Seminal fluid regulates accumulation of FOXP3+ regulatory T cells in the preimplantation mouse uterus through expanding the FOXP3+ cell pool and CCL19-mediated recruitment

FOXP3+ T cells and immune dysregulation in canine pyometra

Canine pyometra is a suppurative uterine infection associated with immune dysregulation. This study investigated the role of regulatory T cells (Tregs) and associated factors in the pus accumulation within the canine uterus. Sixteen client-owned intact bitches, eight diagnosed with pyometra and the other eight healthy animals undergoing elective ovariohysterectomy, were enrolled. Blood samples were collected into ethylenediaminetetraacetic acid (EDTA)-coated tubes for flow cytometry. Tissue samples were obtained after ovariohysterectomy and used to examine localization of interleukin (IL)-2 and IL-2Rα as key regulators of Treg functions. Gene expression was analyzed by reverse transcription quantitative polymerase chain reaction (RT-qPCR). Results of flow cytometry analysis revealed a significant increase in the population of Tregs in the uterine tissue and their corresponding decrease in the peripheral blood. This shift is likely reflective of the recruitment of Tregs from the peripheral blood to the decidua in pyometra. There was a marked upregulation in the expression of IL-2 in the uterine tissue. There was dysregulation in the expression of anti-inflammatory cytokines produced by Tregs (such as IL-10) and pro-inflammatory factors secreted by effector T cells (such as RORγt and IL-17A), which gave a deeper insight into the mechanism underlying the immune dysfunction in canine pyometra. Taken together, these observations elucidate the dynamic changes in Tregs and related factors during canine uterine pyometra, thus providing a new perspective on the equilibrium of the uterine immune microenvironment.

The maternal-fetal interface at single-cell resolution: uncovering the cellular anatomy of the placenta and decidua

The maternal-fetal interface represents a critical site of immunological interactions that can greatly influence pregnancy outcomes. The unique cellular composition and cell-cell interactions taking place within these tissues has spurred substantial research efforts focused on the maternal-fetal interface. With the recent advent of single-cell technologies, multiple investigators have applied such methods to gain an unprecedented level of insight into maternal-fetal communication. Here, we provide an overview of the dynamic cellular composition and cell-cell communications at the maternal-fetal interface as reported by single-cell investigations. By primarily focusing on data from pregnancies in the second and third trimesters, we aim to showcase how single-cell technologies have bolstered the foundational understanding of each cell's contribution to physiologic gestation. Indeed, single-cell technologies have enabled the examination of classical placental cells, such as the trophoblast, as well as uncovered new roles for structural cells now recognized as active participants in pregnancy and parturition, such as decidual and fetal stromal cells, which are reviewed herein. Furthermore, single-cell data investigating the ontogeny, function, differentiation, and interactions among immune cells present at the maternal-fetal interface, namely macrophages, T cells, dendritic cells, neutrophils, mast cells, innate lymphoid cells, natural killer cells, and B cells are discussed in this review. Moreover, a key output of single-cell investigations is the inference of cell-cell interactions, which has been leveraged to not only dissect the intercellular communications within specific tissues but also between compartments such as the decidua basalis and placental villi. Collectively, this review emphasizes the ways by which single-cell technologies have expanded the understanding of cell composition and cellular processes underlying pregnancy in mid-to-late gestation at the maternal-fetal interface, which can prompt their continued application to reveal new pathways and targets for the treatment of obstetrical disease.

Unveiling Gestational Diabetes: An Overview of Pathophysiology and Management

Gestational diabetes mellitus (GDM) is characterized by an inadequate pancreatic β-cell response to pregnancy-induced insulin resistance, resulting in hyperglycemia. The pathophysiology involves reduced incretin hormone secretion and signaling, specifically decreased glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), impairing insulinotropic effects. Pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), impair insulin receptor substrate-1 (IRS-1) phosphorylation, disrupting insulin-mediated glucose uptake. β-cell dysfunction in GDM is associated with decreased pancreatic duodenal homeobox 1 (PDX1) expression, increased endoplasmic reticulum stress markers (CHOP, GRP78), and mitochondrial dysfunction leading to impaired ATP production and reduced glucose-stimulated insulin secretion. Excessive gestational weight gain exacerbates insulin resistance through hyperleptinemia, which downregulates insulin receptor expression via JAK/STAT signaling. Additionally, hypoadiponectinemia decreases AMP-activated protein kinase (AMPK) activation in skeletal muscle, impairing GLUT4 translocation. Placental hormones such as human placental lactogen (hPL) induce lipolysis, increasing circulating free fatty acids which activate protein kinase C, inhibiting insulin signaling. Placental 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) overactivity elevates cortisol levels, which activate glucocorticoid receptors to further reduce insulin sensitivity. GDM diagnostic thresholds (≥92 mg/dL fasting, ≥153 mg/dL post-load) are lower than type 2 diabetes to prevent fetal hyperinsulinemia and macrosomia. Management strategies focus on lifestyle modifications, including dietary carbohydrate restriction and exercise. Pharmacological interventions, such as insulin or metformin, aim to restore AMPK signaling and reduce hepatic glucose output. Emerging therapies, such as glucagon-like peptide-1 receptor (GLP-1R) agonists, show potential in improving glycemic control and reducing inflammation. A mechanistic understanding of GDM pathophysiology is essential for developing targeted therapeutic strategies to prevent both adverse pregnancy outcomes and the progression to overt diabetes in affected women.

Seminal fluid effects on uterine receptivity to embryo implantation: transcriptomic strategies to define molecular mechanisms

Embryo implantation requires both a developmentally competent embryo and a receptive uterus. Impaired uterine receptivity is a common constraint on implantation success and reproductive outcome. Ovarian steroid hormones oestrogen and progesterone play a central role in establishing uterine receptivity, but other factors also contribute. One additional regulating factor is male partner seminal fluid. However, the full physiological impacts of seminal fluid on uterine receptivity and the specific molecular pathways involved are not yet completely defined. New advances in RNA-sequencing technologies provide a powerful means to examine how uterine tissues and cells respond to seminal fluid contact. Findings utilising sequencing technology provide strong cellular and molecular evidence in humans and mice that seminal fluid contact around the time of ovulation drives immune and vascular changes with potential to affect endometrial receptivity in the peri-implantation phase. This approach has led to the discovery of novel mediators and regulatory factors subsequently shown to facilitate embryo implantation in genetic mouse models, enabling functional validation. Here, we summarise the evidence from recent microarray and RNA-sequencing findings that seminal fluid contact can directly and indirectly impact the transcriptional state of endometrial tissue during the implantation window in mice and also in humans. Progress in elucidating the female reproductive tract response to seminal fluid will improve understanding of male partner effects on endometrial receptivity, and the knowledge gained will have practical applications for achieving healthy pregnancy and offspring outcomes.

Assessing Seminal Fluid Interaction with Female Reproductive Tract Tissues: In Vivo and In Vitro Models for Mouse

After intromission of seminal fluid at mating in mammals, the seminal fluid interacts with the lining of the female reproductive tract and elicits a female immune response. This response is triggered by signals in seminal fluid (carried by both the sperm and seminal plasma components) that bind receptors on female tract epithelial cells, causing a change in their transcriptional program to upregulate expression of pro-inflammatory cytokines and chemokines. The ensuing leukocyte recruitment and immune activation facilitates conception, embryo development, and progression of pregnancy. In this chapter, we report methods for evaluating effects of seminal fluid and its components (seminal plasma and sperm) on the female reproductive tract immune response in mice.

Treg cells promote decidual vascular remodeling and modulate uterine NK cells in pregnant mice

Regulatory T (Treg) cells are essential for maternal immune tolerance of the fetus and placenta. In preeclampsia, aberrant Treg cell tolerance is implicated, but how Treg cells affect the uterine vascular dysfunction thought to precede placental impairment and maternal vasculopathy is unclear. We used Foxp3-diphtheria toxin receptor mice to test the hypothesis that Treg cells are essential regulators of decidual spiral artery adaptation to pregnancy. Transient Treg cell depletion during early placental morphogenesis caused impaired remodeling of decidual spiral arteries, altered uterine artery function, and fewer Dolichos biflorus agglutinin+ uterine natural killer (uNK) cells, resulting in late-gestation fetal loss and fetal growth restriction. Replacing the Treg cells by transfer from wild-type donors mitigated the impact on uNK cells, vascular remodeling, and fetal loss. RNA sequencing of decidua revealed genes associated with NK cell function and placental extravillous trophoblasts were dysregulated after Treg cell depletion and normalized by Treg cell replacement. These data implicate Treg cells as essential upstream drivers of uterine vascular adaptation to pregnancy, through a mechanism likely involving phenotypic regulation of uNK cells and trophoblast invasion. The findings provide insight into mechanisms linking impaired adaptive immune tolerance and altered spiral artery remodeling, 2 hallmark features of preeclampsia.

IL-2 Complexed With Anti-IL-2 Antibody Expands the Maternal T-Regulatory Cell Pool and Alleviates Fetal Loss in Abortion-Prone Mice

Regulatory T (Treg) cells are essential for immune tolerance of embryo implantation, and insufficient Treg cells provokes early pregnancy loss. An abortion-prone mouse model was used to evaluate IL-2 complexed with JES6-1 anti-IL-2 antibody (IL-2/JES6-1) to boost uterine Treg cells and improve reproductive success. IL-2/JES6-1, but not IL-2/IgG, administered in periconception to CBA/J females mated with DBA/2 males elicited a greater than twofold increase in the proportion of CD4+ T cells expressing forkhead box P3 (FOXP3), and an increased ratio of FOXP3+ Treg cells/FOXP3- T conventional cells in the uterus and its draining lymph nodes at embryo implantation that was sustained into midgestation. An attenuated phenotype was evident in both thymic-derived and peripheral Treg cells with elevated cytotoxic T-lymphocyte antigen-4, CD25, and FOXP3 indicating improved suppressive function, as well as increased proliferative marker Ki-67. IL-2/JES6-1 treatment reduced fetal loss from 31% to 10%, accompanied by a 6% reduction in late gestation fetal weight, despite comparable placental size and architecture. Similar effects of IL-2/JES6-1 on Treg cells and fetal growth were seen in CBA/J females with healthy pregnancies sired by BALB/c males. These findings show that expanding the uterine Treg cell pool through targeting IL-2 signaling is a strategy worthy of further investigation for mitigating risk of immune-mediated fetal loss.

The Effect of Seminal Plasma on the Equine Endometrial Transcriptome

The establishment of pregnancy involves a fine-tuned balance between protection and tolerance within the maternal immune system, as the female needs to accept a foreign antigen (the semi-allogenic fetus) while still being able to combat pathogens from the uterus. In the horse, the first uterine exposure to paternal antigens is during mating when sperm is introduced to the tissue and draining lymphatics of the uterus. Additionally, it has been suggested that seminal plasma and its proteins within it play an essential role in preparing the female tract for a suitable immunologic environment but this has not been confirmed in the horse. Therefore, the objective of this study was to evaluate the endometrial transcriptome following insemination either with seminal plasma or with reduced seminal plasma. We hypothesised that reduced seminal plasma would alter the endometrial transcriptome and affect transcripts relating to immunotolerance, antigen presentation and embryo growth and development. To do so, six (n = 6) mares were inseminated in a randomised switch-back design over the course of four oestrous cycles. Mares were rectally palpated and scanned via ultrasonography for the detection of a pre-ovulatory follicle (>35 mm) alongside increasing uterine oedema and relaxed cervix, and then treated with one of four treatment groups including (1) 30 mL lactated Ringers solution (LRS; NegCon), (2) 500 × 106 spermatozoa in conjunction with 30 mL seminal plasma (SP+), (3) 30 mL lactated Ringers solution (LRS; wash out) and (4) 500 × 106 spermatozoa with seminal plasma reduced via gradient centrifugation and resuspended in 30 mL LRS (SP-). Human chorionic gonadotropin (hCG) was administered to standardise the time to ovulation and endometrial biopsies were collected 7 days after insemination. RNA was isolated utilising Trizol, and RNA-Seq was performed by Novogene, with 97.79% total mapping and 40 million read depth. p value was set to <0.05. When comparing SP+ to SP-, 158 differentially expressed genes (DEGs) were identified. Biological processes impacted included antigen processing and regulation, cholesterol synthesis, and immune/inflammatory response. Gene ontology (GO) enrichment analysis using DAVID v6.8 revealed that many of these DEGs were involved in biological process such as antigen presentation (HLA-DM beta chain, HLA-DRB, HLA-DQA and RASGRP1), immune cell signalling (CXCL9, CXCL1, DEFB1 and MIP-2B), embryo growth and development (INHA, KLF2, RDH10, LAMA3 and SLC34A2) and embryo metabolism (ABCA1, ABCA2, APOA1, LDL, INSR, IGFBP2 and IGFBP3). Overall, reduction of seminal plasma from the insemination dose impacted the endometrial transcriptome at the time of early embryonic exposure to the uterine environment. Further work is justified to evaluate these alterations impact on embryo maturation, placental development, pregnancy outcome and development of offspring.

Interaction of semen with female reproductive tract tissues: what we know, what we guess and what we need to do

For nearly 100 years the postcoital inflammatory response has been described in the female reproductive tract of rodents. Since the 1950's this observation has been made in a number of animals including humans and domestic species. Yet pregnancy can be initiated and maintained by using embryo transfer which bypasses insemination and the related postcoital inflammatory response. Thus, the role of semen exposure beyond sperm transport and subsequent postcoital inflammatory response in female reproductive tissues has yet to be given a true physiological purpose. Historically the postcoital inflammatory response of female tissues was suggested to remove spermatozoa and male derived pathogens from the female reproductive tract. More recently, semen exposure and the postcoital inflammatory response have been suggested to play a role in long-term preparation of the maternal immune system to the semi-allogeneic pregnancy, ancillary support of the preimplantation embryo, and potentially fetal programing that improves pregnancy outcomes, while the absence or inappropriate postcoital inflammation has been suggested to contribute to pregnancy complications. Although the postcoital inflammatory response has been robustly characterized, the evidence for its role in promoting positive pregnancy outcomes or reducing pregnancy complications remains tenuous. This manuscript is designed to balance the information we know regarding semen exposure and postcoital inflammation in various animal systems, with the information we perceive to be factual but perhaps not yet fully tested, along with the data we have yet to generate if we intend to postulate a physiological purpose of the postcoital inflammatory response to pregnancy outcomes.

Beyond Immune Balance: The Pivotal Role of Decidual Regulatory T Cells in Unexplained Recurrent Spontaneous Abortion

Recurrent spontaneous abortion (RSA) is defined as two or more consecutive pregnancy failures, which brings tremendous stress to women of childbearing age and seriously affects family well-being. However, the reason in about 50% of cases remains unknown and is defined as unexplained recurrent spontaneous abortion (URSA). The immunological perspective in URSA has attracted widespread attention in recent years. The embryo is regarded as a semi-allogeneic graft to the mother. A successful pregnancy requires transition to an immune environment conducive to embryo survival at the maternal-fetal interface. As an important member of regulatory immunity, regulatory T (Treg) cells play a key role in regulating immune tolerance at the maternal-fetal interface. This review will focus on the phenotypic plasticity and lineage stability of Treg cells to illustrate its relationship with URSA.

In vivo effect of vaginal seminal plasma application on the human endometrial transcriptome: a randomized controlled trial

Studies in humans and animals suggest that seminal plasma, the acellular seminal fluid component, stimulates the endometrium to promote immune tolerance and facilitate implantation. We designed a randomized, double-blinded, placebo-controlled trial to investigate changes in the endometrial transcriptomic profile after vaginal application of seminal plasma. The study participants were randomized into two groups. Five women received a vaginal application of seminal plasma, and four received a placebo application with saline solution. The application was performed 2 days after HCG-triggered ovulation in an unstimulated cycle. After 5-8 days, an endometrial biopsy was collected to analyze differences in the endometrial transcriptomic profile using microarray analyses. A differential gene expression analysis and a gene set analysis were performed. The gene set enrichment analysis showed a positive enrichment of pathways associated with the immune response, cell viability, proliferation, and cellular movement. Moreover, pathways involved in implantation, embryo development, oocyte maturation, and angiogenesis were positively enriched. The differential gene expression analysis, after adjusting for multiple testing, showed no significantly differentially expressed genes between the two groups. A comparative analysis was also performed with similar studies conducted in other animals or in vitro using human endometrial cells. The comparative analysis showed that the effect of seminal plasma effect on the endometrium is similar in pigs, mice, and in vitro human endometrial cells. The present study provides evidence that seminal plasma might impact the endometrium during the implantation window, with potential to affect endometrial receptivity and embryo development.

The endometrial transcriptome transition preceding receptivity to embryo implantation in mice

BACKGROUND

Receptivity of the uterus is essential for embryo implantation and progression of mammalian pregnancy. Acquisition of receptivity involves major molecular and cellular changes in the endometrial lining of the uterus from a non-receptive state at ovulation, to a receptive state several days later. The precise molecular mechanisms underlying this transition and their upstream regulators remain to be fully characterized. Here, we aimed to generate a comprehensive profile of the endometrial transcriptome in the peri-ovulatory and peri-implantation states, to define the genes and gene pathways that are different between these states, and to identify new candidate upstream regulators of this transition, in the mouse.

RESULTS

High throughput RNA-sequencing was utilized to identify genes and pathways expressed in the endometrium of female C57Bl/6 mice at estrus and on day 3.5 post-coitum (pc) after mating with BALB/c males (n = 3-4 biological replicates). Compared to the endometrium at estrus, 388 genes were considered differentially expressed in the endometrium on day 3.5 post-coitum. The transcriptional changes indicated substantial modulation of uterine immune and vascular systems during the pre-implantation phase, with the functional terms Angiogenesis, Chemotaxis, and Lymphangiogenesis predominating. Ingenuity Pathway Analysis software predicted the activation of several upstream regulators previously shown to be involved in the transition to receptivity including various cytokines, ovarian steroid hormones, prostaglandin E2, and vascular endothelial growth factor A. Our analysis also revealed four candidate upstream regulators that have not previously been implicated in the acquisition of uterine receptivity, with growth differentiation factor 2, lysine acetyltransferase 6 A, and N-6 adenine-specific DNA methyltransferase 1 predicted to be activated, and peptidylprolyl isomerase F predicted to be inhibited.

CONCLUSIONS

This study confirms that the transcriptome of a receptive uterus is vastly different to the non-receptive uterus and identifies several genes, regulatory pathways, and upstream drivers not previously associated with implantation. The findings will inform further research to investigate the molecular mechanisms of uterine receptivity.

Immune Regulation of Seminal Plasma on the Endometrial Microenvironment: Physiological and Pathological Conditions

Seminal plasma (SP) accounts for more than 90% of semen volume. It induces inflammation, regulates immune tolerance, and facilitates embryonic development and implantation in the female reproductive tract. In the physiological state, SP promotes endometrial decidualization and causes changes in immune cells such as macrophages, natural killer cells, regulatory T cells, and dendritic cells. This leads to the secretion of cytokines and chemokines and also results in the alteration of miRNA profiles and the expression of genes related to endometrial tolerance and angiogenesis. Together, these changes modulate the endometrial immune microenvironment and contribute to implantation and pregnancy. However, in pathological situations, abnormal alterations in SP due to advanced age or poor diet in men can interfere with a woman's immune adaptation to pregnancy, negatively affecting embryo implantation and even the health of the offspring. Uterine pathologies such as endometriosis and endometritis can cause the endometrium to respond negatively to SP, which can further contribute to pathological progress and interfere with conception. The research on the mechanism of SP in the endometrium is conducive to the development of new targets for intervention to improve reproductive outcomes and may also provide new ideas for semen-assisted treatment of clinical infertility.

Immune responses in the uterine mucosa: clues for vaccine development in pigs

The immune system in the upper reproductive tract (URT) protects against sexually transmitted pathogens, while at the same time providing immune tolerance responses against allogenic sperm and the developing fetus. The uterine environment is also responsive to hormonal variations during the estrus cycle, although the most likely timing of exposure to pathogens is during estrus and breeding when the cervix is semi-permissive. The goal for intrauterine immunization would be to induce local or systemic immunity and/or to promote colostral/lactogenic immunity that will passively protect suckling offspring. The developing fetus is not the vaccine target. This minireview article focuses on the immune response induced in the pig uterus (uterine body and uterine horns) with some comparative references to other livestock species, mice, and humans.

Fetal-maternal interactions during pregnancy: a 'three-in-one' perspective

A successful human pregnancy requires the maternal immune system to recognize and tolerate the semi-allogeneic fetus, allowing for appropriate trophoblasts invasion and protecting the fetus from invading pathogens. Therefore, maternal immunity is critical for the establishment and maintenance of pregnancy, especially at the maternal-fetal interface. Anatomically, the maternal-fetal interface has both maternally- and fetally- derived cells, including fetal originated trophoblasts and maternal derived immune cells and stromal cells. Besides, a commensal microbiota in the uterus was supposed to aid the unique immunity in pregnancy. The appropriate crosstalk between fetal derived and maternal originated cells and uterine microbiota are critical for normal pregnancy. Dysfunctional maternal-fetal interactions might be associated with the development of pregnancy complications. This review elaborates the latest knowledge on the interactions between trophoblasts and decidual immune cells, highlighting their critical roles in maternal-fetal tolerance and pregnancy development. We also characterize the role of commensal bacteria in promoting pregnancy progression. Furthermore, this review may provide new thought on future basic research and the development of clinical applications for pregnancy complications.

Profiling of Immunomodulatory Genes and Quantification of CD25+ Cells in Different Types of Early Pregnancy Loss

INTRODUCTION

Maternal regulatory T (Treg) cells play a pivotal role in establishing general immune homeostasis in the decidua for maintenance of pregnancy. We aimed in this study to investigate the relationship between mRNA expression of immunomodulatory genes and CD25+ Treg cells with early pregnancy losses.

METHODS

Our study included 3 groups of early pregnancy losses including sporadic spontaneous abortions, recurrent spontaneous abortions, sporadic spontaneous abortions post IVF treatment and the control group. We performed RT-PCR for analyzing mRNA expression levels of 6 immunomodulatory genes and CD25 immunohistochemistry for quantification of Treg cells.

RESULTS

Only FOXP3, CD274 (PDL1), and TGFβ1 mRNA expression levels were significantly decreased in the miscarriage groups in comparison to the control group, whereas there was no significant mRNA expression change of CD4, IL2RA, and IL10. We also found significantly lower number of CD25+ cells in the miscarriages.

CONCLUSION

We conclude that decreased expression of FOXP3 and PD-L1 may play a significant role in the pathogenesis of spontaneous abortion cases whereas decreased expression of TGFβ1 gene may be associated with the occurrence of early loss in IVF-treated pregnancies. Additional immunoprofiling of Treg cell population is needed to quantify Treg cells in early pregnancy losses.

The role of thymus- and extrathymus-derived regulatory T cells in maternal-fetal tolerance

Regulatory T (Treg) cells could be divided into thymus-derived Treg (tTreg) cells and peripherally derived Treg (pTreg) cells, and in vitro induced Treg (iTreg) cells. To date, the functions of tTreg versus pTreg and their relative contributions to maternal-fetal immune tolerance remain insufficiently defined due to a lack of a specific marker to distinguish tTreg cells from pTreg cells. In this study, we investigated the role of thymus- and extrathymus-derived Treg cells in pregnancy tolerance using transgenic ACT-mOVA, Foxp3^DTR and Foxp3^GFP mice, and Treg cell adoptive transfer, etc. We found that the frequencies of Treg cells in the thymus, spleen and lymph nodes (LNs) in either syngeneically- or allogeneically-mated pregnant mice were not different from non-pregnant mice. However, percentages of blood Treg cells in pregnant mice increased at mid-gestation, and percentages of decidua Treg cells in pregnant mice increased as the pregnancy progressed compared with non-pregnant mice, and were significantly higher in allogeneic mice than those in syngeneic group. Compared with syngeneic mice, levels of CCR2 and CCR6 on blood and decidua Treg cells and CCL12 in the decidua significantly increased in allogeneic mice. A surrogate fetal antigen mOVA that was recognized by naïve T cells from OT-IIFoxp3^GFP mice induced the generation of pTreg cells in vivo. Transfusion of thymus and spleen Treg cells significantly decreased diphtheria toxin (DT)-increased embryo resorption rates (ERRs) and IFN-γ levels in the blood and decidua. iTreg cells also decreased ERRs and IFN-γ levels in the blood and decidua to an extent lower than thymus and spleen Treg cells. In conclusion, increased blood and decidua Treg cells in pregnancy and increased ERRs in DT-treated Foxp3^DTR mice suggest an important immunosuppressive role of Treg cells in pregnancy. Elevated decidua Treg cells in pregnancy could be derived from the recruitment of tTreg cells to the decidua, or from the transformation of naïve T cells in the decidua to pTreg cells. While the immune-suppression effects of thymus and spleen Treg cells are comparable, iTreg cells might play a weaker role in maternal-fetal tolerance.

Dynamics of neuropilin1 (Nrp1)-positive thymus-derived and Nrp1-negative peripherally induced paternal antigen specific regulatory T cells in the uterus and spleen during pregnancy in mice

Paternal antigen-specific regulatory T (PA-Treg) cells suppress the immune response against the fetus. Naturally occurring Treg (nTreg) cells derived from the thymus and peripherally induced Treg (iTreg) cells are functional for sustaining pregnancy. This study aimed to compare the variation in PA-Treg cells between the feto-maternal interface and the spleen and to elucidate the dynamics of nTreg and iTreg cells during the gestational period. PA-Treg cells, defined as Treg cells with paternally derived Mls-1a antigen-specific T cell receptors Vβ6, from allogeneic pregnant mice on days 3.5, 5.5, 11.5, and 18.5 post-coitum (pc) were evaluated by flow cytometry. The percentage of Vβ6⁺ Ki67⁺ PA-Treg cells activated by the paternal antigen increased on day 11.5 pc in the decidua (p < 0.05) compared to non-pregnant mice. On day 18.5 pc, this percentage in the decidua parietalis decreased to the level of the non-pregnant state but was significantly higher (p < 0.05) in the decidua basalis. No changes were observed in the spleens. We used two nTreg cell markers, neuropilin1 (Nrp1) and Helios, to distinguish between nTreg cells and iTreg cells. Nrp1⁺ PA-Treg cell levels decreased in late pregnancy compared to those observed in early pregnancy (day 3.5 pc: 57.14 ± 6.16% vs. day 18.5 pc: 30.43 ± 3.09%; p < 0.05), whereas Helios⁺ cell levels did not change. In conclusion, PA immune tolerance is induced by Nrp1⁺ nTreg cells in early pregnancy and Nrp1-negative Treg cells in late pregnancy.

Inflammatory Molecules Responsible for Length Shortening and Preterm Birth

It is estimated that inflammation at the placental-maternal interface is directly responsible for or contributes to the development of 50% of all premature deliveries. Chorioamnionitis, also known as the premature rupture of the amniotic membrane in the mother, is the root cause of persistent inflammation that preterm newborns experience. Beyond contributing to the onset of early labor, inflammation is a critical element in advancing several conditions in neonates, including necrotizing enterocolitis, retinopathy of prematurity, bronchopulmonary dysplasia, intraventricular hemorrhage, retinopathy of prematurity and periventricular leukomalacia. Notably, the immune systems of preterm infants are not fully developed; immune defense mechanisms and immunosuppression (tolerance) have a delicate balance that is easily upset in this patient category. As a result, premature infants are exposed to different antigens from elements such as hospital-specific microbes, artificial devices, medications, food antigens and hypoxia/hyperoxia. This has detrimental implications for preterm deliveries of less than 28 weeks because they have not yet evolved the mechanisms to tolerate maternal and self-antigens.

Immunology of Pregnancy and Systemic Consequences

Pregnancy is an immunological paradox, with renowned Nobel Prize winning transplantation biologist Sir Peter Brian Medawar being the first to introduce this concept back in 1953. This concept considers how the maternal immune system can tolerate the developing fetus, which is 50% antigenically foreign to the uterus. There have been significant advances in our understanding of the immune system in regulating fertility, pregnancy and in complications of these, and what was once considered a paradox can be seen as a highly evolved system. Indeed, the complexity of the maternal-fetal interface along with our ever-advancing knowledge of immune cells and mediators means that we have a better understanding of these interactions, with gaps still present.  This chapter will summarise the key aspects of the role of the immune system at each stage of pregnancy and highlight the recent advances in our knowledge.

Immune–Metabolic Interactions and T Cell Tolerance in Pregnancy

Pregnancy depends on a state of maternal immune tolerance mediated by CD4+ regulatory T (Treg) cells. Uterine Treg cells release anti-inflammatory factors, inhibit effector immunity, and support adaptation of the uterine vasculature to facilitate placental development. Insufficient Treg cells or inadequate functional competence is implicated in infertility and recurrent miscarriage, as well as pregnancy complications preeclampsia, fetal growth restriction, and preterm birth, which stem from placental insufficiency. In this review we address an emerging area of interest in pregnancy immunology–the significance of metabolic status in regulating the Treg cell expansion required for maternal–fetal tolerance. We describe how hyperglycemia and insulin resistance affect T cell responses to suppress generation of Treg cells, summarize data that implicate a role for altered glucose metabolism in impaired maternal–fetal tolerance, and explore the prospect of targeting dysregulated metabolism to rebalance the adaptive immune response in women experiencing reproductive disorders.

Pregnancy preparation: redistribution of CCR7-positive cells in the rat uterus

In brief

Changes in the endometrium prior to implantation may be critical in predicting pregnancy outcomes. This study shows that the endocrine system directs positional changes in CCR7+ cells before implantation, which may be critical for developing maternal tolerance.

Abstract

Suppression of the maternal immune system is vital for the implantation of the semi-allogeneic embryo. Although progress in understanding the dialogue between mother and embryo has been made, key interactions between maternal immune cells, hormones, and chemokines remain elusive. Uterine expression of the C-C chemokine receptor type 7 (CCR7) could recruit T regulatory cells and facilitate localized immune suppression. To test this concept, Ccr7 mRNA and protein were assessed in uterine tissue. Ccr7 mRNA expression peaked at day 4 in pregnant rat uteri and then declined at days 5 and 6. CCR7 protein showed similar quantitative changes. To test if female sex steroids affected the spatial distribution of CCR7-expressing cells, uteri from ovariectomized rats, progesterone-pretreated rats (2 mg daily), and progesterone-pretreated rats injected with estradiol (0.2 µg) were analyzed. Progesterone increased CCR7-positive (+) cells in the antimesometrial stroma. Progesterone and estradiol increased CCR7+ cells in the mesometrial stroma. Estradiol increased the density of cluster of differentiation 4 (CD4) positive cells in the mesometrial stromal region over progesterone alone. The density of cells expressing the T regulatory cell marker, forkhead box protein 3 (FOXP3), increased in the antimesometrial stroma in response to progesterone alone. Progesterone and estradiol increased FOXP3+ cells in the antimesometrial region of the stroma. Co-localization of CCR7, CD4, and FOXP3 in the stroma suggests CCR7+ cells are T regulatory cells. Polarization of CCR7+ cells in the endometrial stroma was an intrinsic response regulated by sex steroids and did not require the presence of an embryo.

CRISPR/Cas9-mediated Serine protease 2 disruption induces male sterility in Spodoptera litura

Male fertility is essential for reproduction and population growth in animals. Many factors affect male fertility, such as courtship behavior, sperm quantity, and sperm motility, among others. Seminal Fluid Proteins (SFPs) are vital components of seminal fluid in the male ejaculate, which affect male fertility, sperm activation, and female ovulation. However, the knowledge of SFPs is insufficient; the function of many SFPs remains unknown, and most described functions were mainly characterized in Drosophila or other laboratory models. Here, we focus on the Serine protease 2 (Ser2) gene in the lepidopteran pest Spodoptera litura. The Ser2 gene was specifically expressed in male adults. Disruption of the Ser2 gene mediated by CRISPR/Cas9 induced male sterility but females remained fertile. PCR-based detection of the next-generation mutants showed that male sterility was stably inherited. The qRT-PCR analysis of SlSer2 mutants showed that motor protein family genes and structural protein family genes were down-regulated, while protein modification family genes were up-regulated, suggesting that SlSer2 may be involved in sperm movement and activity. These results demonstrate that Ser2 is an important component of SFPs in seminal fluid and was identified for a useful sterile gene for pest control that may lead to new control strategies for lepidopteran insect pests such as S. litura.

Composition and effects of seminal plasma in the female reproductive tracts on implantation of human embryos

The function of seminal plasma involves acting as a transport medium for sperm and as a means of communication between the reproductive tissues of the male and female. It is also a vital factor to prime the reproductive tracts of the female for optimal pregnancy. When the reproductive tract of the female is exposed to seminal plasma, serious alterations take place, enhancing pathogen and debris clearance observed in the uterus throughout mating. It is also capable of supporting embryo growth, promoting the receptivity of the uterus, and establishing tolerance to the semi-allogenic embryo. Moreover, seminal plasma is capable of regulating the functions of several female reproductive organs and providing an ideal condition for effective embryo implantation and pregnancy. It is believed that the health state of the offspring is affected by exposure to seminal plasma. For the treatment of infertility, assisted reproductive technologies have been extensively employed. The application of seminal plasma as a therapeutic approach to enhance the development of embryo competency and rate of implantation, receptivity of endometrium, and establishment of maternal immune tolerance in cycles of ART appears possible. Herein, current knowledge on the composition of seminal plasma and the physiological roles it possesses on various parts of the female reproductive tract are summarized. Moreover, the role of seminal plasma in the development of embryos, implantation, and the following fetal growth and survival have been reviewed in this article.

Role of hormones in the pregnancy and sex-specific outcomes to infections with respiratory viruses

Pregnant women infected with pathogenic respiratory viruses, such as influenza A viruses (IAV) and coronaviruses, are at higher risk for mortality, hospitalization, preterm birth, and stillbirth. Several factors are likely to contribute to the susceptibility of pregnant individuals to severe lung disease including changes in pulmonary physiology, immune defenses, and effector functions of some immune cells. Pregnancy is also a physiologic state characterized by higher levels of multiple hormones that may impact the effector functions of immune cells, such as progesterone, estrogen, human chorionic gonadotropin, prolactin, and relaxin. Each of these hormones acts to support a tolerogenic immune state of pregnancy, which helps prevent fetal rejection, but may also contribute to an impaired antiviral response. In this review, we address the unique role of adaptive and innate immune cells in the control of pathogenic respiratory viruses and how pregnancy and specific hormones can impact their effector actions. We highlight viruses with sex-specific differences in infection outcomes and why pregnancy hormones may contribute to fetal protection but aid the virus at the expense of the mother's health.

Double Negative T Regulatory Cells: An Emerging Paradigm Shift in Reproductive Immune Tolerance?

Immune regulation of female reproductive function plays a crucial role in fertility, as alterations in the relationship between immune and reproductive processes result in autoimmune subfertility or infertility. The breakdown of immune tolerance leads to ovulation dysfunction, implantation failure, and pregnancy loss. In this regard, immune cells with regulatory activities are essential to restore self-tolerance. Apart from regulatory T cells, double negative T regulatory cells (DNTregs) characterized by TCRαβ+/γδ+CD3+CD4–CD8– (and negative for natural killer cell markers) are emerging as effector cells capable of mediating immune tolerance in the female reproductive system. DNTregs are present in the female reproductive tract of humans and murine models. However, their full potential as immune regulators is evolving, and studies so far indicate that DNTregs exhibit features that can also maintain tolerance in the female reproductive microenvironment. This review describes recent progress on the presence, role and mechanisms of DNTregs in the female reproductive system immune regulation and tolerance. In addition, we address how DNTregs can potentially provide a paradigm shift from the known roles of conventional regulatory T cells and immune tolerance by maintaining and restoring balance in the reproductive microenvironment of female fertility.

Fetal‐placental antigens and the maternal immune system: Reproductive immunology comes of age

Reproductive physiology and immunology as scientific disciplines each have rich, largely independent histories. The physicians and philosophers of ancient Greece made remarkable observations and inferences to explain regeneration as well as illness and immunity. The scientific enlightenment of the renaissance and the technological advances of the past century have led to the explosion of knowledge that we are experiencing today. Breakthroughs in transplantation, immunology, and reproduction eventually culminated with Medawar’s discovery of acquired immunological tolerance, which helped to explain the transplantation success and failure. Medawar’s musings also keenly pointed out that the fetus apparently breaks these newly discovered rules, and with this, the field of reproductive immunology was launched. As a result of having stemmed from transplantation immunology, scientist still analogizes the fetus to a successful allograft. Although we now know of the fundamental differences between the two, this analogy remains a useful tool to understand how the fetus thrives despite its immunological disparity with the mother. Here, we review the history of reproductive immunology, and how major and minor histocompatibility antigens, blood group antigens, and tissue‐specific “self” antigens from the fetus and transplanted organs parallel and differ.

Mucosal viral infection induces a regulatory T cell activation phenotype distinct from tissue residency in mouse and human tissues

Regulatory T cells (Tregs) mediate immune homeostasis, yet also facilitate nuanced immune responses during infection, balancing pathogen control while limiting host inflammation. Recent studies have identified Treg populations in non-lymphoid tissues that are phenotypically distinct from Tregs in lymphoid tissues (LT), including performance of location-dependent roles. Mucosal tissues serve as critical barriers to microbes while performing unique physiologic functions, so we sought to identify distinct phenotypical and functional aspects of mucosal Tregs in the female reproductive tract. In healthy human and mouse vaginal mucosa, we found that Tregs are highly activated compared to blood or LT Tregs. To determine if this phenotype reflects acute activation or a general signature of vaginal tract (VT)-residency, we infected mice with HSV-2 to discover that VT Tregs express granzyme-B (GzmB) and acquire a VT Treg signature distinct from baseline. To determine the mechanisms that drive GzmB expression, we performed ex vivo assays to reveal that a combination of type-I interferons and interleukin-2 is sufficient for GzmB expression. Together, we highlight that VT Tregs are activated at steady state and become further activated in response to infection; thus, they may exert robust control of local immune responses, which could have implications for mucosal vaccine design.

Histone methyltransferase Nsd2 ensures maternal-fetal immune tolerance by promoting regulatory T-cell recruitment

Regulatory T cells (Tregs) are fundamentally important for maintaining systemic immune homeostasis and are also required for immune tolerance at the maternal-fetal interface during pregnancy. Recent studies have suggested that epigenetic regulation is critically involved in Treg development and function. However, the role of H3K36me has not yet been investigated. Here, we found that the H3K36me2 methyltransferase Nsd2 was highly expressed in Tregs. Although loss of Nsd2 did not impair systemic Treg development or function, the level of Tregs at the maternal-fetal interface was significantly decreased in pregnant Nsd2 conditional knockout mice. Consequently, maternal-fetal immune tolerance was disrupted in the absence of Nsd2 in Tregs, and the pregnant mice showed severe fetal loss. Mechanistically, Nsd2 was found to upregulate CXCR4 expression via H3K36me2 modification to promote Treg cell recruitment into the decidua and suppress the anti-fetal immune response. Overall, our data identified Nsd2 as a critical epigenetic regulator of Treg recruitment for maternal-fetal tolerance.

Specific innate immune cells uptake fetal antigen and display homeostatic phenotypes in the maternal circulation

Pregnancy represents a period when the mother undergoes significant immunological changes to promote tolerance of the fetal semi-allograft. Such tolerance results from the exposure of the maternal immune system to fetal antigens (Ags), a process that has been widely investigated at the maternal-fetal interface and in the adjacent draining lymph nodes. However, the peripheral mechanisms of maternal-fetal crosstalk are poorly understood. Herein, we hypothesized that specific innate immune cells interact with fetal Ags in the maternal circulation. To test this hypothesis, a mouse model was utilized in which transgenic male mice expressing the chicken ovalbumin (OVA) Ag under the beta-actin promoter were allogeneically mated with wild-type females to allow for tracking of the fetal Ag. Fetal Ag-carrying Ly6G+ and F4/80+ cells were identified in the maternal circulation, where they were more abundant in the second half of pregnancy. Such innate immune cells displayed unique phenotypes: while Ly6G+ cells expressed high levels of MHC-II and CD80 together with low levels of pro-inflammatory cytokines, F4/80+ cells up-regulated the expression of CD86 as well as the anti-inflammatory cytokines IL-10 and TGF-β. In vitro studies using allogeneic GFP+ placental particles revealed that maternal peripheral Ly6G+ and F4/80+ cells phagocytose fetal Ags in mid and late murine pregnancy. Importantly, cytotrophoblast-derived particles were also engulfed in vitro by CD15+ and CD14+ cells from women in the second and third trimester, providing translational evidence that this process also occurs in humans. Collectively, this study demonstrates novel interactions between specific maternal circulating innate immune cells and fetal Ags, thereby shedding light on the systemic mechanisms of maternal-fetal crosstalk.

Mucosal tissue regulatory T cells are integral in balancing immunity and tolerance at portals of antigen entry

Foxp3+ regulatory T cells (Tregs) are a subset of CD4+ T cells that exert suppressive control over other immune cells. Tregs are critical for preventing systemic autoimmunity and maintaining peripheral tolerance, and yet they also assist in orchestration of immunity to pathogenic insult, wherein they limit collateral immunopathology and assist in facilitating a fine balance between immune tolerance and effector activity. Tregs have been extensively studied in lymphoid tissues, and a growing body of work has characterized phenotypically distinct Tregs localized in various nonlymphoid tissue compartments. These tissue Tregs can perform location-specific, alternative functions, highlighting their dynamic, context-dependent roles. Tregs have also been identified in mucosal tissues where specialized physiological functions are paramount, including helping the host to respond appropriately to pathogenic versus innocuous antigens that are abundant at mucosal portals of antigen entry. As in other tissue Treg compartments, mucosal Tregs in the respiratory, gastrointestinal, and genitourinary tracts are distinct from circulating counterparts and can carry out mucosa-specific functions as well as classic suppressive functions that are the hallmark of Tregs. In this review, we summarize current knowledge regarding mucosal Tregs in both health and disease.

Cellular immune responses in the pathophysiology of preeclampsia

Preeclampsia, defined as new-onset hypertension accompanied by proteinuria occurring at 20 weeks of gestation or later, is a leading cause of perinatal morbidity and mortality worldwide. The pathophysiology of this major multi-systemic syndrome includes defective deep placentation, oxidative stress, endothelial dysfunction, the presence of an anti-angiogenic state, and intravascular inflammation, among others. In this review, we provide a comprehensive overview of the cellular immune responses involved in the pathogenesis of preeclampsia. Specifically, we summarize the role of innate and adaptive immune cells in the maternal circulation, reproductive tissues, and at the maternal-fetal interface of women affected by this pregnancy complication. The major cellular subsets involved in the pathogenesis of preeclampsia are regulatory T cells, effector T cells, NK cells, monocytes, macrophages, and neutrophils. We also summarize the literature on those immune cells that have been less characterized in this clinical condition, such as γδ T cells, invariant natural killer T cells, dendritic cells, mast cells, and B cells. Moreover, we discuss in vivo studies utilizing a variety of animal models of preeclampsia to further support the role of immune cells in this disease. Finally, we highlight the existing gaps in knowledge of the immunobiology of preeclampsia that require further investigation. The goal of this review is to promote translational research leading to clinically relevant strategies that can improve adverse perinatal outcomes resulting from the obstetrical syndrome of preeclampsia.

Glucocorticoid therapy in assisted reproduction

As glucocorticoids are well-known as important regulators of stress and the immune system, their function and clinical use have elicited substantial interest in the field of reproduction. In particular, the effect of glucocorticoid therapy on endometrial receptivity during assisted reproduction, including in vitro fertilization (IVF) cycles, has led to a great deal of interest and controversy. However, previous studies have not been able to provide consistent and reliable evidence due to their small, non-controlled designs and use of different criteria. Considering the potential risk of exposure to glucocorticoids for mothers and fetuses in early pregnancy, the use of glucocorticoids in IVF cycles should be carefully evaluated, including the balance between risk and benefit. To date, there is no conclusive evidence that the use of glucocorticoids improves the pregnancy rate in IVF cycles with unselected subjects, and a further investigation should be considered with a proper study design.

Semen: A modulator of female genital tract inflammation and a vector for HIV-1 transmission

In order to establish productive infection in women, HIV must transverse the vaginal epithelium and gain access to local target cells. Genital inflammation contributes to the availability of HIV susceptible cells at the female genital mucosa and is associated with higher HIV transmission rates in women. Factors that contribute to genital inflammation may subsequently increase the risk of HIV infection in women. Semen is a highly immunomodulatory fluid containing several bioactive molecules with the potential to influence inflammation and immune activation at the female genital tract. In addition to its role as a vector for HIV transmission, semen induces profound mucosal changes to prime the female reproductive tract for conception. Still, most studies of mucosal immunity are conducted in the absence of semen or without considering its immune impact on the female genital tract. This review discusses the various mechanisms by which semen exposure may influence female genital inflammation and highlights the importance of routine screening for semen biomarkers in vaginal specimens to account for its impact on genital inflammation.

Endometrial mesenchymal stem/stromal cells: The Enigma to code messages for generation of functionally active regulatory T cells

Background

Regulatory T cells (Tregs) play an important role in fine-tuning of immune responses and are pivotal for a successful pregnancy. Recently, the importance of mesenchymal stem cells in regulation of immune responses in general and Tregs in particular has been highlighted. Here, we hypothesized that menstrual stromal/stem cells (MenSCs) contribute to uterine immune system regulation through induction of functionally active Tregs.

Methods

MenSCs were collected from 18 apparently healthy women and characterized. Bone marrow mesenchymal stem cells (BMSCs) served as a control. The effect of MenSCs on proliferation of anti-CD3/CD28-stimulated T CD4 + cells and generation of Tregs with or without pre-treatment with mitomycin C, IFN-γ and IL-1β was evaluated by flow cytometry. The potential role of IDO, PGE2, IL-6, IL-10, and TGF-β on proliferation of T CD4 + cells and generation of Tregs was assessed using blocking antibodies or agents. IDO activity was evaluated in MenSCs and BMSCs culture supernatants by a colorimetric assay. IL-10 and IFN-γ production in MenSCs-primed T CD4 + was measured using intracellular staining. To investigate the functional properties of Tregs induced by MenSCs, Treg cells were isolated and their functional property to inhibit proliferation of anti-CD3/CD28-stimulated PBMCs was assessed by flow cytometry.

Results

According to the results, proliferation of T CD4 + lymphocytes was enhanced in the presence of MenSCs, while pre-treatment of MenSCs with pro-inflammatory cytokines reversed this effect. PGE2 and IDO were the major players in MenSCs-induced T cell proliferation. Non-treated MenSCs decreased the frequency of Tregs, whereas after pre-treatment with IFN-γ and IL-1β, they induced functional Tregs with ability to inhibit the proliferation of anti-CD3/CD28-stimulated PBMCs. This effect was mediated through IL-6, IL-10, TGF-β and IDO. IFN-γ/IL-1β-treated MenSCs induced IL-10 and IFN-γ production in CD4 + T cells.

Conclusion

Collectively, these findings indicate that immunomodulatory impact of menstrual blood stem cells (MenSCs) on generation of Tregs and inhibition of T cells proliferation is largely dependent on pre-treatment with IFN-γ and IL-1β. This is the first report on immunomodulatory impact of MenSCs on Tregs and highlights the pivotal role of endometrial stem cells in regulation of local endometrial immune responses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02603-3.

High-fat Diet Alters Male Seminal Plasma Composition to Impair Female Immune Adaptation for Pregnancy in Mice

Paternal experiences and exposures before conception can influence fetal development and offspring phenotype. The composition of seminal plasma contributes to paternal programming effects through modulating the female reproductive tract immune response after mating. To investigate whether paternal obesity affects seminal plasma immune-regulatory activity, C57Bl/6 male mice were fed an obesogenic high-fat diet (HFD) or control diet (CD) for 14 weeks. Although HFD consumption caused only minor changes to parameters of sperm quality, the volume of seminal vesicle fluid secretions was increased by 65%, and the concentrations and total content of immune-regulatory TGF-β isoforms were decreased by 75% to 80% and 43% to 55%, respectively. Mating with BALB/c females revealed differences in the strength and properties of the postmating immune response elicited. Transcriptional analysis showed >300 inflammatory genes were similarly regulated in the uterine endometrium by mating independently of paternal diet, and 13 were dysregulated by HFD-fed compared with CD-fed males. Seminal vesicle fluid factors reduced in HFD-fed males, including TGF-β1, IL-10, and TNF, were among the predicted upstream regulators of differentially regulated genes. Additionally, the T-cell response induced by mating with CD-fed males was blunted after mating with HFD-fed males, with 27% fewer CD4+ T cells, 26% fewer FOXP3+CD4+ regulatory T cells (Treg) cells, and 19% fewer CTLA4+ Treg cells, particularly within the NRP1+ thymic Treg cell population. These findings demonstrate that an obesogenic HFD alters the composition of seminal vesicle fluid and impairs seminal plasma capacity to elicit a favorable pro-tolerogenic immune response in females at conception.

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.

The Aryl hydrocarbon receptor mediates reproductive toxicity of polychlorinated biphenyl congener 126 in rats

Polychlorinated biphenyls (PCBs) are endocrine disrupting chemicals with documented, though mechanistically ill-defined, reproductive toxicity. The toxicity of dioxin-like PCBs, such as PCB126, is mediated via the aryl hydrocarbon receptor (AHR) in non-ovarian tissues. The goal of this study was to examine the uterine and ovarian effects of PCB126 and test the hypothesis that the AHR is required for PCB126-induced reproductive toxicity. Female Holzman-Sprague Dawley wild type (n = 14; WT) and Ahr knock out (n = 11; AHR-/-) rats received a single intraperitoneal injection of either corn oil vehicle (5 ml/kg: WT_O and AHR-/-_O) or PCB126 (1.63 mg/kg in corn oil: WT_PCB and AHR-/-_PCB) at four weeks of age. The estrous cycle was synchronized and ovary and uterus were collected 28 days after exposure. In WT rats, PCB126 exposure reduced (P < 0.05) body and ovary weight, uterine gland number, uterine area, progesterone, 17β-estradiol and anti-Müllerian hormone level, secondary and antral follicle and corpora lutea number but follicle stimulating hormone level increased (P < 0.05). In AHR-/- rats, PCB126 exposure increased (P ≤ 0.05) circulating luteinizing hormone level. Ovarian or uterine mRNA abundance of biotransformation, and inflammation genes were altered (P < 0.05) in WT rats due to PCB126 exposure. In AHR-/- rats, the transcriptional effects of PCB126 were restricted to reductions (P < 0.05) in three inflammatory genes. These findings support a functional role for AHR in the female reproductive tract, illustrate AHR's requirement in PCB126-induced reprotoxicity, and highlight the potential risk of dioxin-like compounds on female reproduction.

Toll-like receptor-4 null mutation causes fetal loss and fetal growth restriction associated with impaired maternal immune tolerance in mice

Maternal immune adaptation to accommodate pregnancy depends on sufficient availability of regulatory T (Treg) cells to enable embryo implantation. Toll-like receptor 4 is implicated as a key upstream driver of a controlled inflammatory response, elicited by signals in male partner seminal fluid, to initiate expansion of the maternal Treg cell pool after mating. Here, we report that mice with null mutation in Tlr4 (Tlr4^−/−) exhibit impaired reproductive outcomes after allogeneic mating, with reduced pregnancy rate, elevated mid-gestation fetal loss, and fetal growth restriction, compared to Tlr4^+/+ wild-type controls. To investigate the effects of TLR4 deficiency on early events of maternal immune adaptation, TLR4-regulated cytokines and immune regulatory microRNAs were measured in the uterus at 8 h post-mating by qPCR, and Treg cells in uterus-draining lymph nodes were evaluated by flow cytometry on day 3.5 post-coitum. Ptgs2 encoding prostaglandin-endoperoxide synthase 2, cytokines Csf2, Il6, Lif, and Tnf, chemokines Ccl2, Cxcl1, Cxcl2, and Cxcl10, and microRNAs miR-155, miR-146a, and miR-223 were induced by mating in wild-type mice, but not, or to a lesser extent, in Tlr4^−/− mice. CD4⁺ T cells were expanded after mating in Tlr4^+/+ but not Tlr4^−/− mice, with failure to expand peripheral CD25⁺FOXP3⁺ NRP1⁻ or thymic CD25⁺FOXP3⁺ NRP1⁺ Treg cell populations, and fewer Treg cells expressed Ki67 proliferation marker and suppressive function marker CTLA4. We conclude that TLR4 is an essential mediator of the inflammation-like response in the pre-implantation uterus that induces generation of Treg cells to support robust pregnancy tolerance and ensure optimal fetal growth and survival.

Prednisolone in early pregnancy inhibits regulatory T cell generation and alters fetal and placental development in mice

Corticosteroids have been utilised in the assisted reproduction setting with the expectation of suppressing aberrant immune activation and improving fertility in women. However, the effects of corticosteroids on fertility, and on pregnancy and offspring outcomes, are unclear. In this study, mice were administered prednisolone (1 mg/kg) or PBS daily in the pre-implantation phase, and effects on the adaptive immune response, the implantation rate, fetal development and postnatal outcomes were investigated. Prednisolone disrupted the expected expansion of CD4+ T cells in early pregnancy, inhibiting generation of both regulatory T cells (Treg cells) and effector T cells and suppressing IFNG required for T cell functional competence. Prednisolone caused an 8-20% increase in the embryo implantation rate and increased the number of viable pups per litter. In late gestation, fetal and placental weights were reduced in a litter size-dependent manner, and the canonical inverse relationship between litter size and fetal weight was lost. The duration of pregnancy was extended by ~ 0.5 day and birth weight was reduced by ~ 5% after prednisolone treatment. Viability of prednisolone-exposed offspring was comparable to controls, but body weight was altered in adulthood, particularly in male offspring. Thus, while prednisolone given in the pre-implantation phase in mice increases maternal receptivity to implantation and resource investment in fetal growth, there is a trade-off in long-term consequences for fetal development, birth weight and offspring health. These effects are associated with, and likely caused by, prednisolone suppression of the adaptive immune response at the outset of pregnancy.

Tumor Extracellular Vesicles Regulate Macrophage-Driven Metastasis through CCL5

Simple Summary

About 10–20 percent of patients with breast cancer are diagnosed with triple-negative breast cancer (TNBC). These tumors are named for their lack of expression of estrogen receptor (ER), progesterone receptor (PR), and amplification of human epidermal growth factor receptor 2 (HER2). These genes are targeted by therapies in other breast cancer patients. However, most TNBC patients recur within 5 years. Understanding how and why these tumors metastasize will help clinicians better treat these underserved cancer patients. TNBC tumors are highly infiltrated by tumor-associated macrophages (TAMs) that promote tumorigenesis and metastasis. Our study elucidates how the tumor co-opts macrophages recruited to the tumor through extracellular vesicles (EVs), further increasing tumor metastasis. Expression of tumor CCL5 regulates EV secretion and cargo that further alters macrophage phenotype to drive tumor metastasis. Together, our data suggest a more extensive role of EVs in the biology of tumor metastasis as well as their potential use as biomarkers.

Abstract

Purpose: To understand how tumor cells alter macrophage biology once they are recruited to triple-negative breast cancer (TNBC) tumors by CCL5. Method: Mouse bone marrow derived macrophage (BMDMs) were isolated and treated with recombinant CCL5 protein alone, with tumor cell conditioned media, or with tumor extracellular vesicles (EVs). Media from these tumor EV-educated macrophages (TEMs) was then used to determine how these macrophages affect TNBC invasion. To understand the mechanism, we assayed the cytokine secretion from these macrophages to determine how they impact tumor cell invasion. Tumor CCL5 expression was varied in tumors to determine its role in regulating macrophage biology through EVs. Results: Tumor EVs are a necessary component for programming naïve macrophages toward a pro-metastatic phenotype. CCL5 expression in the tumor cells regulates both EV biogenesis/secretion/cargo and macrophage EV-education toward a pro-metastatic phenotype. Analysis of the tumor EV-educated macrophages (TEMs) showed secretion of a variety of factors including CXCL1, CTLA-4, IFNG, OPN, HGF, TGFB, and CCL19 capable of remodeling the surrounding tumor stroma and immune infiltrate. Injection of tumor cells with macrophages educated by metastatic tumor cell EVs into mice increased tumor metastasis to the lung. Conclusion: These results demonstrate that tumor-derived EVs are key mediators of macrophage education and likely play a more complex role in modulating tumor therapeutic response by regulating the tumor immune infiltrate.

Sperm modulate uterine immune parameters relevant to embryo implantation and reproductive success in mice

Seminal fluid factors modulate the female immune response at conception to facilitate embryo implantation and reproductive success. Whether sperm affect this response has not been clear. We evaluated global gene expression by microarray in the mouse uterus after mating with intact or vasectomized males. Intact males induced greater changes in gene transcription, prominently affecting pro-inflammatory cytokine and immune regulatory genes, with TLR4 signaling identified as a top-ranked upstream driver. Recruitment of neutrophils and expansion of peripheral regulatory T cells were elevated by seminal fluid of intact males. In vitro, epididymal sperm induced IL6, CXCL2, and CSF3 in uterine epithelial cells of wild-type, but not Tlr4 null females. Collectively these experiments show that sperm assist in promoting female immune tolerance by eliciting uterine cytokine expression through TLR4-dependent signaling. The findings indicate a biological role for sperm beyond oocyte fertilization, in modulating immune mechanisms involved in female control of reproductive investment.

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.

Application of Ligilactobacillus salivarius CECT5713 to Achieve Term Pregnancies in Women with Repetitive Abortion or Infertility of Unknown Origin by Microbiological and Immunological Modulation of the Vaginal Ecosystem

In this study, the cervicovaginal environment of women with reproductive failure (repetitive abortion, infertility of unknown origin) was assessed and compared to that of healthy fertile women. Subsequently, the ability of Ligilactobacillus salivarius CECT5713 to increase pregnancy rates in women with reproductive failure was evaluated. Vaginal pH and Nugent score were higher in women with reproductive failure than in fertile women. The opposite was observed regarding the immune factors TGF-β 1, TFG-β 2, and VEFG. Lactobacilli were detected at a higher frequency and concentration in fertile women than in women with repetitive abortion or infertility. The metataxonomic study revealed that vaginal samples from fertile women were characterized by the high abundance of Lactobacillus sequences, while DNA from this genus was practically absent in one third of samples from women with reproductive failure. Daily oral administration of L. salivarius CECT5713 (~9 log₁₀ CFU/day) to women with reproductive failure for a maximum of 6 months resulted in an overall successful pregnancy rate of 56%. The probiotic intervention modified key microbiological, biochemical, and immunological parameters in women who got pregnant. In conclusion, L. salivarius CECT5713 has proved to be a good candidate to improve reproductive success in women with reproductive failure.

Cryopreservation and oxidative stress in porcine oocytes

Several vitrification protocols have been established for porcine oocytes so as to facilitate gene banking of female germplasm. Although live piglets have been successfully produced from pig oocytes vitrified at the germinal vesicle (GV) stage, the competence of vitrified oocytes to develop into the blastocyst stage is greatly compromised following cryopreservation. The focus of this review is to elucidate the impact of cryopreservation on the redox balance of pig oocytes, making special reference to the relevance of non-enzymatic and enzymatic antioxidant defences. Besides, the regulation of gene expression in response to oxidative stress is also considered. Finally, we discuss the effects of supplementing maturation and vitrification media with the exogenous non-enzymatic antioxidants that have hitherto yielded the most relevant results.

Endocrine Disruptor Compounds-A Cause of Impaired Immune Tolerance Driving Inflammatory Disorders of Pregnancy?

Endocrine disrupting compounds (EDCs) are prevalent and ubiquitous in our environment and have substantial potential to compromise human and animal health. Amongst the chronic health conditions associated with EDC exposure, dysregulation of reproductive function in both females and males is prominent. Human epidemiological studies demonstrate links between EDC exposure and infertility, as well as gestational disorders including miscarriage, fetal growth restriction, preeclampsia, and preterm birth. Animal experiments show EDCs administered during gestation, or to either parent prior to conception, can interfere with gamete quality, embryo implantation, and placental and fetal development, with consequences for offspring viability and health. It has been presumed that EDCs operate principally through disrupting hormone-regulated events in reproduction and fetal development, but EDC effects on maternal immune receptivity to pregnancy are also implicated. EDCs can modulate both the innate and adaptive arms of the immune system, to alter inflammatory responses, and interfere with generation of regulatory T (Treg) cells that are critical for pregnancy tolerance. Effects of EDCs on immune cells are complex and likely exerted by both steroid hormone-dependent and hormone-independent pathways. Thus, to better understand how EDCs impact reproduction and pregnancy, it is imperative to consider how immune-mediated mechanisms are affected by EDCs. This review will describe evidence that several EDCs modify elements of the immune response relevant to pregnancy, and will discuss the potential for EDCs to disrupt immune tolerance required for robust placentation and optimal fetal development.

Paternal contributors in recurrent pregnancy loss: Cues from comparative proteome profiling of seminal extracellular vesicles

Recent evidence entail paternal factors as plausible contributors in spontaneous recurrent pregnancy loss (RPL). Seminal extracellular vesicles secreted from cells of male reproductive tract carry regulatory proteins and RNAs. They are proposed to regulate sperm maturation and function while their fusion to endometrial stromal cells helps in decidualization. Nevertheless, the mechanism(s) involved in these processes are poorly understood. This study aims at elucidating the molecular basis of paternal contribution by comparative proteomics (label-free LC-MS/MS) of isolated seminal extracellular vesicles from fertile men and partners of patients with RPL (n = 21 per group). Bioinformatics analysis revealed the identified differentially expressed proteins to be involved in DNA replication, recombination and repair, gene expression, cellular assembly and organization, cell death, and survival. Major disease pathways affected were identified as developmental, hereditary, and immunological disorders. Of the three identified hub genes regulating the above disease pathways, two (HNRNPC and HNRNPU) are overexpressed while RUVBL1 is underexpressed along with over expression of HIST1H1C, DDX1, surmising defective chromatin packaging, and histone removal in spermatozoa resulting in improper expression in paternal genes thereby leading to abnormal embryo development. Besides, alteration in GSTP1 expression points oxidative predominance in RPL group. Differential expression of C3, C4a/C4b, CFB, and GDF 15 may be involved in altered maternal immune response to paternal antigens resulting in impaired decidualization.

Got your mother in a whirl: The role of maternal T cells and myeloid cells in pregnancy

Appropriate development of the placenta is required for healthy pregnancy to occur. After implantation of the fertilized blastocyst, fetal trophoblasts invade the endometrium and myometrium of the mother's uterus to establish placentation. In this process, fetal trophoblasts encounter maternal immune cells. In this review, we focus on the role of maternal T cells and myeloid cells (macrophages, dendritic cells) in pregnancy and their interaction with trophoblasts. To retain immunologic tolerization, trophoblasts evade immune recognition by T cells and produce factors that modulate their phenotype and function. On top of that, the local environment at the maternal-fetal interface favors expansion of regulatory T cells. Macrophages and dendritic cells are essential in maintaining a healthy pregnancy. They produce soluble factors and act as antigen-presenting cells, thereby interacting with T cells. Herein, M2 macrophages, immature dendritic cells, CD4⁺ Th2 cells, and regulatory T cells represent an axis that maintains a local immune tolerant environment. We consider outstanding issues concerning these cell types and their pathways, which need to be addressed in future investigations. Data from recent single-cell sequencing experiments of the placental bed, to study heterogeneity of maternal immune cells and to predict cell-cell interactions, are discussed. Novel ways for long-term culturing of primary trophoblasts allow for cell-cell interaction studies in a functional way. Future directions should include study of the functionality of currently known and newly identified decidual immune cell subsets in healthy and complicated pregnancies, and their interaction with and modulation by trophoblast cells.