sperm mixed-agglutination reaction test with the peroxidase-labelled protein A test for detecting antisperm antibodies in infertile men with varicocele

OBJECTIVE

To compare the sperm mixed-agglutination reaction (sMAR) with the peroxidase-labelled protein A method (POPA) in infertile patients with varicocele.

PATIENTS, SUBJECTS AND METHODS

The study comprised 30 men with a history of varicocele-associated infertility and 30 fertile men (control group). Antisperm antibodies against spermatozoa in the semen and against progenitor spermatozoa in testicular tissue were detected using the two methods.

RESULTS

The tests were positive in 15 (50%) of patients with both the sMAR and the POPA methods, while no autoantibodies were detected in the control group. There were no significant differences between the methods. The sensitivity and specificity of both tests was approximately 93%, with no significant difference between them (P>0. 05).

CONCLUSION

Both methods may be used for detecting sperm autoantibodies in infertile patients with varicocele.

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.

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.

Male infertility. Evaluation and nonsurgical therapy

Male infertility is a complicated and often poorly understood pathologic process. The cause of a man's infertility frequently remains unknown even after a thorough evaluation. Many of the currently available medical therapeutic options are empirical and lack documentation of efficacy. New diagnostic tests are emerging that may help define some previously obscure causes of infertility. Only when these abnormalities have been clearly identified will more specific and cost-effective treatment regimens be instituted.

Recombinant fertilization antigen-1 causes a contraceptive effect in actively immunized mice

Recombinant (r) fertilization antigen (FA)-1 was investigated for its immunocontraceptive effect using the mouse as a model. Active immunization with the murine rFA-1 antigen raised high antibody titers in all the immunized mice (n = 16 in two trials); these titers were long lasting and reached preimmunization levels by the 255th day. There was a significant (p < 0.0001) effect (64% reduction in trial I and 70% reduction in trial II) in fertility of immunized animals compared to PBS-control animals (n = 22 in two trials). The effect on fertility was reversible. When the antibody titers declined to control levels, all the animals conceived and delivered healthy babies without a significant (p > 0.05) effect on the litter size compared to that of controls. There was a significant (p = 0.025) correlation (r = 0.76) between the reduction in fertility and the circulating rFA-1 antibody titers. Anti-rFA-1 antibodies from immunized mice, and not the immunoglobulins from the PBS-control mice, significantly (p < 0.001) blocked murine sperm binding to zona pellucida and in vitro fertilization of murine oocytes. In a Western blot procedure, the anti-rFA-1 antibodies specifically recognized the protein band of approximately 47 kDa (dimeric form of cognate FA-1 antigen) only in the protein extract of testes and not in the extracts of somatic tissues tested, namely kidney, liver, intestine, spleen, muscle, heart, lung, brain, and ovary. In conclusion, our data indicate that active immunization with rFA-1 antigen induces a strong and sperm/testis-specific antibody response that causes a reversible inhibition of fertility by affecting sperm-zona binding and the fertilization process. These findings suggest that rFA-1 antigen is an exciting candidate for the development of a contraceptive vaccine.

Multivariant analysis of men from infertile couples with and without antisperm antibodies

PROBLEM

Research studies in animal and human systems have demonstrated conclusively that antisperm antibodies can interfere with fertilization. In the male, autoantibodies to sperm can be detected both in the sera and seminal plasma.

METHOD OF STUDY

Ninety-seven men who were tested for antisperm antibodies as a part of an infertility evaluation were identified. Complete medical history was obtained, including information related to events suspected of being associated with antisperm antibodies. History of surgery (varicocele repair, hernia repair, and vas reversal) and infection (epididymitis, sexually transmitted disease, and orchitis) were compared with semen parameters (motility less than 60%, concentration less than 20 x 10(6), and volume less than 2 cc). These were compared to antisperm antibody results of mixed agglutination reaction (MAR) and direct immunobead binding test (IBT) for immunoglobulin G (IgG). Statistical analysis was performed using Fishers exact two-tailed test.

RESULTS

As expected, prior vas reversal was significantly associated with the presence of antisperm antibodies (P = 0.0002) by MAR or IBT with a fivefold increased relative risk (95% confidence interval, 1.97-12.38). Other surgeries manipulating the cord structures independent of vas reversal were not associated with antisperm antibodies (P = 0.09). Prior infections, independent of vas reversal, were significantly associated with antisperm antibodies by MAR (P = 0.04) with a 3.8-fold increased relative risk (95% confidence interval, 1.06-13.87) but not by IBT. Sperm concentration less than 20 x 10(6), motility less than 60%, and a volume less than 2 cc were not associated with antisperm antibodies by MAR or IBT.

CONCLUSION

These findings suggest that manipulation of the cord structures excluding the vas were not associated with antisperm antibodies; however, vas reversal and prior infection are significant risk factors for the development of antisperm antibodies.