In vivo dendritic cell depletion reduces breeding efficiency, affecting implantation and early placental development in mice

Dendritic Cells and the Establishment of Fetomaternal Tolerance for Successful Human Pregnancy

Pregnancy is a remarkable event where the semi-allogeneic fetus develops in the mother's uterus, despite genetic and immunological differences. The antigen handling and processing at the maternal-fetal interface during pregnancy appear to be crucial for the adaptation of the maternal immune system and for tolerance to the developing fetus and placenta. Maternal antigen-presenting cells (APCs), such as macrophages (Mφs) and dendritic cells (DCs), are present at the maternal-fetal interface throughout pregnancy and are believed to play a crucial role in this process. Despite numerous studies focusing on the significance of Mφs, there is limited knowledge regarding the contribution of DCs in fetomaternal tolerance during pregnancy, making it a relatively new and growing field of research. This review focuses on how the behavior of DCs at the maternal-fetal interface adapts to pregnancy's unique demands. Moreover, it discusses how DCs interact with other cells in the decidual leukocyte network to regulate uterine and placental homeostasis and the local maternal immune responses to the fetus. The review particularly examines the different cell lineages of DCs with specific surface markers, which have not been critically reviewed in previous publications. Additionally, it emphasizes the impact that even minor disruptions in DC functions can have on pregnancy-related complications and proposes further research into the potential therapeutic benefits of targeting DCs to manage these complications.

Energy metabolism and maternal-fetal tolerance working in decidualization

One pivotal aspect of early pregnancy is decidualization. The decidualization process includes two components: the differentiation of endometrial stromal cells to decidual stromal cells (DSCs), as well as the recruitment and education of decidual immune cells (DICs). At the maternal-fetal interface, stromal cells undergo morphological and phenotypic changes and interact with trophoblasts and DICs to provide an appropriate decidual bed and tolerogenic immune environment to maintain the survival of the semi-allogeneic fetus without causing immunological rejection. Despite classic endocrine mechanism by 17 β-estradiol and progesterone, metabolic regulations do take part in this process according to recent studies. And based on our previous research in maternal-fetal crosstalk, in this review, we elaborate mechanisms of decidualization, with a special focus on DSC profiles from aspects of metabolism and maternal-fetal tolerance to provide some new insights into endometrial decidualization in early pregnancy.

Predictive role of endometrial T-bet/GATA3 ratio during mid-luteal phase for live birth in patients undergoing in vitro fertilization: A retrospective observational study

OBJECTIVES

To investigate whether endometrial T-bet (Th1 lineage-committed transcription factor)/GATA3 (Th2 lineage-committed transcription factor) ratio has predictive potential for embryo implantation in infertile women undergoing in vitro fertilization-embryo transfer (IVF-ET).

STUDY DESIGN

We performed a retrospective observational study. In total, this study included 319 infertile women (253 women as the development cohort and 66 women as the validation cohort). Samples were obtained by endometrial scratching in the mid-luteal phase before IVF-ET treatment.

MAIN OUTCOME MEASURES

Immunohistochemistry was utilized to analyze the expression levels of T-bet and GATA3 in the endometrium. Predictive value of endometrial T-bet/GATA3 for live birth were analyzed.

RESULTS AND CONCLUSIONS

In the development cohort, the T-bet/GATA3 ratio was significantly lower in women with live birth than those patients with non-live birth [0.148 (0.101, 0.212) vs. 0.246 (0.170, 0.399), P＜0.0001]. In the validation cohort, changes in endometrial T-bet/GATA3 were similar among these groups. The endometrial T-bet/GATA3 ratio was an independent predictor of live birth after correction for patient age, anti-Mullerian hormone (AMH), quality of embryos transferred and other clinical characteristics (aOR = 0.280, 95 % CI: 0.169-0.462, P＜0.001). We developed and validated that an endometrial T-bet/GATA3 ratio at the cut-off of 0.22 had significant predictive value for live birth (developmental cohort: AUC = 0.76, 95 % CI: 0.70-0.81, P < 0.0001. validation cohort: AUC = 0.85 95 % CI: 0.76-0.95, P < 0.0001). Our results suggest that elevated endometrial T-bet/GATA3 ratio is an independent marker of live birth in infertile patients.

Protective role of IL33 signaling in negative pregnancy outcomes associated with lipopolysaccharide exposure

Interleukin 33 (IL33) signaling has been implicated in the establishment and maintenance of pregnancy and in pregnancy disorders. The goal of this project was to evaluate the role of IL33 signaling in rat pregnancy. The rat possesses hemochorial placentation with deep intrauterine trophoblast invasion; features also characteristic of human placentation. We generated and characterized a germline mutant rat model for IL33 using CRISPR/Cas9 genome editing. IL33 deficient rats exhibited deficits in lung responses to an inflammatory stimulus (Sephadex G-200) and to estrogen-induced uterine eosinophilia. Female rats deficient in IL33 were fertile and exhibited pregnancy outcomes (gestation length and litter size) similar to wild-type rats. Placental weight was adversely affected by the disruption of IL33 signaling. A difference in pregnancy-dependent adaptations to lipopolysaccharide (LPS) exposure was observed between wild-type and IL33 deficient pregnancies. Pregnancy in wild-type rats treated with LPS did not differ significantly from pregnancy in vehicle-treated wild-type rats. In contrast, LPS treatment decreased fetal survival rate, fetal and placental weights, and increased fetal growth restriction in IL33 deficient rats. In summary, a new rat model for investigating IL33 signaling has been established. IL33 signaling participates in the regulation of placental development and protection against LPS-induced fetal and placental growth restriction.

The Immune Atlas of Human Deciduas With Unexplained Recurrent Pregnancy Loss

Recurrent pregnancy loss (RPL) is a common fertility problem that affects 1%-2% of couples all over the world. Despite exciting discoveries regarding the important roles of the decidual natural killer cell (dNK) and regulatory T cell in pregnancy, the immune heterogeneity in patients with unexplained recurrent pregnancy loss (URPL) remains elusive. Here, we profiled the transcriptomes of 13,953 CD45⁺ cells from three normal and three URPL deciduas. Based on our data, the cellular composition revealed three major populations of immune cells including dNK cell, T cell, and macrophage, and four minor populations including monocytes, dendritic cell (DC), mast cell, and B cell. Especially, we identified a subpopulation of CSF1+ CD59+ KIRs-expressing dNK cells in normal deciduas, while the proportion of this subpopulation was decreased in URPL deciduas. We also identified a small subpopulation of activated dDCs that were accumulated mainly in URPL deciduas. Furthermore, our data revealed that in decidua at early pregnancy, CD8⁺ T cells exhibited cytotoxic properties. The decidual macrophages expressed high levels of both M1 and M2 feature genes, which made them unique to the conventional M1/M2 classification. Our single-cell data revealed the immune heterogeneity in decidua and the potentially pathogenic immune variations in URPL.

Functional Ambivalence of Dendritic Cells: Tolerogenicity and Immunogenicity

Dendritic cells (DCs) are the most potent professional antigen-presenting cells (APCs) and inducers of T cell-mediated immunity. Although DCs play a central role in promoting adaptive immune responses against growing tumors, they also establish and maintain peripheral tolerance. DC activity depends on the method of induction and/or the presence of immunosuppressive agents. Tolerogenic dendritic cells (tDCs) induce immune tolerance by activating CD4⁺CD25⁺Foxp3⁺ regulatory T (Treg) cells and/or by producing cytokines that inhibit T cell activation. These findings suggest that tDCs may be an effective treatment for autoimmune diseases, inflammatory diseases, and infertility.

Mifepristone regulates Tregs function mediated by dendritic cells through suppressing the expression of TGF-β

BACKGROUND

Previous studies have demonstrated that mifepristone in the daily low-dose affects the function of endometrium. These researches also implied an alteration of endometrium immune balance, which might be involved in regulating endometrial function. However, the detailed mechanisms remain to be further explored.

METHODS

In this study, the expressions of CD80, CD86, and ICAM-1 in dendritic cells (DCs), which were stimulated with different concentrations of mifepristone (20, 65, and 200 nM), were detected by FACS. After that, we further evaluated the expression of Forkhead box P3 (FOXP3) and IL-10 in Tregs, which co-cultured with mifepristone treated DCs. In mechanism, we compared the indoleamine 2,3-dioxygenase (IDO) and TGF-β expression with enzyme-linked immunosorbent assay (ELISA).

RESULTS

The results indicated that mifepristone promoted the expressions of CD80, CD86, and ICAM-1 in a dosage dependent manner. Reversely, FOXP3 and IL-10 expression levels in Tregs co-cultured with mifepristone-treated DCs were significantly decreased compared with those co-cultured with nontreated DC. Furthermore, a significant reduce in IDO and TGF-β expression was observed in DCs treated with mifepristone. By using the IDO inhibitor (1-methyl tryptophan, 1-MT) or TGF-b supplement, we confirmed that TGF-β, but not IDO could rescue the downregulation of FOXP3 and IL-10 in Tregs co-cultured with mifepristone treated DCs. All of these results suggest that mifepristone may regulate DC function by decreasing TGF-β expression, which further results in the downregulations of FOXP3 and IL-10 in Tregs.

CONCLUSION

Therefore, our research provides a theoretical basis for a potentially clinical application of mifepristone as a novel contraceptive.

Dendritic cells in pregnancy and pregnancy-associated diseases

Dendritic cells (DCs) play a critical immuno-modulating role in pregnancy, which requires the maternal immune system to tolerate semiallogeneic fetus and at the same time to maintain adequate defense against pathogens. DCs interact closely with other immune components such as T cells, natural killer cells and macrophages, as well as the endocrine system to keep a pregnancy-friendly environment. Aberrant DC activities have been related to various pregnancy-associated diseases such as recurrent spontaneous abortion, preterm birth, pre-eclampsia, peripartum cardiomyopathy and infectious pregnancy complications. These findings make DCs an attractive candidate for prevention or therapy on the pregnancy-associated diseases. Here, we review recent findings that provide new insights into the roles of DCs in pregnancy and the related diseases. We also discuss the medical potentials to manipulate DCs in clinics. Whereas this is an emerging area with much work remaining, we anticipate that a better understanding of the role of DCs in maternal-fetal immunotolerance and a therapeutic manipulation of DCs will help women suffering from the pregnancy-associated diseases.

PlGF Immunological Impact during Pregnancy

During pregnancy, the mother’s immune system has to tolerate the persistence of paternal alloantigens without affecting the anti-infectious immune response. Consequently, several mechanisms aimed at preventing allograft rejection, occur during a pregnancy. In fact, the early stages of pregnancy are characterized by the correct balance between inflammation and immune tolerance, in which proinflammatory cytokines contribute to both the remodeling of tissues and to neo-angiogenesis, thus, favoring the correct embryo implantation. In addition to the creation of a microenvironment able to support both immunological privilege and angiogenesis, the trophoblast invades normal tissues by sharing the same behavior of invasive tumors. Next, the activation of an immunosuppressive phase, characterized by an increase in the number of regulatory T (Treg) cells prevents excessive inflammation and avoids fetal immuno-mediated rejection. When these changes do not occur or occur incompletely, early pregnancy failure follows. All these events are characterized by an increase in different growth factors and cytokines, among which one of the most important is the angiogenic growth factor, namely placental growth factor (PlGF). PlGF is initially isolated from the human placenta. It is upregulated during both pregnancy and inflammation. In this review, we summarize current knowledge on the immunomodulatory effects of PlGF during pregnancy, warranting that both innate and adaptive immune cells properly support the early events of implantation and placental development. Furthermore, we highlight how an alteration of the immune response, associated with PlGF imbalance, can induce a hypertensive state and lead to the pre-eclampsia (PE).

Dynamic Changes in the Phenotype of Dendritic Cells in the Uterus and Uterine Draining Lymph Nodes After Coitus

Dendritic cells (DCs) are essential for successful embryo implantation. However, the properties of uterine DCs (uDCs) during the implantation period are not well characterized. In this study, we investigated the dynamic changes in the uDC phenotypes during the period between coitus and implantation. In virgin mice, we evaluated the expressions of CD103 and XCR1, this is the first report to demonstrate uDCs expressing CD103 in XCR1⁺cDC1s and XCR1⁺cDC2s. On day 0.5 post coitus (pc), the number of uterine CD11c⁺CD103^–MHC classII^highCD86^high–mature DCs rapidly increased and then decreased to non-pregnancy levels on days 1.5 and 2.5 pc. On day 3.5 pc just before implantation, the number of CD11c⁺CD103⁺MHC class II^dimCD86^dim–immature DCs increased in the uterus. The increase in mature uDCs on day 1.5 pc was observed in both allogeneic- and syngeneic mating, suggesting that sexual intercourse, or semen, play a role in this process. Meanwhile, the increase in immature uDCs on day 3.5 pc was only observed in allogeneic mating, suggesting that allo-antigens in the semen contribute to this process. Next, to understand the turnover and migration of uDCs, we monitored DC movement in the uterus and uterine draining lymph nodes (dLNs) using photoconvertible protein Kikume Green Red (KikGR) mice. On day 0.5 pc, uDCs were composed of equal numbers of remaining DCs and migratory DCs. However, on day 3.5 pc, uDCs were primarily composed of migratory DCs, suggesting that most of the uDCs migrate from the periphery just before implantation. Finally, we studied the expression of PD-L2—which induces immunoregulation—on DCs. On day 3.5 pc, PD-L2 was expressed on CD103⁺-mature and CD103^–-mature DCs in the uterus. However, PD-L2 expression on CD103^–-immature DCs and CD103⁺-immature DCs was very low. Furthermore, both remaining and migratory DCs in the uterus and uterus-derived-DCs in the dLNs on day 3.5 pc highly expressed PD-L2 on their surface. Therefore, our study findings provide a better understanding of the dynamic changes occurring in uterine DCs and dLNs in preparation for implantation following allogeneic- and syngeneic mating.

T Helper (Th) Cell Profiles in Pregnancy and Recurrent Pregnancy Losses: Th1/Th2/Th9/Th17/Th22/Tfh Cells

During pregnancy, various immune effectors and molecules participating in the immune-microenvironment establish specific maternal tolerance toward the semi-allogeneic fetus. Activated maternal immune effectors by the trophoblast antigens, such as T helper (Th), T cytotoxic (Tc), T regulatory (Treg), and B cells, are involved in the regulation of adaptive immunity. Recognition of active signal through the T cell receptors stimulate the differentiation of naive CD3⁺CD4⁺ T cells into specific T cell subsets, such as Th1, Th2, Th9, Th17, Th22, and follicular Th cells (Tfh). Each of these subsets has a significant and distinct role in human pregnancy. Th1 immunity, characterized by immune-inflammatory responses, becomes dominant during the peri-implantation period, and the “controlled” Th1 immunity benefits the invading trophoblasts rather than harm. Quickly after the placental implantation, the early inflammatory Th1 immunity is shifted to the Th2 anti-inflammatory immune responses. The predominant Th2 immunity, which overrules the Th1 immunity at the placental implantation site, protects a fetus by balancing Th1 immunity and accommodate fetal and placental development. Moreover, Treg and Th9 cells regulate local inflammatory immune responses, potentially detrimental to the fetus. Th17 cells induce protective immunity against extracellular microbes during pregnancy. However, excessive Th17 immunity may induce uncontrolled neutrophil infiltration at the maternal-fetal interface. Other Th cell subsets such as Tfh cells, also contribute to pregnancy by setting up favorable humoral immunity during pregnancy. However, dysregulation of Th cell immunity during pregnancy may result in obstetrical complications, such as recurrent pregnancy losses (RPL) and preeclampsia (PE). With this review, we intend to deliver a comprehensive overview of CD4⁺ Th cell subsets, including Th1, Th2, Th9, Th17, Th22, and Tfh cells, in human pregnancy by reviewing their roles in normal and pathological pregnancies.

Altered Glycosylation Contributes to Placental Dysfunction Upon Early Disruption of the NK Cell-DC Dynamics

Immune cells [e. g., dendritic cells (DC) and natural killer (NK) cells] are critical players during the pre-placentation stage for successful mammalian pregnancy. Proper placental and fetal development relies on balanced DC-NK cell interactions regulating immune cell homing, maternal vascular expansion, and trophoblast functions. Previously, we showed that in vivo disruption of the uterine NK cell-DC balance interferes with the decidualization process, with subsequent impact on placental and fetal development leading to fetal growth restriction. Glycans are essential determinants of reproductive health and the glycocode expressed in a particular compartment (e.g., placenta) is highly dependent on the cell type and its developmental and pathological state. Here, we aimed to investigate the maternal and placental glycovariation during the pre- and post-placentation period associated with disruption of the NK cell-DC dynamics during early pregnancy. We observed that depletion of NK cells was associated with significant increases of O- and N-linked glycosylation and sialylation in the decidual vascular zone during the pre-placental period, followed by downregulation of core 1 and poly-LacNAc extended O-glycans and increased expression of branched N-glycans affecting mainly the placental giant cells and spongiotrophoblasts of the junctional zone. On the other hand, expansion of DC induced a milder increase of Tn antigen (truncated form of mucin-type O-glycans) and branched N-glycan expression in the vascular zone, with only modest changes in the glycosylation pattern during the post-placentation period. In both groups, this spatiotemporal variation in the glycosylation pattern of the implantation site was accompanied by corresponding changes in galectin-1 expression. Our results show that pre- and post- placentation implantation sites have a differential glycopattern upon disruption of the NK cell-DC dynamics, suggesting that immune imbalance early in gestation impacts placentation and fetal development by directly influencing the placental glycocode.

Pregnancy immune tolerance at the maternal-fetal interface

Pregnancy is a natural process that poses an immunological challenge because non-self fetus must be accepted. During the pregnancy period, the fetus as 'allograft' inherits maternal and also paternal antigens. For successful and term pregnancy, the fetus is tolerated and nurtured enjoying immune privileges that minimize the risk of being rejected by maternal immune system. Multiple mechanisms contribute to tolerate the semi-allogeneic fetus. Here, we summarize the recent progresses on how the maternal immune system actively collaborates to maintain the immune balance and maternal-fetal tolerance.

The Interplay Between Reproductive Tract Microbiota and Immunological System in Human Reproduction

In the last decade, the microbiota, i.e., combined populations of microorganisms living inside and on the surface of the human body, has increasingly attracted attention of researchers in the medical field. Indeed, since the completion of the Human Microbiome Project, insight and interest in the role of microbiota in health and disease, also through study of its combined genomes, the microbiome, has been steadily expanding. One less explored field of microbiome research has been the female reproductive tract. Research mainly from the past decade suggests that microbial communities residing in the reproductive tract represent a large proportion of the female microbial network and appear to be involved in reproductive failure and pregnancy complications. Microbiome research is facing technological and methodological challenges, as detection techniques and analysis methods are far from being standardized. A further hurdle is understanding the complex host-microbiota interaction and the confounding effect of a multitude of constitutional and environmental factors. A key regulator of this interaction is the maternal immune system that, during the peri-conceptional stage and even more so during pregnancy, undergoes considerable modulation. This review aims to summarize the current literature on reproductive tract microbiota describing the composition of microbiota in different anatomical locations (vagina, cervix, endometrium, and placenta). We also discuss putative mechanisms of interaction between such microbial communities and various aspects of the immune system, with a focus on the characteristic immunological changes during normal pregnancy. Furthermore, we discuss how abnormal microbiota composition, “dysbiosis,” is linked to a spectrum of clinical disorders related to the female reproductive system and how the maternal immune system is involved. Finally, based on the data presented in this review, the future perspectives in diagnostic approaches, research directions and therapeutic opportunities are explored.

Regulatory mechanisms of endometrial decidualization and pregnancy-related diseases

Endometrial decidualization is one of the earliest changes by which the uterus adapts to pregnancy. During this period, the endometrium undergoes complex changes in its biochemistry, physiology, and function at various levels, providing a suitable microenvironment for embryo implantation and development. Favorable decidualization lays an essential foundation for subsequent gestation, without which pregnancy failure or pregnancy complications may occur. The interaction between pregnancy-related hormones and cytokines produced by embryonic and uterine cells is known to be essential for decidualization, in which some transcription factors also play pivotal roles. Increasing evidence has revealed the importance of metabolism in regulating decidualization. Here, we summarize and discuss these crucial elements in decidualization and the relationship between decidualization and pregnancy complications. A better comprehension of these issues should help to improve the prediction of pregnancy outcomes and the use of appropriate intervention.

Cytochrome c injection induced embryo loss

Cytochrome c has been used as first-aid in the clinic for organs which are lacking oxygen. But recent report show cytochrome c injection destroys dendritic cells (DCs) which play a pivotal role in feto-maternal tolerance. However, it is not clear whether cytochrome c injection causes abortion. The cytochrome c was injected by tail vein of mice at the Day 5.5 of pregnancy (E5.5) after mating with male BALB/c mice. The total number of implantations and resorption sites was recorded at the E12.5 in pregnant mice. Expression of interferon-γ, tumor necrosis-α interleukin (IL)-4, IL-10, IL-12 and transforming growth factor-β in the mouse endometrium was measured by ELISA. Injection of cytochrome c via tail vein at the E5.5 induced fetal resorption at E12.5, and evoked an immune imbalance at the maternal-fetal interface. Notably, injection of mouse bone marrow-derived DCs (BM-DCs) rescued the cytochrome c-evoked embryo resorption. The present study suggests cytochrome c injection causes embryo resorption in mice, hinting caution regarding the use of cytochrome c in pregnant women. In addition, it may provide an easy and novel way to establish a mouse model of abortion.HighlightsCytochrome c injection induced fetal rejection.Cytochrome c injection leads to a T helper 1/T helper 2 imbalance at the maternal-fetal interface.A mouse model of abortion was established by injecting tail vein with cytochrome c.

Uterine Dendritic Cells Modulation by Mesenchymal Stem Cells Provides A Protective Microenvironment at The Feto-Maternal Interface: Improved Pregnancy Outcome in Abortion-Prone Mice

Objective

Dendritic cells (DCs) as major regulators of the immune response in the decidua play a pivotal role in establishment and maintenance of pregnancy. Immunological disorders are considered to be the main causes of unexplained recurrent spontaneous abortions (RSAs). Recently, we reported that mesenchymal stem cells (MSCs) therapy could improve fetal survival and reduce the abortion rate in abortion-prone mice, although the precise mechanisms of this action are poorly understood. Since MSCs have been shown to exert immunomodulatory effects on the immune cells, especially DCs, this study was performed to investigate the capability of MSCs to modulate the frequency, maturation state, and phenotype of uterine DCs (uDCs) as a potential mechanism for the improvement of pregnancy outcome.

Materials and Methods

In this experimental study, adipose-derived MSCs were intraperitoneally administered to abortion-prone pregnant mice on the fourth day of gestation. On the day 13.5 of pregnancy, after the determination of abortion rates, the frequency, phenotype, and maturation state of uDCs were analyzed using flow cytometry.

Results

Our results indicated that the administration of MSCs, at the implantation window, could significantly decrease the abortion rate and besides, increase the frequency of uDCs. MSCs administration also remarkably decreased the expression of DCs maturation markers (MHC-II, CD86, and CD40) on uDCs. However, we did not find any difference in the expression of CD11b on uDCs in MSCs-treated compared to control mice.

Conclusion

Regarding the mutual role of uDCs in establishment of a particular immunological state required for appropriate implantation, proper maternal immune responses and development of successful pregnancy, it seems that the modulation of uDCs by MSCs could be considered as one of the main mechanisms responsible for the positive effect of MSCs on treatment of RSA.

Cytochrome P450 26A1 modulates uterine dendritic cells in mice early pregnancy

Cytochrome P450 26A1 (CYP26A1) plays important roles in the mice peri‐implantation period. Inhibiting its expression or function leads to pregnancy failure. However, little is known about the underlying mechanisms involved, especially the relationship between CYP26A1 and immune cells. In this study, using Cyp26a1‐specific antisense morpholigos (Cyp26a1‐MO) knockdown mice model and pCR3.1‐Cyp26a1 vaccine mice model, we found that the number of uterine CD45⁺CD11c⁺MHCII^lo‐hiF4/80⁻ dendritic cells (DCs) was significantly decreased in the treated mice. The percentage of mature DCs (CD86^hi) was obviously lower and the percentage of immature DCs (CD86^lo) was remarkably higher in uterine DCs in the treatment group than that of the control group. Further experiments found that ID2, a transcription factor associated with DCs development, and CD86, a DC mature marker molecule, were both significantly reduced in mice uteri in the treated group. In vitro, ID2 and CD86 also decreased in bone marrow‐derived DCs under Cyp26a1‐MO treatment. These findings provide novel information that CYP26A1 might affect the embryo implantation via modulating the differentiation and maturation of uterine DCs.

Dydrogesterone: pharmacological profile and mechanism of action as luteal phase support in assisted reproduction

The pharmacological and physiological profiles of progestogens used for luteal phase support during assisted reproductive technology are likely to be important in guiding clinical choice towards the most appropriate treatment option. Various micronized progesterone formulations with differing pharmacological profiles have been investigated for several purposes. Dydrogesterone, a stereoisomer of progesterone, is available in an oral form with high oral bioavailability; it has been used to treat a variety of conditions related to progesterone deficiency since the 1960s and has recently been approved for luteal phase support as part of an assisted reproductive technology treatment. The primary objective of this review is to critically analyse the clinical implications of the pharmacological and physiological properties of dydrogesterone for its uses in luteal phase support and in early pregnancy.

Defective trophoblast invasion underlies fetal growth restriction and preeclampsia-like symptoms in the stroke-prone spontaneously hypertensive rat

STUDY QUESTION

What is the impact of chronic hypertension on placental development, fetal growth and maternal outcome in the stroke-prone spontaneously hypertensive rat (SHRSP)?

SUMMARY ANSWER

SHRSP showed an impaired remodeling of the spiral arteries and abnormal pattern of trophoblast invasion during placentation, which were associated with subsequent maternal glomerular injury and increased baseline hypertension as well as placental insufficiency and asymmetric fetal growth restriction (FGR).

WHAT IS KNOWN ALREADY

A hallmark in the pathogenesis of preeclampsia (PE) is abnormal placentation with defective remodeling of the spiral arteries preceding the onset of the maternal syndrome. Pregnancies affected by chronic hypertension display an increased risk for PE, often associated with poor maternal and fetal outcomes. However, the impact of chronic hypertension on the placentation process as well as the nature of the factors promoting the development of PE in pregnant hypertensive women remain elusive.

STUDY DESIGN, SIZE, DURATION

Timed pregnancies [n = 5] were established by mating 10-12-week-old SHRSP and Wistar Kyoto (WKY, normotensive controls) females with congenic males. Maternal systolic blood pressures (SBPs) were recorded pre-mating, throughout pregnancy (GD1-19) and post-partum by the tail-cuff method. On selected dates, 24 h urine- and blood samples were collected, and animals were euthanized for isolation of implantation sites and kidneys for morphometrical analyses.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The 24 h proteinuria and the albumin:creatinine ratio were used for evaluation of maternal renal function. Renal injury was assessed on periodic acid Schiff, Masson's trichrome and Sirius red stainings. Placental and fetal weights were recorded on gestation day (GD)18 and GD20, followed by determination of fetal cephalization indexes and developmental stage, according to the Witschi scale. Morphometric analyses of placental development were conducted on hematoxylin-eosin stained tissue sections collected on GD14 and GD18, and complemented with immunohistochemical evaluation of isolectin B4 binding for assessment of placental vascularization. Analyses of vascular wall alpha actin content, perforin-positive natural killer (NK) cells and cytokeratin expression by immunohistochemistry were used for evaluation of spiral artery remodeling and trophoblast invasion.

MAIN RESULTS AND THE ROLE OF CHANCE

SHRSP females presented significantly increased SBP records from GD13 to GD17 (SBPGD13 = 183.9 ± 3.9 mmHg, P < 0.005 versus baseline) and increased proteinuria at GD18 (P < 0.01 versus WKY). Histological examination of GD18 kidneys revealed glomerular enlargement and mesangial matrix expansion, which were not evident in pregnant WKY or age-matched virgin SHRSP. At GD20, SHRSP displayed a significant reduction of placental mass (P < 0.01 versus WKY) and signs of placental insufficiency (i.e. hypertrophy and reduced branching morphogenesis of the labyrinth layer), associated with decreased offspring weights and increased cephalization index (both P < 0.001 versus WKY) indicating asymmetric FGR. Notably, SHRSP placentas displayed an incomplete remodeling of spiral arteries starting as early as GD14, with luminal narrowing and reduced densities of perivascular NK cells followed by decreased infiltration of endovascular trophoblasts at GD18.

LARGE SCALE DATA

n/a.

LIMITATIONS, REASONS FOR CAUTION

A pitfall of the present study is the differences in the blood pressure profiles between rats and humans (i.e. unlike pregnancies affected by PE, blood pressure in SHRSP and other hypertensive rat models decreases pre-delivery), which limits extrapolation of the results.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings provide new insights on the role of chronic hypertension as a risk factor for PE by interfering with early events during the placentation process. The SHRSP strain represents an attractive model for further studies aimed at addressing the relative contribution of intrinsic (i.e. placental) and extrinsic (i.e. decidual/vascular) factors to defective spiral artery remodeling in pregnancies affected by PE.

STUDY FUNDING AND COMPETING INTEREST(S)

This work was supported by research grants from Fundación Florencio Fiorini to G.B., from Charité Stiftung to S.M.B. and University of Buenos Aires (UBACyt) to J.T. The authors have no competing interests to declare.

Innate immune cells in the placental bed in healthy pregnancy and preeclampsia

Immune cells in the placental bed are important for adequate development of the placental bed. The most prominent immune cells in the placental bed early in pregnancy are uterine natural killer cells (uNK) cells and macrophages. Also dendritic cells and mast cells can be found in the early placental bed. These cells not only have an immune regulatory function, but are also involved in the regulation of trophoblast invasion, angiogenesis and spiral artery remodeling. In preeclampsia, one of the major complications of pregnancy, decreased trophoblast invasion and spiral artery remodeling has been found. This is associated with decreased numbers of uNK cells, increased numbers of macrophages around the spiral arteries and similar or increased numbers of dendritic cells in the placental bed. In this review, we discuss the current insights in the functions of uNK cells, macrophages, dendritic cells and mast cells in the placental bed in humans during healthy pregnancy and during preeclampsia. As animal models are instrumental in understanding the role of immune cells in the placental bed, we also review studies on the function and phenotype of these innate immune cells in experimental preeclampsia. A better understanding of the dynamics and functional changes of these immune cells in the placental bed may eventually lead to new therapeutic targets for preeclampsia.

Immunometabolism, pregnancy, and nutrition

The emerging field of immunometabolism has substantially progressed over the last years and provided pivotal insights into distinct metabolic regulators and reprogramming pathways of immune cell populations in various immunological settings. However, insights into immunometabolic reprogramming in the context of reproduction are still enigmatic. During pregnancy, the maternal immune system needs to actively adapt to the presence of the fetal antigens, i.e., by functional modifications of distinct innate immune cell subsets, the generation of regulatory T cells, and the suppression of an anti-fetal effector T cell response. Considering that metabolic pathways have been shown to affect the functional role of such immune cells in a number of settings, we here review the potential role of immunometabolism with regard to the molecular and cellular mechanisms necessary for successful reproduction. Since immunometabolism holds the potential for a therapeutic approach to alter the course of immune diseases, we further highlight how a targeted metabolic reprogramming of immune cells may be triggered by maternal anthropometric or nutritional aspects.

Decidualisation and placentation defects are a major cause of age-related reproductive decline

Mammalian reproductive performance declines rapidly with advanced maternal age. This effect is largely attributed to the exponential increase in chromosome segregation errors in the oocyte with age. Yet many pregnancy complications and birth defects that become more frequent in older mothers, in both humans and mice, occur in the absence of karyotypic abnormalities. Here, we report that abnormal embryonic development in aged female mice is associated with severe placentation defects, which result from major deficits in the decidualisation response of the uterine stroma. This problem is rooted in a blunted hormonal responsiveness of the ageing uterus. Importantly, a young uterine environment can restore normal placental as well as embryonic development. Our data highlight the pivotal, albeit under-appreciated, impact of maternal age on uterine adaptability to pregnancy as major contributor to the decline in reproductive success in older females.Advanced maternal age has been associated with lower reproductive success and higher risk of pregnancy complications. Here the authors show that maternal ageing-related embryonic abnormalities in mouse are caused by decidualisation and placentation defects that can be rescued by transferring the embryo from an old to a young uterus.

NK cell-derived IL-10 is critical for DC-NK cell dialogue at the maternal-fetal interface

DC-NK cell interactions are thought to influence the development of maternal tolerance and de novo angiogenesis during early gestation. However, it is unclear which mechanism ensures the cooperative dialogue between DC and NK cells at the feto-maternal interface. In this article, we show that uterine NK cells are the key source of IL-10 that is required to regulate DC phenotype and pregnancy success. Upon in vivo expansion of DC during early gestation, NK cells expressed increased levels of IL-10. Exogenous administration of IL-10 was sufficient to overcome early pregnancy failure in dams treated to achieve simultaneous DC expansion and NK cell depletion. Remarkably, DC expansion in IL-10^−/− dams provoked pregnancy loss, which could be abrogated by the adoptive transfer of IL-10^+/+ NK cells and not by IL-10^−/− NK cells. Furthermore, the IL-10 expressing NK cells markedly enhanced angiogenic responses and placental development in DC expanded IL-10^−/− dams. Thus, the capacity of NK cells to secrete IL-10 plays a unique role facilitating the DC-NK cell dialogue during the establishment of a healthy gestation.

Effect of Acupuncture on Endometrial Angiogenesis and Uterus Dendritic Cells in COH Rats during Peri-Implantation Period

This study was to explore the mechanism of acupuncture on regulating the endometrial angiogenesis and uterus dendritic cells (uDCs) during the peri-implantation period. Rats, in early pregnancy, were randomized into five groups: normal (N), model (M), acupuncture (A), progesterone (P), and A + P groups. The COH model was established using pregnant mare serum, combined with human chorionic gonadotrophin. Endometrium was collected on days 4, 6, and 8 (D4, D6, and D8) of gestation. Compared with group M, both VEGF and FGF-2 protein and mRNA levels were significantly lower on D4 and higher on D6 and D8 (P < 0.05), except for VEGF of group P on D8; the proportion of uterus dendritic cells (uDCs) in the endometrium was significantly lower on D4 and D6 and higher on D8 (P < 0.05). In vitro, except for the proliferation of group P on D8, proliferation, tube formation, and migration of uDCs were significantly decreased on D4 and increased on D8 (P < 0.05). In addition, acupuncture or progesterone regulated the secretion levels of VEGF, IL-15, and IL-18 secreted by uDCs instead of soluble sFLT-1. In conclusion, acupuncture may regulate angiogenesis of the endometrium and the number and roles of uDCs after COH, and the specific mechanism may be different with progesterone.

A study on regional differences in decidualization of the mouse uterus

Although regional differences in mouse decidualization have been recognized for decades, the molecular mechanisms remain understudied. In the present study, by using RNA-seq, we compared transcriptomic differences between the anti-mesometrial (AM) region and the mesometrial (M) region of mouse uterus on day 8 of pregnancy. A total of 1423 differentially expressed genes were identified, of which 811 genes were upregulated and 612 genes were downregulated in the AM region compared to those in the M region. Gene ontology analysis showed that upregulated genes were generally involved in cell metabolism and differentiation, whereas downregulated genes were associated with lymphocyte themes and immune response. Through network analysis, we identified a total of 6 hub genes. These hub genes are likely more important than other genes due to their key positions in the network. We also examined the promoter regions of differentially expressed genes for the enrichment of transcription factor-binding sites. In the end, we demonstrated that a similar regional gene expression pattern can be observed in the artificial decidualization model. Our study contributes to an increase in the knowledge on the molecular mechanisms underlying regional decidualization in mice.

The decidua-the maternal bed embracing the embryo-maintains the pregnancy

The decidua has been known as maternal uterine tissue, which plays essential roles in protecting the embryo from being attacked by maternal immune cells and provides nutritional support for the developing embryo prior to placenta formation. However, there are questions that still remain to be answered: (1) How does the decidua supply nutrition and provide a physical scaffold for the growing embryo, before placental vascular connection is established? (2) How is the balance between preventing an anti-embryo immune response and protecting both embryo and mother from infections established? To understand basic personas in decidual tissues, we review the structure of the decidua composed of terminally differentiated uterine stromal cells, blood vessels, and a number of repertoire of uterine local immune cells, including the well-known uterine natural killer (uNK) cells and recently discovered innate lymphoid cells (ILCs). Decidual macrophages and uterine dendritic cells (DCs) are supposed to modulate adaptive immunity via balancing cytokines and promoting generation of regulatory T (Treg) cells. During decidualization, vascular and tissue remodeling in the uterus provide nutritional and physical support for the developing embryo. Secretion of various cytokines and chemokines from both the embryo and the decidual cells activates multiple signaling network between the mother and the embryo upon implantation. Defects in the decidual development during early pregnancy result in loss of pregnancy or complications in later gestational stage.

Role of Paternal Antigen-Specific Treg Cells in Successful Implantation

Maternal lymphocytes recognize fetal antigens, so tolerance is necessary to prevent rejection. Seminal plasma is important for induction of paternal antigen-specific Treg cells in the uterine draining lymph nodes and the pregnant uterus. Elimination of Treg cells during implantation or early pregnancy induces implantation failure or fetal resorption in mice. Immunosuppressive therapy with an anti-TNF antibody or the immunosuppressive agent tacrolimus improves the pregnancy rate in women with repeated implantation failure and recurrent pregnancy loss of unknown etiology, suggesting that Treg cells play an essential role in successful implantation and pregnancy in humans.

To serve and to protect: the role of decidual innate immune cells on human pregnancy

The maternal-fetal interface undergoes dynamic changes that promote successful development of the embryo/fetal allograft during pregnancy. This immune privilege of the conceptus is mediated through local and systemic cellular responses. In species in which endometrial decidualization accompanies pregnancy, unique immune cell niches are found. Many studies have addressed the enigmatic roles of uterine (u)NK cells as killers and helpers because they are frequently found in the uterine lining and decidua of normal and pathological pregnancies. Accumulating evidence indicates that uNK cells are induced and transformed by sensing signals within their microenvironment to both protect the mother from the fetal allograft and support the fetus during its development. Here, we review the mechanisms that modulate these functions of uNK cells during pregnancy. We suggest that uNK cells must be tightly regulated in order to serve these two roles and support a healthy pregnancy.

Dynamic changes in maternal decidual leukocyte populations from first to second trimester gestation

INTRODUCTION

Decidual leukocytes are critical to the development of the fetomaternal interface, regulating tolerance to the semi-allogeneic fetus and vascular transformation of the uterine spiral arteries. Despite the continuation of these processes beyond the first trimester of pregnancy, the second trimester has largely been unstudied, with investigation focusing on early gestation and term tissues. We sought to characterize changes in decidual leukocyte populations from first to second trimester.

METHODS

Multicolor flow cytometry was performed on isolated decidual leukocytes from elective terminations of pregnancy between 6 and 20 weeks of gestation for study of first (6-12 weeks) and second trimesters (13-20 weeks). Specific subpopulations were identified by comparison to isotype and fluorescent-minus-one (FMO) controls.

RESULTS

Decidual natural killer cells (CD56(+)CD16(-)CD3(-)) did not change in number, although a population of dNK with decreased CD56 brightness was observed in second trimester decidua. CD14(+)HLA-DR(+) macrophage numbers declined from first to second trimester (p = 0.031), yet a CD163(+)CD206(+) subset designating alternatively activated M2-like macrophages increased during the same period (p = 0.015). Intermediate CD205(+) dendritic cells demonstrated significant decline (p = 0.022), but immature CD209(+) and mature CD83(+) dendritic cells did not differ between trimesters. Total CD3(+) and CD3(+)CD4(+) T lymphocytes increased (p = 0.0079, p = 0.0028); CD3(+)CD8(+) T cells trended towards increase but did not differ significantly.

CONCLUSION

Several changes in leukocyte subsets are observed in the second trimester that promote a tolerogenic and angiogenic decidual microenvironment through mid-gestation.

Influence of relative NK-DC abundance on placentation and its relation to epigenetic programming in the offspring

Normal placentation relies on an efficient maternal adaptation to pregnancy. Within the decidua, natural killer (NK) cells and dendritic cells (DC) have a critical role in modulating angiogenesis and decidualization associated with pregnancy. However, the contribution of these immune cells to the placentation process and subsequently fetal development remains largely elusive. Using two different mouse models, we here show that optimal placentation and fetal development is sensitive to disturbances in NK cell relative abundance at the fetal–maternal interface. Depletion of NK cells during early gestation compromises the placentation process by causing alteration in placental function and structure. Embryos derived from NK-depleted dams suffer from intrauterine growth restriction (IUGR), a phenomenon that continued to be evident in the offspring on post-natal day 4. Further, we demonstrate that IUGR was accompanied by an overall reduction of global DNA methylation levels and epigenetic changes in the methylation of specific hepatic gene promoters. Thus, temporary changes within the NK cell pool during early gestation influence placental development and function, subsequently affecting hepatic gene methylation and fetal metabolism.

Liaison between natural killer cells and dendritic cells in human gestation

A successful pregnancy relies on immunological adaptations that allow the fetus to grow and develop in the uterus, despite being recognized by maternal immune cells. Among several immunocompetent cell types present within the human maternal/fetal interface, DC-SIGN(+) dendritic cells (DCs) and CD56(+) natural killer (NK) cells are of major importance for early pregnancy maintenance, not only generating maternal immunological tolerance but also regulating stromal cell differentiation. Previous reports show the presence of NK-DC cell conjugates in first trimester human decidua, suggesting that these cells may play a role in the modulation of the local immune response within the uterus. While effective immunity is necessary to protect the mother from harmful pathogens, some form of tolerance must be activated to avoid an immune response against fetal antigens. This review article discusses current evidence concerning the functions of DC and NK cells in pregnancy and their liaison in human decidua.

Balanced levels of nerve growth factor are required for normal pregnancy progression

Nerve growth factor (NGF), the first identified member of the family of neurotrophins, is thought to play a critical role in the initiation of the decidual response in stress-challenged pregnant mice. However, the contribution of this pathway to physiological events during the establishment and maintenance of pregnancy remains largely elusive. Using NGF depletion and supplementation strategies alternatively, in this study, we demonstrated that a successful pregnancy is sensitive to disturbances in NGF levels in mice. Treatment with NGF further boosted fetal loss rates in the high-abortion rate CBA/J x DBA/2J mouse model by amplifying a local inflammatory response through recruitment of NGF-expressing immune cells, increased decidual innervation with substance P(+) nerve fibres and a Th1 cytokine shift. Similarly, treatment with a NGF-neutralising antibody in BALB/c-mated CBA/J mice, a normal-pregnancy model, also induced abortions associated with increased infiltration of tropomyosin kinase receptor A-expressing NK cells to the decidua. Importantly, in neither of the models, pregnancy loss was associated with defective ovarian function, angiogenesis or placental development. We further demonstrated that spontaneous abortion in humans is associated with up-regulated synthesis and an aberrant distribution of NGF in placental tissue. Thus, a local threshold of NGF expression seems to be necessary to ensure maternal tolerance in healthy pregnancies, but when surpassed may result in fetal rejection due to exacerbated inflammation.

The immune privilege of testis and gravid uterus: same difference?

The fetus in the gravid uterus and the developing spermatogenic cells in the adult testis both comprise special challenges for the host immune system. Protection of the neoantigens of the fetus and male germ cells from immune attack, defined as immune privilege, is fundamental for the propagation of species. Immune privilege is not simply the absence of leukocytes, but involves immune and non-immune cells acting synergistically together at multiple levels to create a unique tolerogenic environment. A number of the pathways are shared by the testis and gravid uterus. Amongst them steroid hormones, namely testosterone in the male and progesterone in the female, seem to function as key molecules that govern the local production of immunoregulatory factors which finally control the overall immune environment.

Myeloid cell alterations in the mouse placenta precede the onset of labor and delivery

OBJECTIVE

Immature myeloid cells (IMCs) are bone marrow-derived cells that normally differentiate into granulocytes, macrophages, and dendritic cells (DCs) but expand in pathological conditions such as malignancy. DCs are antigen-presenting cells that regulate the immune response. Both IMCs and DCs were shown to take part in angiogenesis; however, little is known of their function in the placenta. We sought to determine whether alterations in DC and IMC populations in the placenta precede the onset of delivery.

STUDY DESIGN

Experiments were performed on 6-8 week old C57Bl/6 female mice. Placentas from pregnant mice that were killed on designated days, immunostained using fluorescently labeled anti-CD11b, Gr-1, CD11c, major histocompatibility II (MHCII), and CD45, and analyzed by flow cytometry and immunofluorescent microscopy.

RESULTS

Throughout the latter part of pregnancy toward labor and delivery, the CD45(+)CD11b(+)Gr1(+)-IMC population decreased 29 ± 9.1% (day 12) and 30 ± 9.9% (day 15), vs 21 ± 8.1% (day18, n = 21, 15, and 27; P = .006 and P = .004, respectively), whereas the CD45(+)CD11c(+)MHCII(+)-DC population increased 0.87 ± 0.3% (day 12) and 0.70 ± 0.3% (day 15) vs 1.81 ± 1.3% (day 18, n = 21, 15, and 27, P = .002 and P = .001, respectively). Both myeloid cell populations were localized adjacent to CD31(+) endothelial cells in sites of placental angiogenesis.

CONCLUSION

Labor and delivery are preceded by proangiogenic-myeloid cell alterations, reflected by a decrease in IMCs and an increase in DCs populating the mouse placenta. The intriguing possibility that delivery is preceded by the maturation of IMCs in part into DCs warrants further studies.

From mice to women: the conundrum of immunity to infection during pregnancy

Resistance to infection is the ability of the host to evoke a strong immune response sufficient to eliminate the infectious agent. In contrast, maternal tolerance to the fetus necessitates careful regulation of immune responses. Successful pregnancy requires the maternal host to effectively balance the opposing processes of maternal immune reactivity and tolerance to the fetus. However, this balance can be perturbed by infections which are recognized as the major cause of adverse pregnancy outcome including pre-term labor. Select pathogens also pose a serious threat of severe maternal illness. These include intracellular and chronic pathogens that have evolved immune evasive strategies. Murine models of intracellular bacteria and parasites that mimic pathogenesis of infection in humans have been developed. While human epidemiological studies provide insight into maternal immunity to infection, experimental infection in pregnant mice is a vital tool to unravel the complex molecular mechanisms of placental infection, congenital transmission and maternal illness. We will provide a comprehensive review of the pathogenesis of several infection models in pregnant mice and their clinical relevance. These models have revealed the immunological function of the placenta in responding to, and resisting infection. Murine feto-placental infection provides an effective way to evaluate new intervention strategies for managing infections during pregnancy, adverse fetal outcome and long-term effects on the offspring and mother.

Immunology of the maternal-fetal interface

The immune cells that reside at the interface between the placenta and uterus are thought to play many important roles in pregnancy. Recent work has revealed that the composition and function of these cells are locally controlled by the specialized uterine stroma (the decidua) that surrounds the implanted conceptus. Here, I discuss how key immune cell types (natural killer cells, macrophages, dendritic cells, and T cells) are either enriched or excluded from the decidua, how their function is regulated within the decidua, and how they variously contribute to pregnancy success or failure. The discussion emphasizes the relationship between human and mouse studies. Deeper understanding of the immunology of the maternal-fetal interface promises to yield significant insight into the pathogenesis of many human pregnancy complications, including preeclampsia, intrauterine growth restriction, spontaneous abortion, preterm birth, and congenital infection.

Physiological and molecular determinants of embryo implantation

Embryo implantation involves the intimate interaction between an implantation-competent blastocyst and a receptive uterus, which occurs in a limited time period known as the window of implantation. Emerging evidence shows that defects originating during embryo implantation induce ripple effects with adverse consequences on later gestation events, highlighting the significance of this event for pregnancy success. Although a multitude of cellular events and molecular pathways involved in embryo-uterine crosstalk during implantation have been identified through gene expression studies and genetically engineered mouse models, a comprehensive understanding of the nature of embryo implantation is still missing. This review focuses on recent progress with particular attention to physiological and molecular determinants of blastocyst activation, uterine receptivity, blastocyst attachment and uterine decidualization. A better understanding of underlying mechanisms governing embryo implantation should generate new strategies to rectify implantation failure and improve pregnancy rates in women.

CXCR4(+) dendritic cells promote angiogenesis during embryo implantation in mice

Early pregnancy is characterized by decidual adaption to the developing embryo involving angiogenesis and vascular growth. Failure of decidual vascular expansion is linked to diseases of pregnancy. Dendritic cells (DC) have been associated with vascular growth during early gestation, though it is unknown whether their capacity to modulate angiogenesis is ubiquitous to all DC subsets. Here, we show that DC normally found associated with the decidual vasculature co-express the C-X-C chemokine receptor type 4 (CXCR4). In addition, we demonstrate that impaired homing of CXCR4(+)DC during early gestation provoked a disorganized decidual vasculature with impaired spiral artery remodeling later in gestation. In contrast, adoptive transfer experiments provided evidence that CXCR4(+)DC are able to rescue early pregnancy by normalizing decidual vascular growth and delivery of pro-angiogenic factors, which results in adequate remodeling of the spiral arteries during placental development. Taken together, our results indicate an important role of CXCR4(+)DC in the regulation of decidual angiogenesis and highlight the importance of the CXCL12/CXCR4 pathway during this process, suggesting that this may represent a key pathway to evaluate during pregnancy pathologies associated with impaired vascular expansion.

Uterine NK cells are critical in shaping DC immunogenic functions compatible with pregnancy progression

Dendritic cell (DC) and natural killer (NK) cell interactions are important for the regulation of innate and adaptive immunity, but their relevance during early pregnancy remains elusive. Using two different strategies to manipulate the frequency of NK cells and DC during gestation, we investigated their relative impact on the decidualization process and on angiogenic responses that characterize murine implantation. Manipulation of the frequency of NK cells, DC or both lead to a defective decidual response characterized by decreased proliferation and differentiation of stromal cells. Whereas no detrimental effects were evident upon expansion of DC, NK cell ablation in such expanded DC mice severely compromised decidual development and led to early pregnancy loss. Pregnancy failure in these mice was associated with an unbalanced production of anti-angiogenic signals and most notably, with increased expression of genes related to inflammation and immunogenic activation of DC. Thus, NK cells appear to play an important role counteracting potential anomalies raised by DC expansion and overactivity in the decidua, becoming critical for normal pregnancy progression.

Early expression of pregnancy-specific glycoprotein 22 (PSG22) by trophoblast cells modulates angiogenesis in mice

Mouse and human pregnancy-specific glycoproteins (PSG) are known to exert immunomodulatory functions during pregnancy by inducing maternal leukocytes to secrete anti-inflammatory cytokines that promote a tolerogenic decidual microenvironment. Many such anti-inflammatory mediators also function as proangiogenic factors, which, along with the reported association of murine PSG with the uterine vasculature, suggest that PSG may contribute to the vascular adaptations necessary for successful implantation and placental development. We observed that PSG22 is strongly expressed around the embryonic crypt on Gestation Day 5.5, indicating that trophoblast giant cells are the main source of PSG22 during the early stages of pregnancy. PSG22 treatment up-regulated the secretion of transforming growth factor beta 1 and vascular endothelial growth factor A (VEGFA) in murine macrophages, uterine dendritic cells, and natural killer cells. A possible role of PSGs in uteroplacental angiogenesis is further supported by the finding that incubation of endothelial cells with PSG22 resulted in the formation of tubes in the presence and absence of VEGFA. We determined that PSG22, like human PSG1 and murine PSG17 and PSG23, binds to the heparan sulfate chains in syndecans. Therefore, our findings indicate that despite the independent evolution and expansion of human and rodent PSG, members in both families have conserved functions that include their ability to induce anti-inflammatory cytokines and proangiogenic factors as well as to induce the formation of capillary structures by endothelial cells. In summary, our results indicate that PSG22, the most abundant PSG expressed during mouse early pregnancy, is likely a major contributor to the establishment of a successful pregnancy.

A cross-talk of decidual stromal cells, trophoblast, and immune cells: a prerequisite for the success of pregnancy

Embryo implantation and formation of a functional placenta are complex processes that require a plethora of regulatory mechanisms involving both mother and embryo cells. Recently, an important role in this complicated cells and factors network was assigned to the decidual stromal cells (DSC) and trophoblast cells. Decidualization includes biochemical changes that trigger DSC to produce a number of factors required for the implantation and induction of immunotolerance in maternal immune system. Immunotolerance is achieved by a cascade of strictly controlled events starting with selective homing of immune cells to the feto-maternal site, regulated proliferation, and predominant differentiation into a regulatory type of immune cells. Furthermore, cytotoxic effector functions are reduced owing to the influence of steroid hormones, factors, cytokines, and inhibitory receptors. Altogether the entire immune system of the mother is switched to tolerogenic functional state which is a prerequisite for the successful maintenance of pregnancy.