Etiology of sperm immunity in women

Transcription

1 CORRESPONDENCE Etiology of sperm immunity in women Sperm immunity in females can reduce the likelihood of natural conception, and sperm antibodies from female sera have been shown to inhibit IVF in humans and in several animal models. The etiology of sperm immunity in human females is unknown, but several possible mechanisms have been proposed, including cross-reactivity with microbial antigens and interferon gamma mediated potentiation of the antisperm immune response in women whose male partners have sperm autoantibodies in their semen. This article reviews these ideas and postulates a novel hypothesis based on the potential for the generation of anti-idiotype antibodies in women whose partners have sperm antibodies in their semen. (Fertil Steril Ò 2009;91: Ó2009 by American Society for Reproductive Medicine.) HISTORICAL BACKGROUND Possibly the earliest observations of sperm antibody activity in women were recorded by Samuel R. Meaker, M.D., in an article published in the Boston Medical and Surgical Journal in In four cases he had mixed the wife s serum with the husband s semen and noted that in two cases there was prompt loss of motility and definite agglutination of the spermatozoa (1). Before this report, during the first few decades of the twentieth century, many studies in animals had indicated that homologous or heterologous immunization of females with sperm or testis preparations could induce sperm antibody activity and infertility (see reference 2). The evidence was very convincing and prompted the following comment in an editorial in the Journal of the American Medical Association in 1921: If spermatozoa invade the female tissues and cause formation of specific antibodies which are capable of preventing fertilization, may not such a process participate in the problem of sterility? (cited in reference 2). The solid evidence derived from animal work, combined with initial tests on patients, provided the impetus for clinical trials involving immunization of women with their partner s semen with the aim of inducing immunocontraception. Baskin (3) reported on a study of 20 fertile women immunized three times IM at weekly intervals with their partner s whole ejaculate mixed with 1 ml of hexylresorcinol (antibacterial agent). All but one of the women showed sperm-immobilizing activity in their serum by 1 week after the last injection (that is, 3 weeks after the first injection), which persisted for 6 12 months. One woman became pregnant after 12 months when the sperm-immobilizing activity was no longer detectable in her serum. Although ethically unacceptable by current standards, this trial did demonstrate that women could be immunized to develop sperm-immobilizing activity and that this was associated with reduced fecundity. Received November 1, 2007; revised and accepted November 15, Reprint requests: Gary N. Clarke, D.Sc., Andrology Unit, Royal Women s Hospital, 321 Cardigan Street, Carlton, Melbourne, Victoria 3053, Australia (FAX: ; gary.clarke@rch.org.au). Further significant evidence for female antisperm antibody association with human infertility was found in the report by Franklin and Dukes in 1964 (4). They found that 20.1% of 214 women undergoing infertility investigations had detectable sperm-agglutinating activity in their serum. Women with unexplained infertility had a much higher incidence (72.1%) than women with organic causes for their infertility (8.4%) or fertile women (5.7%). They also reported on a trial of occlusive therapy wherein 13 couples used condoms and/or abstained for 2 6 months. They reported that antibody titers declined markedly in all 13 women and dropped to undetectable levels in ten. These ten patients were encouraged to resume unrestricted intercourse at the time of expected ovulation, with the result that nine became pregnant. It should be noted that this study gave a very high incidence of sperm antibodies and the results are not supported by recent studies using immunologically specific procedures. However, this report was important historically in that it stimulated, or maybe rekindled, significant interest in the idea that female immunological reactions to sperm could be involved in the development of otherwise unexplained infertility and in the concept of an antisperm contraceptive vaccine. MORE RECENT STUDIES ON SPERM IMMUNITY IN FEMALES Since the early historical reports, numerous investigations have been conducted into the role of sperm immunity in sperm-cervical mucus penetration, IVF failure, and infertility. There are many review articles describing the clinical and experimental research in this area (5 8). It is useful, however, to review some of the background knowledge and studies that are more pertinent to explaining the pathogenesis of female immunoinfertility associated with sperm antibodies. The uterine cervix is a highly competent mucosal immune site (for review, see reference 9), which contains many IgA-positive plasma cells located in the subepithelial layers of the endocervix. Most of the immunoglobulin /09/$36.00 Fertility and Sterility â Vol. 91, No. 2, February doi: /j.fertnstert Copyright ª2009 American Society for Reproductive Medicine, Published by Elsevier Inc.

2 A (IgA) in cervical mucus is secretory IgA consisting of two IgA monomers linked by a J chain and secretory piece. The secretory IgA antibodies directed against potential pathogens and occasionally sperm (10) can immobilize the invaders by cross-linking them to the cervical mucus strands, effectively blocking their progress to the upper reaches of the reproductive tract (11). There are obviously mechanisms that normally prevent such immunological reactions to sperm. However, in a small percentage of couples these are somehow circumvented or disrupted, resulting in local and often circulating antisperm antibody production and reduced chances of natural conception. In women with otherwise unexplained infertility, sperm antibody activity has been detected in cervical mucus in more than 10% of cases (12 14). Investigations using zona-free hamster eggs or saltstored human zona pellucidae indicated that high-level sperm antibodies might be expected to interfere with human fertilization (5), but this could not be adequately confirmed using fresh human oocytes until the availability of routine clinical IVF around Retrospective analysis of IVF results by Clarke et al. (15) provided some of the first evidence that sperm antibodies from female serum could inhibit the fertilization of viable human oocytes by human spermatozoa. They observed a fertilization rate of only 15% for patients who had significant titers of IgG and IgA class sperm antibodies in their serum, which was used as a supplement in the IVF culture medium, versus 69% for those patients in whom replacement serum was used during the fertilization culture. Their later experimental results confirmed that high-titer sperm antibodies of the IgG immunoglobulin class in female serum could effectively inhibit fertilization of fresh human oocytes (16).Subsequent reports from other laboratories have also indicated that high-level sperm antibodies can inhibit human fertilization (17 19). In addition, more recent animal studies have also provided considerable evidence that experimentally induced sperm isoimmunity could have detrimental effects on fertility and IVF (5). Consequently, it is now generally accepted, at least with strong sperm immunity, that sperm antibodies can block sperm functions such as cervical mucus penetration and fertilization and thereby impair fertility. ETIOLOGY OF SPERM IMMUNITY IN FEMALES What information is currently available regarding the development of or predisposing factors for sperm immunity in females? Observations of potential relevance to understanding the etiology of sperm immunity in women include evidence that they are more likely to have detectable sperm antibodies if their male partner also has sperm antibodies in his semen (20). Another interesting observation was that in about one-third of cases women apparently react only to their partner s sperm antigens rather than to sperm-specific antigens (21). Two main hypotheses have been proposed to explain the origins of female sperm immunity and the observed association between male and female sperm immunity in a proportion of couples. The first hypothesis is based on observations that human spermatozoa have antigens that cross-react immunologically with certain microbial antigens. Thus, Sarkar (22) reported that antibodies with specificity for certain yeast mannan molecular configurations cross-reacted with sperm membrane antigens. For example, 75% of sera from men with sperm antibodies were found to react with the 1,6 yeast mannan linkage specificity. In addition, some patients reacted with the 1,3 mannan specificity or with chemotype C1 from Salmonella paratyphi C. In another investigation, Blum et al. (23) observed a strong association between Chlamydia antibodies and sperm antibodies in young women using oral contraceptives. Similarly, Cunningham et al. (24) reported that 56% of women with primary pelvic inflammatory disease had sperm antibodies detectable by the indirect mixed agglutination reaction. Sera from these patients uniformly reacted with a 69-Kd band by western blotting. Because both partners would be likely to be exposed to the same microbes during unprotected sexual intercourse, they would also be expected to have an increased chance of developing sperm antibodies at about the same time. In summary, although several clinics have reported significant associations between genital tract infections and sperm antibodies (23, 24), a more recent and very thorough study did not confirm such an association (25). Consequently, although this hypothesis is interesting, it requires more supporting data before it can be accepted as a significant explanation for the development of sperm immunity in women. The second hypothesis is based on the observation by Steven Witkin (26) that antibody-coated sperm stimulated in vitro interferon-gamma (IFN-g) synthesis by lymphocytes from female donors. In contrast, antibody-free sperm did not cause IFN-g production. Given the evidence that IFN-g induces macrophages to express Ia antigen (major histocompatibility complex [MHC] class II marker) on the cell surface, the resulting juxtaposition of sperm antigen and Ia on the macrophage cell surface would be expected to facilitate the recruitment of T-helper cells and subsequent initiation of sperm antibody production by B-lymphocytes. Although supported by solid experimental data in the original publication by Witkin, this hypothesis does not appear to have been rigorously tested by other laboratories. THE POTENTIAL ROLE OF IDIOTYPES IN THE GENERATION OF SPERM ANTIBODIES A novel hypothesis can now be postulated based on the high probability that, if a male had sperm antibodies in his semen, then during repeated acts of sexual intercourse his female partner would eventually develop a spectrum of anti-idiotype antibodies that could facilitate an immune response to his sperm. Before explaining the anti-idiotype hypothesis in more detail, it is pertinent to briefly review some 640 Clarke Correspondence Vol. 91, No. 2, February 2009

3 of the immunological background associated with the idiotype theory. Jerne (27) proposed that antibodies should be antigenic to the individual s own immune system, resulting in the production of auto-antibodies directed against the unique (idiotypic) parts of the antibody that make up the antigenbinding site. The result is a network of idiotype/antiidiotype interactions that are involved in regulation and modulation of the immune system. The antigen-binding site or paratope of the anti-idiotype often mimics the original antigenic epitope that the idiotype itself recognized (Fig. 1). Thus, the antigen-binding sites of a proportion of the anti-idiotype antibodies essentially form internal antigen images. Consequently, immunization against a particular antibody idiotype can provide an effective means of stimulating or at least facilitating an immune response directed toward the original native antigen. There have been numerous investigations into the application of antiidiotypes for generating enhanced immune responses to cancer cells and infectious agents (28). Several groups have shown that polyclonal heterologous anti-idiotype antibodies can be generated against the idiotypes on monoclonal antisperm antibodies (29 31) and that the anti-idiotype could significantly inhibit the binding of the monoclonal antibody to sperm. Testing of the antiidiotype strongly supported the hypothesis that its ability to inhibit the original monoclonal antibody was due to its antigen-binding site forming a similar shape to the original antigenic epitope, the so-called internal antigen image (30) noted above. What role therefore might anti-idiotypes be expected to play in the generation of an immune response to sperm in some women? Under normal physiological conditions, it would obviously be quite unexpected to observe deleterious female immune reactions to sperm. However, if the male partner had sperm antibodies in his semen, how would the female immune system respond to repeated exposure to these antibodies? In light of the above information about idiotype/anti-idiotype responses, it can be hypothesized that the female should produce anti-idiotype antibodies that could ultimately potentiate an antisperm immune response that would have been unlikely to have occurred under normal conditions with native insoluble sperm membrane antigens not associated with MHC determinants. Thus, because of the different molecular structure (e.g., Fc component) and solubility of the antibody-associated epitope (internal antigen image) versus the native sperm membrane epitope, T-helper cells would be more likely to be recruited. At this point it is also important to note that the female could potentially form anti-idiotype antibodies directed against the male partner s antibodies specific for internal sperm components, in addition to those specific for sperm membrane antigens. The associated parallel set of antianti-idiotypes could potentially react with some sperm FIGURE 1 The immune response to antigen (Ag) generates antibodies bearing unique idiotypic (Id) signatures comprising the antigen-binding (Fab) site or paratope of the antibody. The individual s immune system subsequently sees the unique Id as foreign and responds by forming anti-id (a-id) antibodies, some of which recognize public Ids (Id-pub) present on other antibodies of different Ag specificity, while some recognize internal or private (Id-pri) parts of the Fab (internal Ag image). The former may recruit B-lymphocytes, producing antibodies of various specificities (the parallel set), while the latter can potentially augment the production of antibodies reacting with the original Ag. Clarke. Sperm antibodies in women. Fertil Steril surface epitopes. In other words, it is feasible that the idiotype hypothesis could explain all or most of the observed range of female sperm antibody activity. At the next level in this proposed scheme, the anti-antiidiotype response will contain a subset of antibodies reactive with sperm antigen because they are complementary to the so-called internal antigen image of the anti-idiotype but in addition will contain other antibodies (the so-called parallel set referred to above), which bear the same public idiotype but whose antigen-binding site is directed against other antigenic moieties (e.g., anti-dna, anti-phospholipids, etc.). The idiotype hypothesis is strongly supported by the observations of el-roeiy et al. (32), which indicated that there Fertility and Sterility â 641

4 is apparent cross-reactivity between sperm antibodies and some autoantibodies and that consequently many females with sperm antibodies show strong evidence of polyclonal B-cell activation. El-Roeiy et al. studied antisperm antibody positive sera from 27 men and 25 women for autoantibodies (antinuclear, antiphospholipid, antihistone, and anti-dna) and various autoantibody idiotypes. Women were more likely than men to have antinuclear and antiphospholipid autoantibodies associated with the presence of sperm antibodies. However, the most striking difference between men and women was observed when the antibody idiotypes were analyzed. Thus, the anti-dna 16/6 antibody idiotype was found in 24% of the women but in none of the men. The two anticardiolipin idiotypes investigated were detected in 52% 56% of women but in only one (4%) man. The presence of the idiotypic markers was also significantly correlated with both the presence and titers of sperm antibodies. El-Roeiy et al. (32) concluded that The detection of idiotypic markers in more than half of women with sperm antibodies, together with significant autoantibody abnormalities and marked IgG and IgM gammopathies, strongly suggests a broadly based B-cell abnormality in these women. However, the detection of idiotypic markers in many women, but in very few men with sperm antibodies, is also consistent with the idiotype hypothesis for explaining the stimulation of sperm antibody formation in many women. Men would be unlikely to form anti-idiotype autoantibodies directed against public germ-line idiotypes because of immune tolerance to such epitopes. Thus, the strong circumstantial support from the results of el-roeiy et al. (32) suggests that the idiotype hypothesis warrants serious experimental investigation. It is quite possible that the development of sperm immunity in some women may involve one or more of the three main postulated mechanisms operating in concert. For example, the stimulation by antibody-coated sperm of IFNg gamma synthesis in the female partner s lymphocytes could potentially augment her immunological response to antibody idiotypes in semen. It is also feasible that some women initially respond to microbial antigens (microbes attached to the sperm surface can also stimulate IFN-g gamma production by the female s lymphoid cells), resulting in the formation of antibodies that cross-react with sperm; this immune response could then be maintained over a longer period by her ongoing exposure and response to antisperm idiotypes in semen. The relationship among the three hypothesized mechanisms requires investigation. TESTING THE IDIOTYPE HYPOTHESIS How could we proceed to test the idiotype hypothesis? If the hypothesis is correct, then anti-idiotype antibodies in the female serum, if present in sufficient amounts, might be able to inhibit the binding of the male partner s antibodies bearing the corresponding idiotypic epitopes to sperm in vitro. It could also be surmised that under equimolar concentrations, there should be an immunoprecipitation reaction with the partner s sera. This could be tested, for example, by standard techniques such as gel immunodiffusion. Because semen will also contain small concentrations of blood group antibodies, with certain blood group combinations between partners, we might expect to observe some anomalies with respect to blood typing in the female due to the effect of anti-idiotype antibodies directed against the male partner s blood group antibody idiotypes. For example, if the male partner was blood group B, he should have anti-a antibodies in his semen, which could potentially stimulate anti-a idiotype antibodies in his female partner. If the female had a significant level of antibodies to the anti-a internal antigen image, then these anti-idiotype antibodies could potentially inhibit or reduce the agglutination titer of A-positive erythrocytes by her serum. Investigations are now being planned to examine these interesting possibilities. CONCLUSIONS Unfortunately there has been relatively little research interest in female sperm immunity in recent years. Further understanding of the reactivity of the female immune system to semen antigenicity, including experimental investigation of the idiotype hypothesis, may help to explain immunoinfertility but could also have significant implications for the development of immunocontraceptive vaccines and for the wider understanding of normal pregnancy and its associated pathology. Thus, the recognition of the male partner s antibody idiotype spectrum in semen by the female s immune system provides a potentially important means of cross talk that could prove vital for the establishment of normal pregnancy. It would also be very interesting to explore the possible implications of idiotype responses within the seminal priming hypothesis proposed by Robertson et al. (33). Gary N. Clarke, D.Sc. Andrology Unit, Royal Women s Hospital, Melbourne, Australia REFERENCES 1. Meaker S. Some aspects of the problem of sterility. Boston Med Surg J 1922;187: Katsh S. Immunology, fertility, and infertility: a historical survey. Am J Obstet Gynecol 1959;77: Baskin MJ. Temporary sterilization by the injection of human spermatozoa. Am J Obstet Gynecol 1932;24: Franklin RR, Dukes CD. Further studies on sperm-agglutinating antibody and unexplained infertility. JAMA 1964;190: Clarke GN. Sperm antibodies and human fertilization. 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