The immunological "Wars of the Roses": disagreements amongst reproductive immunologists

Redirecting reproductive immunology research toward pregnancy as a period of temporary immune tolerance

Referring to two recent publications, we here propose that clinical reproductive immunology has for decades stagnated because reproductive medicine, including assisted reproduction (AR), has failed to accept embryo implantation as an immune system-driven process, dependent on establishment of maternal tolerance toward the implanting fetal semi-allograft (and complete allograft in cases of oocyte donation). Pregnancy represents a biologically unique period of temporary (to the period of gestation restricted) tolerance, otherwise only known in association with parasitic infections. Rather than investigating the immune pathways necessary to induce this rather unique state of tolerance toward the rapidly growing parasitic antigen load of the fetus, the field, instead, concentrated on irrelevant secondary immune phenomena (i.e., "immunological noise"). It, therefore, does not surprise that interesting recent research, offering new potential insights into maternal tolerance during pregnancy, was mostly published outside of the field of reproductive medicine. This research offers evidence for existence of inducible maternal tolerance pathways with the ability of improving maternal fecundity and, potentially, reducing such late pregnancy complications as premature labor and preeclampsia/eclampsia due to premature abatement of maternal tolerance. Increasing evidence also suggests that tolerance-inducing immune pathways are similar in successful pregnancy, successful organ transplantation and, likely also in the tolerance of "self" (i.e., prevention of autoimmunity). Identifying and isolating these pathways, therefore, may greatly benefit all three of these clinical areas, and research in reproductive immunology should be accordingly redirected.

Disruption of estrous cycle homeostasis in mice with experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is widely viewed as a prototypic human autoimmune disease involving proinflammatory T cells that induce lesions in the central nervous system (CNS) in response to myelin self proteins. Although the impact of sex hormones on MS is well recognized, the converse effects of autoimmunity on sex hormones are still unclear. The current study was designed to assess the impact of CNS autoimmunity on female reproductive physiology. In order to identify subtle hormonal disturbances as a result of autoimmunity, we analyzed the estrous cycle in SJL/J mice after active induction of experimental autoimmune encephalomyelitis (EAE), an animal model with substantial similarities to MS. Here we show that CNS autoimmunity significantly shortens the murine estrous cycle. This shortening of the estrous cycle is characterized by a dramatic decrease in the length of the metestrus-diestrus luteal phase partially offset by a highly significant but less dramatic elongation of the proestrus-estrus follicular phase of the uterine cycle. Thus, our study provides experimental evidence for a direct causal link between CNS autoimmunity and disruption of the homeostatic balance of the uterine cycle often observed in women with MS.

Study of the frequency of occurrence of genetic and acquired thrombophilia in infertile women prior IVF

This study of infertile women prior in vitro fertilization (IVF) is focused at the genetic and acquired thrombophilia before the IVF program, the identification of the frequency of occurrence of thrombophilia in them, the impact of thrombophilia of the offensive, the course and outcome of pregnancies, to improve the quality of cycles in terms of a pregnancy and childbirth. Forty-five women with infertility were examined. Thirty-two (71%) were identified thrombophilia: genetic thrombophilia in 32 cases (100%), among them a combination of several forms of genetic thrombophilia - 21 (63%) of them, other forms of thrombophilia (genetic and acquired) - in 5 of them (16%). In IVF 23 (72%) women became pregnant. In 87% of pregnancies ended in spontaneous birth, in 13% of cases of preterm birth.

T CD3+CD8+ lymphocytes are more susceptible for apoptosis in the first trimester of normal human pregnancy

Aims. Normal human pregnancy is a complex process of many immunoregulatory mechanisms which protect fetus from the activation of the maternal immune system. The aim of the study was to investigate the apoptosis of lymphocytes in peripheral blood of normal pregnant patients and healthy nonpregnant women. Methods. Sixty pregnant women and 17 nonpregnant women were included in the study. Lymphocytes were isolated and labeled with anti-CD3, anti-CD4, and anti-CD8 monoclonal antibodies. Apoptosis was detected by CMXRos staining and analyzed using the flow cytometric method. Results. We found significantly higher apoptosis of total lymphocytes in peripheral blood of pregnant patients when compared to healthy nonpregnant women. The percentage of apoptotic T CD3⁺CD8⁺ cells in the first trimester was significantly higher when compared to the third trimester of normal pregnancy. The ratio of T CD3⁺CD4⁺ : T CD3⁺CD8⁺ apoptotic lymphocytes was significantly lower in the first trimester when compared to other trimesters of pregnancy and to both of the phases of the menstrual cycle. Conclusions. The higher apoptosis of T CD3⁺CD8⁺ lymphocytes and the lower ratio of T CD3⁺CD4⁺ : T CD3⁺CD8⁺ apoptotic cells in the first trimester of normal pregnancy may suggest a higher susceptibility of T CD3⁺CD8⁺ cells for apoptosis as a protective mechanism at the early stage of pregnancy.

The "graying" of infertility services: an impending revolution nobody is ready for

BACKGROUND

As demand for infertility services by older women continues to grow, because achievable in vitro fertilization (IVF) outcomes are widely underestimated, most fertility centers do not offer maximal treatment options with use of autologous oocytes. Limited data suggest that clinical IVF outcomes in excess of what the American Society for Reproductive Medicine (ASRM) considers "futile" can, likely, be achieved up to at least age 45 years.

METHODS

In an attempt to point out an evolving demographic trend in IVF, we here report our center's IVF data for 2010-2012 and national U.S. data for 1997-2010. Though our center's data are representative of only one IVF center's patients, they, likely, are unique since they probably represent the most adversely selected IVF patient population ever reported and, thus, are predictive of future demographic trends. In addition we performed a systematic review of the literature on the subject based on PubMed, Medline and Google Scholar searches till year-end 2013. The literature search was performed using key words and phrases relevant to fertility treatments in older women.

RESULTS

As demonstrated by our center's patient demographics and national U.S. data, IVF centers are destined to treat increasingly adversely selected patients. Despite our center's already extremely adversely selected patient population, age-specific IVF cycle outcomes in women above age 40 years, nevertheless, exceeded criteria for "futility" by the ASRM and widely quoted outcome expectations in the literature for patient ages. Age 43 discriminates between better and poorer clinical pregnancy and live birth rates.

CONCLUSIONS

"Graying" of the infertility populations in the developed world, a problem with potentially far-reaching medical and societal consequences, has so far been only insufficiently addressed in the literature. As women's postmenopausal life spans already exceed postmenarcheal life spans at the start of the 20th century, the "graying" of infertility services can be expected to further accelerate, no longer as in recent decades bringing only women in their 40s into maternity wards but also women in their 50s and 60s. Medicine and society better get ready for this revolution.

Differences in regulatory T-cell and dendritic cell pattern in decidual tissue of placenta accreta/increta cases

INTRODUCTION

Primary infertility, miscarriage, and preeclampsia have been correlated with reduced numbers of regulatory T-cells (Treg) suggesting that decreased extravillous trophoblast (EVT) invasion originates from inadequate EVT tolerance. In contrast increased numbers of Treg-cells may be responsible for over-invasion of EVT. As the maturation status of dendritic cells (DC) influences T-cell behavior (tolerance or immune activation), altered relation between immature and mature DCs may also influence EVT invasion.

METHOD

Paraffin-embedded specimens of placenta accreta/increta (Pc; n = 11) and healthy intrauterine pregnancy (IUG; n = 18) were double-stained for cytokeratin and CD45, CD68, CD56, CD20, CD3, or CD8 as well as FoxP3/CD4 and FoxP3/CD8 and single-stained for CD4, CD25, FoxP3, CD209, Dec205 and CD83. Quantification of the leukocyte subpopulations was performed for decidua parietalis and basalis as characterized by cytokeratin-positive EVT. Statistical analysis was performed by using the Mann-Whitney test.

RESULT

There were significantly fewer CD4(+) cells in Pc than in IUG. Concerning the Treg-markers, FoxP3(+) cells are significantly increased. CD25(+) cells showed a small non-significant increase in Pc in comparison to IUG. Concerning dendritic cells, immature non-activated CD209(+) DCs were significantly decreased in Pc while immature activated CD205(+) DCs were slightly but non-significantly increased. Mature activated CD83(+) DC were non-significantly decreased in IUG vs Pc.

DISCUSSION AND CONCLUSION

The increased number of Treg-cells in Pc suggests significance for these cells in the regulation of trophoblast invasion. Their adequate interaction with other lymphocyte populations (e.g. adequately maturated dendritic cells) may be one mechanism to assure controlled EVT invasion.

Low-intensity IVF: real progress?

A recent publication in this journal strongly advocated low-intensity IVF (LI-IVF) after presenting the authors' experience with minimal ovarian stimulation (mini-IVF). The data presented failed to support their conclusions. Therefore, presented here is a critique of their manuscript and of uncontrolled clinical use of LI-IVF, in general. In the absence of properly controlled studies, all forms of LI-IVF should be considered experimental and be offered only in well-controlled research settings and with appropriate informed consent.

Cutting edge assessment of the impact of autoimmunity on female reproductive success

There, likely, is no more controversial issue in reproductive medicine than the effects of autoimmunity on female reproductive success. Published studies are, therefore, often biased. We performed PubMed, Google Scholar and Medline searches for the years 2000-2010 under various key words and phrases, referring to effects of autoimmunity/autoimmune diseases on pregnancy/pregnancy outcomes/pregnancy rates/reproduction/reproductive outcomes/fertility/infertility/fertility treatments/infertility treatments, and a number of similar terms. Reference lists of selected manuscripts were evaluated for additional, potential references. All selected manuscripts were reviewed by at least one author (N.G.). Opinions were reached based on preferential review of only selected studies, which offered data, primarily developed in pursuit of unrelated scientific questions. Data from various medical fields point, surprisingly effectively, toward significant impacts of autoimmunity on female reproductive success. Autoimmunity not only increases miscarriage risks but also reduces female fecundity and infertility treatment success. A, likely, reason why differences of opinion have persisted is that effects are primarily observed in genetically predisposed women, with specific fragile X mental retardation 1 (FMR1) genotypes. This discovery coincides with recently increasing appreciation of the importance of the long arm of the X chromosome (Xq) in control of functional ovarian reserve (reflective of female fertility) and autoimmunity, with FMR1at Xq27.3, located at cross roads of both. Autoimmune effects on female reproductive success deserve recognition. Further investigations must not ignore patient stratification, based on ovarian FMR1 genotypes. Genetic definition of high-risk patients should lead to development of successful therapeutic interventions.

Association of FMR1 genotypes with in vitro fertilization (IVF) outcomes based on ethnicity/race

The FMR1 gene, mapping to an area of the X chromosome closely associated with autoimmunity also affects ovarian reserve, with specific genotypes associated with distinct ovarian aging patterns. They, therefore, could also be associated with differences of in vitro fertilization (IVF) outcomes, reported between races/ethnicities. We analyzed 339 consecutive IVF patients, 232 Caucasian, 59 African and 48 Asian, for FMR1 genotypes, and tested by multiple logistic regressions for associations between race/ethnicity, FMR1 genotype, autoimmunity and pregnancy chances with IVF. FMR1 genotypes were predictive of pregnancy (P = 0.046), het-norm/low most significantly and with decreasing chance in comparison to norm genotypes (OR 0.44; 95% CI 0.23–0.85; P = 0.014). Race/ethnicity was, overall, independently associated (P = 0.03), African demonstrating decreased odds in comparison to Caucasian (OR 0.33. 95%CI 0.13–0.79; P = 0.014). Autoimmunity did not differ but interaction of autoimmunity with FMR1 genotype almost reached significance (P = 0.07). Logistic regression with race/ethnicity and interaction between FMR1 genotype and autoimmunity in the model, demonstrated 2.5-times the odds of being associated with autoimmune positivity (OR 2.5, 1.34–4.55; P = 0.004). FMR1 genotypes offer a possible explanation for differences in IVF outcomes between races/ethnicities.

Is the immunological noise of abnormal autoimmunity an independent risk factor for premature ovarian aging?

OBJECTIVE

The risk for premature ovarian failure increases in association with two principal known etiologies: in the presence of excessive triple CGG expansions on the FMR1 (fragile X) gene (genetic etiology) and in association with a variety of autoimmune conditions (autoimmune etiology). To what degree milder forms of premature ovarian aging are also associated with these two etiologies is, however, unknown.

METHODS

We, therefore, investigated 119 consecutive, so identified, infertile women and statistically correlated by linear and logistic regression analyses ovarian function parameters to markers of a possible genetic etiology (number of CGG triple repeats on the FMR1 gene) and to markers of possible abnormal immune function (immune panel).

RESULTS

Sixty (50.4%) of 119 participants demonstrated at least one immune abnormality. Both groups did not differ statistically in age, mean follicle-stimulating hormone, estradiol, and antimüllerian hormone levels, although antimüllerian hormone suggested a trend toward higher levels in autoimmune participants (P = 0.19). Autoimmune participants also demonstrated lower mean triple CGG expansion sizes (P < 0.05) and included fewer women with greater than or equal to 35 triple repeats (relative risk, 4.0; 95% CI, 1.3-11.9; P < 0.01), previously reported to demarcate increased risk for premature ovarian aging.

CONCLUSIONS

Even minimal evidence of abnormal autoimmune function ("immunological noise") seems to increase risk toward premature ovarian aging, often manifesting as infertility. Evidence of abnormal autoimmune function, such as increased CGG triple expansion sizes, in young women, therefore, warrants vigilance for development of prematurely diminished ovarian reserve and infertility.

Autoantibodies and coagulation in reproductive medicine

Management of recurrent pregnancy loss (RPL) is considered to be difficult, in part because of cunfusion between autoantibodies and coagulation disorders. Autoantibodies and coagulation are related; two groups of multicenter studies concerning autoantibodies and coagulation reported that factor XII deficiency, hypofibrinolysis, anti-phosphatidylethanolamine (aPE), anti-beta2-glycoprotein I, anti-annexin A5, and lupus anticoagulant (LA) were found to be frequent risk factors in RPL women. Therefore, discrimination of autoantibodies and coagulation is important in understanding RPL well. We propose three types of pathways regarding reproduction, which are different and independent: (1) Negatively charged-phospholipid related antibodies (anti-phosphatidylserine; aPS, anti-cardiolipin; aCL, lupus anticoagulant; LA, anti-annexin A5; aANX), (2) factor XII-aPE-fibrinolysis: suppression of fibrinolysis, (3) protein C-protein S-factor V: loss of inactivation against activated factor V. Women with RPL and infertility showed similar findings in terms of the above clinical tests. Available data, however, is not enough to conclude whether these are pathogenic to infertile women.

A pilot study of premature ovarian senescence: II. Different genotype and phenotype for genetic and autoimmune etiologies

OBJECTIVE

To assess whether abnormal autoimmune function and number of triple CGG repeats on the FMR1 (fragile X) gene, both historically associated with risk toward premature ovarian senescence, represent independent risk factors.

DESIGN

Retrospective cohort study.

SETTING

Academically affiliated, private fertility center.

PATIENT(S)

Forty consecutive, new infertility patients, of which 11 presented with a primary diagnosis of repeat pregnancy loss, 23 with prematurely elevated, age-specific baseline follicle stimulating hormone (FSH) levels (i.e., premature ovarian aging) and 6 with premature ovarian failure.

INTERVENTION(S)

Determination of triple CGG repeats on both alleles of the FMR1 gene, assessment of ovarian reserve via FSH and anti-Müllerian hormone levels, and evaluation of autoimmune status by antiphospholipid antibody panel, antinuclear antibody panel, total immunoglobulin levels (IgG, IgM, IgA), thyroid antibodies (antiglobulin and antimicrosomal), antiovarian, and antiadrenal antibodies.

RESULT(S)

Twenty-two of 40 patients (55%) demonstrated autoimmune abnormalities. Women with and without autoimmune abnormalities did not differ in age. Patients with autoimmune abnormalities, however, demonstrated significantly lower FSH levels and higher anti-Mullerian hormone levels. Although triple repeats on the lower count allele (allele-1) of the FMR1 gene did not differ statistically, autoimmune patients demonstrated in the higher count allele (allele-2) significantly fewer triple repeats, significantly fewer triple repeats >or=30, and, in contrast to nonautoimmune patients, a normal mean level of triple repeats.

CONCLUSION(S)

Abnormal autoimmune function and expansions in triple CGG repeats on the FMR1 gene represent distinctively different etiologies for premature ovarian senescence in infertile patients and may, indeed, constitute its two principal causes.

IgG-antiphospholipid antibodies in follicular fluid of IVF-ET patients are related to low fertilization rate of their oocytes

PROBLEM

Patients undergoing in vitro fertilization and embryo transfer (IVF-ET) failures show an increased incidence of antiphospholipid antibodies (aPL) in their blood. The physiological manifestations of aPL in this patient group are nonetheless controversial. Pathological effects of aPL on embryos in vitro have been documented. We questioned whether aPL if found in follicular fluids (FFs) could result in embryonic damage.

METHOD OF STUDY

Blood from 44 patients with three or more IVF-ET failures were tested by enzyme-linked immunosorbent assays (ELISA) for the presence of immunoglobulin (Ig)G, IgM and IgA aPL. Both the 29 aPL-positive and 15 aPL-negative patients gave permission for FF collection during their next IVF-ET attempt for additional aPL determinations.

RESULTS

Patients with no aPL in their blood, had no aPL in their FFs. Patients with IgG and/or IgM aPL in their blood had IgG but not IgM in their respective FFs.

CONCLUSIONS

The presence of IgG aPL in FFs and increased infertility length were significantly related to lower fertilization rates, independently. Follicular fluid IgG aPL appears as a risk factor in association with successful IVF-ET outcomes.

Alloimmune and Autoimmune Background in Recurrent Pregnancy Loss - Successful Immunotherapy by Intravenous Immunoglobulin

PROBLEM

Immunotherapies [leukocyte immunization, intravenous immunoglobulin (IVIG)] introduced to treat women with recurrent spontaneous abortions (RSA) have still controversial results in most clinical trials. A selection of these patients would be advantageous for higher efficacy.

METHOD OF STUDY

A complex immunological panel assay was offered to patients with reproductive failure without any other known cause. We focused here on the cellular immunological parameters.

RESULTS

High cytotoxic T lymphocyte precursor frequency and cell-mediated cytotoxic activity and a rather high natural killer cell activity were found in alloimmune RSA patients. Thirty-two patients were investigated by immunological assays and in 78% of the women an alloimmune background could be defined. The efficacy of IVIG treatment was 96% in this group.

CONCLUSIONS

The novel cellular immunological assays proved to be favourable for the indication of RSA patients and showed the usefulness of this selection process for effective immunotherapy.

Antiphospholipid antibodies and coagulation defects in women with implantation failure after IVF and recurrent miscarriage

Evaluation of patients with IVF implantation failure or recurrent miscarriage often frustratingly fails to elicit any particular cause for their problem. Testing for antiphospholipid antibodies or thrombophilia is commonly carried out, and interpretation of results in the light of the current evidence is extremely difficult. This paper reviews the purported pathogenetic mechanisms and clinical associations between both antiphospholipid antibodies and inherited thrombophilias, and reproductive failure. The current management strategies are also critically evaluated and recommendations are made for optimal, evidence-based clinical practice.

Recurrent implantation failure in assisted reproduction: how to counsel and manage. B. Treatment options that have not been proven to benefit the couple

The success of assisted reproduction, although gradually increasing over the years, is still less than satisfactory. Many couples have benefited from this treatment; however, many have also been left frustrated following multiple failed attempts. Couples who fail to conceive after multiple IVF/intracytoplasmic sperm injection (ICSI) treatments often seek treatment options that are new and that have not been offered before. Some of these include immunological testing and treatment, allogenic lymphocyte therapy, intratubal transfer of zygotes and embryos, blastocyst transfer, sequential embryo transfer, assisted hatching, co-cultures, and preimplantation genetic screening for aneuploidy. Although the evidence behind some of these is more robust, most suffer from lack of well designed randomized trials comparing them with other treatment options. Randomized studies are extremely difficult to conduct, as couples will resist being randomized into a treatment group where previously failed procedures will be repeated. In the mean time, assisted reproduction programmes should resist offering treatment options that are not evidence based, or at least they should share with the couple the information that is available and should stress that none of these is a panacea for their problem.

Apoptosis of extravillous trophoblast cells limits the trophoblast invasion in uterine but not in tubal pregnancy during first trimester

During the first trimester of pregnancy extravillous trophoblast cells (EVT) invade the maternal decidua. Invasion normally is reduced from the second trimester onwards and stops in the inner third of the myometrium. By contrast, in extrauterine tubal pregnancy, trophoblast invasion may even penetrate the tubal wall, which ultimately leads to the rupture of the fallopian tube. Induction of apoptosis of EVT cells, by maternal immune competent cells, may be an important mechanism to limit EVT invasion in uterine pregnancy. Tissue specimens from first and second trimester uterine pregnancy and first trimester tubal pregnancy were analyzed for apoptosis by TUNEL- and M30-staining. By immunohistochemical double labelling, maternal leukocyte subtypes were co-localized to apoptotic cells and in this context, the number of CD56(+)NK cells was analyzed. Our data show that apoptosis is confined to the decidua basalis. Most apoptotic cells are single cytokeratin-positive epithelial cells residing in the stromal compartment. Consequently these cells can only be EVT cells. Maternal leukocytes are not apoptotic. They are located in close contact to apoptotic cells. The number of apoptotic cells in the second trimester (1.8+/-0.7 per cent) is reduced compared to first trimester (5.6+/-0.7 per cent) of uterine pregnancy. In parallel, the number of NK cells declines from first (24.4+/-2.9) to second (12.4+/-1.8) trimester. Furthermore, apoptosis is significantly reduced in ectopic (0.9+/-0.3 per cent) compared to eutopic first trimester pregnancies. Consequently, we suggest that in first trimester uterine pregnancy, induction of EVT cell apoptosis by the maternal immune system is one mechanism to limit EVT invasion. During the second trimester, in parallel to declining numbers of NK cells, the mechanism changes. However, in tubal pregnancy due to differing immunological microenvironments at the ectopic implantation site, apoptosis induction fails, which deleteriously may result in uncontrolled invasion and penetration of the tubal wall.

Immunology of endometriosis

Endometriosis is a benign gynecologic disorder characterized by the ectopic growth of misplaced endometrial cells. A unifying hypothesis to explain endometriosis has not been elucidated as yet but numerous investigations have implicated disturbances in the immune response as fundamental to its etiology and pathogenesis. Clearly, the immune system is involved in endometriosis. It is not clear, however, whether and to what extent this involvement is a primary response leading to the initiation, promotion, and progression of the disease or a secondary response to the ectopic endometrial growth in an attempt to restore homeostasis. Thus, although numerous studies have shown alterations in cell-mediated and humoral immunity in subjects with endometriosis, the importance of these changes remains obscure. This review considers the past two decades of investigation of immune function changes in women with endometriosis with the expectation that this information will ultimately provide the basis for developing new approaches to patient management.

A randomized, double-blind, placebo-controlled trial of heparin and aspirin for women with in vitro fertilization implantation failure and antiphospholipid or antinuclear antibodies

OBJECTIVE

To investigate whether heparin and low-dose aspirin increase the pregnancy rate in antiphospholipid antibody or antinuclear antibody-seropositive women with IVF implantation failure.

DESIGN

A double-blind, randomized, transfer-by-transfer of fresh or cryopreserved embryos, crossover trial.A hospital infertility clinic and associated IVF service.

PATIENT(S)

Women seropositive for at least one antiphospholipid (APA), antinuclear (ANA), or beta(2) glycoprotein I autoantibody and >or=10 embryos transferred without achieving pregnancy (n = 143).

INTERVENTION(S)

Subcutaneous unfractionated heparin (5000 IU b.i.d.) and aspirin (100 mg daily) (158 transfers of 296 embryos) or placebo (142 transfers of 259 embryos) from the day of embryo transfer.

MAIN OUTCOME MEASURE(S)

Fetal heart per embryo transferred (implantation rate).

RESULT(S)

There was no significant difference in pregnancy rates or implantation rates between treated and placebo cycles; for example, fetal hearts per embryo transferred implantation rates were 6.8% (20/296) and 8.5% (22/259), respectively, and the generalized estimating equation covariate adjusted relative pregnancy rate was 0.65 (95% confidence interval, 0.33-1.28). The implantation rate for seropositive trial participants (42/555, 7.6%) compared favorably with that for IVF implantation-failure patients continuing treatment outside the trial (147/3237, 4.5%).

CONCLUSION(S)

Heparin and aspirin did not improve pregnancy or implantation rates for APA-positive or ANA-positive patients with IVF implantation failure.

Some thoughts on the reproductive autoimmune failure syndrome (RAFS) and Th-1 versus Th-2 immune responses

PROBLEM

The concept of immunologically induced reproductive failure has remained very controversial. Especially the question whether abnormal immune function can cause infertility has recently been subject to strong disagreement. This opinion piece is an attempt to reconcile difference of opinion by integrating clinical data from the human experience with well-established experimental models in animals.

METHOD OF STUDY

Review of published literature.

RESULTS

Experimental animal data, especially in the mouse, have suggested that normal pregnancy requires a switch to an immune response with T helper (Th)-2 preponderance. Recent data from the human experience suggest that infertility, repeated pregnancy loss and certain complications of pregnancy may be the consequence of abnormal Th-1 preponderance. In analogy, to animal models, immunologic reproductive failure in humans, may therefore not be the consequence of specific autoantibody abnormalities or natural killer (NK)-cell abnormalities, but the reflection of a misdirection of a more broadly based immune response.

CONCLUSIONS

Under such a model, both diagnosis and treatment of immunologically induced forms of reproductive failure require re-evaluation. Such a model, however, provides a satisfactory explanation for contradictory findings in the human experience that have led to strong disagreements among investigations.