Sperm antibodies and human fertilization

Antisperm antibodies: invaluable tools toward the identification of sperm proteins involved in fertilization

The identification of sperm proteins involved in fertilization has been the subject of numerous investigations. Much interest has been dedicated to naturally occurring antisperm antibodies (ASA) and their impact in fertility. Their presence in men and women has been associated with 2-50% of infertility cases. ASA may impair pre- and post-fertilization steps. Experimental models have been developed using sperm proteins as immunogens to evaluate their involvement in sperm function. Our team has pursued investigations to assess ASA presence in biological fluids from patients consulting for infertility and their effect on fertilization. We found ASA in follicular fluids with ability of inducing the acrosome reaction and blocking sperm-zona pellucida interaction and used them to identify sperm entities involved in these events. We generated and utilized antibodies against proacrosin/acrosin to characterize the sperm protease system. We implemented an ELISA to detect proacrosin/acrosin antibodies in human sera and evaluated their impact upon fertility by developing in vitro assays and a gene immunization model. This review presents a summary of ASA history, etiology, current approaches for detection and effects upon fertility. ASA (naturally occurring, generated by animal immunization and/or of commercial origin) are invaluable tools to understand the molecular basis of fertilization, better diagnose/treat immunoinfertility and develop immunocontraceptive methods.

Antisperm antibodies and conception

Sperm have been known to be antigenic for more than a century. There is a strong body of evidence that in humans and in other species at least some antibodies that bind to sperm antigens can cause infertility. Therefore, these antibodies are of interest today for two practical reasons. Firstly, the association of the antibodies with infertility means that they must be detected and then the couples treated appropriately. Secondly, because these antibodies can induce infertility they have the potential to be developed for contraceptive purposes in humans and also for the control of feral animal populations.

Association between sperm autoantibodies and enhanced embryo implantation rates during in vitro fertilization

Previous investigations have demonstrated the propensity of strong IgA-class sperm autoantibodies to impede fertilization. However, because there has not been a general consensus on this issue, the aim of this retrospective analysis was to focus on the effects of different levels of IgA-class antibodies on each stage of the IVF procedure. This study has confirmed that high level IgA class antibodies significantly reduce fertilization rates but, unexpectedly, also has shown a very significant improvement in embryo implantation rates in patients with weak to moderate antibody levels. Interlaboratory prospective collaborative studies are being planned to test this preliminary observation more stringently.

Seminal Factor VIII and von Willebrand Factor: a possible role of the conventional clotting system in human semen?

Factor (F) VIII circulates in blood complexed with von Willebrand Factor (vWF). Deficiency or defect accounts for haemophilia A and vWF disease. In blood, FVIII functions as a co-factor for FIXa in the activation of FX. Human semen coagulates and liquefies in a process that resembles and has some links with the conventional haemostatic process. A study elsewhere has detected traces, but not measurable levels, of FVIII coagulant activity (FVIII:C). In the present study we have assessed FVIII antigen (FVIII:Ag), FVIII:C and vWF antigen (vWF:Ag) levels in 159 semen specimens obtained from sub-fertile (n = 21), normally fertile (n = 38), fertile donors (n = 32), and vasectomized men (n = 57). Seminal FVIII:Ag levels were also measured in a group defined by several parameters derived from the World Health Organization (WHO) fertility criteria, termed "pooled normal semen parameters" (PNSP). Factor VIII:Ag levels were compared with conventional fertility parameters. In addition, both FVIII:C and vWF:Ag were assessed in a separate group of normal individuals (n = 11). Factor VIII:Ag, FVIII:C and vWF were present and quantifiable in human semen. Factor VIII:Ag levels were significantly lower in vasectomy subjects compared with donors (p = 0.01) or PNSP group (p = 0.01). Several trends taken together suggest an associations between FVIII:Ag and semen quality. Parallel investigations demonstrate FV, FVII, FVIIa, FIX, FIXa, FXa, FXI, FXII, tissue factor (TF) and tissue factor pathway inhibitor (TFPI) in semen. The present report therefore provides further evidence for the presence of a functioning clotting system in human semen.

Antisperm immunity in assisted reproduction

Antisperm antibodies (ASA) can impair the fertilising capacity of human spermatozoa, acting negatively on sperm motility and cervical mucus penetration, and at the level of in vitro gamete interaction. Several methods attempt to improve the potentially deleterious effects of ASA-mediated infertility: by decreasing ASA production, by removing ASA already bound to sperm, artificial insemination (AIH) and fertilisation (IVF, ICSI). Only ICSI seems able to overcome the problem, with fertilisation and pregnancy rates of ASA-positive patients undergoing this technique in the same range as ASA-negative patients. As immunological infertility is relatively rare, literature in the field is quite scarce and more studies need to be conducted to confirm that embryo quality is not impaired.

Value of flow cytometric assay for the detection of antisperm antibodies in women with a history of recurrent abortion

PROBLEM

To verify the proposed relationship between recurrent spontaneous abortions and the presence of maternal antisperm antibodies (ASA) in women as detected by a sensitive and reliable method.

METHOD OF STUDY

The presence of maternal antipaternal immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies were determined against three different paternal antigens comprising T, B lymphocytes and semen cells by a sensitive flow cytometric crossmatch method to examine their possible correlation with pregnancy outcome. Group 1 consisted of sera obtained from 24 women with a history of abortion, and lymphocytes and semen samples collected from their husbands at the same time of visiting the in vitro fertilization (IVF) Clinic at King Faisal Specialist Hospital and Research Center. Sera, lymphocytes and semen samples were also collected from six couples with no history of abortion who served as controls (Group 2).

RESULTS

Using a sensitive flow cytometric assay to analyse the samples, without knowledge of clinical status, elevated levels of both IgG and IgM were detected in Group 1. However, no significant association was found when compared with normal females who had healthy pregnancies.

CONCLUSION

Flow cytometry is a highly sensitive and specific tool for the detection of alloantibodies in human sera from patients with rejected transplanted organs. Our findings suggest that maternal antipaternal antibodies with respect to IgG and IgM classes do not play a major role in women with a history of recurrent abortions, despite the presence of increased levels of antibodies against three different sources of paternal antigens.

Seminal plasma immunoglobulin concentrations in autoimmune male subfertility

The presence of anti-sperm antibodies (ASAs) in seminal plasma is associated with infertility. They have been shown to reduce sperm motility, interfere with cervical mucus penetration and gamete interaction, and have been shown to reduce spontaneous fertilization and pregnancy rates. Although some causes can be determined, in the majority of cases the initial event causing the immune sensitisation and the reasons for the continuing antibody secretion remains unknown. Quantitative determination of total IgG, IgA and IgM within seminal plasma had not been previously reported in patients with and without specific ASAs. Semen samples from 512 men presenting with infertility were analyzed. One hundred and forty-six men (28.5%) had seminal fluid ASAs as determined by the MAR or TAT tests. The total seminal plasma IgG and IgA concentrations were significantly elevated in the ASA-positive groups compared with ASA-negative groups (IgG: 8.83 mg/100 ml vs. 7.15, P = 0.0008; and IgA: 2.88 mg/100 ml vs. 1.64, P = 0.0001). Only 19 samples showed seminal fluid IgM, and there was no difference between the ASA positive or ASA negative samples. The significance of these findings is discussed.

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.

Antisperm antibody detection: 1. Methods and standard protocol

PROBLEM

Today, antisperm antibody (ASA) detection is one of the most important steps in the evaluation of male infertility. This practice is generally accepted even though there is still some disagreement about the meaning of antisperm immunity and a good deal of controversy about the test regarded as the most suitable for the detection of antibodies directed against sperm antigens. International workshops have tried to standardize universally accepted protocols. A panel of three or four methods is generally advised to provide a correct and complete screening of patients with antisperm immunity.

METHOD OF STUDY

This paper reports on the results of a serum exchange workshop for the standardization of the ASA detection in the sera carried out under the auspices of the Italian Society of Endocrinology, which was used as reference laboratory. A careful description of the most widely used methods is reported and proposed as a standard protocol also on the basis of the results of the correlation studies carried out by our group is also reported.

CONCLUSIONS

If the proposed methods and procedures will be accepted by the members of the Alps-Adria Society for Immunology of Reproduction, a Study Group for Sperm Antibody Testing, could start its activity having the goal of reaching a consensus on methodology and carrying out a European serum exchange workshop.

The effect of the antisperm auto-antibody-bound sperm on in vitro fertilization outcome

To evaluate the effects of antisperm auto-antibody-bound sperm on the outcome of in vitro fertilization-embryo transfer (IVF-ET), 160 infertile couples undergoing treatment by in vitro fertilization were recruited in this study. In the study group (11 couples, 15 cycles), the male partners were positive for antisperm autoantibodies determined by immunobead test (IBT). In the control group (149 couples, 152 cycles), the men had no such antibodies. The percentages of fertilization rate, cleavage rate and pregnancy rate of the study group and control group wer 75.0 +/- 5.2% vs. 69.3 +/- 2.4%; 82.8% +/- 3.7% and 6.7% +/- 11.8%, respectively. There were no significant differences in in vitro region, type and/or percentage of sperm-bound antibodies also had no effect on the in vitro fertilization outcome. In conclusion, in vitro fertilization-embryo transfer is not significantly affected by antisperm autoantibody-bound sperm determined by immunobead test.

Impact of immunoglobulin isotype and sperm surface location of antisperm antibodies on fertilization in vitro in the human

OBJECTIVE

To investigate the impact of immunoglobulin (Ig) isotypes and their location on the human sperm surface on fertilization in vitro.

DESIGN

Restrospective review and analysis.

SETTING

Reproductive endocrine division of a level 3 academic center.

PATIENTS

Forty-eight couples (80 IVF cycles) with males showing positive antisperm antibodies on the sperm surface by immunobead test, treated by IVF at the Norfolk Program.

MAIN OUTCOME MEASURE

Evaluation of total fertilization rate of preovulatory oocytes (metaphase II-metaphase I).

RESULTS

Immunoglobulin G and IgA antibody levels have no significant correlation with total fertilization rate of preovulatory oocytes by logistic regression. Immunoglobulin M, present in 44% of the couples, had a strong correlation with fertilization. When IgA showed very high levels of binding (> 68%) and IgM binding was > 40%, the fertilization rate dropped significantly. A strong correlation between presence of antibodies and fertilization rate was seen when IgM was directed to the head or tail tip of the sperm. Immunoglobulin A induced a statistically significant reduction of fertilization only when it was present on the head.

CONCLUSION

Two male antisperm Ig isotypes significantly impaired fertilization rates. Immunoglobulin A exerted its impact only when high level of binding was detected on the head. Immunoglobulin M, present in 44% of the males, was the Ig isotype that most significantly affected fertilization rates when localized both at the head and at the tail tip level.

Prospective study of leukocytes and leukocyte subpopulations in semen suggests they are not a cause of male infertility

OBJECTIVE

To determine the effects of leukocytes in semen on sperm quality and the ability to achieve conception.

DESIGN

A prospective analysis of 512 couples attending a regional infertility clinic. Leukocyte subsets were quantified using a monoclonal antibody-based staining procedure. In addition to basic seminal parameters (density, motility, morphology, and antisperm antibodies), reactive oxygen species and immature germ cells were also quantified in the semen of each patient. The presence or absence of a treatment-independent conception was determined 22 months after the start of the study. Semen parameters were then related to the ability to conceive.

SETTING

University-based center for reproductive medicine.

PARTICIPANTS

Success or failure to conceive was recorded from 512 couples. Couples were then selected to minimize the influence of any pathology of the female on outcome. A final study group of 229 couples, in which the women had regular menstrual cycles, ovulatory midluteal serum P levels of > 18 nmol/L, and patent fallopian tubes was finally selected for analysis.

MAIN OUTCOME MEASURE

Pregnancy.

RESULTS

Leukocyte concentration (total or individual subsets) was not associated with either reduced semen quality or conception rates. Similarly, neither reactive oxygen species or antisperm antibody (immunobead) concentration had any bearing on the outcome. Of all semen parameters measured, only the level of immature germ cells was found to be negatively associated with the rate of conception.

CONCLUSION

Measurement of seminal leukocytes in routine semen analysis appears to be of little prognostic value with regard to male fertilizing potential. As reactive oxygen species and antisperm measurement were of similar predictive value, the term "immunologic male infertility" should be redefined.

Effect of ionophore challenge on hamster egg penetration and acrosome reaction of antibody-coated human sperm

PROBLEM

Following the demonstration that antisperm antibodies do not affect the spontaneous acrosome reactions (AR) of human sperm used for the hamster egg penetration assay (HEPA), we evaluated the effect of the ionophore challenge on HEPA and AR of antibody-coated sperm.

METHOD

Motile sperm suspensions from donors were exposed to serum and seminal plasma samples with sperm-head-directed antibodies, washed, capacitated, and challenged with ionomycin.

RESULTS

The proportion of acrosome-reacted sperm, assessed by fluoresceinated Pisum sativum agglutinin and supravital stain Hoechst 33258, was significantly higher in the antibody-exposed sperm than in the controls (47.0 +/- 13.2% vs. 39.3 +/- 12.1, respectively; P < 0.05). However, the hamster egg penetration rate and index were not significantly different between antibody-exposed sperm and controls (98.0 +/- 3.7% vs. 85.9 +/- 16.2% and 6.64 +/- 4.1 vs. 6.81 +/- 4.8, respectively). Only one of eight test samples with antisperm antibodies, where the highest increase of AR rate compared with controls was observed (55.0% vs. 35.6%) produced a substantial increase of penetrations per oocyte (7.4 vs. 4.1).

CONCLUSION

The ionophore challenge enabled us to recognize a subtle effect of anti-sperm antibodies on the dynamics of acrosomal loss, the clinical relevance of which needs to be elucidated.

Characterization of human sperm antigens and antisperm antibodies in infertile patients

OBJECTIVE

To identify which sperm antigens may elicit the production of functionally important antisperm antibodies.

DESIGN

Immunoblot analysis was performed on 69 serum and 9 seminal plasma samples from infertile patients, using detergent extracts of pooled donor sperm as the antigen source. Serum and seminal plasma had been previously tested by an indirect immunobead binding test (IBT); 61 IBT-positive and 17 IBT-negative samples were included in the study. Proteins recognized by IBT-positive but not IBT-negative samples were most likely to be cell surface antigens, whereas proteins recognized by both IBT-positive and IBT-negative samples were probably intracellular. Antibodies directed toward surface antigens would be most likely to affect fertilization. Characterization of sperm surface proteins on both acrosome-intact and -reacted sperm used labeling of cell surface proteins with an N-hydroxysuccinimide ester of biotin, fractionation of sperm heads and tails, and lectin binding to determine glycosylation.

RESULTS

Specific immunoreactivity (with respect to IBT results) was observed to 35K, 40 to 45K, 57K, 66K, and 88 to 90K MW proteins. Characterization studies identified an 88K MW glycosylated plasma membrane protein, a 66K MW inner acrosomal membrane protein, a 34K MW inner acrosomal membrane protein, and a 35K MW prominent tail protein.

CONCLUSION

Immunological infertility may involve several antigens characterized in this study. Further studies are necessary to determine if antibodies to these specific proteins interfere with sperm function.

Antisperm antibodies and in vitro fertilization

The purpose of this study was to investigate the influence of antisperm antibodies in the male, the female, or both partners on the outcome of in vitro fertilization treatment. The results in terms of ongoing pregnancies in the male and female antibody-positive group were the same as in the antibody-negative group. In the double antibody-positive group two of the three patients became pregnant. When high levels of antisperm antibodies were present on the spermatozoa, the fertilization rate was significantly reduced. In the female positive group no clear relationship between the antibody titer and the fertilization percentage could be detected. Abnormal semen quality was responsible for a much lower fertilization rate than the presence of antibodies. The conclusion of this study is that in vitro fertilization provides an equal change of conception in couples with antisperm antibodies in comparison with couples with no antibodies if the other semen parameters are normal.

In vitro sperm capacitation to treat antisperm antibodies bound to the sperm surface

Our objective was to study antisperm antibody bound to the acrosome region during in vitro capacitation and to determine whether acrosome-antibody free sperm can be obtained from previously acrosome-antibody-coated sperm. The spermatozoa from a selected series of 14 patients were tested for sperm antibodies bound to the sperm surface using d-IBT and focusing on the acrosome positivity. The tests were carried out before the incubation and after 3, 6, 9, and 12 h of incubation in Tyrode's solution with 0.5% human serum albumin as the capacitation medium. Tests to evaluate acrosome region, sperm motion parameters, and zonae binding ability were carried out. In this way we were able to evaluate sperm function during capacitation protocol. The patients were 14 subjects selected according to good seminal characteristics, good post-rise sperm parameters, and high percentage of ASA bound to the sperm surface. In all cases the results showed that antisperm antibodies bound to the acrosome region were shed prior to the acrosome reaction. During sperm capacitation in human a modification, migration, or shedding of plasma membrane molecules takes place. The presence of antibodies in such an important area of the sperm head could certainly interfere in the fertilization process. Our data indicate that in vitro capacitation could provide an in vitro therapy capable of eluting antibodies from the acrosome region.

Capacitated sperm cells react with different types of antisperm antibodies than fresh ejaculated sperm

OBJECTIVE

To determine if sera of some women have antibodies against capacitated but not freshly ejaculated sperm.

DESIGN

The sera of 66 women undergoing in vitro fertilization (IVF) were tested for sperm antibodies after 1 hour and 18 hours of sperm incubation in the maternal sera. Subsequently, 5 sera were tested with capacitated versus noncapacitated sperm cells.

SETTING

The study was carried out in a university hospital department.

PATIENTS, PARTICIPANTS

The patients were 66 consecutive couples undergoing IVF.

INTERVENTIONS

Sera and semen that were taken for routine tests as part of the IVF procedures were used.

MAIN OUTCOME MEASURES

A case with IVF failure associated with late appearance of sperm antibodies prompted us to study the detection of sperm antibodies after 1 hour and 18 hours incubation.

RESULTS

Of 37 cases negative for sperm antibodies after 1 hour incubation, 7 demonstrated high levels of antibodies after 18 hours incubation. In 21 of 23 cases with low or intermediate levels of antibodies after 1 hour incubation, significantly higher levels (P less than 0.05) of antibodies were found after 18 hours. Different and higher levels of sperm antibodies were observed in five sera after incubation of 1 hour with capacitated sperm as compared with noncapacitated controls.

CONCLUSIONS

Major antigenic differences may exist between capacitated and noncapacitated sperm. In some women sperm antibodies are reactive against capacitated sperm only. This has no certain clinical significance but may explain certain cases of IVF failure, unexplained infertility, and part of the variation in sperm antibodies testing methods.

The predominance of IgG1 and IgG3 subclass antisperm antibodies in infertile patients with serum antisperm antibodies

Mouse monoclonal antibodies (MAb) specific for each of the four human IgG subclasses and immunofluorescence flow cytometry were used to evaluate the subclass of the IgG antibody response to sperm in serum samples from 13 men and 6 women with a high titer (greater than 1:15,625) of IgG antisperm antibodies (ASA] determined by an indirect immunobead test. Five sera without ASA were also studied as a control. All 19 (100%) of the ASA-positive sera contained immunoglobulin (Ig)G ASA of the IgG1 and IgG3 subclasses. A 1:1 correlation was observed between the presence of IgG1 and IgG3 ASA. IgG2 was essentially undetectable, while IgG4 reactivity, although less intense than IgG1 and IgG3, was more prominent in the sera from the five vasectomized men. The ability of the IgG1 and IgG3 ASA-positive sera to deposit complement (C) on sperm was demonstrated by the concomitant binding to antibody-laden sperm of polyclonal antibodies to the membrane attack complex (C5b-9) of C. Both C-fixing and non-C-fixing ASA-positive sera were found to possess IgG1 and IgG3 antisperm antibodies. The predominance of IgG1 and IgG3 subclasses suggested a T-cell dependent immune response to sperm antigens.

Characterisation of 24-kD proteins from rat testes using polyclonal sera reactive to human sperm antigens

A group of antigens of 24-kD Mr from rat testes were characterised biochemically. These antigens were part of a larger molecule of approximately 200 kD. On treatment with disulfide bond reducing agent, the 200-kD molecule was reduced to subunits. Immunoreactivity was confined to a doublet of approximately 24 kD and a single band of approximately 50 kD Mr after the reduction. Glycoprotein in nature, this antigen shared immunoreactive epitopes with a 40-kD antigen on human spermatozoa. Antiserum raised in rabbits against the 24-kD antigen from rat testes reacted with antigens on the acrosome of human spermatozoa. Agglutination of sperm could be induced by the antiserum. The carbohydrate residue could be removed by mannosidase digestion. Chemical deglycosylation studies showed a slight decrease in molecular weight. Immunoreactivity was however not completely lost after chemical deglycosylation. Isoelectric focusing of the antigen identified nine isoelectric species. Two relatively minor species showed immunoreactivity. Acrosome-reacted spermatozoa showed loss of antigens from acrosome.

Antisperm antibodies to sperm surface antigens in women with genital tract infection

Antisperm antibodies to sperm surface antigens in nulligravid women with primary upper genital tract infections were measured by the sperm mixed agglutination reaction assay. As many as 56% of women with a primary episode of pelvic inflammatory disease had antisperm antibodies. In addition, 69% of those women with no history of genital tract infection but with laparoscopic evidence of past pelvic infection had significant levels of circulating antisperm antibodies. Electroimmunoblots of sperm preparations probed with the sera of women who had either known or presumed upper genital tract infection revealed a uniformly recognized 69 kd antigen. In contrast, women with circulating antisperm antibodies before primary upper genital tract infection recognized up to five distinct sperm antigen determinants of 27, 54, 131, 146, and 174 kd. It is a distinct possibility that genital tract infections may lead to immunopotentiation of antisperm antibodies that could affect fertility.

Effect of sperm-antibodies on acrosome reaction of human sperm used for the hamster egg penetration assay

The effect of anti-sperm antibodies (ASA) on the rate of acrosome reactions (AR) during "in vitro" capacitation of human sperm used for the hamster egg penetration assay (HEPA) was assessed. Motile sperm suspensions from donors were exposed to several sera and seminal plasma with sperm head-directed ASA, then they were washed and capacitated "in vitro." After capacitation, the proportion of acrosome-reacted viable sperm was assessed by staining with Fluoresceinated Pisum Sativum Agglutinin and supravital stain Hoechst 33258. ASA of any immunoglobulin class did not significantly affect either the AR rate, or the hamster egg penetration rate. In conclusion, interference of ASA on spontaneous AR rate during "in vitro" capacitation can not be advocated as an explanation of the impairment of the interaction of human sperm with egg or its vestments, which have been reported in several studies.