Decidua-associated suppressor activity and viability of individual implantation sites of allopregnant C3H mice

An update in recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) is defined as three or more consecutive pregnancy losses prior to the 20th week of gestation. The etiology of recurrent spontaneous abortion is often unclear and may be multifactorial, with much controversy regarding diagnosis and treatment. Reasonably accepted etiologic causes include, genetics, anatomical, endocrine, placental anomalies, hormonal problems, infection, smoking and alcohol consumption, exposure to environmental factors, psychological trauma and stressful life event, certain coagulation and immunoregulatory protein defects. Detection of an abnormality in any of these areas may result into specific therapeutic measures, with varying degrees of success. However, the majority of cases of RSA remains unexplained and is found to be associated with certain autoimmune (APA, ANA, ACA, ATA, AECA) and alloimmune (APCA, Ab2, MLR-Bf) antibodies that may play major role in the immunologic failure of pregnancy and may lead to abortion. Alteration in the expression of HLA-G molecules, T-helper-1 (Th-1) pattern of cytokines and natural killer (NK) cells activity may also induce abortion. Various forms of treatment like antithrombotic therapies such as aspirin and heparin, intravenous immunoglobulin (IVIg) therapy, immunotherapy with paternal lymphocytes and vitamin D3 therapy are effective mode of treatment for unexplained cause of fetal loss in women with RSA.

MD-1 is a critical part of the mechanism causing Th1-cytokine-triggered murine fetal loss syndrome

PROBLEM

Fetal loss syndrome (abortion/resorption) occurring on or after gestation day (gd) 9.5 in CBA/JxDBA/2 matings is dependent upon presence of TNF-alpha + IFN-gamma, which act by increasing expression of fg12 prothrombinase at the feto-maternal interface. The magnitude by which the abortion rate can be boosted by an injection of these cytokines on gd 7.5 depends on endogenous rate of loss, and appears to depend on microbial flora. Is cytokine-triggered abortion dependent upon a third signaling pathway that senses 'danger'?

METHODS

Female CBA/J were mated to DBA/2 males and, C57B1/6 and C57B1/6 TNFalphaR1-/-Mak were mated to C57B1/6 control or TNFalphaR1-/-Mak males. LPS from Escherichia coli and Salmonella enteritidis, or the combination of TNF-alpha + IFN-gamma, was injected to stimulate abortions. The effect of anti-MD-1, which interferes with expression of CD14 and, hence, with signaling by LPS via the CD14-tlr4 complex, on TNF-alpha + IFN-gamma was tested. The presence of MD-1 in the uterus was evaluated by in situ hybridization, and effect of lipopolysaccharide (LPS) on mice lacking TNF-alphaR1 was tested.

RESULTS

Anti-MD-1 completely abrogated TNF-alpha + IFN-gamma-induced abortions. MD-1 was expressed on trophoblast and in deciduas on gd 8.5 but LPS could not abort mice that lacked the type 1 receptor for TNF-alpha. Pregnant CBA/J females had classical resorptions (abortions) countable on gd 13.5-14.5 in response to LPS from E. coli or S. enteritidis, but C57B1/6 strain mice resorbed only in response to the latter, and E. coli LPS appeared to induce 'occult' losses. 'Occult' loss did not require TNF-alphaR1.

CONCLUSIONS

TNF-alpha + IFN-gamma could not induce murine abortions without co-presence of a 'danger' signal such as LPS acting via CD14 on toll receptors, and LPS could not act without co-signaling by TNF-alpha. Classical resorptions/abortions and 'occult' losses have a different mechanism in these models as reflected in type of endotoxin and requirement for TNF-alphaR1 signaling.

Thinking outside the box: mechanisms of environmental selective pressures on the outcome of the materno-fetal relationship

PROBLEM

Study of mechanisms causing spontaneous abortion of the vascularized placenta have focused primarily on the feto-maternal immunological relationship within the pregnant mother. The Th1 cytokines such as tumor necrosis factor (TNF)-alpha + interferon (IFN)-gamma derived in part from natural killer (NK) and NKgammadeltaT cells have been implicated in causing abortion via up-regulation of the novel prothrombinase fgl2 at the feto-maternal interface; Th2/3 cytokines such as interleukin (IL)-10, progesterone-induced blocking factor (PIBF), and TGF-beta2 derived from gammadeltaT cells stimulated by embryo antigens in the context of the OX-2 (CD200) tolerance signal have been viewed as counteracting the Th1 effect. These mechanisms are distinct from those causing and preventing occult pregnancy loss during the periimplantation phase of pregnancy prior to development of a vascularized placenta. Spontaneous abortions in the CBA/J x DBA/2 can be boosted by injecting TNF-alpha + IFN-gamma, but the boosted abortion rates can range from < or = 30 to > 80%, depending on the loss rate in uninjected mice, and this is not explainable by the endogenous level of these cytokines. Furthermore, there is a poor correlation between Th1/Th2.3 cytokine ratios and abortion rates. Could there be a third factor involved, and if so, what might this mean?

METHODS

Known precipitants of recurrent abortion in mice were reviewed with particular attention to stress and endotoxin absorption. The effect of antagonizing the response to bacterial lipopolysaccharide (LPS) (endotoxin) was tested. Data on environmental selective pressures were considered (i.e. thinking outside the 'box', which typifies the conventional approach to thinking about materno-fetal interactions).

RESULTS

Th1 cytokine-triggered abortions appear to depend on availability/presence of LPS.

CONCLUSIONS

Environmental selective pressures are implicated in eliminating 'genetically weaker' embryos in early pregnancy.

The emerging role of immunoregulation of fibrinogen-related procoagulant Fgl2 in the success or spontaneous abortion of early pregnancy in mice and humans

PROBLEM

Abortion of chromosomally normal embryos in the CBA X DBA/2 mating combination is triggered by release of Th1 cytokines (tumor necrosis factor [TNF]-alpha, interferon [IFN]-gamma, and interleukin [IL]-1), which cause abortion via a novel prothrombinase, Fgl2, and polymorphonuclear leukocytes. The site of activation may be maternal vascular endothelium on arteries and veins nourishing the placenta. Activation of coagulation is also prominent in spontaneous abortion of chromosomally normal human embryos. We asked where is Fgl2 up-regulated in the uterus in murine abortions, and if similar Fgl2 expression occurs in human pregnancy failure.

METHODS

Control CBA X DBA/2 pregnant mice, or from mice injected with TNF-alpha + IFN-gamma on day 7.5 of gestation, were removed on day 8.5, fixed, sectioned, and subject to in situ hybridization for Fgl2. Sections were also stained for fibrin. Elective first trimester termination samples or biopsies taken early in the course of a recurrent miscarriage were similarly fixed, sectioned, and analyzed by in situ hybridization. Control and cytokine-treated mice were anticoagulated with heparin, an activator of antithrombin III, and/or the direct anti-thrombin inhibitor hirudin.

RESULTS

Low level Fgl2 expression localized to basal decidua remote from the embryo was noted in control mice; cytokine treatment, which causes greater than 80% of abortions, produced a striking up-regulation in this area as well as in a band at the junction of decidua and myometrium. Trophoblast also became strikingly positive. Fgl2 expression was associated with increased fibrin staining. Anticoagulation significantly protected against abortions, but doses were limited by the complication of retroplacental hemorrhage. In tissue from normal first trimester pregnancy, minimal Fgl2 positivity was seen in some villous syncytiotrophoblast, in villous stroma, cytotrophoblast, and in some cells in decidua. In spontaneous abortion of normal embryo, striking Fgl2 positivity was seen in syncytiotrophoblast and extravillous cytotrophoblast, in association with areas of thrombus formation.

CONCLUSIONS

Fgl2 appears to be physiologically expressed and may protect against the internal danger of maternal and/or fetal bleeding during pregnancy and at parturition; a role in inhibiting transplacental traffic is also possible. External dangers in the form of stress, endotoxin, and antigens eliciting Th1 cytokine responses upregulate Fgl2 prothrombinase in trophoblast as well as in decidua, which results in spontaneous abortion of immunogenetically "weaker" embryos.

Why did your mother reject you? Immunogenetic determinants of the response to environmental selective pressure expressed at the uterine level

PROBLEM

Maternal "rejection" of the implanted conceptus is considered to account for a significant proportion of miscarriages (abortions) in both humans and animals. Our understanding of mechanisms has been limited, and hence, explanations for nonrejection have remained largely speculative. Losses, when they occur, could represent either random accidental failure of protective mechanisms or a more purposeful discrimination.

METHOD OF STUDY

An analysis of the most recent data.

RESULTS AND CONCLUSIONS

The embryo is most akin to a parasite, and pregnancy is most akin to a host-parasite interaction. If one excludes chromosome abnormalities in the embryo as a cause of death, activation of coagulation mechanisms, leading to vasculitis affecting the maternal blood supply to the implanted embryo, appears to represent a major loss-causing mechanisms--a form of ischemic autoamputation. Proinflammatory T-helper (Th) 1-type cytokines trigger this process via upregulation of a novel prothrombinase, fgl2. Th2/3 cytokines, such as interleukin (IL)-4, IL-10, and transforming growth factor (TGF)-beta 2, may antagonize the processes involved. Cytokine balance is determined by the genetics of the mother, which regulate her response to stress; endotoxin (LPS); and paternal antigens, selectively expressed on the trophoblast of the embryo, via imprinting. Based on studies in abortion-prone mice, where immunity to paternal alloantigens prevents loss, three distinct gene products in the embryo are proposed to determine the cytokine response to maternal lymphomyeloid cells in the uterus.

Tumor necrosis factor-alpha mRNA-positive cells in spontaneous resorption in rodents

PROBLEM

It has been proposed that high rates of resorption/spontaneous abortion may result from interaction in the decidua of gamma-interferon-producing natural killer (NK) cells and tumor necrosis factor (TNF)-alpha-producing macrophages. An increased release of TNF-alpha from placental tissue of resorptions has been reported, but macrophages producing TNF-alpha have so far not been demonstrated at the feto-maternal interface. Therefore, we have sought to identify TNF-alpha-producing cells by in situ hybridization at the feto-maternal interface in two inbred, well-characterized, and stable strains of laboratory rodents with high and low resorption rates.

METHOD OF STUDY

Pregnant DBA/2-mated CBA/J mice with a resorption rate of 20% to 30% (dependent on NK cells and macrophages) and diabetes-resistant Bio-Breeding/Edinburgh (DR-BB/E) rats with low resorption rates (presumed to result from chromosomal abnormalities) were studied. AsialoGM1+ cells were detected by immunohistochemistry, and TNF-alpha mRNA+ cells were detected by in situ hybridization.

RESULTS

TNF-alpha mRNA+ cells were detected in DBA/2-mated CBA/J mice at the time of resorption but only at the trophoblast-decidual junction. AsialoGM1+ cells were present in decidua, as assessed by immunohistochemistry, but few if any gave a positive signal for TNF-alpha. In rat resorptions, TNF-alpha mRNA-positive cells were present within the yolk sac and in contact with the trophoblast, but not at the trophoblast-decidual junction. In neither species did a significant accumulation of detectable TNF-alpha mRNA+ cells occur before the usual time of onset of resorption.

CONCLUSIONS

In the DBA/2-mated CBA/J mouse, the removal of the placenta is associated with removal of a thin rim of adherent decidua similar to the location of the TNF-alpha mRNA+ cells detected in this study. Our data suggest that increased TNF-alpha in tissues associated with failing feto-placental units may arise from infiltration/activation of scavenger cells from decidua that are likely to be macrophages. Local TNF-alpha production in decidua, which occurs as a prelude to resorption in the CBA x DBA/2 model, could not be detected due to the insensitivity of the TNF-alpha probe we used; the release of TNF-alpha from decidual tissue left after the removal of the placenta does not differ between resorbing and healthy implant sites. AsialoGM1+ cells did not seem to be major producers of TNF-alpha. TNF-alpha mRNA+ cells in a low rate of resorption (rat) model were only found on the fetal side of the trophoblast, and they may also represent a macrophage response (to dying embryo tissue) derived from a nondecidual source. The location of TNF-alpha mRNA+ cells may identify distinct and different mechanisms of resorption in rodents.

Psycho-neuro-cytokine/endocrine pathways in immunoregulation during pregnancy

PROBLEM

Some mammalian pregnancy failure is thought to occur by immunological or immunologically modifiable mechanisms. The original model wherein spontaneous abortion was proposed to represent rejection of the conceptus as an allograft has been supplanted by a model of maternal paraimmunological natural effector cell toxicity to fetal trophoblast more closely related to tumor rejection. The problem is to integrate current information concerning the role of immunological, paraimmunological, endocrinological, and stress-triggered neural factors that determine whether or not abortion will occur.

METHODS

Review of existing data.

RESULTS

An integrated model is proposed.

CONCLUSION

Immunological factors play an important role in abortion processes and prevention of abortions. The existence of abortogenic mechanisms and their regulation appears to be based upon optimizing survival of the species. Two new conceptual models provide a useful framework for further investigation of human pregnancy failure and its treatment.

Transforming growth factor-beta 2-related-decidual suppressor factor is not related to TJ6 protein

Transforming growth factor (TGF)-beta 2-related-decidual suppressor factor (DSF) and TJ6 protein are both immunosuppressive molecules present in murine and human pregnancy. Treatment of mice with either anti-TJ6 or anti-TGF-beta 2 neutralizing antibodies results in increased fetal loss. Western blots of supernatants from pregnant mouse decidua probed with anti-TJ6 (soluble form) showed a doublet at a similar molecular size as when the blot was probed with anti-TGF-beta 2 antibody. The problem is to determine whether TJ6 and DSF are the same protein. In order to determine if TJ6 and DSF are the same or different proteins, we used affinity column purified TGF-beta 2-DSF and stained Western blots with anti-TJ6. The TGF-beta 2-monoclonal antibody affinity column-purified DSF that stained with anti TGF-beta 2 was not reactive with anti-TJ6 antibody. TJ6 has only a 30% gene sequence homology and a 13% amino acid homology to TGF-beta 2. TJ6 and TGF-beta 2-related DSF appear to be different immunosuppressive proteins in decidua.

Progesterone induced blocking factor seen in pregnancy lymphocytes soon after implantation

PROBLEM

The immunomodulatory effect of progesterone (P) in pregnancy manifested via a protein named the P-induced blocking factor (PIBF) was previously reported. The goal of this study was to measure and compare the PIBF expression on lymphocytes between pregnant and non-pregnant women especially in early pregnancy.

METHODS

PIBF expression was determined by immunocytochemistry using a PIBF-specific polyclonal antibody. Levels were assessed during the mid-cycle, luteal phase, and first trimester of pregnancy.

RESULTS

PIBF expression was found in 24.9% of mid-cycle sera, 49% of luteal phase sera of women who failed to conceive, and 75% of luteal phase sera of women who conceived.

CONCLUSIONS

These data indicate that the percentage of PIBF expressing lymphocytes increases as a result of pregnancy and that the stimulus for PIBF induction occurs soon after implantation. These data support the concept that PIBF may play an important role in early implantation possibly by inhibiting the destructive function of natural killer lymphocytes.

A subset of patients with recurrent spontaneous abortion is deficient in transforming growth factor beta-2-producing "suppressor cells" in uterine tissue near the placental attachment site

PROBLEM

To determine if patients with unexplained recurrent miscarriage have a deficiency of decidual immunosuppressor cells that produce transforming growth factor beta type 2, as has been found in mice with abortion due to rejection and/or trophoblast failure.

METHODS

Decidual biopsy specimens were taken as near to the placental attachment site as possible under ultrasound guidance from first trimester legal termination (control) patients with recurrent miscarriage and non-viable pregnancy, and from patients with sporadic missed abortion. The tissue was tested for TGF beta-2+ suppressor cells by in situ hybridization, immunohistochemistry, and analysis of supernatants.

RESULTS

TGF beta-2-related suppressor molecules similar but not identical to those identified in pregnant mice were released by decidual lymphoid cells. Fifty percent of 14 recurrent miscarriage patients showed a lack of suppressor cells and 59% were subnormal in comparison to 20 controls and 5 sporadic miscarriage patients, where 80-85% of the patients had detectable suppressor cells.

CONCLUSIONS

Suppressor cell deficiency is compatible with a role for rejection and/or trophoblast failure in some patients with recurrent miscarriage. Presence of suppressor cells in most patients with missed abortion (4/5) is compatible with an alternative cause of fetal death, similar to findings reported in genetic fetal death mice.

Presence of activated macrophages in a murine model of early embryo loss

PROBLEM

Even though our knowledge of the phenomenon at play at the fetoplacental interface has greatly advanced during the past years, a complete understanding of the reasons why the developing embryo is not rejected by maternal immune effector cells remains largely unknown.

METHODS

We have used immunohistochemistry with the macrophage-specific markers F4/80 and MHC II to study the relationship between decidual infiltration and resorption in murine models of embryo loss between days 6 and 10 of gestation.

RESULTS

Analysis of day 8 CBA/J x DBA/2 pregnancies has revealed 2 distinct populations of embryos. The majority (69.4%) expressed low levels of F4/80+ cells, but a minority (30.6%) expressed much higher level of the macrophage marker. In FBA/J x BALB/c, most embryos (91.7%) expressed low numbers of F4/80+ cells. As earlier experiments established that products of activated macrophages (TNF-alpha and nitric oxide) were implicated in embryo loss in this model, the activation status of the F4/80+ macrophages was assessed through the cell surface expression of MHC II. Again, a similar association was established: 30.6% of the CBA/J x DBA/2 embryos were infiltrated by significantly more MHC II+ cells than the control CBA/J x BALB/c mating. Finally, when coordinate expression of F4/80, MHC II and CD11b was assessed, it was found that an embryo significantly infiltrated by cells bearing one of the 3 markers was also heavily infiltrated by cells bearing the 2 other markers.

CONCLUSIONS

This study has shown that the augmented infiltration of the deciduum with maternal macrophages is an early event which precedes spontaneous abortion of the early embryo.

Is spontaneous resorption in the DBA/2-mated CBA/J mouse due to a defect in "seed" or in "soil"?

PROBLEM

Recurrent spontaneous resorption in DBA/2-mated CBA/J mice has been attributed to damage by NK-lineage cells and TNF-alpha beginning several days after implantation. However, some recent data have suggested CBA/J female mice have a high proportion of preimplantation embryo abnormalities resulting in defective in vitro implantation and impaired trophoblast outgrowth. Could spontaneous abortion be due to a defective embryo ("seed") rather than a hostile post-implantation uterine lining ("soil").

METHOD

Mated CBA/J females were manipulated so as to have high spontaneous abortion rates and a high percent abnormal embryos, or low resorption rates and a low percent abnormal embryos. Embryos from low aborting females were transferred into high aborting female recipients that were pseudopregnant, and vice versa.

RESULTS

Abnormal embryos from females with high abortion rates implanted in low aborting females and did not show any greater tendency to resorb than normally developed embryos in these recipients. By contrast, normal embryos to some extent and abnormal embryos to a much greater extent, gave a high abortion rate when the recipient female was a high aborter.

CONCLUSION

Properties of the "soil" into which embryos implant determines the likelihood of success or failure (abortion). Abnormal pre-implantation embryos can be "rescued" by "good soil"; "sick soil" damages both normal and abnormal embryos. Defining the cellular and molecular mechanisms may be useful in understanding basic mechanisms leading to aborting and nonaborting pregnancy.

Systemic CD56+ cells can predict pregnancy outcome

PROBLEM

To evaluate differences in circulating CD56+ cells between successful and unsuccessful pregnancies, 114 pregnant women were studied prospectively.

METHOD

Seventy women had a history of infertility (INF) and 44 had two or more previous spontaneous abortions (RSA). Among the infertile women, 12 were donor egg recipients (DER) and 15 underwent intracytoplasmic sperm injection (ICSI) for treatment of male factor infertility. Nineteen women were carrying multiple gestations (MG) and 55 had singleton gestations (SG). Thirteen additional women were receiving intravenous immunoglobulin (IVIg).

RESULTS

The percentage of CD56+ cells was determined in 310 blood samples from 114 pregnant women by flow cytometry. The prevalence of women with persistent elevation of percent of 56+ cells (> 12%) was 58% among DER, 73% among ICSI, 37% among MG, 22% among SG, 18% among RSA, and 39% among INF. Thirteen women with SG received IVIG, 10 had CD56+ cells greater than 12% and all 13 experienced live births. Women with percentage CD56+ cells persistently greater than 12% who were not DER, not ICSI, not receiving IVIg, and not carrying MG had a live birth rate of 11%. Women with greater than 12% CD56+ cells had normal karyotype in 78% of concepti studied in contrast to women less than 12% CD56+ cells who had 68% abnormal karyotypes (P = 0.04).

CONCLUSION

Elevated CD56+ cells in pregnant women who are not DER, not ICSI, not receiving IVIg, and not carrying MG predicts loss of a karyotypically normal conceptus with a specificity of 87% and positive predictive value of 78%. While the specificity value of this test is high in both infertile and RSA populations, the sensitivity is 86% in RSA and only 54% in INF suggesting this test does not identify all losses among INF. It may identify a subset of pregnancies at risk for loss of a karyotypically normal embryo that may respond to treatment with IVIg.

The effectiveness of allogeneic leukocyte immunization in unexplained primary recurrent spontaneous abortion. Recurrent Miscarriage Immunotherapy Trialists Group

PROBLEM

Unexplained primary recurrent spontaneous abortion (RSA) can be viewed as a partner-specific problem for which immunization with allogeneic leukocytes is being offered as therapy. Published data from randomized controlled trials have produced conflicting results regarding treatment effectiveness. The aim of this study was to perform a subgroup analysis of the data from a recent worldwide collaborative meta-analysis using the raw data for patients with primary RSA entered into randomized controlled trials of immunotherapy.

METHODS

Data from randomized controlled trials in eight centers were included in this analysis. Individual patients were included only if they had had three or more spontaneous abortions, no previous pregnancy beyond 20 weeks' gestation, no identifiable cause for the abortions, and no evidence of antipaternal antibodies. Meta-analysis by centre and logistic regression analysis were performed to determine the overall effect of treatment in achieving live birth and to identify variables that affect the prognosis for a successful outcome.

RESULTS

In the meta-analysis by center, immunotherapy significantly improved the live birth rate (common odds ratio = 1.94, 95% confidence interval (CI) = 1.20 to 3.12). In the analysis by patient, the likelihood of a successful outcome was also significantly better with treatment (relative risk = 1.46, 95% CI 1.19 to 1.69). The absolute treatment effect was 16.3% producing a number needed to treat of 6. The number of previous abortions had a significant negative correlation with live birth rate, such that for each additional pregnancy loss beyond three, the likelihood of live birth was reduced by 23%.

CONCLUSION

Allogeneic leukocyte immunization is an effective treatment for unexplained primary RSA when pretreatment antipaternal antibodies are absent. Better diagnostic tests are required to identify patients who may derive maximal benefit from this therapeutic approach.

Spontaneous abortion in immunodeficient SCID mice

PROBLEM

Immunodeficient SCID mice on the CB-17 have been used to test the role of "rejection" in a xenogeneic blastocyst transfer model of recurrent miscarriage, but interpretation of the data requires knowing syngeneic within-species matings have a high success rate and do not require immunotrophic factors expected only in immunocompetent non-T-cell deficient mice.

METHOD

Resorption rates were studied in a SCID CB-17 barrier facility that provided the mice used to test the role of immunology in the resorption model.

RESULTS

Spontaneous resorption in syngeneically mated immunodeficient SCID mice on the CB-17 background occurred at an unexpectedly high rate and could not be prevented by treatment with anti-asialo GM1 antibody or GM-CSF, both of which are effective in ameliorating abortion in DBA/2J-mated CBA/J mice. Immunocompetent CB-17 +/+ mice showed an even higher rate of loss. The latter was also not affected by treatment with antiasialo GM1 antibody or by GM-CSF and was not prevented by tetracycline (which is effective in the DBA/2-CBA/J system) or progesterone treatment. Mating experiments showed a scid/+ x scid@+ cross gave the highest rate of loss, and it appeared that the presence of +/(+)-type embryos in the uterus could be augmenting abortion with selective discrimination against scid/scid embryos. High abortion rates were associated both with appearance of a coagulase-negative Staphylococcus sp. in feces and with loss of one component of the SPF flora. Decidual tissue from mated CB-17 +/+ mice showed premature release of TNF-alpha in absence of TGF-beta 2-related suppressor activity, and vascular lesions (fibrinoid necrosis), varying in extent, were associated with both scid/scid x scid/scid and +/+ x +/+ pregnancies. TNF-alpha also appeared prematurely in pregnant scid/scid mice, but the levels were lower (and areas of necrosis smaller than in +/+ x +/+ pregnancies). Outcrossing onto a C57B1/6 background dramatically reduced the abortion rate, indicating an important genetic effect on susceptibility with heterogeneity protecting against abortion.

CONCLUSIONS

SCID mice on the CB-17 background do not have a high rate of successful syngeneic pregnancies, and a TNF-alpha induced vasculopathy may be responsible. Abortion was not caused by immunodeficiency leading to loss of immunotrophism because immunocompetent non-SCID CB-17 mice had a higher rate of loss. Factors augmenting the abortion rate included the presence of embryos of the +/+ genotype in the uterus and treatment with anti-asialo GM1 antibody. Abortion rates were not reduced by treatments effective in the DBA/2-mated CBA/J mouse model but were reduced by re-establishing a new colony with defined flora (a temporary effect) and by outcrossing mice with a different (C57B1/6) background. Together, the data suggest an infectious trigger (identity uncertain) of the vasculopathy and an important genetic influence on susceptibility with heterozygosity and a SCID mouse mutation providing against abortion a degree of protection.

Decidual-trophoblast interactions: decidual lymphoid cell function in normal, anembryonic, missed abortion and ectopic human pregnancy

This study was designed to investigate the consequences of decidua-trophoblast interactions on the phenotype, spontaneous and induced proliferation and immunoregulatory potential of decidual leukocytes in normal pregnancies (NP), anembryonic pregnancies (AP), missed abortions (MA) and ectopic pregnancies (EP). Spontaneous proliferation of decidual non-adherent cells (NAD) from pregnancies with viable trophoblast inside the uterus is significantly higher than proliferation of peripheral blood lymphocytes (PBL) from the same groups (P < 0.001 for NP; P < 0.05 for AP). Spontaneous proliferation of decidual NAD cells from NP was higher (P < 0.001) when compared with AP and EP. The induced (PHA and Con A) responses of PBL from women with normal and pathological pregnancies were significantly higher than that of decidual NAD cells (P < 0.001). Higher proliferation of NAD decidual cells was obtained when Con A-stimulated NP were compared with MA and EP (P < 0.01). The interaction of viable trophoblast with intrauterine decidua appears to be a prerequisite for the activation of NAD suppressor cells, since NAD cells from MA produced stimulation instead of suppression, and NAD cells from EP had no suppressive effect. On the contrary, both NAD and adherent (AD) decidual leukocytes from NP and AP produced very strong suppression of PHA or alloantigen-induced PBL proliferation. The contact between trophoblast and AD decidual leukocytes is not necessary for their suppressive function, since even higher suppression is obtained with the cells from ectopic pregnancies.

Effect of prostaglandin synthesis inhibitors on spontaneous and endotoxin-induced abortion in mice

The putative role of prostaglandin E2 (PGE2) in suppressing rejection of the 'fetal allograft' (resorption) in C3H/HeJ and CBA/J allopregnant mice was tested by administration of the prostaglandin synthesis inhibitors indomethacin (INDO) and acetylsalicylic acid (ASA). When the resorption rate was low, INDO fed at a dose of 15 micrograms/ml in drinking water after implantation had a slight augmenting effect when the endogenous resorption rate was < 30%, but had no effect when the endogenous rate was higher or when bacterial lipopolysaccharide (LPS) was given. ASA fed at 50 micrograms/ml had no augmenting effect and did not increase sensitivity to the abortogen LPS in either CBA/J (LPS sensitive) or C3H/HeJ (LPS resistant) mice. Both INDO and ASA fed to CBA/J mice significantly reduced endogenous PGE2 extractable from the uteri of hormonally pseudopregnant mice after deciduoma induction. Feeding INDO at doses up to 30 micrograms/ml from day 2.5 of pregnancy impaired but failed to completely block implantation in CBA/J mice, and with daily administration, some of the mice became sick: all of the implants in sick mice resorbed. INDO at doses of 150-200 micrograms per day known to inhibit implantation in vivo by sufficiently blocking PGE2 synthesis, was injected on one or more days beginning after the time of implantation. This failed to cause abortion in CBA/J mice and although some mice became ill, provided this happened after day 8.5 of pregnancy when sensitivity to the abortogenic effects of injected LPS decreased substantially in these mice, all implants in the sick mice were 'healthy' (i.e. non-resorbing). We were unable to increase the rate of resorption in syngeneically pregnant CD1 mice above 13% with 15 ml INDO in drinking water. Our data do not support the view that PGE2 represents an important intrauterine suppressor molecular blocking the processes mediating embryo death at the time of abortion. Spontaneous abortion in DBA/2-mated CBA/J mice appears to be determined by the level of bacterial LPS (endotoxin) and treatment with antibiotics or intralipid (which enhances endotoxin clearance), reduces the abortion rate. A sufficient dose of INDO may cause abortion, but the data taken together suggest this may be due to effects on the gut whereby permeability to bacterial LPS is increased.

Murine trophoblast failure and spontaneous abortion

PROBLEM

Infection has been proposed to initiate abortion, and the role of viruses in spontaneous resorption in mice has not been tested.

METHOD

The anti-viral drug ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) was fed to CBA/J and C3H/HeJ female mice beginning on the morning after mating with DBA/2J males.

RESULTS

Ribavirin treatment increased the rate of abortion (resorption) on day 13.5, and this was associated with retardation of the rate of embryo development and hypoplasia of the trophoblast. There was a reduction in trophoblast-dependent decidua-associated soluble suppressor activity, but there was no maternal mononuclear cell infiltrate of the type reported in association with resorption of semiallogeneic and xenogeneic mouse embryos. This may be due to an immunosuppressive effect of ribavirin. Ribavirin was able to potently suppress proliferation of mouse trophoblast and mastocytoma cell lines in vitro.

CONCLUSIONS

There are several drug-induced murine abortion models that provide useful insights into potential mechanisms underlying spontaneous pregnancy failure, but in the ribavirin mode, a direct impairment of trophoblast development appears to be responsible.

Stress-triggered abortion in mice prevented by alloimmunization

PROBLEM

To determine if immunotherapy can prevent abortion triggered by mechanisms that in humans may be treatable by psychotherapy.

METHOD

The effects of alloimmunization against paternal strain antigens were tested in pregnant mice subjected to stress.

RESULTS

Restraint stress boosted the resorption rate assessed on day 13.5 of pregnancy in DBA/2-mated C3H/HeJ mice with an optimal effect on day 4.5 of pregnancy, and premating alloimmunization greatly reduced the effect. By contrast, CBA/J and A/J mice proved resistant to abortion boosting by restraint stress. A/J mice mated to DBA/2 or C3H/HeJ males showed reduced fertility, perhaps due to failure of pregnancy immediately after the stress, but this was not corrected by alloimmunization with either DBA/2 [class I + class II major histocompatibility complex (MHC) immunogen] or C3H/HeJ (class I MHC immunogen) splenocytes. There was a reduction in the endogenous resorption rate, however, and implantation number was slightly increased by preimmunization using DBA/2 cells. The abortion rate could be boosted, however, by ultrasonic noise stress of high abortion rate CBA/J, and preimmunization using BALB/c (H-2d) splenocytes protected. A similar boosting of loss in low abortion rate BALB/k mice was ameliorated (albeit not completely) by preimmunization with allogenic paternal but not syngeneic splenocytes.

CONCLUSIONS

Immunotherapy may protect against a variety of potential triggers of spontaneous abortion, including those that may be amenable to psychological remedies, and possible mechanisms are discussed.

Further evaluation of the pregnancy-linked down-regulation of the paternal antigen-specific splenic cytotoxic T lymphocyte activity in allogeneically pregnant mice

Cytotoxic T lymphocyte (CTL) activity directed against paternal alloantigen was examined in allogeneically pregnant mice using various allogeneic combinations. The spleen cells from pregnant C57BL/6 (H-2b) mice mated with BALB/c (H-2d) male mice generated less anti-H-2d CTL after in vitro sensitization than those from unpregnant or syngeneically mated C57BL/6 mice. Different allogeneic combinations including the incompatibility at only D region of H-2 or minor histocompatibility loci were effective for downregulating the anti-paternal CTL activity in pregnancy. The downregulation of anti-paternal CTL activity induced by allogeneic pregnancy occurred at day 10 to day 18 of pregnancy, most extensively at day 14. The allogeneic pregnancy also downregulated the allogeneic CTL activities that had been amplified by injecting alloantigens before mating.

In vitro and in vivo immunosuppressive effects of supernatants from human choriocarcinoma cell lines

Local immunosuppression mediated by placental suppressor factors may contribute to the absence of consistently demonstrable cellular immunity against the fetus. In this context, we have investigated the immunosuppressive capabilities of supernatants from human trophoblastic choriocarcinoma cell lines (HCS) by testing the effects of HCS on immune responses in vitro and in vivo in the human and murine systems. HCS suppresses mitogen-induced proliferation and mixed lymphocyte reactions in humans and in mice, as well as antigen-induced T cell proliferation in mice. HCS also suppresses the in vivo response of mice to allogeneic cells. Furthermore, HCS when injected intraperitoneally causes the induction of suppressor cells in mice which in turn prevent the mounting of an allogeneic response in other strains of mice. These results indicate that human choriocarcinoma cell lines secrete a suppressor factor(s) which induces suppression in vitro as well as in vivo through the generation of suppressor cells.