Ecology of Danger-dependent Cytokine-boosted Spontaneous Abortion in the CBA × DBA/2 Mouse Model. I. Synergistic Effect of LPS and (TNF-α + IFN-γ) on Pregnancy Loss

Tolerance signaling molecules and pregnancy: IDO, galectins, and the renaissance of regulatory T cells

PROBLEM

Is the concept of maternal tolerance preventing rejection of the semi-allogeneic 'fetal allograft' still valid?

METHOD OF STUDY

Compilation of expert reviews of literature and recent advances in research on indoleamine-2,3 dioxygenase (IDO), regulatory T cells and galectin-1.

RESULTS AND CONCLUSION

A role for IDO in pregnancy success remains speculative, but solid data exist to support a role for Treg cells, and for galectin-1 in induction and action of Treg cells. Just as several signals may need to be simultaneously present to induce Th1 cytokine-triggered abortions, more than 1 signal may need to be simultaneously present to prevent rejection and ensure success. Both complement and coagulation pathways appear necessary for embryo execution.

Preeclampsia: a view through the danger model

Classical thinking suggests that the immune system undergoes activation on the basis of discrimination between 'self' and 'non-self'. Accordingly, the fetus activates the mother's immune system because the fetus is in part 'non-self'. Thus, successful pregnancy depends on constraint of maternal immunity. Preeclampsia is an outcome of lost constraint. Instead, the danger model suggests that normal pregnancy, regardless of the expression of 'non-self' antigens, does not activate the maternal immune system unless that pregnancy expresses danger signals. Thus, preeclampsia stems from stress or abnormal cell death in pregnancy-related tissues. This compels expression of specific danger signals and potential activation of anti-fetal immunity, which secondarily feeds the syndrome. Study of preeclampsia from this perspective may bring forth novel mechanisms and indicators of vascular and metabolic dysfunction during pregnancy.

Nitric oxide mediates prostaglandins' deleterious effect on lipopolysaccharide-triggered murine fetal resorption

Genital tract bacterial infections could induce abortion and are some of the most common complications of pregnancy; however, the mechanisms remain unclear. We investigated the role of prostaglandins (PGs) in the mechanism of bacterial lipopolysaccharide (LPS)-induced pregnancy loss in a mouse model, and we hypothesized that PGs might play a central role in this action. LPS increased PG production in the uterus and decidua from early pregnant mice and stimulated cyclooxygenase (COX)-II mRNA and protein expression in the decidua but not in the uterus. We also observed that COX inhibitors prevented embryonic resorption (ER). To study the possible interaction between nitric oxide (NO) and PGs, we administered aminoguanidine, an inducible NO synthase inhibitor. NO inhibited basal PGE and PGF(2alpha) production in the decidua but activated their uterine synthesis and COX-II mRNA expression under septic conditions. A NO donor (S-nitroso-N-acetylpenicillamine) produced 100% ER and increased PG levels in the uterus and decidua. LPS-stimulated protein nitration was higher in the uterus than in the decidua. Quercetin, a peroxynitrite scavenger, did not reverse LPS-induced ER. Our results suggest that in a model of septic abortion characterized by increased PG levels, NO might nitrate and thus inhibit COX catalytic activity. ER prevention by COX inhibitors adds a possible clinical application to early pregnancy complications due to infections.

Toll-like receptor 3 agonist enhances IFN-gamma and TNF-alpha production by murine uterine NK cells

To understand the response of murine uterine natural killer (uNK) cells to Toll-like receptor (TLR) 3 agonist at the early gestation stage, CBA x DBA/2 mice were intraperitoneally (i.p.) injected with polyinosinic-polycytidylic acid (poly I:C), the specific TLR3 agonist, at a dose of 10 microg/g BW or PBS at gestation day (gd) 6.5. The CD69 expression of uNK (DX5(+)CD3(-)) cells was highly up-regulated and reached 92.3+/-0.9%, the percentage of intracellular TNF-alpha(+) or IFN-gamma(+) uNK (DX5(+)CD3(-)) cells in the implantation sites of CBAxDBA/2 matings was also significantly increased 24 h after poly I:C injection. Surprisingly, poly I:C treatment significantly decreased the total number of uNK cells (either DX5(+)CD3(-) or DBA(+)) at fetal-maternal surface, but had no influence on local NKT cells, T cells and DCs. This investigation will help to explain the central role for hyperactivated uNK cells in the progress of mice pregnancy.

Uterine natural killer cells: a specialized differentiation regulated by ovarian hormones

In adult females of many species, a transient population of natural killer (NK) cells appears in cycles within the uterine endometrium (lining). Appearance of these lymphocytes coincides with specific phases of the ovarian hormone cycle and/or early pregnancy. Studies in rodents, women, and pigs dominate the literature and suggest the uterine (u)NK cells are an activated subset sharing many but not all features with circulating or lymphoid organ-residing NK cells. During successful murine pregnancy, uNK cells appear to regulate initiation of structural changes in the feed arterial systems that support maternal endometrial tissue at sites of implantation and subsequent placental development. These changes, which reverse after pregnancy, create a higher volume arterial bed with flaccid vessels unresponsive to vasoactive compounds. These unique pregnancy-associated arterial changes elevate the volume of low-pressure, nutrient-rich, maternal arterial blood available to conceptuses. Regulation of the differentiation, activation, and functions of uNK cells is only partially known, and there is lively debate regarding whether and how uNK cells participate in infertility or spontaneous abortion. This review highlights the biology of uNK cells during successful pregnancy.

Toll-like receptor 3 agonist induces impairment of uterine vascular remodeling and fetal losses in CBA x DBA/2 mice

The objective of this study was to examine the expression of Toll-like receptor (TLR) 3 at the maternal-fetal interface and determine whether exposure to TLR3 agonist would induce an innate immune response and trigger pregnancy loss. To address this, abortion-prone male DBA/2J mated-CBA/J female mice were given polyinosinic-polycytidylic acid (poly I:C; 10 microg/g body weight, i.p.) or PBS at gestation day (gd) 6.5. All implantation sites appeared viable at gd 7.5 when endometrium was dissected for immunohistological examination. It was noted that poly I:C treatment increased fetal losses to 40.2+/-1.7% at midgestation stage compared with control animals (11.0+/-3.0%). It was observed also that the ratio of vessel to lumen area significantly increased at gd 10.5 and gd 12.5 after poly I:C treatment, indicating that the spiral artery (SA) modification was impaired. Meanwhile, 24h after poly I:C injection, expression of TLR3 was markedly elevated within decidua basalis (DB), and endometrial TNF-alpha increased 2.7-fold but IFN-gamma remained unchanged in homogenized endometrium. These results suggest that enhanced TNF-alpha expression in endometrial stroma may play a critical role in inflammatory factor production and impairment of uterine spiral artery remodeling in the pregnancy failure of CBA x DBA/2 mating.

Toll-like receptor 4 polymorphisms and idiopathic chromosomally normal miscarriage

BACKGROUND

Lipopolysaccharide (LPS or endotoxin) exposure resulting from microbial invasion of the endometrium disturbs the Th1/Th2 balance at the feto-maternal interface and has been linked to the risk of idiopathic miscarriage in a range of human and animal studies. Toll-like receptor 4 (TLR4) mediates LPS signalling, and the human TLR4 gene harbours two single-nucleotide polymorphisms (SNPs) known to reduce LPS responsiveness. We hypothesized that genetic variation altering TLR4 function may influence the risk of idiopathic pregnancy loss.

METHODS AND RESULTS

We examined fetal TLR4 genotypes in a case-control cohort of chromosomally normal miscarriages (n=96) and healthy term newborns (n=113). The allele frequencies of the Asp299Gly and Thr399Ile TLR4 SNPs were determined by quantitative PCR using DNA extracted from extraembryonic tissues and umbilical cord blood, respectively. TLR4 genotype frequencies were not significantly different between cases and controls.

CONCLUSIONS

There was no association between fetal TLR4 polymorphisms, Asp299Gly and Thr399Ile, known to blunt LPS responsiveness, and the risk of idiopathic, chromosomally normal miscarriage. Nevertheless, TLR4 or perhaps other LPS-binding chaperone molecules are biologically plausible candidate genes that may alter the risk of idiopathic miscarriage.

Reduced uterine indoleamine 2,3-dioxygenase versus increased Th1/Th2 cytokine ratios as a basis for occult and clinical pregnancy failure in mice and humans

PROBLEM

Indoleamine 2,3-dioxygenase (IDO) expression in fetal trophoblast and decidual antigen-presenting cells has been proposed to inactivate maternal T cells and thereby prevent rejection of the "fetal allograft" in early pregnancy. Psychic stress has been proposed to cause miscarriages as well as infertility, at the same time in pregnancy when blockade of IDO causes loss, but the suggested mechanism of stress-triggered loss has been an increased ratio of pro-rejection Th1-type cytokines to anti-rejection Th2/3 cytokines. Could stress act by reducing IDO expression?

METHODS

Using DBA/2-mated A/J mice where stress causes early pregnancy failure, we examined the role of stress in reducing IDO versus increasing Th1/Th2 ratio in deciduas. IDO loss was also examined in human decidua associated with pregnancy failure.

RESULTS

A post-implantation sonic stress increased the pregnancy failure rate, increased the Th1/Th2 ratio, but did not reduce IDO. IDO was reduced, and Th1/Th2 ratios increased in A/J mice pre-immunized against paternal DBA/2 antigens, and concomitant stress increased these effects. The rate of pregnancy failure was not further increased consistent with recent discoveries of factors that limit the impact of Th1 cytokines at the feto-maternal interface. In deciduas from spontaneous miscarriage patients, IDO(+) cell frequencies were low in only 30% of patients. CD3(+) T-cell numbers and percentage terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end-labelling (TUNEL)(+) apoptotic T cells were increased, but the level of IDO did not correlate with likelihood of apoptosis.

CONCLUSIONS

Loss of an allogeneic embryo in early pregnancy is more likely to be due to a high Th1/Th2 ratio than loss of putative protection by IDO.

Cytokine-Induced Hepatic Apoptosis Is Dependent on FGL2/Fibroleukin: The Role of Sp1/Sp3 and STAT1/PU.1 CompositecisElements

Previous studies from our laboratory have shown that fulminant hepatitis caused by the mouse hepatitis virus, MHV-3, is dependent on production of the novel immune coagulant fgl2/fibroleukin. In this study, we investigate the role of IFN-gamma and TNF-alpha in the induction of fgl2 expression and fgl2-dependent hepatic apoptosis. Infusion of IFN-gamma in combination with TNF-alpha through the portal vein of fgl2+/+ mice led to widespread hepatic apoptosis and fibrin deposition. Livers from fgl2-/- mice were normal, although strong expression of the fgl2 knockout reporter gene Lac Z was seen in both resident hepatic macrophages and endothelial cells. In vitro, IFN-gamma and TNF-alpha induced fgl2 expression in a macrophage and endothelial cell-specific manner. In macrophages (peritoneal and RAW 264.7 cells), IFN-gamma, but not IFN-alpha, LPS, TNF-alpha, or IL-1 induced fgl2 mRNA transcription and protein expression, while in endothelial cells TNF-alpha, but not IFN-gamma, induced fgl2 transcription. In addition, while TNF-alpha enhanced IFN-gamma-induced macrophage fgl2 transcription, IFN-gamma also enhanced TNF-alpha-induced endothelial cell fgl2 transcription. The induction of fgl2 by IFN-gamma in macrophages involved a STAT1-dependent pathway, involving the composite cis elements Sp1/Sp3 and GAS/PU.1. The latter interacted with IFN-gamma-dependent Sp1/Sp3, STAT1, and the ETS family of transcription factors member PU.1. The interaction of PU.1 with the IFN-gamma-activated sequence/ETS family of transcription factors site determined the macrophage-specific induction of fgl2 by IFN-gamma. Overall, this study demonstrates that IFN-gamma and TNF-alpha induce hepatocyte apoptosis in vivo, which is dependent on induction of fgl2, and defines the molecular basis of transcription of fgl2 in vitro.

Is intravenous immunoglobulins (IVIG) efficacious in early pregnancy failure? A critical review and meta-analysis for patients who fail in vitro fertilization and embryo transfer (IVF)

PROBLEM

Intravenous Immunoglobulins (IVIG) are widely used off label in the treatment of early reproductive failure. As IVIG is expensive, and may have side-effects, evidence of efficacy is needed. Previous results have suggested that the pre-conception treatment of primary recurrent abortion patients might be effective, but the data set has been too small for adequate statistical power. More recently it has been suggested that IVIG may improve the success rate of in vitro fertilization and embryo transfer (IVF) in patients with prior IVF failures, but clinical trials have given conflicting results that need explanation. Systematic reviews generating inconclusive results have focused on methodological rigor to the exclusion of biological plausibility.

METHODS

Review of current basic science of design, measurement, and evaluation of clinical trials and basic science mechanisms providing a rationale for treatment. Meta-analysis of published randomized controlled and cohort-controlled trials (updated with two unpublished data sets) evaluating IVIG treatment in IVF failure patients. Live birth rate was used as the most relevant endpoint. The ability of different sources of IVIG to suppress natural killer (NK) cell activity was determined using a standard (51)Cr-release assay in vitro.

RESULTS AND CONCLUSIONS

Meta-analysis of three published randomized controlled trials (RCTs) of IVIG in IVF failure patients shows a significant increase in the live birth rate per woman (p = 0.012; Number Needed to Treat for 1 additional live birth, NNT = 6.0 women). Using live birth rate per embryo transferred, and adding data from two cohort-controlled trials to the meta-analysis further supports this conclusion (overall p = 0.000015, NNT = 3.7 women). Relevant variables appear to include properties and scheduling of the IVIG, and selection of patients with abnormal immune test results. Different IVIG preparations vary significantly in their ability to suppress NK activity in vitro. A rationale for use of IVIG is provided by a review of mechanisms of IVIG action and mechanisms underlying failure of chromosomally normal embryos.