Placental fractalkine mediates adhesion of THP-1 monocytes to villous trophoblast

CX3CL1 (Fractalkine): An important cytokine in physiological and pathological pregnancies

C-X3-C motif chemokine ligand 1 (CX3CL1), commonly known as Fractalkine, is an important chemokine with dual functions of chemotaxis and adhesion. It plays a pivotal role in a variety of physiological processes and pathological conditions, particularly in conjunction with its receptor, C-X3-C motif chemokine receptor 1 (CX3CR1). This review focuses on the expression and intricate regulatory mechanisms of CX3CL1 at the maternal-fetal interface, emphasizing its multifaceted role during pregnancy. CX3CL1 was detected in the trophoblast and decidua tissues, playing a crucial role in recruitment of immune cells, enhancing endometrial receptivity, and modulating trophoblast cell activities. Abnormal expression of CX3CL1 has been correlated with adverse pregnancy outcomes such as spontaneous abortion, gestational diabetes, preeclampsia, and preterm births. By elucidating the complex interplay of CX3CL1 at the maternal-fetal interface, this review aims to shed light on its potential roles in pregnancy-related complications.

High expression of CX3CL1/CX3CR1 at the mother-fetus interface of preeclampsia inhibits trophoblast invasion and migration

INTRODUCTION

Preeclampsia is associated with maternal inflammatory overreaction and imbalanced immunity at the mother-fetus interface. The pro-inflammatory chemokine fractalkine (CX3CL1) is recently recognized apart from imbalanced immunity. In this study, CX3CL1- CX3C chemokine receptor 1(CX3CR1) regulation of decidual macrophage function and trophoblast invasion ability in preeclampsia was initially explored.

METHODS

The study comprised 60 women allocated to NP group (normotensive pregnant woman, n = 30) and sPE group (woman with severe preeclampsia, n = 30). After the delivery, the expression of CX3CL1 in placental tissues of the two groups was detected by immunohistochemical analysis. The protein level of CX3CL1 in placental tissue and CX3CR1 in decidua tissue was detected by Western Blot and the localization of CX3CR1 expression in decidua was detected by immunofluorescence. Macrophages were polarized into classically activated (M1) macrophages. M1 were treat with PBS (control group), recombinant human CX3CL1 (CX3CL1 group), recombinant human CX3CL1+ selective CX3CR1 antagonist-JMS-17-2 (CX3CL1+anti-CX3CR1 group) and recombinant human CX3CL1 + selective CX3CR1 antagonist-JMS-17-2 + VS-6063 (CX3CL1+anti-CX3CR1+ FAK inhibitor group). M1 and HTR8/SVneo cells were co-cultured as described previously to assess invasion and migration capacity by transwell assays and Wound-healing assay.

RESULTS

In this study, CX3CL1 expression is high in the placental tissues of severe preeclampsia (sPE) patients than in normotensive pregnancies (NP). CX3CR1 expression is high in the decidual tissues of severe preeclampsia patients and mainly expressed in macrophages of decidual tissues. CX3CL1/CX3CR1 decreased VEGF expression in M1 macrophages and reduced the invasion and migration function of HTR-8/SVneo through the FAK signaling pathway.

DISCUSSION

These findings revealed that CX3CL1-CX3CR1 regulate the trophoblast function by FAK and provided new insights into the pathogenesis of preeclampsia.

CX3CL1 (Fractalkine)-CX3CR1 Axis in Inflammation-Induced Angiogenesis and Tumorigenesis

The chemotactic cytokine fractalkine (FKN, chemokine CX3CL1) has unique properties resulting from the combination of chemoattractants and adhesion molecules. The soluble form (sFKN) has chemotactic properties and strongly attracts T cells and monocytes. The membrane-bound form (mFKN) facilitates diapedesis and is responsible for cell-to-cell adhesion, especially by promoting the strong adhesion of leukocytes (monocytes) to activated endothelial cells with the subsequent formation of an extracellular matrix and angiogenesis. FKN signaling occurs via CX3CR1, which is the only known member of the CX3C chemokine receptor subfamily. Signaling within the FKN-CX3CR1 axis plays an important role in many processes related to inflammation and the immune response, which often occur simultaneously and overlap. FKN is strongly upregulated by hypoxia and/or inflammation-induced inflammatory cytokine release, and it may act locally as a key angiogenic factor in the highly hypoxic tumor microenvironment. The importance of the FKN/CX3CR1 signaling pathway in tumorigenesis and cancer metastasis results from its influence on cell adhesion, apoptosis, and cell migration. This review presents the role of the FKN signaling pathway in the context of angiogenesis in inflammation and cancer. The mechanisms determining the pro- or anti-tumor effects are presented, which are the cause of the seemingly contradictory results that create confusion regarding the therapeutic goals.

Culture and Maintenance of Immune Cells to Model Innate Immune Status at the Feto-maternal Interface

The inflammatory process leading to human labor is mostly facilitated by immune cells, which can be studied by isolating and characterizing primary immune cells from the feto-maternal interface. However, difficulty and inconsistency in sampling approaches of immune cells and short lifespan in vitro prevent their usage in mechanistic studies to understand the maternal-fetal immunobiology. To address these limitations, existing cell line models can be differentiated into immune-like cells for use in reproductive biology experiments. In this chapter, we discussed cell culture methods of maintaining and differentiating HL-60, THP-1, and NK-92 cells to obtain neutrophil-like, macrophage-like, and decidual natural killer-like cells, respectively, which can then be used together with intrauterine cells to elucidate and investigate immune mechanisms that contribute to parturition.

Immune checkpoint molecules B7-1 and B7-H1 as predictive markers of pre-eclampsia: A case-control study in a Ghana

BACKGROUND/AIM

Immune tolerance in the fetal-maternal junction is maintained by a balance in the Th1/Th2 system. Th1-type immunity is associated with pro-inflammatory cytokines and immune checkpoint molecules (ICMs) such as B7-H1, while Th2-type immunity is characterized by anti-inflammatory cytokines and ICMs such as B7-1. Any imbalance in the Th1/Th2 immune system may lead to adverse pregnancy outcomes such as pre-eclampsia (PE). Hitherto, the potential of serum B7-1 and B7-H1 proteins as early markers of PE has not been explored in the Ghanaian population.

MATERIALS AND METHODS

This was a case-control study from May 2020 to April 2022 at the War Memorial and the Upper East Regional Hospitals. The study involved 291 women, including 180 (61.9%) with normotensive pregnancy and 111 (38.1%) with PE. Venous blood samples were collected and assayed for blood cell count, serum interleukins (ILs)-4, -6, -12, -18, and TNF-α as well as serum B7-1 and B7-H1 proteins.

RESULTS

The monocyte count (p = .007), the serum levels of IL-18 (p = .035), TNF-α (p = .001), and B7-H1 (p = .006) were significantly higher in PE than in normotensive pregnancy. In addition, the monocyte count (p = .002), the serum levels of IL-12 (p = .029), TNF-α (p = .016), and B7-1 (p = .009) levels were significantly higher in the third trimester than the second trimester PE. In predicting PE, the area under the curve of cytokines and ICMs ranged from 0.51 for IL-6 to 0.62 for TNF-α.

CONCLUSION

PE may be characterized by a dominant Th1-type immunity with higher levels of pro-inflammatory cytokines and B7-H1 proteins, but these variables may not be suitable for predicting PE.

Platelet-derived factors dysregulate placental sphingosine-1-phosphate receptor 2 in human trophoblasts

RESEARCH QUESTION

Sphingosine-1-phosphate (S1P) is an essential and bioactive sphingolipid with various functions, which acts through five different G-protein-coupled receptors (S1PR1-5). What is the localization of S1PR1-S1PR3 in the human placenta and what is the effect of different flow rates, various oxygen concentrations and platelet-derived factors on the expression profile of S1PR in trophoblasts?

DESIGN

Expression dynamics of placental S1PR1-S1PR3 were determined in human first trimester (n = 10), pre-term (n = 9) and term (n = 10) cases. Furthermore, the study investigated the expression of these receptors in different primary cell types isolated from human placenta, verified the findings with publicly available single-cell RNA-Seq data from first trimester and immunostaining of human first trimester and term placentas. The study also tested whether the placental S1PR subtypes are dysregulated in differentiated BeWo cells under different flow rates, different oxygen concentrations or in the presence of platelet-derived factors.

RESULTS

Quantitative polymerase chain reaction revealed that S1PR2 is the predominant placental S1PR in the first trimester and reduces towards term (P < 0.0001). S1PR1 and S1PR3 increased from first trimester towards term (P < 0.0001). S1PR1 was localized in endothelial cells, whereas S1PR2 and S1PR3 were predominantly found in villous trophoblasts. Furthermore, S1PR2 was found to be significantly down-regulated in BeWo cells when co-incubated with platelet-derived factors (P = 0.0055).

CONCLUSION

This study suggests that the placental S1PR repertoire is differentially expressed across gestation. S1PR2 expression in villous trophoblasts is negatively influenced by platelet-derived factors, which could contribute to down-regulation of placental S1PR2 over time of gestation as platelet presence and activation in the intervillous space increases from the middle of the first trimester onwards.

Interaction between endothelial cell-derived extracellular vesicles and monocytes: A potential link between vascular thrombosis and pregnancy-related morbidity in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune disease driven by a wide group of autoantibodies primarily directed against phospholipid-binding proteins (antiphospholipid antibodies). APS is defined by two main kinds of clinical manifestations: vascular thrombosis and pregnancy-related morbidity. In recent years, in vitro and in vivo assays, as well as the study of large groups of patients with APS, have led some authors to suggest that obstetric and vascular manifestations of the disease are probably the result of different pathogenic mechanisms. According to this hypothesis, the disease could be differentiated into two parallel entities: Vascular APS and obstetric APS. Thus, vascular APS is understood as an acquired thrombophilia in which a generalised phenomenon of endothelial activation and dysfunction (coupled with a triggering factor) causes thrombosis at any location. In contrast, obstetric APS seems to be due to an inflammatory phenomenon accompanied by trophoblast cell dysfunction. The recent approach to APS raises new issues; for instance, the mechanisms by which a single set of autoantibodies can lead to two different clinical entities are unclear. This review will address the monocyte, a cell with well-known roles in haemostasis and pregnancy, as a potential participant in vascular thrombosis and pregnancy-related morbidity in APS. We will discuss how in a steady state the monocyte-endothelial interaction occurs via extracellular vesicles (EVs), and how antiphospholipid antibodies, by inducing endothelial activation and dysfunction, may disturb this interaction to promote the release of monocyte-targeted procoagulant and inflammatory messages.

Immunophenotyping of peripheral blood monocytes could help identify a baseline pro-inflammatory profile in women with recurrent reproductive failure

Recurrent pregnancy loss (RPL) and recurrent implantation failure (RIF) are two well-defined clinical entities, but the role of the monocytes in their pathophysiology needs to be clarified. This study aimed to evaluate the role of the three monocyte subsets (classical, intermediate, and non-classical) and relevant cytokines/chemokines in a cohort of RPL and RIF women to better characterize a baseline proinflammatory profile that could define inflammatory pathophysiology in these two different conditions. We evaluated 108 non-pregnant women: 53 RPL, 24 RIF, and 31 fertile healthy controls (HC). Multiparametric flow cytometry was used to quantify the frequency of surface chemokine receptors (CCR2, CCR5, and CX3CR1) on the monocyte subsets. Cytokines were assessed in plasma samples using a multiplex assay. The CX3CR1⁺ and CCR5⁺ intermediate monocytes were significantly higher in RPL and RIF compared to HC. A significant positive correlation was observed between CX3CR1⁺ intermediate monocytes and IL-17A (P = .03, r = 0.43). The Boruta algorithm followed by a multivariate logistic regression model was used to select the most relevant variables that could help define RPL and RIF: in RPL were CX3CR1 non-classical monocytes, TGF-β1, and CCR5 intermediate monocytes; in RIF: CCR5 intermediate monocytes and TGF-β3. The combination of these variables could predict RPL and RIF with 90 % and 82 %, respectively. Our study suggests that a combination of specific blood monocyte subsets and cytokines could aid in identifying RPL and RIF women with a pro-inflammatory profile. These findings could provide a more integrated understanding of these pathologies. Further investigation and validation in independent cohorts are warranted.

Is there an inflammatory stimulus to human term labour?

Inflammation is thought to play a pivotal role in the onset of term and some forms of preterm labour. Although, we recently found that myometrial inflammation is a consequence rather than a cause of term labour, there are several other reproductive tissues, including amnion, choriodecidua parietalis and decidua basalis, where the inflammatory stimulus to labour may occur. To investigate this, we have obtained amnion, choriodecidual parietalis and decidua basalis samples from women at various stages of pregnancy and spontaneous labour. The inflammatory cytokine profile in each tissue was determine by Bio-Plex Pro® cytokine multiplex assays and quantitative RT-PCR. Active motif assay was used to study transcription activation in the choriodecidua parietalis. Quantitative RT-PCR was use to study the pro-labour genes (PGHS-2, PGDH, OTR and CX43) in all of the tissues at the onset of labour and oxytocin (OT) mRNA expression in the choriodecidual parietalis and decidua basalis. Statistical significance was ascribed to a P value <0.05. In the amnion and choriodecidua parietalis, the mRNA levels of various cytokines decreased from preterm no labour to term no labour samples, but the protein levels were unchanged. The choriodecidua parietalis showed increase in the protein levels of IL-1β and IL-6 in the term early labour samples. In the amnion and decidua basalis, the protein levels of several cytokines rose in term established labour. The multiples of the median derived from the 19-plex cytokine assay were greater in term early labour and term established labour samples from the choriodecidua parietalis, but only in term established labour for myometrium. These data suggest that the inflammatory stimulus to labour may begin in the choriodecidua parietalis, but the absence of any change in prolabour factor mRNA levels suggests that the cytokines may act on the myometrium where we observed changes in transcription factor activation and increases in prolabour gene expression in earlier studies.

The potential association between a new angiogenic marker fractalkine and a placental vascularization in preeclampsia

Purpose

Impaired angiogenesis is one of the most common findings in preeclamptic placentas. A new angiogenetic role of fractalkine (CX3CL1) is recently recognized apart from inflammatory activity. In this study, a link between CX3CL1 and the development of placental vasculature in preeclampsia was examined.

Methods

The study comprised 52 women allocated to Group 1 (normotensive, n = 23) and Group 2 (preeclampsia, n = 29). In each group Doppler parameters, serum levels of CX3CL1, soluble fms-like tyrosine kinase-1 (sFlt-1), and placental growth factor (PlGF) were assessed between 30 and 32 week of pregnancy. After the delivery, placental samples were taken and the vascularization and expression of CX3CR1 receptor were assessed after immunostaining.

Results

CX3CL1 and sFlt-1 serum levels were significantly higher levels in Group 2 vs Group 1, while PlGF serum levels was significantly lower in Group 2. Lower cerebroplacental ratio (CPR) was observed in Group 2. The vascular/extravascular tissue index (V/EVTI) was significantly lower in Group 2, while compared to Group 1, with the lowest value in the fetus growth restriction (FGR) subgroup (0.18 ± 0.02; 0.24 ± 0.03; 0.16 ± 0.02, respectively). The expression of examined CX3CR1 was higher in Group 2, while compared to Group 1, reaching the highest values in FGR subgroup. There was a moderate negative correlation between birth weight, V/EVTI and CX3CL1 serum level and CX3CR1 placental expression in the group of pregnancies complicated with preeclampsia.

Conclusion

The significant underdevelopment of placental vascular network in preeclampsia is associated with the change in the CX3CL1/CX3CR1 system, especially in FGR complicated pregnancies.

The Role of Inflammation in the Pathogenesis of Preeclampsia

Preeclampsia (PE) affects 5-8% of pregnant women, and it is the major cause of perinatal morbidity and mortality. It is defined as arterial hypertension in women after 20 weeks of gestation which cooccurs with proteinuria (300 mg/d) or as arterial hypertension which is accompanied by one of the following: renal failure, liver dysfunction, hematological or neurological abnormalities, intrauterine growth restriction, or uteroplacental insufficiency. Currently, pathophysiology of preeclampsia poses a considerable challenge for perinatology. Preeclampsia is characterized by excessive and progressive activation of the immune system along with an increase in proinflammatory cytokines and antiangiogenic factors in fetoplacental unit as well as in vascular endothelium in pregnant women. A single, major underlying mechanism of preeclampsia is yet to be identified. This paper discusses the current understanding of the mechanisms which underlie the development of the condition. Some significant factors responsible for PE development include oxidative stress, abnormal concentration and activity in mononuclear phagocytic system, altered levels of angiogenic and antiangiogenic factors, and impaired inflammatory response triggered by inflammasomes. Detailed understanding of pathophysiology of inflammatory process in PE can largely contribute to new, targeted anti-inflammatory therapies that may improve perinatal outcomes in PE patients.

Data-driven discovery of mid-pregnancy immune markers associated with maternal lifetime stress: results from an urban pre-birth cohort

Changes to the maternal inflammatory milieu may be a mechanism through which maternal psychosocial stress is transmitted to the fetus. Research investigating a limited number of immune markers may miss important signals. We take a proteomics approach to investigate maternal lifetime stress and 92 biomarkers of immune system status. Participants were enrolled in an urban, dual-site (Boston, n = 301 and New York City, n = 110) pregnancy cohort. We measured maternal lifetime history of stress and trauma using the validated Life Stressor Checklist-Revised (LSC-R). We measured a panel of 92 immune-related proteins in mid-pregnancy serum using proximity extension assay technology. We leveraged the dual-site study design to perform variable selection and inference within the cohort. First, we used LASSO to select immune markers related to maternal stress among Boston mothers. Then, we performed OLS regression to examine associations between maternal stress and LASSO-selected proteins among New York City mothers. LASSO regression selected 19 immune proteins with non-null coefficients (CCL11, CCL23, CD244, CST5, CXCL1, CXCL5, CXCL10, CX3CL1, FGF-23, IL-5, IL-7, IL-10, IL-17C, MCP-2, MMP-1, SLAMF1, ST1A1, TNF-β, and TWEAK). Of these, only the chemotactic cytokine CX3CL1 (i.e. fractalkine) was significantly associated with maternal stress among the validation sample (percent change in LSC-R score per 1% increase in relative fractalkine expression: 0.74, 95% confidence interval: 0.19, 1.28). Expanding research suggests fractalkine plays an important role in many aspects of pregnancy and fetal development and is stress-sensitive. We found that maternal lifetime history of stress and trauma was significantly associated with elevated serum fractalkine levels during pregnancy.

Maternal Platelets—Friend or Foe of the Human Placenta?

Human pregnancy relies on hemochorial placentation, including implantation of the blastocyst and deep invasion of fetal trophoblast cells into maternal uterine blood vessels, enabling direct contact of maternal blood with placental villi. Hemochorial placentation requires fast and reliable hemostasis to guarantee survival of the mother, but also for the neonates. During human pregnancy, maternal platelet count decreases gradually from first, to second, and third trimester. In addition to hemodilution, accelerated platelet sequestration and consumption in the placental circulation may contribute to a decline of platelet count throughout gestation. Local stasis, turbulences, or damage of the syncytiotrophoblast layer can activate maternal platelets within the placental intervillous space and result in formation of fibrin-type fibrinoid. Perivillous fibrinoid is a regular constituent of the normal placenta which is considered to be an important regulator of intervillous hemodynamics, as well as having a role in shaping the developing villous trees. However, exaggerated activation of platelets at the maternal-fetal interface can provoke inflammasome activation in the placental trophoblast, and enhance formation of circulating platelet-monocyte aggregates, resulting in sterile inflammation of the placenta and a systemic inflammatory response in the mother. Hence, the degree of activation determines whether maternal platelets are a friend or foe of the human placenta. Exaggerated activation of maternal platelets can either directly cause or propagate the disease process in placenta-associated pregnancy pathologies, such as preeclampsia.

Role of the Monocyte-Macrophage System in Normal Pregnancy and Preeclampsia

The proper functioning of the monocyte-macrophage system, an important unit of innate immunity, ensures the normal course of pregnancy. In this review, we present the current data on the origin of the monocyte-macrophage system and its functioning in the female reproductive system during the ovarian cycle, and over the course of both normal and complicated pregnancy. Preeclampsia is a crucial gestation disorder characterized by pronounced inflammation in the maternal body that affects the work of the monocyte-macrophage system. The effects of inflammation at preeclampsia manifest in changes in monocyte counts and their subset composition, and changes in placental macrophage counts and their polarization. Here we summarize the recent data on this issue for both the maternal organism and the fetus. The influence of estrogen on macrophages and their altered levels in preeclampsia are also discussed.

Placental CX3CL1 is Deregulated by Angiotensin II and Contributes to a Pro-Inflammatory Trophoblast-Monocyte Interaction

CX3CL1, which is a chemokine involved in many aspects of human pregnancy, is a membrane-bound chemokine shed into circulation as a soluble isoform. Placental CX3CL1 is induced by inflammatory cytokines and is upregulated in severe early-onset preeclampsia. In this study, the hypothesis was addressed whether angiotensin II can deregulate placental CX3CL1 expression, and whether CX3CL1 can promote a pro-inflammatory status of monocytes. qPCR analysis of human placenta samples (n = 45) showed stable expression of CX3CL1 and the angiotensin II receptor AGTR1 throughout the first trimester, but did not show a correlation between both or any influence of maternal age, BMI, and gestational age. Angiotensin II incubation of placental explants transiently deregulated CX3CL1 expression, while the angiotensin II receptor antagonist candesartan reversed this effect. Overexpression of recombinant human CX3CL1 in SGHPL-4 trophoblasts increased adhesion of THP-1 monocytes and significantly increased IL8, CCL19, and CCL13 in co-cultures with human primary monocytes. Incubation of primary monocytes with CX3CL1 and subsequent global transcriptome analysis of CD16⁺ subsets revealed 81 upregulated genes, including clusterin, lipocalin-2, and the leptin receptor. Aldosterone synthase, osteopontin, and cortisone reductase were some of the 66 downregulated genes present. These data suggest that maternal angiotensin II levels influence placental CX3CL1 expression, which, in turn, can affect monocyte to trophoblast adhesion. Release of placental CX3CL1 could promote the pro-inflammatory status of the CD16⁺ subset of maternal monocytes.

Plasmodium falciparum proteins involved in cytoadherence of infected erythrocytes to chemokine CX3CL1

Malaria caused by Plasmodium falciparum is associated with cytoadherence of infected red blood cells (iRBC) to endothelial cells. Numerous host molecules have been involved in cytoadherence, including the adhesive chemokine CX3CL1. Most of the identified parasite ligands are from the multigenic and hypervariable Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) family which makes them poor targets for the development of a broadly protective vaccine. Using proteomics, we have identified two 25-kDa parasite proteins with adhesive properties for CX3CL1, called CBP for CX3CL1 Binding Proteins. CBPs are coded by single-copy genes with little polymorphic variation and no homology with other P. falciparum gene products. Specific antibodies raised against epitopes from the predicted extracellular domains of each CBP efficiently stain the surface of RBC infected with trophozoites or schizonts, which is a strong indication of CBP expression at the surface of iRBC. These anti-CBP antibodies partially neutralize iRBC adherence to CX3CL1. This adherence is similarly inhibited in the presence of peptides from the CBP extracellular domains, while irrelevant peptides had no such effect. CBP1 and CBP2 are new P. falciparum ligands for the human chemokine CX3CL1. The identification of this non-polymorphic P. falciparum factors provides a new avenue for innovative vaccination approaches.

Prolonged activation of innate antiviral gene signature after childbirth is determined by IFNL3 genotype

Maternal innate and adaptive immune responses are modulated during pregnancy to concurrently defend against infection and tolerate the semiallogeneic fetus. The restoration of these systems after childbirth is poorly understood. We reasoned that enhanced innate immune activation may extend beyond gestation while adaptive immunity recovers. To test this hypothesis, the transcriptional profiles of total peripheral blood mononuclear cells following delivery in healthy women were compared with those of nonpregnant control subjects. Interestingly, interferon-stimulated genes (ISGs) encoding proteins such as IFIT1, IFIT2, and IFIT3, as well as signaling proteins such as STAT1, STAT2, and MAVS, were enriched postpartum. Antiviral genes were primarily expressed in CD14(+) cells and could be stratified according to genetic variation at the interferon-λ3 gene (IFNL3, also named IL28B) SNP rs12979860. Antiviral gene expression was sustained beyond 6 mo following delivery in mothers with a CT or TT genotype, but resembled baseline nonpregnant control levels following delivery in mothers with a CC genotype. CT and TT IFNL3 genotypes have been associated with persistent elevated ISG expression in individuals chronically infected with hepatitis C virus. Together, these data suggest that postpartum, the normalization of the physiological rheostat controlling IFN signaling depends on IFNL3 genotype.

Maternal monocytes in pregnancy and preeclampsia in humans and in rats

Monocytes are short-lived cells, arising from the bone marrow and maturing in the circulation. They play an important role in immune responses and are thought to be important for healthy pregnancy. In humans, 3 subpopulations of monocytes have been identified: classical, intermediate and non-classical monocytes. These subpopulations have different functions and phenotypical characteristics. Healthy pregnancy is characterized by a pro-inflammatory condition, with increased numbers of monocytes and monocyte activation as well as with increased numbers of intermediate monocytes and decreased numbers of classical monocytes. This may suggest monocyte maturation. Preeclampsia is an important pregnancy complication characterized by hypertension and proteinuria developing in the second half of pregnancy. The pathophysiology of preeclampsia is associated with further activation of the inflammatory response, further activation of monocytes and further monocyte maturation. In the present review we focus on the role of monocyte activation and maturation in healthy and preeclamptic pregnancy.

The role of CX3CL1 in fetal-maternal interaction during human gestation

Embryo implantation and subsequent placentation require a fine balanced fetal-maternal cross-talk of hormones, cytokines and chemokines. Amongst the group of chemokines, CX3CL1 (also known as fractalkine) has recently attracted attention in the field of reproductive research. It exists both as membrane-bound and soluble isoforms. On the basis of current experimental evidence, fractalkine is suggested to regulate adhesion and migration processes in fetal-maternal interaction at different stages of human pregnancy. Expressed by uterine glandular epithelial cells, predominantly during the mid-secretory phase of the menstrual cycle, fractalkine appears to prime the blastocyst for forthcoming implantation. After implantation, fractalkine is suggested to regulate invasion of extravillous trophoblasts by altering their expression profile of adhesion molecules. With onset of perfusion of the intervillous space at the end of first trimester, fractalkine present at the apical microvillous plasma membrane of the syncytiotrophoblast may mediate close interaction of placental villi with circulating maternal blood cells.

Cellular Regulation of the Uterine Microenvironment That Enables Embryo Implantation

Implantation of the fertilized egg into the maternal uterus is a crucial step in pregnancy establishment. Increasing evidence suggests that its success depends on various cell types of the innate immune system and on the fine balance between inflammatory and anti-inflammatory processes. In addition, it has recently been established that regulatory T cells play a superordinate role in dictating the quality of uterine environment required for successful pregnancy. Here, we discuss the cellular regulation of uterine receptivity with emphasis on the function and regulation of cells from the innate and adaptive immune system.