Detection of antisperm antibodies: their localization to human sperm antigens that are transferred to the surface of zona-free hamster oocytes during the sperm penetration assay

Detection using antisperm monoclonal antibodies of shared epitopes expressed by human spermatozoa and oocytes

OBJECTIVE

To determine whether human spermatozoa and oocytes share common antigenic epitopes, supporting the hypothesis that their cross-linking by antisperm antibodies present in the clinical sera of infertile couples could promote sperm adhesion to the oolemma.

DESIGN

Human and hamster eggs were studied for the presence of antigens recognized by a panel of World Health Organization Task Force monoclonal antibodies (mAbs) originally raised against human spermatozoa. A new technique was devised, using frozen sections of paraformaldehyde-fixed individual human and hamster eggs, to screen rapidly antisperm mAbs for egg reactivity. Living zona-free human and hamster eggs then were exposed to Covaspheres (Duke Scientific, Palo Alto, CA) coupled with these mAbs to document the presence of reactive epitopes on the oolemma.

SETTING

Academic research environment.

MAIN OUTCOME MEASURE(S)

Indirect immunofluorescence and Covasphere rosetting.

RESULT(S)

Eleven of 37 antisperm mAbs tested reacted with fixed hamster eggs and 10 reacted with human eggs. Five of 6 mAbs reactive with both fixed eggs also reacted with the oolemma of living, zona-free eggs.

CONCLUSION(S)

Common antigenic epitopes, some of which are shared with somatic tissues, exist on the oolemma of human eggs and on the plasma membrane of human spermatozoa.

Expression of complement regulatory proteins on human eggs and preimplantation embryos

PROBLEM

To investigate the relation between the complement system and reproduction, expression of complement regulatory proteins (C3b receptors and inhibitor of the membrane attack complex) were screened on unfixed human eggs and preimplantation embryos.

METHODS

Unfixed unfertilized oocytes and preimplantation embryos obtained from an in vitro fertilization program were stained by indirect immunofluorescence using monoclonal antibodies raised against membrane cofactor protein, (MCP or CD46), decay accelerating factor (DAF or CD55), protectin (CD59), human C3b/C4b receptor (CR1 or CD35), and major histocompatibility complex class I antigen (MHC class I).

RESULTS

CD55 and CD59 were both expressed by the plasma membrane of unfertilized oocytes and pre-implantation embryos. CD46 was not expressed by unfertilized oocytes but appeared at the 6-to-8 cell stage embryo when human gene expression first occurs. CD35 and MHC class I antigens were not expressed at all on oocytes and preimplantation embryos.

CONCLUSIONS

Selective expression of complement regulatory proteins (DAF and protectin) associated with the lack of MHC class I antigens may represent an immune protective mechanism by which human oocytes and preimplantation embryos escape complement-mediated damage during their travel through the female genital tract. Furthermore, participation of these complement regulatory proteins including MCP in cell to cell interaction during fertilization and/or implantation cannot be excluded.

Radiosensitive target in the early mouse embryo exposed to very low doses of ionizing radiation

We exposed mouse preimplantation embryos in vitro to either tritiated water (HTO) or tritiated thymidine (TdR) to determine whether the radiosensitive target was nuclear or extranuclear for embryonic cell proliferation disadvantage in the mouse embryo chimera assay. 8-cell embryos were incubated in either HTO or TdR for 2 h and paired with non-irradiated control embryos to form chimeras. Chimeras were cultured for an average of 20.2 h to allow for 2-3 cell cycles and then partially dissociated to obtain the number of progeny cells contributed by the two partner embryos for each chimera. These values were expressed as a "proliferation ratio" (number of cells from the irradiated embryo: total number of cells in the chimera). A ratio significantly less than 0.50 indicates that the experimental embryo expressed an embryonic cell proliferation disadvantage, which is the endpoint of this assay. The activity concentrations of HTO and TdR were adjusted so that both would deliver comparable mean absorbed nuclear doses during the combined initial 2-h irradiation incubation and subsequent 20.2 h chimera incubation periods. Although nuclear doses were comparable under these conditions, the extranuclear dose delivered by the uniformly distributed HTO was about 100 times greater than the extranuclear dose delivered by TdR for each given nuclear dose. Consequently, obtaining mean TdR proliferation ratios < or = mean HTO proliferation ratios would be evidence for a nuclear target while obtaining mean HTO proliferation ratios < mean TdR proliferation ratios would be evidence for an extranuclear target. TdR consistently produced lower mean proliferation ratios over a range of doses from 0.14 Gy to 0.43 Gy. Therefore, we conclude that the radiosensitive target for this endpoint is nuclear.

Association between human in vitro fertilization rate and pregnancy outcome: a possible involvement of spermatozoal quality in subsequent embryonic viability

A conventional view of mammalian fertilization is that the active component of the process: the spermatozoon, by virtue of its progressive motility and acrosomal enzymes, penetrates an otherwise passive oocyte. This concept has placed bias on spermatozoal normality as largely determining the outcome of fertilization; once this has been achieved then the contribution of the spermatozoon is often forgotten, and attention switches to the maternally derived "blue-print" for early embryonic development. Paternal genomic contribution is known to start at the eight-cell stage in the human, but this is usually after the time when early cleavage stage (2 to 8-cell stage) embryos are replaced in human assisted reproductive technologies (ART) procedures such as in vitro fertilization and embryo transfer (IVF-ET). Hence, fundamental abnormal contributions to embryogenesis derived from the fertilizing spermatozoon have often been ignored. Human IVF-ET has permitted far greater powers of analysis of the fertilization event, and fertilization success appears to be determined in such a system by three main factors: spermatozoal quality, oocyte quality, and quality of in vitro culture conditions (the gamete environment). If the second two factors are more carefully controlled than the first, as is the usual emphasis in routine human IVF practice, then any large variation in fertilization rates that are also significantly related to embryonic viability and ultimately pregnancy outcome, may be thought to be more directly associated with original quality of the fertilizing spermatozoon. An analysis of results of 758 IVF cases provides preliminary evidence to show that there is a close association between human in vitro fertilization rate and subsequent embryo viability following replacement. In accepting this hypothesis as a possibility, we should drastically change our attitude from one of the spermatozoon as a robust, simple initiator of embryonic development, and embrace the idea of the vulnerability of such germ cells both during and after their production, and how detrimental influences on this might profoundly affect embryogenesis after successful fertilization.

Relationship of sperm antibodies in women and men to human in vitro fertilization, cleavage, and pregnancy rate

PROBLEM

The presence of anti-sperm antibodies (ASA) in female serum has been correlated with decreased fertilization in the in vitro fertilization (IVF) program; however, the impact of each type of ASA (IgG, IgA, IgM) is not known.

METHOD

To clarify the role of each ASA subtype, the immunobead binding technique was used to identify IgG, IgA, and IgM ASA in the female sera and on the spermatozoa from 137 couples undergoing the IVF program.

RESULTS

Couples with ASA on spermatozoa had a lower fertilization rate and lower number of transferred embryos: and IgG was the major immunoglobin involved. Couples with ASA in female sera showed significant decreases in the rates of fertilization, cleavage, and number of transferred embryos only when IgM was detected, but not IgG or IgA. However, the presence of IgA ASA in female sera was only associated with a decrease in pregnancy rate, although the number of transferred embryos was not reduced.

CONCLUSION

These findings suggest that ASA can influence the results of IVF and that the specific effect is dependent upon the subtypes of ASA.

Leucocyte populations in semen and male accessory gland function: relationship with antisperm antibodies and seminal quality

Semen samples from 279 infertility patients attending an Immunological Centre were analysed to evaluate the relationship between the populations of leucocytes, seminal quality, antisperm antibodies, and seminal vesicle function. The most frequent finding between leucocytospermic samples was asthenozoospermia (57%), whereas in non-leucocytospermic samples normozoospermia was the most frequent finding (47%). In the samples with asthenozoospermia, granulocytes predominated, whereas in those with oligozoospermia and azoospermia a reduction in the number of macrophages and lymphocytes was observed, suggesting an obstructive process at the level of epididymis and/or vas deferens where these leucocytes are mostly produced. In the case of hypofunction of the seminal vesicles there was a predominance in granulocytes. The increased levels of each type of leucocytes affected seminal quality only when seminal vesicles were affected. Only the elevated granulocytes count was related to a decrease in sperm motility. In those samples with leucocytospermia, positive antisperm antibodies (ASA) were associated with low sperm motility, low sperm normal morphology, and low value of seminal corrected fructose, whereas, in the absence of leucocytospermia, ASA, were more related to low sperm counts. These data suggest that granulocytes were more related to seminal vesicles dysfunction and sperm motility changes, and that ASA may be observed in the presence or absence of leucocytospermia.

Sperm antibodies

Anti-sperm antibodies (ASA) occur in 1% to 30% of infertile couples. Mechanisms by which ASA impair fertility include prevention of fertilization by decreasing acrosome reaction and/or zona pellucida binding, and postfertilization effects. Treatment for ASA involves assisted reproductive technologies.

Sperm antibodies and human fertilization

Previous investigations using zona-free hamster oocytes and salt-stored human zonae pellucidae, and retrospective analysis of routine human in vitro fertilization (IVF) results have suggested that sperm antibodies can impair the fertilizing capacity of human spermatozoa. The results of our investigations using viable human oocytes confirm that human antispermatozoal antibodies can inhibit fertilization by human spermatozoa. In the future we plan to examine the mechanism of fertilization inhibition, including characterization of the sperm antigens involved. These studies may facilitate the development of immunocontraceptive vaccines and of new treatments for immunological infertility.

Detection in human sera of antibodies directed against the hamster egg oolemma

Heteroantibodies were demonstrated by indirect immunofluorescence in human sera, which reacted with unfertilized and fertilized hamster eggs. Oolemmal antigens to which these antibodies were directed were distinct from antigen present on the surface of living human spermatozoa. Both species-specific and tissue-specific heteroantibodies were demonstrated by absorption with hamster liver and ovary. An increased degree of heteroantibody binding was noted following penetration of zona-free hamster eggs by human spermatozoa, indicating that an alteration in oolemmal antigen distribution had occurred. No evidence was found, however, that antisperm antibodies in these sera reacted with zona-free hamster eggs following their fertilization.