How mothers tolerate their children.

Shifting pools of antigen can influence pregnancy-induced immune tolerance.

Reproductive outcomes after pregnancy-induced displacement of preexisting microchimeric cells.

Pregnancy confers partner-specific protection against complications in future pregnancy that parallel persistence of fetal microchimeric cells (FMcs) in mothers after parturition. We show that preexisting FMcs become displaced by new FMcs during pregnancy and that FMc tonic stimulation is essential for expansion of protective fetal-specific forkhead box P3 (FOXP3)-positive regulatory T cells (Treg cells). Maternal microchimeric cells and accumulation of Treg cells with noninherited maternal antigen (NIMA) specificity are similarly overturned in daughters after pregnancy, highlighting a fixed microchimeric cell niche. Whereas NIMA-specific tolerance is functionally erased by pregnancy, partner-specific resiliency against pregnancy complications persists in mothers despite paternity changes in intervening pregnancy. Persistent fetal tolerance reflects FOXP3 expression plasticity, which allows mothers to more durably remember their babies, whereas daughters forget their mothers with new pregnancy-imprinted immunological memories.

A spatially resolved timeline of the human maternal-fetal interface.

Beginning in the first trimester, fetally derived extravillous trophoblasts (EVTs) invade the uterus and remodel its spiral arteries, transforming them into large, dilated blood vessels. Several mechanisms have been proposed to explain how EVTs coordinate with the maternal decidua to promote a tissue microenvironment conducive to spiral artery remodelling (SAR)1-3. However, it remains a matter of debate regarding which immune and stromal cells participate in these interactions and how this evolves with respect to gestational age. Here we used a multiomics approach, combining the strengths of spatial proteomics and transcriptomics, to construct a spatiotemporal atlas of the human maternal-fetal interface in the first half of pregnancy. We used multiplexed ion beam imaging by time-of-flight and a 37-plex antibody panel to analyse around 500,000 cells and 588 arteries within intact decidua from 66 individuals between 6 and 20 weeks of gestation, integrating this dataset with co-registered transcriptomics profiles. Gestational age substantially influenced the frequency of maternal immune and stromal cells, with tolerogenic subsets expressing CD206, CD163, TIM-3, galectin-9 and IDO-1 becoming increasingly enriched and colocalized at later time points. By contrast, SAR progression preferentially correlated with EVT invasion and was transcriptionally defined by 78 gene ontology pathways exhibiting distinct monotonic and biphasic trends. Last, we developed an integrated model of SAR whereby invasion is accompanied by the upregulation of pro-angiogenic, immunoregulatory EVT programmes that promote interactions with the vascular endothelium while avoiding the activation of maternal immune cells.

Transplacental transfer of anti-SARS-CoV-2 neutralizing antibodies in comparison to other pathogens total antibodies.

BACKGROUNDS: Due to immaturity of their immune system, passive maternal immunization is essential for newborns during their first months of life. Therefore, in the current context of intense circulation of SARS-CoV-2, identifying factors influencing the transfer ratio (TR) of neutralizing antibodies against SARS-CoV-2 (NAb) appears important. METHODS: Our study nested in the COVIPREG cohort (NCT04355234), included mothers who had a SARS-CoV-2 PCR positive during their pregnancy and their newborns. Maternal and neonatal NAb levels were measured with the automated iFlash system. RESULTS: For the 173 mother-infant pairs included in our study, the median gestational age (GA) at delivery was 39.4 weeks of gestation (WG), and 29.7 WG at maternal SARS-CoV-2 infection. Using a multivariate logistic model, having a NAb TR above 1 was positively associated with a longer delay from maternal positive SARS-CoV-2 PCR to delivery (aOR 1.09, 95% CI: 1.03 - 1.17) and with a later GA at delivery (aOR = 1.58, 95% CI: 1.09 - 2.52). It was negatively associated with being a male newborn (aOR 0.21, 95% CI: 0.07 - 0.59). In 3rd trimester SARS-CoV-2 infected mothers, NAb TR was inferior to VZV, toxoplasmosis, CMV, measle and rubella's TR. However, in 1st or 2nd trimester infected mothers, only measle TR was different from NAb TR. CONCLUSION: Male newborn of mothers infected by SARS-CoV-2 during their pregnancy appear to have less protection against SARS-CoV-2 in their first months of life than female newborns. Measle TR was superior to NAb TR even in case of 1st or 2nd trimester maternal SARS-CoV-2 infection. Future studies are needed to investigate possible differences in transmission of NAb following infection vs vaccination and its impact on TR.

Prenatal disruption of blood-brain barrier formation via cyclooxygenase activation leads to lifelong brain inflammation.

Gestational maternal immune activation (MIA) in mice induces persistent brain microglial activation and a range of neuropathologies in the adult offspring. Although long-term phenotypes are well documented, how MIA in utero leads to persistent brain inflammation is not well understood. Here, we found that offspring of mothers treated with polyriboinosinic­polyribocytidylic acid [poly(I:C)] to induce MIA at gestational day 13 exhibit blood­brain barrier (BBB) dysfunction throughout life. Live MRI in utero revealed fetal BBB hyperpermeability 2 d after MIA. Decreased pericyte­endothelium coupling in cerebral blood vessels and increased microglial activation were found in fetal and 1- and 6-mo-old offspring brains. The long-lasting disruptions result from abnormal prenatal BBB formation, driven by increased proliferation of cyclooxygenase-2 (COX2; Ptgs2)-expressing microglia in fetal brain parenchyma and perivascular spaces. Targeted deletion of the Ptgs2 gene in fetal myeloid cells or treatment with the inhibitor celecoxib 24 h after immune activation prevented microglial proliferation and disruption of BBB formation and function, showing that prenatal COX2 activation is a causal pathway of MIA effects. Thus, gestational MIA disrupts fetal BBB formation, inducing persistent BBB dysfunction, which promotes microglial overactivation and behavioral alterations across the offspring life span. Taken together, the data suggest that gestational MIA disruption of BBB formation could be an etiological contributor to neuropsychiatric disorders.

Uterine damage induces placenta accreta and immune imbalance at the maternal-fetal interface in the mouse.

INTRODUCTION: Placenta accreta spectrum (PAS) disorder is one of the major complications resulting in maternal death and serious adverse pregnancy outcomes. Uterine damage - principally that associated with cesarean section - is the leading risk factor for the development of PAS. However, the underlying pathogenesis of PAS related to uterine damage remains unclear. METHODS: For this study, we constructed a mouse PAS model using hysterotomy to simulate a cesarean section in humans. Pregnant mice were sacrificed on embryonic days 12.5 (E12.5) and E17.5. Trophoblast invasion and placental vascularization were analyzed using Hematoxylin-Eosin (H&E) staining and immunohistochemistry (IHC), and the proportions of immune cells at the maternal-fetal interface were analyzed using flow cytometry. We analyzed the expressions of genes in the decidua and placenta using RNA sequencing and subsequent validation by QPCR, and measured serum angiogenic factors by ELISA. RESULTS: Uterine damage led to increased trophoblast invasion and placental vascularization, with extensive changes to the immune-cell profiles at the maternal-fetal interface. The proportions of T and NK cells in the deciduas diminished significantly, with the decidual NK cells and M - 2 macrophages showing the greatest decline. The expression of TNF-α and IL4 was upregulated in the deciduas, while that of IFN-γ and IL10 was downregulated significantly. The expression of Mmp2, Mmp9, Mmp3, and Dock4 was significantly elevated in the placenta, and the serum levels of anti-angiogenic factors were significantly attenuated. DISCUSSION: Uterine damage can cause immune imbalance at the maternal-fetal interface, which may contribute to abnormal trophoblast invasion and enhanced vascularization of the mouse placenta.

Respiratory viral infections during pregnancy: effects of SARS-CoV-2 and other related viruses over the offspring.

Little is known about the consequences of viral infection for pregnant woman or for the fetus. This issue became important with the appearance of the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2). The infection with SARS-CoV-2 causes a respiratory syndrome known as COVID-19. The fast spreading around the world and the fact that without a treatment or vaccine humans are completely exposed, converts emerging viral diseases in a significant risk for pregnant women and their infants. At this time, during SARS-CoV-2 pandemics pregnant women are not considered as a risk population and little is known about the effects of viral infections over the offspring although the amount of emerging evidence showing detrimental effects for the mother and the fetus. This issue highlights the importance to understand the effects of viral infections during pregnancy. In this work, we analyze the effects of viral infections, like SARS-CoV-2 and other related viruses during pregnancy over the mother and the consequences for the offspring.

Whole embryonic detection of maternal microchimeric cells highlights significant differences in their numbers among individuals.

During pregnancy in placental mammals, small numbers of maternal cells (maternal microchimeric cells, or MMc cells) migrate into the fetus and persist decades, or perhaps for the rest of their lives, and higher frequencies of MMc cells are reported to correlate with variety of phenomena, such as immune tolerance, tissue repair, and autoimmune diseases. While detection of these MMc cells is considered in all pregnancies, their frequency differs largely according to tissue type and disease cases, and it remains unclear whether the number of MMc cells differs significantly among embryos in normal pregnancies. Here, for the first time, we developed a whole embryonic detection method for MMc cells using transgenic mice and counted live MMc cells in each individual embryo. Using this technique, we found that the number of MMc cells was comparable in most of the analyzed embryos; however, around 500 times higher number of MMc cells was detected in one embryo at the latest stage. This result suggests that the number of MMc cells could largely differ in rare cases with unknown underlying mechanisms. Our methodology provides a basis for testing differences in the numbers of MMc cells among individual embryos and for analyzing differences in MMc cell type repertoires in future studies. These data could provide a hint toward understanding the mechanisms underlying the variety of apparently inconsistent MMc-related phenomena.

Self-Centered Function of Adaptive Immunity in Regulation of Immune Responses and in Tolerance.

The search for common mechanisms underlying the pathogenesis of chronic inflammatory conditions has crystalized the concept of continuous dual resetting of the immune repertoire (CDR) as a basic principle of the immune system function. Consequently, outlined was the first dynamic comprehensive picture of the immune system function. The goal of this study is to elaborate on regulation of immune responses and mechanisms of tolerance, particularly focusing on adaptive immunity. It is well established that the T/B cell repertoire is selected and maintained based on interactions with self. However, their activation also requires interaction with a self-specific major histocompatibility complex (MHC) "code," i.e., the context of MHC molecules. Therefore, not only repertoire selection and maintenance but also the T/B cell activation and function are self-centered. Thus, adaptive effectors may be primarily focused on the state of self and maintenance of integrity of the self, and only to a certain degree on elimination of the foreign. As examples of such function are used immunologically poorly understood MHC-disparate settings typical for transplantation and pregnancy. Transplantation represents an extreme setting of strong systemic compartment-level adaptive/MHC-restricted immune responses. Described are clinically identified conditions for operational tolerance of MHC-disparate tissues/living systems in allotransplantation, which are in line with the CDR-proposed self-centered regulatory role of T/B cells. In contrast, normal pregnancy is coexistence of semiallogeneic or entirely allogeneic mother and fetus, but without alloreactivity akin to transplantation settings. Presented data support the notion that maintenance of pregnancy is a process that relies predominantly on innate/MHC-independent immune mechanisms. By the inception of hemotrophic stage of pregnancy (second and third trimester), both mother and child are individual living systems, with established adaptive immune repertoires. Although mother-fetus interactions at that point become indirect systemic compartment-level communications, their interactions throughout gestation remain within the innate realm of molecular-level adaptations.

The Role of Maternal Immune Activation in the Pathogenesis of Autism: A Review of the Evidence, Proposed Mechanisms and Implications for Treatment.

Autism spectrum disorder (ASD) is a neurodevelopmental disease that is characterized by a deficit in social interactions and communication, as well as repetitive and restrictive behaviors. Increasing lines of evidence suggest an important role for immune dysregulation and/or inflammation in the development of ASD. Recently, a relationship between inflammation, oxidative stress, and mitochondrial dysfunction has been reported in the brain tissue of individuals with ASD. Some recent studies have also reported oxidative stress and mitochondrial abnormalities in animal models of maternal immune activation (MIA). This review is focused on the hypothesis that MIA induces microglial activation, oxidative stress, and mitochondrial dysfunction, a deleterious trio in the brain that can lead to neuroinflammation and neurodevelopmental pathologies in offspring. Infection during pregnancy activates the mother's immune system to release proinflammatory cytokines, such as IL-6, TNF-α, and others. Furthermore, these cytokines can directly cross the placenta and enter the fetal circulation, or activate resident immune cells, resulting in an increased production of proinflammatory cytokines, including IL-6. Proinflammatory cytokines that cross the blood-brain barrier (BBB) may initiate a neuroinflammation cascade, starting with the activation of the microglia. Inflammatory processes induce oxidative stress and mitochondrial dysfunction that, in turn, may exacerbate oxidative stress in a self-perpetuating vicious cycle that can lead to downstream abnormalities in brain development and behavior.

Grandmaternal cells in cord blood.

BACKGROUND: During pregnancy a feto-maternal exchange of cells through the placenta conducts to maternal microchimerism (Mc) in the child and fetal Mc in the mother. Because of this bidirectional traffic of cells, pregnant women have also acquired maternal cells in utero from their mother and could transfer grandmaternal (GdM) cells to their child through the maternal bloodstream during pregnancy. Thus, cord blood (CB) samples could theoretically carry GdMMc. Nevertheless this has never been demonstrated. METHODS: Using Human Leukocyte Antigen (HLA)-specific quantitative PCR assays on three-generation families, we were able to test 28 CB samples from healthy primigravid women for GdMMc in whole blood (WB) and isolated cells (PBMC, T, B, granulocytes, stem cells). FINDINGS: Five CB samples (18%) had GdMMc which could not be confounded with maternal source, with quantities 100 fold lower than maternal Mc in WB and PBMC. Risk of aneuploidies and/or related invasive prenatal procedures significantly correlated with the presence of GdMMc in CB (p=0.024). Significantly decreased HLA compatibility was observed in three-generation families from CB samples carrying GdMMc (p=0.019). INTERPRETATION: Transgenerational transfer of cells could have implications in immunology and evolution. Further analyses will be necessary to evaluate whether GdMMc in CB is a passive or immunologically active transfer and whether invasive prenatal procedures could trigger GdMMc. FUNDING: Provence-Alpes-Côte d'Azur APEX grant # 2012_06549E, 2012_11786F and 2014_03978) and the Foundation for Medical Research (FRM Grant #ING20140129045).

Regulation of the innate immune cells during pregnancy: An immune checkpoint perspective.

The foetus can be regarded as a half-allograft implanted into the maternal body. In a successful pregnancy, the mother does not reject the foetus because of the immune tolerance mechanism at the maternal-foetal interface. The innate immune cells are a large part of the decidual leukocytes contributing significantly to a successful pregnancy. Although the contributions have been recognized, their role in human pregnancy has not been completely elucidated. Additionally, the accumulated evidence demonstrates that the immune checkpoint molecules expressed on the immune cells are co-inhibitory receptors regulating their activation and biological function. Therefore, it is critical to understand the immune microenvironment and explore the function of the innate immune cells during pregnancy. This review summarizes the classic immune checkpoints such as PD-1, CTLA-4 and some novel molecules recently identified, including TIM-3, CD200, TIGIT and the Siglecs family on the decidual and peripheral innate immune cells during pregnancy. Furthermore, it emphasizes the role of the immune checkpoint molecules in pregnancy-associated complications and reproductive immunotherapy.

Metabolic Reprogramming of Immune Cells at the Maternal-Fetal Interface and the Development of Techniques for Immunometabolism.

Immunity and metabolism are interdependent and coordinated, which are the core mechanisms for the body to maintain homeostasis. In tumor immunology research, immunometabolism has been a research hotspot and has achieved groundbreaking changes in recent years. However, in the field of maternal-fetal medicine, research on immunometabolism is still lagging. Reports directly investigating the roles of immunometabolism in the endometrial microenvironment and regulation of maternal-fetal immune tolerance are relatively few. This review highlights the leading techniques used to study immunometabolism and their development, the immune cells at the maternal-fetal interface and their metabolic features required for the implementation of their functions, explores the interaction between immunometabolism and pregnancy regulation based on little evidence and clues, and attempts to propose some new research directions and perspectives.

Biologia futura: embryo-maternal communication via progesterone-induced blocking factor (PIBF) positive embryo-derived extracellular vesicles. Their role in maternal immunomodulation.

Paternal antigens expressed by the foetus are recognized as foreign. Therefore,-according to the rules of transplantation immunity-the foetus ought to be "rejected". However, during normal gestation, maternal immune functions are re-adjusted, in order to create a favourable environment for the developing foetus. Some of the mechanisms that contribute to the altered immunological environment, for example, the cytokine balance and NK cell function, with special emphasis on the role of progesterone and the progesterone-induced blocking factor (PIBF) will be reviewed.

Elevated inflammatory mediators from the maternal-fetal interface to fetal circulation during labor.

BACKGROUND: Elevated cytokines, like IL-1ßand IL-6, are known to contribute to the pathogenesis of labor. However, the change of inflammatory mediators in maternal-fetal interface to fetal circulation is obscure. STUDY DESIGN AND METHODS: We investigated the changes of inflammatory cytokines, chemokines and macrophage in maternal-fetal interface tissues and fetal circulation of women in labor vs. non-labor. Human myometrium, placenta, decidua, fetal membrane and umbilical blood were obtained from in-labor and non-in-labor women who eventually delivered live, singleton infants at term (>37 weeks gestation) by elective caesarean section. Luminex was used to measure the level of cytokines (TNF-α, IL-1ß, IL-6, IL-8) and chemokines (MCP-1, GM-CSF, MIP-1α, MIP-1ß) in each sample (tissue and umbilical blood). Macrophage infiltration was demonstrated by immunohistochemistry. RESULTS: During labor, the level of cytokines TNF-α, IL-1ß, IL-6 and IL-8 and chemokine MCP-1 and MIP-1ß in myometrium is significantly higher (p < 0.05), than those obtained from non-laboring patients. This increase coincides with the influx of macrophage into the myometrium. In addition, IL-1ß and IL-8 (p < 0.05) are also up regulated in fetal membrane during labor compared to non-labor. The cytokines do not change significantly in placenta and decidua tissue. In fetal circulation, IL-6 (p < 0.05) is up regulated in umbilical vein blood in labor group. IL-8 (p = 0.08) in umbilical vein also show an increasing trend during labor. CONCLUSIONS: There are markedly elevated inflammatory mediators in maternal-fetal interface during labor. The increased maternal inflammatory factors released into the fetal circulation through placenta circulation at the time of labor. This increase coincides with the influx of macrophage into the pregnancy tissue, suggesting that the inflammatory response might play an important role in the onset of labor.

TLRs induce Th1/Th2 responses by affecting the secretion of CCL2 at the maternal-foetal interface.

RESEARCH QUESTION: In previous studies, we demonstrated that the human decidua and decidual stromal cells express high levels of CCL2 (chemokine (C-C motif) ligand 2, also known as monocyte chemotactic protein-1) and its receptor CCR2 (chemokine receptor 2). DSC-derived CCL2 interacts with CCR2 on DICs, causing the production and secretion of Th2-type cytokines, which promotes a Th2 bias at the maternal-foetal interface. Many pathogens may be present in the genital tract during pregnancy, but whether they affect immune regulation, especially Th2 regulation remains unknown. Toll-like receptors (TLRs) are a family of pattern-recognition receptors that recognise specific components of microbes and certain host molecules and play an important role in the host innate immune response. We examined TLR expression and evaluated whether TLRs could affect CCL2 secretion and subsequently induce Th1/Th2 responses. DESIGN: We used quantitative real-time PCR to measure TLR expression in the decidua and DSCs (decidual stromal cells). DSCs were cultured in the presence or absence of the TLR2 agonists PAM3CSK4, PGN-Sa, and zymosan, the TLR3 agonist poly (I:C) and the TLR4 agonist LPS. Then, the supernatants were assayed for CCL2 secreted by DSCs and IL-4, IFN-γ, IL-10, and TNF-α produced by DICs. RESULTS: Costimulation with TLR2, TLR3 and TLR4 agonists resulted in enhancing CCL2 production compared with that in the controls. Additionally, these TLR2, 3, and 4 agonists stimulated CD80/CD86 on DSCs and regulated IL-4 and IL-10 secretion on DICs. TLR2 and TLR3 agonists may promote Th1/Th2 immune bias. CONCLUSIONS: TLRs may induce Th1/Th2 responses by affecting the secretion of CCL2 at the maternal-foetal interface.

Tryptophan metabolism and immune regulation in the human placenta.

The placenta represents the maternal-fetal vascular interface. It is capable of supplying the bioenergetic needs of the developing conceptus. It is composed of different cell types that engage in highly varied functions, ranging from attachment, invasion and vascular remodeling to cell fusion, hormone production, and nutrient transport. A deep knowledge of the immunological mechanisms responsible for maintaining an active tolerance towards an allogeneic fetus and the anti-inflammatory properties of the placenta can be useful to clarify the pathogenesis of adverse events in pregnancy. While the systemic mechanisms of this immunological regulation in pregnancy have been well studied, the metabolic processes involved in the placental immune response are still poorly understood. The aim of this review is to summarize the most important information concerning the immune regulation in pregnancy, focusing on the role of tryptophan (Trp) catabolism performed by indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO) in the placenta.

Placental Immune Tolerance and Organ Transplantation: Underlying Interconnections and Clinical Implications.

The immune system recognizes and attacks non-self antigens, making up the cornerstone of immunity activity against infection. However, during organ transplantation, the immune system also attacks transplanted organs and leads to immune rejection and transplantation failure. Interestingly, although the embryo and placenta are semi-allografts, like transplanted organs, they can induce maternal tolerance and be free of a vigorous immune response. Also, embryo or placenta-related antibodies might adversely affect subsequent organ transplantation despite the immune tolerance during pregnancy. Therefore, the balance between the immune tolerance in maternal-fetal interface and normal infection defense provides a possible desensitization and tolerance strategy to improve transplantation outcomes. A few studies on mechanisms and clinical applications have been performed to explore the relationship between maternal-fetal immune tolerance and organ transplantation. However, up to now, the mechanisms underlying maternal-fetal immune tolerance remain vague. In this review, we provide an overview on the current understanding of immune tolerance mechanisms underlying the maternal-fetal interface, summarize the interconnection between immune tolerance and organ transplantation, and describe the adverse effect of pregnancy alloimmunization on organ transplantation.