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

Decoding immune tolerance in infertility: Exploring immune pathways and non-coding RNAs as pioneering biomarkers and therapeutic targets

Infertility, impacting a significant number of couples, is characterized by the failure to conceive after one year of consistent, unprotected sexual intercourse. It is multifactorial, with etiological contributors including ovulatory dysfunction, male reproductive anomalies, and tubal patency issues. Approximately 15% of infertility cases are classified as "unexplained," highlighting the complexity of this condition. Lifestyle determinants such as obesity and smoking further complicate reproductive outcomes, while infertility can also indicate underlying chronic health conditions. A specialized category, immune infertility, arises from a breakdown of immunological tolerance, an essential aspect for conception and the maintenance of pregnancy. The role of various immunological components, including immune cells, cytokines, chemokines, factors like HLA-G, etc., is pivotal in this context. Moreover, non-coding RNAs (ncRNAs) have emerged as critical regulators of immune tolerance within the reproductive axis. This review synthesizes the complex immunological pathways vital for successful implantation and the early stages of pregnancy alongside the regulatory roles of ncRNAs in these processes. Offering an integrated view of molecular and immunological interactions associated with infertility seeks to enhance our understanding of potential strategies to facilitate successful conception and sustain early pregnancy.

Preterm Birth in African American Women: A Multi-Omic Pilot Study in Early Pregnancy

Preterm birth (PTB; <37 weeks completed gestation) is a devastating problem affecting over 13 million live births worldwide. In the U.S., African Americans experience significantly higher rates of PTB compared to non-Hispanic Whites. PTB disparities have been linked to social determinants of health (e.g., socioeconomic status, discrimination). However, the biological underpinnings related to these associations are unclear. DNA methylation (DNAm) is subject to environmental influences, and DNAm modifications are known to affect gene expression. Using a multi-omic approach, we examined differences in combined DNA methylation (DNAm) and messenger RNA (mRNA) transcriptomic data from 20 pregnant African American women (12 PTB; 8 term birth) early in pregnancy (8-18 weeks gestation). We found that the HLA-DQB2 gene was both differentially methylated (cg12296550; p = .02) and differentially expressed (p = .014; log2FC = 2.5) between women with PTB and term birth. Gene expression analysis showed HLA-DQB2 and HLA-DRB4 (p = .028; log2FC = -3.6) were the two most highly expressed genes. HLA-DQB2 expressed higher in PTB and HLA-DRB4 expressed higher in term birth. However, no genes remained significant (p < .05) after Bonferroni correction. HLA-DRB4 and AKR1C1 were identified as a potential biomarkers in dimensionality reduction models and are also important to immune function and allogenic breakdown. Altered gene expression may lead to inflammatory imbalances or allogenic intolerance resulting in PTB. This study provides proof-of-concept evidence for the feasibility and importance of future multi-omics studies with larger populations to further explore the genes and pathways identified here.

Association of (TG)n(GA)m repeats downstream CMA1 gene with preeclampsia in Mexican population

Preeclampsia is a leading cause of maternal and fetal complications, often associated with endothelial dysfunction. Chymase, a proteolytic enzyme encoded by the CMA1 gene, has emerged as a potential contributor to this dysfunction. Although most preeclampsia (PE) studies have focused on maternal genetic factors, the role of paternal genetics remains underexamined. This study aimed to evaluate the association between the -1903 G/A SNV (rs1800875) and (TG)n(GA)m repeats downstream of the CMA1 gene with preeclampsia in pregnant women and their partners. A cross-sectional study was conducted involving women with PE, healthy pregnant women (HPW), and their corresponding partners, with genotyping, gene expression, and circulating protein levels assessed. A total of 141 participants were included, divided into preeclampsia (n = 80) and HPW (n = 61) groups. Women with PE showed significantly lower gestational age and higher recurrence of preeclampsia history compared to HPW. No significant association was found between the rs1800875 variant and preeclampsia; however, the (TG)n(GA)m repeat downstream of CMA1 gene was significantly associated with PE in women. Additionally, elevated serum IgE levels were significantly associated with preeclampsia (OR = 0.990; 95 % CI:0.983-0.998, p = 0.01). These findings suggest a possible role of polymorphic repeats in CMA1 as susceptibility factors for preeclampsia, indicating that both maternal and paternal genetic variations may contribute to the risk of this condition.

Roles for Siglec-glycan interactions in regulating immune cells

Cell surface complex carbohydrates, known as glycans, are positioned to be the first point of contact between two cells. Indeed, interactions between glycans with glycan-binding can modulate cell-cell interactions. This concept is particularly relevant for immune cells, which use an array of glycan-binding proteins to help in the process of differentiating 'self' from 'non-self'. This is exemplified by the sialic acid-binding immunoglobulin-type lectins (Siglecs), which recognize sialic acid. Given that sialic acid is relatively unique to vertebrates, immune cells leverage Siglecs to recognize sialic acid as a marker of 'self'. Siglecs serve many biological roles, with most of these functions regulated through interactions with their sialoglycan ligands. In this review, we provide a comprehensive update on the ligands of Siglecs and how Siglec-sialoglycan interactions help regulate immune cells in the adaptive and innate immune system.

Molecular and cellular morphology of placenta unveils new mechanisms of reproductive immunology

INTRODUCTION

Despite of numerous studies of the placenta, some molecular and cellular characteristics, particularly the relationship among different cell types, have not been well understood. We aim to investigate the basic and intricate details of cellular and molecular elements in early and late phase placentas to gain better understanding of the immune regulation of human reproductive process.

METHODS

A novel combination of techniques of spatial transcriptomics(ST), multiple immunohistochemistry, and a dual labeling combining immunohistochemistry and (fluorescence in situ hybridization) FISH on normal and ectopic pregnancy and animal models was employed to investigate the placenta at tissue, cell, protein and molecular levels and to trace the fetal and maternal origin of every cell in early and late placentas.

RESULTS

Original discoveries include early expression of immune checkpoint proteins in embryo trophoblasts even before implantation. The detailed distributional relationships among different cell types of fetal and maternal origins in placenta and decidua indicate an immune rejection of the mother towards the fetus and this was counterbalanced by immune inhibitory proteins and blocking antibody Immunoglobulin G4 (IgG4) at the junction between the fetus and the mother. In contrary to common believe, we found that vascular endothelial and glandular epithelial cells in the decidua remain maternal in origin and were not replaced by fetal cells. At term placenta, fetal immune cells infiltrated into the maternal side of the decidus and vice versa indicating a possible immune reaction between fetal and maternal immune systems and suggesting a possible immune mechanism for trigger of parturition. The ability of trophoblasts to create an immune suppressed environment was also supported by findings in ectopic pregnancy and the animal models.

CONCLUSION

The findings indicate a fetus-driven mechanism of immune balance involving both cellular and humoral immunity in human reproduction.

Birth Order and Family Size of UK Biobank Subjects Identified as Asexual, Bisexual, Heterosexual, or Homosexual According to Self-Reported Sexual Histories

This study used a recently developed statistical technique to investigate the relations between various elements of a subject's family background and the odds of that subject reporting a sexual history indicative of a minority sexual orientation. The subjects were 78,983 men and 92,150 women who completed relevant questionnaire items in the UK Biobank, a large-scale biomedical database of volunteers aged 40-69 years. The men were divided into three sexual minority groups-homosexual, bisexual, and asexual-and a comparison group of heterosexual men. The same was done for the women. The analytic procedure consisted of logistic regressions specifically designed to disentangle the effects of birth order and family size. The results showed that older brothers increased the odds of homosexuality in both men and women, and that older sisters increased the odds in men. In contrast, neither older brothers or older sisters affected the odds of bisexuality or asexuality in men or in women. These results suggest that birth order effects may be specific to homosexuality and not common to all minority orientations. The only family size finding was the negative association between family size and the odds of asexuality in both men and women. The outcomes of this study indicate that the maternal immune hypothesis, which was advanced to explain the relation between older brothers and homosexuality in later-born males, might have to be abandoned or else expanded to explain the findings concerning females. A few such modifications are considered.

B cells: roles in physiology and pathology of pregnancy

B cells constitute a diverse and adaptable immune cell population with functions that can vary according to the environment and circumstances. The involvement of B cells in pregnancy, as well as the associated molecular pathways, has yet to be investigated. This review consolidates current knowledge on B cell activities and regulation during pregnancy, with a particular focus on the roles of various B cell subsets and the effects of B cell-derived factors on pregnancy outcomes. Moreover, the review examines the significance of B cell-associated autoantibodies, cytokines, and signaling pathways in relation to pregnancy complications such as pregnancy loss, preeclampsia, and preterm birth.

Extracellular vesicles-coupled miRNAs from oviduct and uterus modulate signaling pathways related to lipid metabolism and bovine early embryo development

BACKGROUND

Extracellular vesicles (EVs) present in oviductal (OF) and uterine fluid (UF) have been shown to enhance bovine embryo quality during in vitro culture by reducing lipid contents and modulating lipid metabolism-related genes (LMGs), while also influencing cell proliferation, suggesting their involvement on the regulation of different biological pathways. The regulation of signaling pathways related to cell differentiation, proliferation, and metabolism is crucial for early embryo development and can determine the success or failure of the pregnancy. Bioactive molecules within EVs in maternal reproductive fluids, such as microRNAs (miRNAs), may contribute to this regulatory process as they modulate gene expression through post-transcriptional mechanisms.

RESULTS

From the 20 differentially expressed miRNAs, 19 up-regulated in UF-EVs (bta-miR-134, bta-miR-151-3p, bta-miR-155, bta-miR-188, bta-miR-181b, bta-miR-181d, bta-miR-224, bta-miR-23b-3p, bta-miR-24-3p, bta-miR-27a-3p, bta-miR-29a, bta-miR-324, bta-miR-326, bta-miR-345-3p, bta-miR-410, bta-miR-652, bta-miR-677, bta-miR-873 and bta-miR-708) and one (bta-miR-148b) in OF-EVs. These miRNAs were predicted to modulate several pathways such as Wnt, Hippo, MAPK, and lipid metabolism and degradation. Differences in miRNAs found in OF-EVs from the early luteal phase and UF-EVs from mid-luteal phase may reflect different environments to meet the changing needs of the embryo. Additionally, miRNAs may be involved, particularly in the uterus, in the regulation of embryo lipid metabolism, immune system, and implantation. This study evaluated miRNA cargo in OF-EVs from the early luteal phase and UF-EVs from the mid-luteal phase, coinciding with embryo transit within oviduct and uterus in vivo, and its possible influence on LMGs and signaling pathways crucial for early embryo development. A total of 333 miRNAs were detected, with 11 exclusive to OF, 59 to UF, and 263 were common between both groups.

CONCLUSIONS

Our study suggests that miRNAs within OF- and UF-EVs could modulate bovine embryo development and quality, providing insights into the intricate maternal-embryonic communication that might be involved in modulating lipid metabolism, immune response, and implantation during early pregnancy.

Changes in Immune Response during Pig Gestation with a Focus on Cytokines

Pigs have the highest percentage of embryonic death not associated with specific diseases of all livestock species, at 20-45%. During gestation processes, a series of complex alterations can arise, including embryonic migration and elongation, maternal immunological recognition of pregnancy, and embryonic competition for implantation sites and subsequent nutrition requirements and development. Immune cells and cytokines act as mediators between other molecules in highly complex interactions between various cell types. However, other non-immune cells, such as trophoblast cells, are important in immune pregnancy regulation. Numerous studies have shed light on the crucial roles of several cytokines that regulate the inflammatory processes that characterize the interface between the fetus and the mother throughout normal porcine gestation, but most of these reports are limited to the implantational and peri-implantational periods. Increase in some proinflammatory cytokines have been found in other gestational periods, such as placental remodeling. Porcine immune changes during delivery have not been studied as deeply as in other species. This review details some of the immune system cells actively involved in the fetomaternal interface during porcine gestation, as well as the principal cells, cytokines, and molecules, such as antibodies, that play crucial roles in sow pregnancy, both in early and mid-to-late gestation.

Immunological Aspects of Infertility-The Role of KIR Receptors and HLA-C Antigen

The mechanisms of immune tolerance of a mother against an antigenically foreign fetus without a concomitant loss of defense capabilities against pathogens are the factors underlying the success of a pregnancy. A significant role in human defense is played by killer immunoglobulin-like receptor (KIR) receptors, which regulate the function of the natural killer (NK) cells capable of destroying antigenically foreign cells, virus-infected cells, or tumor-lesioned cells. A special subpopulation of NK cells called uterine NK cells (uNK) is found in the uterus. Disruption of the tolerance process or overactivity of immune-competent cells can lead to immune infertility, a situation in which a woman's immune system attacks her own reproductive cells, making it impossible to conceive or maintain a pregnancy. Since the prominent role of the inflammatory response in infertility, including KIR receptors and NK cells, has been postulated, the process of antigen presentation involving major histocompatibility complex (MHC) molecules (HLA) appears to be crucial for a successful pregnancy. Proper interactions between KIR receptors on female uNK cells and HLA class I molecules, with a predominant role for HLA-C, found on the surface of germ cells, are strategically important during embryo implantation. In addition, maintaining a functional balance between activating and inhibitory KIR receptors is essential for proper placenta formation and embryo implantation in the uterus. A disruption of this balance can lead to complications during pregnancy. The discovery of links between KIR and HLA-C has provided valuable information about the complexity of maternal-fetal immune interactions that determine the success of a pregnancy. The great diversity of maternal KIR and fetal HLA-C ligands is associated with the occurrence of KIR/HLA-C combinations that are more or less favorable for reproductive success.

Single-cell transcriptomic architecture and cellular communication circuits of parametrial adipose tissue in pregnant mice

AIMS

The activity and interactions of cellular subpopulations in the adipose tissue microenvironment are critical for the coordination of local and systemic adaptation during pregnancy. With a particular interest in parametrial adipose tissue (PmAT), single-cell RNA-sequencing (scRNA-seq) was utilized to unveil the gestative cellular composition and functional shift.

MATERIALS AND METHODS

To identify cell-type-enriched transcriptome profiles, a total of 18,074 cells in adipose tissue were studied. The cell populations were cataloged, and signaling crosstalk between adipocytes and other composition factions via soluble and membrane-bound factors were evaluated.

KEY FINDINGS

A marked decline of pregnancy adipocytes and relative elevation of non-adipocyte fractions were observed. A subpopulation of adipocytes, Adipo_5, with unique properties in the response to estrogen and the embryonic processes involved in pregnancy, was defined. Interactome analysis revealed the potential contribution of PmAT to the establishment of maternal-fetal immune tolerance. During gestation, adipocytes shut down outgoing signaling, resulting in deterioration of the resistin-related incoming signaling network in B cells, which would therefore benefit tissue-specific maternal-fetal tolerance. Furthermore, a subpopulation of adipocytes, Aipo_2, was also considered to take part in a paradigm shift in the process of pregnancy-induced chemical stiffness-triggered vesicular remodeling via the THBS signaling pathway network.

SIGNIFICANCE

These data-derived findings will encourage investigation into the role of pregnant PmTA in pregnancy-related immunological, hypertensive and metabolic disorders, with the ultimate goal of establishing preventive strategies to mitigate these pregnancy-related health challenges. This translational aspect of our work holds significant promise for improving maternal and fetal well-being.

Immune plasticity in pregnancy-associated breast cancer tumorigenesis

Pregnancy-associated breast cancer (PrBC) is a rare tumor that requires complex management. The coexistence of cancer and pregnancy involves several proliferative, invasive, and immune tolerance mechanisms that are shared between the two conditions. In normal pregnancy, successful fetal development is achieved through suppression of the maternal immune response toward the fetus. Similar immunosuppressive patterns during the malignant transformation supporting tumor growth, progression, and metastasis are also exhibited by tumors. An improved understanding of the immunosuppressive mechanisms and pathways underlying the immunological synergy in PrBC could lead to the identification of novel biomarkers that potentially improve patients' clinical management. In this review article, we outline some of the paramount features of immune plasticity during pregnancy, discussing the similarities shared between normal pregnancy and breast cancer in terms of immune suppression mechanisms. Emphasis is also placed on how the current knowledge of the immune milieu of these conditions may be translated into consequent therapeutic opportunities.

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.

The Role of Interferon (IFN)-γ in Extravillous Trophoblast Cell (EVT) Invasion and Preeclampsia Progression

The involvement of the immune system in pregnancy is a controversial subject. The functions of T helper (Th) 1 and Th2 cells have been proposed, that Th1 cytokines promoting allograft rejection may impair pregnancy, whereas Th2-type cytokines suppressing Th1 responses improve allograft tolerance and hence embryonic survival. Maternal-fetal tolerance begins in the uterus; therefore, optimal adaptation to the fetus is the result of a complex interference. The invasion of extravillous trophoblast cells (EVTs) into the decidua and the inner third of the myometrium is essential for a healthy pregnancy. The mechanisms that influence trophoblast invasion are unknown; however, cytokines from uterine natural killer (uNK) cells, NKT cells, macrophages, and T cells appear to be involved. All these cells are major sources of interferon gamma (IFN-γ). Recent studies have shown that IFN-γ can inhibit EVT invasion via a mechanism dependent on an increase in EVT apoptosis and a decrease in matrix metalloproteinases (MMPs). Regarding controversies in this context, this study aimed to comprehensively review the role of IFN-γ and IFN-γ-producing cells in EVT invasion, successful pregnancy, and preeclampsia.