Structural basis for recognition of the nonclassical MHC molecule HLA-G by the leukocyte Ig-like receptor B2 (LILRB2/LIR2/ILT4/CD85d)

HLA-G is a nonclassical MHC class I (MHCI) molecule that can suppress a wide range of immune responses in the maternal-fetal interface. The human inhibitory immune receptors leukocyte Ig-like receptor (LILR) B1 [also called LIR1, Ig-like transcript 2 (ILT2), or CD85j] and LILRB2 (LIR2/ILT4/CD85d) preferentially recognize HLA-G. HLA-G inherently exhibits various forms, including beta(2)-microglobulin (beta(2)m)-free and disulfide-linked dimer forms. Notably, LILRB1 cannot recognize the beta(2)m-free form of HLA-G or HLA-B27, but LILRB2 can recognize the beta(2)m-free form of HLA-B27. To date, the structural basis for HLA-G/LILR recognition remains to be examined. Here, we report the 2.5-A resolution crystal structure of the LILRB2/HLA-G complex. LILRB2 exhibits an overlapping but distinct MHCI recognition mode compared with LILRB1 and dominantly recognizes the hydrophobic site of the HLA-G alpha3 domain. NMR binding studies also confirmed these LILR recognition differences on both conformed (heavy chain/peptide/beta(2)m) and free forms of beta(2)m. Binding studies using beta(2)m-free MHCIs revealed differential beta(2)m-dependent LILR-binding specificities. These results suggest that subtle structural differences between LILRB family members cause the distinct binding specificities to various forms of HLA-G and other MHCIs, which may in turn regulate immune suppression.

Innate Immune Cells and Toll-like Receptor-Dependent Responses at the Maternal-Fetal Interface

During pregnancy, the placenta, the mother and the fetus exploit several mechanisms in order to avoid fetal rejection and to maintain an immunotolerant environment throughout nine months. During this time, immune cells from the fetal and maternal compartments interact to provide an adequate defense in case of an infection and to promote a tolerogenic milieu for the fetus to develop peacefully. Trophoblasts and decidual cells, together with resident natural killer cells, dendritic cells, Hofbauer cells and other macrophages, among other cell types, contribute to the modulation of the uterine environment to sustain a successful pregnancy. In this review, the authors outlined some of the various roles that the innate immune system plays at the maternal-fetal interface. First, the cell populations that are recruited into gestational tissues and their immune mechanisms were examined. In the second part, the Toll-like receptor (TLR)-dependent immune responses at the maternal-fetal interface was summarized, in terms of their specific cytokine/chemokine/antimicrobial peptide expression profiles throughout pregnancy.

Trophoblast-derived CXCL16 induces M2 macrophage polarization that in turn inactivates NK cells at the maternal-fetal interface

Decidual macrophages (dMΦ) are distinct from the conventional macrophages present in other tissues and express M2 macrophage markers, but the molecular mechanisms of formation and the roles of M2 MΦ during pregnancy have not been completely elucidated. The crosstalk between decidual natural killer cells (dNK) and dMΦ plays an important role in the maintenance of maternal-fetal immune tolerance. Here, CXCL16 derived from first-trimester trophoblast cells induces the polarization of human M2 macrophages. The M2 MΦ polarized by CXCL16 exhibit decreased interleukin-15 production, which facilitates the inactivation of NK cells. The cytotoxicity of NK cells is attenuated by the CXCL16-polarized M2 MΦ. The data shown in the present study provide evidence to support the hypothesis that CXCL16 secreted by trophoblast cells is a key molecule involved in decidual M2 MΦ polarization, which in turn regulates the killing ability of NK cells, thereby contributing to the homeostatic and immune-tolerant milieu required for successful fetal development.

The role of extracellular matrix in normal and pathological pregnancy: Future applications of microphysiological systems in reproductive medicine

IMPACT STATEMENT

Extracellular matrix in the womb regulates the initiation, progression, and completion of a healthy pregnancy. The composition and physical properties of extracellular matrix in the uterus and at the maternal-fetal interface are remodeled at each gestational stage, while maladaptive matrix remodeling results in obstetric disease. As in vitro models of uterine and placental tissues, including micro-and milli-scale versions of these organs on chips, are developed to overcome the inherent limitations of studying human development in vivo, we can isolate the influence of cellular and extracellular components in healthy and pathological pregnancies. By understanding and recreating key aspects of the extracellular microenvironment at the maternal-fetal interface, we can engineer microphysiological systems to improve assisted reproduction, obstetric disease treatment, and prenatal drug safety.

B7 family molecules as regulators of the maternal immune system in pregnancy

Placental and fetal growth and development are associated with chronic exposure of the maternal immune system to fetally derived, paternally inherited antigens. Because maternal lymphocytes are aware of fetal antigens, active tolerance mechanisms are required to ensure unperturbed progression of pregnancy and delivery of a healthy newborn. These mechanisms of tolerance may include deletion, receptor downregulation, and anergy of fetal antigen-specific cells in lymphoid tissues, as well as regulation at the maternal-fetal interface by a variety of locally expressed immunoregulatory molecules. The B7 family of costimulatory molecules comprises one group of immunoregulatory molecules present in the decidua and placenta. B7 family members mediate both inhibitory and stimulatory effects on T-cell activation and effector functions and may play a critical role in maintaining tolerance to the fetus. Here, we review the known functions of the B7 family proteins in pregnancy.

Role of Human Leukocyte Antigens at the Feto-Maternal Interface in Normal and Pathological Pregnancy: An Update

The successful maternal tolerance of the semi-allogeneic fetus provides an apparent immunologic paradox. Indeed, deep invasion of placental trophoblast cells into maternal uterine tissue and the following growth of the fetus have to be tolerated by a pregnant woman’s immune system. Among the various possible protective mechanisms that may be involved in human pregnancy, the expression of a non-classical pattern of human leukocyte antigen (HLA) class I molecules and the complete lack of expression of HLA class II molecules in placental tissues seem to be the most relevant mechanisms of fetal escape from maternal immune recognition. The importance of HLA molecules in fetal toleration by the maternal immune system is highlighted by pregnancy complications occurring in cases of abnormal HLA molecule expression at the maternal–fetal interface. In this review, we summarize evidences about the role of placental HLA molecules in normal and pathological pregnancies.

Cellular and molecular mechanisms of viral infection in the human placenta

The placenta is a highly specialized organ that is formed during human gestation for conferring protection and generating an optimal microenvironment to maintain the equilibrium between immunological and biochemical factors for fetal development. Diverse pathogens, including viruses, can infect several cellular components of the placenta, such as trophoblasts, syncytiotrophoblasts and other hematopoietic cells. Viral infections during pregnancy have been associated with fetal malformation and pregnancy complications such as preterm labor. In this minireview, we describe the most recent findings regarding virus-host interactions at the placental interface and investigate the mechanisms through which viruses may access trophoblasts and the pathogenic processes involved in viral dissemination at the maternal-fetal interface.

The Role of B7 Family Molecules in Maternal-Fetal Immunity

Pregnancy is a complex but well-arranged process, and a healthy fetus requires immune privilege and surveillance in the presence of paternally derived antigens. Maternal and fetal cells interact at the maternal–fetal interface. The upregulation and downregulation of maternal immunity executed by the leukocyte population predominantly depend on the activity of decidual natural killer cells and trophoblasts and are further modulated by a series of duplex signals. The B7 family, which consists of B7-1, B7-2, B7-H1, B7-DC, B7-H2, B7-H3, B7-H4, B7-H5, BTNL2, B7-H6, and B7-H7, is one of the most characterized and widely distributed signaling molecule superfamilies and conducts both stimulatory and inhibitory signals through separate interactions. In particular, the roles of B7-1, B7-2, B7-H1, and their corresponding receptors in the progression of normal pregnancy and some pregnancy complications have been extensively studied. Together with the TCR–MHC complex, B7 and its receptors play a critical role in cell proliferation and cytokine secretion. Depending on this ligand–receptor crosstalk, the balance between the tolerance and rejection of the fetus is perfectly maintained. This review aims to provide an overview of the current knowledge of the B7 family and its functions in regulating maternal–fetal immunity through individual interactions.

Defensins: defenders of human reproductive health

BACKGROUND

Reproductive tract infection is an important factor leading to male and female infertility. Among female infertility factors, microbial and viral infections are the main factors affecting female reproductive health and causing tubal infertility, ectopic tubal pregnancy and premature delivery. Among male infertility factors, 13-15% of male infertility is related to infection. Defensins are cationic antibacterial and antiviral peptides, classified into α-defensins, β-defensins and θ-defensins. Humans only have α-defensins and β-defensins. Apart from their direct antimicrobial functions, defensins have an immunomodulatory function and are involved in many physiological processes. Studies have shown that defensins are widely distributed in the female reproductive tract (FRT) and male reproductive tract (MRT), playing a dual role of host defence and fertility protection. However, to our knowledge, the distribution, regulation and function of defensins in the reproductive tract and their relation to reproduction have not been reviewed.

OBJECTIVE AND RATIONALE

This review summarizes the expression, distribution and regulation of defensins in the reproductive tracts to reveal the updated research on the dual role of defensins in host defence and the protection of fertility.

SEARCH METHODS

A systematic search was conducted in PubMed using the related keywords through April 2022. Related data from original researches and reviews were integrated to comprehensively review the current findings and understanding of defensins in the human reproductive system. Meanwhile, female and male transcriptome data in the GEO database were screened to analyze defensins in the human reproductive tracts.

OUTCOMES

Two transcriptome databases from the GEO database (GSE7307 and GSE150852) combined with existing researches reveal the expression levels and role of the defensins in the reproductive tracts. In the FRT, a high expression level of α-defensin is found, and the expression levels of defensins in the vulva and vagina are higher than those in other organs. The expression of defensins in the endometrium varies with menstrual cycle stages and with microbial invasion. Defensins also participate in the local immune response to regulate the risk of spontaneous preterm birth. In the MRT, a high expression level of β-defensins is also found. It is mainly highly expressed in the epididymal caput and corpus, indicating that defensins play an important role in sperm maturation. The expression of defensins in the MRT varies with androgen levels, age and the status of microbial invasion. They protect the male reproductive system from bacterial infections by neutralizing lipopolysaccharide and downregulating pro-inflammatory cytokines. In addition, animal and clinical studies have shown that defensins play an important role in sperm maturation, motility and fertilization.

WIDER IMPLICATIONS

As a broad-spectrum antimicrobial peptide without drug resistance, defensin has great potential for developing new natural antimicrobial treatments for reproductive tract infections. However, increasing evidence has shown that defensins can not only inhibit microbial invasion but can also promote the invasion and adhesion of some microorganisms in certain biological environments, such as human immunodeficiency virus. Therefore, the safety of defensins as reproductive tract anti-infective drugs needs more in-depth research. In addition, the modulatory role of defensins in fertility requires more in-depth research since the current conclusions are based on small-size samples. At present, scientists have made many attempts at the clinical transformation of defensins. However, defensins have problems such as poor stability, low bioavailability and difficulties in their synthesis. Therefore, the production of safe, effective and low-cost drugs remains a challenge.

Newly characterized decidual Tim-3+ Treg cells are abundant during early pregnancy and driven by IL-27 coordinately with Gal-9 from trophoblasts

STUDY QUESTION

What is the mechanism of Tim-3+ regulatory T (Treg)-cell accumulation in the decidua during early pregnancy and is its disruption associated with recurrent pregnancy loss (RPL)?

SUMMARY ANSWER

IL-27 and Gal-9 secreted by trophoblasts activate the Tim-3 signaling pathway in CD4+ T cells and Treg cells and so promote accumulation of Tim-3+ Treg cells, the abnormal expression of IL-27 and Gal-9 is associated with impaired immunologic tolerance in RPL patients.

WHAT IS KNOWN ALREADY

Tim-3+ Treg cells are better suppressors of Teff cell proliferation, and display higher proliferative activity than Tim-3- Treg cells. Tim-3+ Treg cells are tissue-specific promoters of T-cell dysfunction in many tumors. These cells express a unique factor that influences and shapes the tumor microenvironment.

STUDY DESIGN, SIZE, DURATION

The animal study included 80 normal pregnant mice. In human study, decidua tissues in the first trimester for flow cytometry analysis were collected from 32 normal pregnant women and 23 RPL patients. Placenta tissues for immunohistochemistry analysis were collected from 15 normal pregnant women. Placenta tissues for western blot analysis were collected from 5 normal pregnant women, 5 RPL patients and 5 women who have experienced one miscarriage. Blood samples for in vitro experiments were collected from 30 normal pregnant women. This study was performed between January 2017 and March 2019.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In this study, we investigated the kinetics of Tim-3+ CD4+ T-cell accumulation, and the proportions of Tim-3+ Treg cells throughout murine pregnancies using flow cytometry. We compared Tim-3 expression on decidual CD4+ T cells and Treg cells during normal pregnancies with expression on the same cell populations in women suffering from RPL. IL-27 and Gal-9 transcription and protein expression in the placenta were determined by RT-PCR and western blot, respectively. An in vitro co-culture model consisting of peripheral CD4+ T cells and primary trophoblasts from early pregnancy was used to mimic the maternal-fetal environment.

MAIN RESULTS AND THE ROLE OF CHANCE

The percentage of Tim-3+ Treg cells present in mouse uteri fluctuates as gestation proceeds but does not change in the spleen. Levels of Tim3+ Treg cells in uteri peaked at pregnancy Day 6.5 (E 6.5), then progressively diminished, and fell to non-pregnant levels by E18.5. In pregnant mice, Tim-3+ Treg cells constituted 40-70% of Treg cells in uteri but were present at much lower abundance in spleens. About 60% of decidual Treg cells were Tim-3 positive at E6.5. Of these decidual Tim3+ Treg cells, nearly 90% were PD-1 positive. However, only about 16% of Tim3- Treg cells expressed PD-1. Blocking the Tim-3 signaling pathway decreased the proportion of Treg cells and led to embryo resorption. Moreover, much lower Tim-3 expression was observed on CD4+ T cells and Treg cells in women who had suffered from RPL at 6-9 gestational weeks compared with those who had normal pregnancies at matched gestations. In a normal pregnancy, Tim-3 expression on decidual CD4+ T cells is induced initially by IL-27. Then Gal-9-Tim-3 interaction promotes differentiation of decidual Tim-3+ CD4+ T cells into Treg cells. IL-27 and Gal-9 cooperatively induced Tim-3+ Treg cells in vitro.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

We did not investigate the kinetics of human decidual Tim-3+ CD4+ T and Tim-3+ Treg cell populations throughout pregnancy due to limited availability of second and third trimester decidua. In addition, functional suppressive data on the decidual Tim-3+ Treg cells are lacking due to limited and low quantities of these cells in decidua.

WIDER IMPLICATIONS OF THE FINDINGS

These findings might have therapeutic clinical implications in RPL.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by research grants from the National Natural Science Foundation of China (No. 81871186) and National Key Research & Developmental Program of China (2018YFC1003900, 2018YFC1003904). The authors declare no conflict of interest.

Natural killer cells in the pathogenesis of preeclampsia: a double-edged sword

Objective: To investigate the relationship between natural killer (NK) cells, extravillous trophoblast cells (EVTs) and vessel remodeling in early human pregnancy, and the association between NK cells and preeclampsia (PE) in late human pregnancy.Methods: Human decidual tissues from women with normal pregnancies were collected and examined for the relationship of NK cells with uterine vessel remodeling using immunohistochemistry. Percentages of peripheral blood NK (pNK) and decidual NK (dNK) cells and the levels of intracellular interferon (IFN)-γ, perforin and granzyme B in normal pregnancies, late-onset and early-onset PE were analyzed using flow cytometry. Cytolytic functions of dNK cells from normal and PE pregnancies were examined. Effects of conditioned medium (CM) of dNK cells from normal and PE pregnancies on first trimester trophoblast invasion and migration were tested.Results: In early pregnancy samples (9-13 weeks of gestation), we noted moderate vessel remodeling with abundant perivascular NK cells but a limited number of surrounding EVTs. The numbers of both human pNK cells and dNK cells and intracellular interferon (IFN)-γ, perforin and granzyme B production were significantly higher in PE compared with normal pregnancies at the time of delivery for both early- and late-onset disease. dNK cells from PE pregnancies not only killed first trimester trophoblasts but also inhibited their invasion and migration when compared to normal controls.Conclusion: Our results suggest that NK cells, in conjunction with EVTs, may play an important role in controlling uterine SA remodeling at the early stages of vessel remodeling, but they contribute to the pathogenesis of PE in late pregnancy.

Gasotransmitters in pregnancy: from conception to uterine involution

Gasotransmitters are endogenous small gaseous messengers exemplified by nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S or sulfide). Gasotransmitters are implicated in myriad physiologic functions including many aspects of reproduction. Our objective was to comprehensively review basic mechanisms and functions of gasotransmitters during pregnancy from conception to uterine involution and highlight future research opportunities. We searched PubMed and Web of Science databases using combinations of keywords nitric oxide, carbon monoxide, sulfide, placenta, uterus, labor, and pregnancy. We included English language publications on human and animal studies from any date through August 2018 and retained basic and translational articles with relevant original findings. All gasotransmitters activate cGMP signaling. NO and sulfide also covalently modify target protein cysteines. Protein kinases and ion channels transduce gasotransmitter signals, and co-expressed gasotransmitters can be synergistic or antagonistic depending on cell type. Gasotransmitters influence tubal transit, placentation, cervical remodeling, and myometrial contractility. NO, CO, and sulfide dilate resistance vessels, suppress inflammation, and relax myometrium to promote uterine quiescence and normal placentation. Cervical remodeling and rupture of fetal membranes coincide with enhanced oxidation and altered gasotransmitter metabolism. Mechanisms mediating cellular and organismal changes in pregnancy due to gasotransmitters are largely unknown. Altered gasotransmitter signaling has been reported for preeclampsia, intrauterine growth restriction, premature rupture of membranes, and preterm labor. However, in most cases specific molecular changes are not yet characterized. Nonclassical signaling pathways and the crosstalk among gasotransmitters are emerging investigation topics.

Proinflammatory changes in the maternal circulation, maternal-fetal interface, and placental transcriptome in preterm birth

BACKGROUND

Preterm birth remains a leading obstetrical complication because of the incomplete understanding of its multifaceted etiology. It is known that immune alterations toward a proinflammatory profile are observed in women with preterm birth, but therapeutic interventions are still lacking because of scarcity of evidence in the integration of maternal and placental interrelated compartments.

OBJECTIVE

This study aimed to obtain an integrated view of the maternal and placental contribution to preterm birth compared with normal term pregnancies for an in-depth understanding of the immune/inflammatory involvement, intending to identify novel strategies to mitigate the negative impact of inflammation.

STUDY DESIGN

We prospectively recruited 79 women with preterm or term deliveries and collected placentas for RNA sequencing, histologic analyses, and to assess levels of inflammatory mediators. Blood samples were also collected to determine the circulating immune profiles by flow cytometry and to evaluate the circulating levels of inflammatory mediators.

RESULTS

Placental transcriptomic analyses revealed 102 differentially expressed genes upregulated in preterm birth, including known and novel targets, which were highly enriched for inflammatory biological processes according to gene ontology analyses. Analysis of maternal immune cells revealed distinct profiles in preterm births vs term births, including an increased percentage of CD3^- cells and monocyte subsets and decreased CD3⁺ cells along with Th17 subsets of CD4⁺ lymphocytes. Supporting our bioinformatic findings, we found increases in proinflammatory mediators in the plasma, placenta, and fetal membranes (primarily the amnion) of women with preterm birth, such as interleukin-6 and tumor necrosis factor-α. These findings were not distinct between spontaneous and iatrogenic preterm births except at a molecular level where spontaneous preterm birth presented with an elevated inflammatory profile compared with iatrogenic preterm birth. Analysis of placental histology revealed increased structural and inflammatory lesions in preterm vs term births. We found that genes upregulated in placentas with inflammatory lesions have enrichment of proinflammatory pathways.

CONCLUSION

This work sheds light on changes within the immune system in preterm birth on multiple levels and compartments to help identify pregnancies at high risk of preterm birth and to discover novel therapeutic targets for preterm birth.

The expression of intracellular cytokines of decidual natural killer cells in unexplained recurrent pregnancy loss

OBJECTIVE

This study aims to investigate the expression levels of TNF-α, IFN-γ, IL-4, and IL-10 in dNK cells and determine whether or not the MAPK signal pathway is involved in the regulation of cytokine secretion by dNK cells at the maternal-fetal interface.

METHODS

In this study, we collected decidua specimens from patients with apparently normal pregnant and unexplained recurrent pregnancy loss (URPL) and extracted dNK cells by enzymatic digestion. Then the expression of cytokines were analyzed by flow cytometry and Real-Time PCR respectively.

RESULTS

The secretions of both IFN-γ and TNF-α in dNK cells in URPL were significantly higher than those in normal pregnancy. Furthermore, p38/MAPK inhibitors can inhibit the secretion of four cytokines in normal pregnancy, while in URPL cases, p38/MAPK inhibitors only significantly inhibit the secretion of IL-4 and IFN-γ. ERK inhibitors had no effect on the expression of all four cytokines and JNK/MAPK inhibitors varied on different cytokines.

CONCLUSION

URPL is associated with a NK1 cytokine profile. MAPK signaling pathway is involved in the regulation of cytokine secretion by decidual NK cells at maternal-fetal interface.

CCL17 Induces Trophoblast Migration and Invasion by Regulating Matrix Metalloproteinase and Integrin Expression in Human First-Trimester Placenta

Chemokines and chemokine receptors have been implicated a pivotal role in trophoblast differentiation and in the formation of a functionally normal placenta. In this study, we present data that highlight the involvement of chemokine ligand 17/chemokine receptor 4 (CCL17/CCR4) expression at the fetomaternal interface and expand its biological relevance of influence during trophoblast differentiation and placentation. By immunohistochemistry, we found that CCL17 was abundantly expressed in the decidua and trophoblasts, especially in cell columns. The receptor for CCL17, CCR4, was specifically expressed in invading interstitial extravillous trophoblasts. Furthermore, by transwell migration, invasion assays, and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, we found that exogenous CCL17 concentrations paralleled the invasive potential of cytotrophoblasts to some extent, with no significant effect on cell proliferation. Using Western blotting, we demonstrated that the stimulatory effect of CCL17 was related to the expression of matrix metalloproteinase 2 (MMP-2), MMP-13, integrin α5, and integrin β1, although it downregulated tissue inhibitors of MMP-1 expression. In conclusion, our findings suggest that CCL17, as a differentiation-related molecule coexpressed by decidua and trophoblast, stimulates extravillous trophoblast migration and directs invasion mainly via modulating integrins, MMPs, and its inhibitor levels.

Tuning Trophoblast Motility in a Gelatin Hydrogel via Soluble Cues from the Maternal-Fetal Interface

Trophoblast cells play multiple critical roles in pregnancy, notably modulating blastocyst attachment to the endometrium as well as invading into and actively remodeling the endometrium to facilitate biotransport needs of the growing embryo. Despite the importance of trophoblast invasion for processes essential at early stages of pregnancy, much remains unknown regarding the balance of signaling molecules that may influence trophoblast invasion into the endometrium. The goal of this study was to use three-dimensional trophoblast spheroid motility assays to examine the effect of cues from the maternal-fetal interface on trophoblast motility. We report use of a methacrylamide-functionalized gelatin hydrogel to support quantitative analysis of trophoblast outgrowth area and cell viability. We show that this multidimensional model of trophoblast motility can resolve quantifiable differences in outgrowth area and viability in the presence of a known invasion promoter, epidermal growth factor, and a known invasion inhibitor, transforming growth factor β1. We then investigate the sensitivity of trophoblast motility to cortisol, a hormone associated with exogenous stressors. Together, this approach provides a toolset to investigate the coordinated action of physiological and pathophysiological processes on early stages of trophoblast invasion.

SARS-CoV-2 Transplacental Transmission: A Rare Occurrence? An Overview of the Protective Role of the Placenta

The outbreak of the coronavirus disease 2019 (COVID-19) pandemic, caused by novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in a global public health crisis, causing substantial concern especially to the pregnant population. Pregnant women infected with SARS-CoV-2 are at greater risk of devastating pregnancy complications such as premature delivery and stillbirth. Irrespective of the emerging reported cases of neonatal COVID-19, reassuringly, confirmatory evidence of vertical transmission is still lacking. The protective role of the placenta in limiting in utero spread of virus to the developing fetus is intriguing. The short- and long-term impact of maternal COVID-19 infection in the newborn remains an unresolved question. In this review, we explore the recent evidence of SARS-CoV-2 vertical transmission, cell-entry pathways, placental responses towards SARS-CoV-2 infection, and its potential effects on the offspring. We further discuss how the placenta serves as a defensive front against SARS-CoV-2 by exerting various cellular and molecular defense pathways. A better understanding of the placental barrier, immune defense, and modulation strategies involved in restricting transplacental transmission may provide valuable insights for future development of antiviral and immunomodulatory therapies to improve pregnancy outcomes.

Galectins: Important Regulators in Normal and Pathologic Pregnancies

Galectins (Gal) are characterized by their affinity for galactoside structures on glycoconjugates. This relationship is mediated by carbohydrate recognition domains, which are multifunctional regulators of basic cellular biological processes with high structural similarity among family members. They participate in both innate and adaptive immune responses, as well as in reproductive immunology. Recently, the discovery that galectins are highly expressed at the maternal–fetal interface has garnerd the interest of experts in human reproduction. Galectins are involved in a variety of functions such as maternal–fetal immune tolerance, angiogenesis, trophoblast invasion and placental development and are considered to be important mediators of successful embryo implantation and during pregnancy. Dysregulation of these galectins is associated with abnormal and pathological pregnancies (e.g., preeclampsia, gestational diabetes mellitus, fetal growth restriction, preterm birth). Our work reviews the regulatory mechanisms of galectins in normal and pathological pregnancies and has implications for clinicians in the prevention, diagnosis and treatment of pregnancy-related diseases.

Molecular Changes on Maternal-Fetal Interface in Placental Abruption-A Systematic Review

Placental abruption is the separation of the placenta from the lining of the uterus before childbirth. It is an infrequent perinatal complication with serious after-effects and a marked risk of maternal and fetal mortality. Despite the fact that numerous placental abruption risk factors are known, the pathophysiology of this issue is multifactorial and not entirely clear. The aim of this review was to examine the current state of knowledge concerning the molecular changes on the maternal–fetal interface occurring in placental abruption. Only original research articles describing studies published in English until the 15 March 2021 were considered eligible. Reviews, book chapters, case studies, conference papers and opinions were excluded. The systematic literature search of PubMed/MEDLINE and Scopus databases identified 708 articles, 22 of which were analyzed. The available evidence indicates that the disruption of the immunological processes on the maternal–fetal interface plays a crucial role in the pathophysiology of placental abruption. The features of chronic non-infectious inflammation and augmented immunological cytotoxic response were found to be present in placental abruption samples in the reviewed studies. Various molecules participate in this process, with only a few being examined. More advanced research is needed to fully explain this complicated process.

Compartmentalized Innate Immune Response of Human Fetal Membranes against Escherichia coli Choriodecidual Infection

An infectious process into the uterine cavity represents a major endangered condition that compromises the immune privilege of the maternal-fetal unit and increases the risk for preterm birth (PTB) and premature rupture of membranes (PROM). Fetal membranes are active secretors of antimicrobial peptides (AMP), which limit bacterial growth, such as Escherichia coli. Nevertheless, the antibacterial responses displayed by chorioamniotic membranes against a choriodecidual E. coli infection have been briefly studied. The objective of this research was to characterize the profile of synthesis, activity, and spatial distribution of a broad panel of AMPs produced by fetal membranes in response to E. coli choriodecidual infection. Term human chorioamniotic membranes were mounted in a two independent compartment model in which the choriodecidual region was infected with live E. coli (1 × 10⁵ CFU/mL). Amnion and choriodecidual AMP tissue levels and TNF-α and IL-1β secretion were measured by the enzyme-linked immunosorbent assay. The passage of bacterium through fetal membranes and their effect on structural continuity was followed for 24 h. Our results showed that E. coli infection caused a progressive mechanical disruption of the chorioamniotic membranes and an activated inflammatory environment. After the challenge, the amnion quickly (2-4 h) induced production of human beta defensins (HBD)-1, HBD-2, and LL-37. Afterwards (8-24 h), the amnion significantly produced HBD-1, HBD-2, HNP-1-3, S100A7, sPLA2, and elafin, whereas the choriodecidua induced LL-37 synthesis. Therefore, we noticed a temporal- and tissue-specific pattern regulation of the synthesis of AMPs by infected fetal membranes. However, fetal membranes were not able to contain the collagen degradation or the bacterial growth and migration despite the battery of produced AMPs, which deeply increases the risk for PTB and PROM. The mixture of recombinant HBDs at low concentrations resulted in increased bactericidal activity compared to each HBD alone in vitro, encouraging further research to study AMP combinations that may offer synergy to control drug-resistant infections in the perinatal period.

Maternal serotonin: implications for the use of selective serotonin reuptake inhibitors during gestation†

Maternal use of antidepressants has increased throughout the last decades; selective serotonin reuptake inhibitors (SSRI) are the most prescribed antidepressants. Despite the widespread use of SSRI by women during reproductive age and pregnant women, an increasing amount of research warns of possible detrimental effects of maternal use of SSRI during pregnancy including low birthweight/small for gestational age and preterm birth. In this review, we revisited the impact of maternal use of SSRI during pregnancy, its impact on serotonin homeostasis in the maternal and fetal circulation and the placenta, and its impact on pregnancy outcomes-particularly intrauterine growth restriction and preterm birth. Maternal use of SSRI increases maternal and fetal serotonin. The increase in maternal circulating serotonin and serotonin signaling likely promotes vasoconstriction of the uterine and placental vascular beds decreasing blood perfusion to the uterus and consequently to the placenta and fetus with potential impact on placental function and fetal development. Several adverse pregnancy outcomes are similar between women, sheep, and rodents (decreased placental size, decreased birthweight, shorter gestation length/preterm birth, neonatal morbidity, and mortality) highlighting the importance of animal studies to assess the impacts of SSRI. Herein, we address the complex interactions between maternal SSRI use during gestation, circulating serotonin, and the regulation of blood perfusion to the uterus and fetoplacental unit, fetal growth, and pregnancy complications.

Emerging role of miRNAs, lncRNAs, and circRNAs in pregnancy-associated diseases

ABSTRACT

Accumulating studies have demonstrated that non-coding RNAs (ncRNAs), functioning as important regulators of transcription and translation, are involved in the establishment and maintenance of pregnancy, especially the maternal immune adaptation process. The endometrial stromal cells (ESCs), trophoblast cells, and decidua immune cells that reside at the maternal-fetal interface are thought to play significant roles in normal pregnancy and pregnancy-associated diseases. Here, we reviewed the up-to-date evidence on how microRNA, long non-coding RNA, and circular RNA regulate ESCs, trophoblast cells, and immune cells and discussed the potential applications of these ncRNAs as diagnostic and therapeutic markers in pregnancy complications.

MDSCs in pregnancy and pregnancy-related complications: an update†

Maternal-fetal immune tolerance is a process that involves complex interactions of the immune system, and myeloid-derived suppressor cells have emerged as one of the novel immunomodulator in the maintenance of maternal-fetal immune tolerance. Myeloid-derived suppressor cells are myeloid progenitor cells with immunosuppressive activities on both innate and adaptive cells through various mechanisms. Emerging evidence demonstrates the accumulation of myeloid-derived suppressor cells during healthy pregnancy to establish maternal-fetal immune tolerance, placentation, and fetal-growth process. By contrast, the absence or decreased myeloid-derived suppressor cells in pregnancy complications like preeclampsia, preterm birth, stillbirth, and recurrent spontaneous abortion have been reported. Here, we have summarized the origin, mechanisms, and functions of myeloid-derived suppressor cells during pregnancy along with the recent advancements in this dynamic field. We also shed light on the immunomodulatory activity of myeloid-derived suppressor cells, which can be a foundation for potential therapeutic manipulation in immunological pregnancy complications.

What Pediatricians Should Know Before Studying Gut Microbiota

Billions of microorganisms, or “microbiota”, inhabit the gut and affect its homeostasis, influencing, and sometimes causing if altered, a multitude of diseases. The genomes of the microbes that form the gut ecosystem should be summed to the human genome to form the hologenome due to their influence on human physiology; hence the term “microbiome” is commonly used to refer to the genetic make-up and gene–gene interactions of microbes. This review attempts to provide insight into this recently discovered vital organ of the human body, which has yet to be fully explored. We herein discuss the rhythm and shaping of the microbiome at birth and during the first years leading up to adolescence. Furthermore, important issues to consider for conducting a reliable microbiome study including study design, inclusion/exclusion criteria, sample collection, storage, and variability of different sampling methods as well as the basic terminology of molecular approaches, data analysis, and clinical interpretation of results are addressed. This basic knowledge aims to provide the pediatricians with a key tool to avoid data dispersion and pitfalls during child microbiota study.

Human Tissue-Resident Memory T Cells in the Maternal-Fetal Interface. Lost Soldiers or Special Forces?

The immune system plays a critical role during pregnancy, but the specific mechanisms and immune cell function needed to support pregnancy remain incompletely understood. Despite decades of research efforts, it is still unclear how the immune system maintains tolerance of fetal-derived tissues, which include most cells of the placenta and of course the fetus itself, without forfeiting the ability to protect against harmful infections. T cells recognize antigen in the context of major histocompatibility complex (MHC) encoded proteins, but classical MHC class I and II expression are diminished in fetal-derived cells. Can T cells present at the maternal–fetal interface (MFI) protect these cells from infection? Here we review what is known in regard to tissue-resident memory T (Trm) cells at the MFI. We mainly focus on how Trm cells can contribute to protection in the context of the unique features of the MFI, such as limited MHC expression as well as the temporary nature of the MFI, that are not found in other tissues.