Low expression of soluble human leukocyte antigen G in early gestation and subsequent placenta-mediated complications of pregnancy

Role of maternal-fetal immune tolerance in the establishment and maintenance of pregnancy

ABSTRACT

Normal pregnancy is a contradictory and complicated physiological process. Although the fetus carries the human leukocyte antigen (HLA) inherited from the paternal line, it does not cause maternal immune rejection. As the only exception to immunological principles, maternal-fetal immune tolerance has been a reproductive immunology focus. In early pregnancy, fetal extravillous trophoblast cells (EVTs) invade decidual tissues and come into direct contact with maternal decidual immune cells (DICs) and decidual stromal cells (DSCs) to establish a sophisticated maternal-fetal crosstalk. This study reviews previous research results and focuses on the establishment and maintenance mechanism of maternal-fetal tolerance based on maternal-fetal crosstalk. Insights into maternal-fetal tolerance will not only improve understanding of normal pregnancy but will also contribute to novel therapeutic strategies for recurrent spontaneous abortion, pre-eclampsia, and premature birth.

Biomarker role of maternal soluble human leukocyte antigen G in pre-eclampsia: A meta-analysis

INTRODUCTION

Human leukocyte antigen-G (HLA-G) is a non-classical class I HLA molecule shown to regulate the immunomodulation of maternal immune cells to prevent fetal tissue destruction. Low levels of freely circulating maternal soluble HLA-G (sHLA-G) have been observed in pre-eclampsia, however, no pooled evidence exists. This meta-analysis aimed to generate pooled findings on the association of sHLA-G levels with pre-eclampsia and is the first study to perform a trimester-wise comparison of the levels of sHLA-G in preeclamptic cases and normal pregnant controls.

METHODS

The databases PubMed, Emba, Web of Science, and Google Scholar through May 31, 2023. Preeclamptic women were defined as cases and normal pregnancies as controls. Data on the level of sHLA-G in cases and controls was extracted and subjected to a meta-analysis using a random-effects model. The pooled effect was expressed in terms of standardized mean difference (SMD). Sensitivity analysis was performed to investigate the effect of the exclusion of each study on the pooled results. Publication bias was assessed statistically.

RESULTS

Nine studies with altogether 567 PE cases and 1132 normal pregnancy controls were included in the meta-analysis. The first and third trimester levels of sHLA-G in PE cases were significantly lower than that of normal pregnant controls: (SMD: -0.84 [-1.29; -0.38]; p = .003; I2 = 54%) and (SMD: -0.39 [-0.71; -0.06]; p = .02; I2 = 79%) respectively. Sensitivity analysis revealed significant fluctuations in the pooled findings when few studies were excluded, raising questions on the consistency of results among studies.

CONCLUSION

Although we found that first and third-trimester sHLA-G levels in pre-eclampsia are significantly lower, taking into consideration the inconsistent results from the sensitivity analysis, our findings advocate the demand for more studies with larger sample sizes to generate solid ground pooled evidence on the predictive role of sHLA-G in pre-eclampsia.

An analysis of placental chorionic villous and decidual basalis tissue immunoreactivity in patients after cesarean section due to a placenta accreta spectrum disorder and elective cesarean section followed by the depressed mood

An analysis of placental chorionic villous and decidual basalis tissue immunoreactivity in patients after cesarean section due to a placenta accreta spectrum disorder and elective cesarean section followed by a depressed mood.

RESEARCH BACKGROUND

Over the past few years, interest in investigating immune dysfunction in patients with psychiatric disorders has increased. B7-H4 is a molecule with immunosuppressive properties that seems to play a key role in establishing maternal tolerance against fetal antigens. The aim of this study was to compare the B7-H4 immunoreactivity levels in patients after cesarean section.

METHODS

Placental and decidual tissue samples were obtained from 49 women who delivered at Bielański Hospital in Warsaw between 2009 and 2015. Fifteen of the patients developed postpartum depression and 14 had a diagnosis of placenta accreta spectrum. The control group consisted of 20 healthy patients on whom cesarean section was performed due to breech presentation at term.

RESULTS

The highest levels of B7-H4 immunoreactivity were found in the placental chorionic villous and decidual basalis tissue samples of the patients who later developed postpartum depression, while the lowest levels were found in the samples of those patients with a placenta accreta spectrum disorder. The difference between the B7-H4 immunoreactivity levels of these two groups was statistically significant. The B7-H4 expression levels were statistically significantly higher in the women in the postpartum depression group than in the control group.

CONCLUSION

Postpartum depression follows a disturbance of the suppressive milieu responsible for rebalancing the maternal immune system after the initial cytotoxic activation during labor.

Circulating Levels of Anti-C1q and Anti-Factor H Autoantibodies and Their Targets in Normal Pregnancy and Preeclampsia

Preeclampsia (PE) generally manifests in the second half of pregnancy with hypertension and proteinuria. The understanding of the origin and mechanism behind PE is incomplete, although there is clearly an immune component to this disorder. The placenta constitutes a complicated immune interface between fetal and maternal cells, where regulation and tolerance are key. Stress factors from placental dysfunction in PE are released to the maternal circulation evoking the maternal response. Several complement factors play a role within this intricate landscape, including C1q in vascular remodeling and Factor H (FH) as the key regulator of alternative pathway complement activation. We hypothesize that decreased levels of C1q or FH, or disturbance of their function by autoantibodies, may be associated with PE. Autoantibodies against C1q and FH and the concentrations of C1q and FH were measured by ELISA in maternal sera from women with preeclamptic and normal pregnancies. Samples originated from cohorts collected in the Netherlands (n=63 PE; n=174 control pregnancies, n=51 nonpregnant), Finland (n=181 PE; n=63 control pregnancies) and Norway (n=59 PE; n=27 control pregnancies). Serum C1q and FH concentrations were higher in control pregnancy than in nonpregnant women. No significant differences were observed for serum C1q between preeclamptic and control pregnancy in any of the three cohorts. Serum levels of FH were lower in preeclamptic pregnancies compared to control pregnancies in two of the cohorts, this effect was driven by the early onset PE cases. Neither anti-C1q autoantibodies nor anti-FH autoantibodies levels differed between women with PE and normal pregnancies. In conclusion, levels of anti-C1q and anti-FH autoantibodies are not increased in PE. C1q and FH are increased in pregnancy, but importantly, a decrease in FH concentration is associated with PE.

Histocompatibility Antigen, Class I, G (HLA-G)'s Role during Pregnancy and Parturition: A Systematic Review of the Literature

Introduction: Immune homeostasis of the intrauterine cavity is vital for pregnancy maintenance. At term or preterm, fetal and maternal tissue inflammation contributes to the onset of labor. Though multiple immune-modulating molecules are known, human leukocyte antigen (HLA)-G is unique to gestational tissues and contributes to maternal–fetal immune tolerance. Several reports on HLA-G’s role exist; however, ambiguity exists regarding its functional contributions during pregnancy and parturition. To fill these knowledge gaps, a systematic review (SR) of the literature was conducted to better understand the expression, localization, function, and regulation of HLA-G during pregnancy and parturition. Methods: A SR of the literature on HLA-G expression and function reported in reproductive tissues during pregnancy, published between 1976–2020 in English, using three electronic databases (SCOPE, Medline, and ClinicalTrials.gov) was conducted. The selection of studies, data extraction, and quality assessment were performed in duplicate by two independent reviewers. Manuscripts were separated into three categories: (1) expression and localization of HLA-G, (2) regulators of HLA-G, and (3) the mechanistic roles of HAL-G. Data were extracted, analyzed, and summarized. Results: The literature search yielded 2554 citations, 117 of which were selected for full-text evaluation, and 115 were included for the final review based on our inclusion/exclusion criteria. HLA-G expression and function were mostly studied in placental tissue and/or cells and peripheral blood immune cells, while only 13% of the studies reported data on amniotic fluid/cord blood and fetal membranes. Measurements of soluble and membranous HLA-G were determined mostly by RNA-based methods and protein by immunostaining, Western blot, or flow cytometric analyses. HLA-G was reported to regulate inflammation and inhibit immune-cell-mediated cytotoxicity and trophoblast invasion. Clinically, downregulation of HLA-G is reported to be associated with poor placentation in preeclampsia and immune cell infiltration during ascending infection. Conclusions: This SR identified several reports supporting the hypothesized role of immune regulation in gestational tissues during pregnancy. A lack of rigor and reproducibility in the experimental approaches and models in several reports make it difficult to fully elucidate the mechanisms of action of HLA-G in immune tolerance during pregnancy.

Evaluation of Maternal Serum sHLA-G Levels for Trisomy 18 Fetuses Screening at Second Trimester

Human leukocyte antigen-G (HLA-G) has been widely acknowledged to play critical roles in fetal-maternal maintenance. However, the significance of using maternal serum sHLA-G to detect prenatal chromosomal abnormality has not been investigated. In China, prenatal screening using maternal α-fetoprotein (AFP), unconjugated estriol (uE3), and free β subunit human chorionic gonadotropin (β-hCG) in the second trimester has been widely applied. In this study, we evaluated the use of sHLA-G as a screening marker, compared with traditional second trimester prenatal screening. Serum samples from 1,019 singleton women in their second trimester were assessed. Among them, 139 infants were confirmed with trisomy 21 (T21) by karyotyping, 83 were confirmed with trisomy 18 (T18), and the remaining 797 infants had no abnormalities. The sHLA-G levels in maternal sera were significantly lower in pregnant women with T18 fetuses (median: 47.8 U/ml, range: 9.8-234.2 U/ml) and significantly higher in those with T21 fetuses (median: 125.7 U/ml, range: 28.7-831.7 U/ml), compared with the normal controls (median: 106.3 U/ml, range: 50.5-1136.4 U/ml) (p < 0.001). The risk values of the screening of T21 or T18 fetuses were assessed using mean and standard deviation log₁₀ analyte multiples of median (MoM) which showed that the predictive values of sHLA-G were the same as free β-hCG, and superior to AFP and uE3 for T18 screening. Logistic regression analysis revealed that sHLA-G MoM was the highest risk factor associated with pregnant women carrying T18 fetuses [Exp(B): 171.26, 95% CI: 36.30-807.97, p < 0.001]. Receiver operating characteristic (ROC) analysis revealed that the area under ROC curve for sHLA-G MoM was 0.915 (95% CI, 0.871-0.959, p < 0.001), for AFP MoM was 0.796 (95% CI, 0.730-0.861, p < 0.001), for free β-hCG MoM was 0.881 (95% CI, 0.829-0.934, p < 0.001), and for uE3 MoM was 0.876 (95% CI, 0.828-0.923, p < 0.001) in the T18 group. sHLA-G MoM demonstrated the best sensitivity and negative predictive value. For the first time, our findings reveal that sHLA-G is a better second trimester screening marker for the detection of T18 fetuses and the combined application of sHLA-G with AFP, free β-hCG, and uE3 could improve clinical screening for T18 fetuses.

HLA-G: Function, polymorphisms and pathology

HLA-G immune modulatory genes and molecules are presently being studied by a widespread number of research groups. In the present study, we do not aim to be exhaustive since the number of manuscripts published every year is overwhelming. Instead, our aim is pointing out facts about HLA-G function, polymorphism and pathology that have been confirmed by several different researchers, together with exposing aspects that may have been overlooked or not sufficiently remarked in this productive field of study. On the other hand, we question whether performing mainly studies on HLA-G and disease associations is going to give a clear answer in the future, since 40 years of study of classical HLA molecules association with disease has still given no definite answer on this issue.

HLA-G whole gene amplification reveals linkage disequilibrium between the HLA-G 3'UTR and coding sequence

Polymorphic sites in the HLA-G gene may influence expression and function of the protein. Knowledge of the association between high-resolution HLA-G alleles and 3-prime untranslated (3'UTR) haplotypes is useful for studies on the role of HLA-G in transplantation, pregnancy, and cancer. We developed a next generation sequencing (NGS)-based typing assay enabling full phasing over the whole HLA-G gene sequence with inclusion of the 3'UTR region. DNA from 171 mother-child pairs (342 samples) was studied for: (a) HLA-G allele information by the NGSgo-AmpX HLA-G assay, (b) 3'UTR haplotype information by an in-house developed sequence-based typing method of a 699/713 base pair region in the 3'UTR, and (c) the full phase HLA-G gene sequence, by combining primers from both assays. The mother to child inheritance allowed internal verification of newly identified alleles and of association between coding and UTR regions. The NGSgo workflow compatible with Illumina platforms was employed. Data was interpreted using NGSengine software. In 99.4% of all alleles analyzed, the extended typing was consistent with the separate allele and 3'UTR typing methods. After repeated analysis of four samples that showed discrepancy, consistency reached 100%. A high-linkage disequilibrium between IPD-IMGT/HLA Database-defined HLA-G alleles and the extended 3'UTR region was identified (D' = 0.994, P < .0001). Strong associations were found particularly between HLA-G*01:04 and UTR-3, between HLA-G*01:01:03 and UTR-7, and between HLA-G*01:03:01 and UTR-5 (for all: r = 1). Six novel HLA-G alleles and three novel 3'UTR haplotype variants were identified, of which three and one, respectively, were verified in the offspring.

Association of Soluble HLA-G Plasma Level and HLA-G Genetic Polymorphism With Pregnancy Outcome of Patients Undergoing in vitro Fertilization Embryo Transfer

Infertility is currently a growing problem observed around the world and is estimated to affect between 8 and 12% of reproductive-aged couples worldwide. Artificial reproductive techniques are the last chance for couples seeking their own child. Human leukocyte antigen (HLA)-G expression has been suggested as an immunomodulatory molecule that influences pregnancy outcome. The HLA-G gene encodes either membrane-bound or/and soluble proteins. The aim of this study was the evaluation of the role of soluble HLA-G (sHLA-G) and its gene polymorphism in successful implantation after in vitro fertilization embryo transfers (IVF-ETs) in different clinical protocols. We tested the HLA-G polymorphism in three positions: rs1632947: c.-964G>A; rs1233334: c.-725G>C/T in promoter region; rs371194629: c.^*65_^*66insATTTGTTCATGCCT in 3′ untranslated region of exon 8, in 389 patients who underwent IVF-ETs and 320 women with healthy children born after natural conception. Among the patient group, 239 women were with recurrent implantation failure and 117 women had an ongoing pregnancy or a child born after IVF-ET. We found that certain rs1632947-rs1233334-rs371194629 HLA-G haplotypes and diplotypes were associated with infertility, while others were protective. The lowest secretors of sHLA-G were G-C-ins haplotype carriers (37.21 IU/ml), while the highest -G-C-del carriers (73.80 IU/ml). Other haplotype carriers were intermediate secretors. In our study, regardless of possessed haplotype by the patient, 59.73 IU/ml sHLA-G was the threshold value with the best sensitivity (58.82%) and specificity (66.10%) to discriminate patients who achieved and maintained pregnancy from those who did not conceive or they had miscarriage (p = 0.0085; likelihood ratio, 1.74; 95% CI = 0.55–0.78). However, we do not exclude that factors other than sHLA-G may also contribute to complications in pregnancy. In addition, we found that IVF patients in cycles when frozen/thawed embryo was transferred secreted higher soluble HLA-G levels than patients with fresh embryo transferred (p = 0.021). Moreover, correlation analysis of sHLA-G concentration measured before and after embryo transfer for particular patients indicated short ovarian stimulation with gonadotropin-releasing hormone antagonist as more beneficial than long protocol with gonadotropin-releasing hormone agonist. Our study confirms a role of HLA-G polymorphism in infertility and soluble HLA-G in the early stages of pregnancy.

The Immunogenetic Conundrum of Preeclampsia

Pregnancy is an immunological challenge to the mother. The fetal tissues including the placenta must be protected from activation of the maternal immune system. On the other hand, the placental tissue sheds into the maternal circulation and must be adequately identified and phagocytized by the maternal immune system. During a healthy pregnancy, numerous immunosuppressive processes take place that allow the allograft fetus to thrive under exposure to humoral and cellular components of the maternal immune system. Breakdown of immune tolerance may result in sterile inflammation and cause adverse pregnancy outcomes such as preeclampsia, a vascular disease of the pregnancy with unpredictable course and symptoms from several organs. Immunological incompatibility between mother and fetus is strongly indicated in preeclampsia. Recently, genetic factors linking immunological pathways to predisposition to preeclampsia have been identified. In this mini-review genetic variation in immunological factors are discussed in the context of preeclampsia. Specifically, we explore immunogenetic and immunomodulary mechanisms contributing to loss of tolerance, inflammation, and autoimmunity in preeclampsia.

Soluble HLA-G Expression Inversely Correlates With Fetal Microchimerism Levels in Peripheral Blood From Women With Scleroderma

Women with scleroderma (SSc) maintain significantly higher quantities of persisting fetal microchimerism (FMc) from complete or incomplete pregnancies in their peripheral blood compared to healthy women. The non-classical class-I human leukocyte antigen (HLA) molecule HLA-G plays a pivotal role for the implantation and maintenance of pregnancy and has often been investigated in offspring from women with pregnancy complications. However data show that maternal HLA-G polymorphisms as well as maternal soluble HLA-G (sHLA-G) expression could influence pregnancy outcome. Here, we aimed to investigate the underlying role of maternal sHLA-G expression and HLA-G polymorphisms on the persistence of FMc. We measured sHLA-G levels by enzyme linked immunosorbent assay in plasma samples from 88 healthy women and 74 women with SSc. Male Mc was quantified by DYS14 real-time PCR in blood samples from 58 women who had previously given birth to at least one male child. Furthermore, eight HLA-G 5'URR/3'UTR polymorphisms, previously described as influencing HLA-G expression, were performed on DNA samples from 96 healthy women and 106 women with SSc. Peripheral sHLA-G was at lower concentration in plasma from SSc (76.2 ± 48.3 IU/mL) compared to healthy women (117.5 ± 60.1 IU/mL, p < 0.0001), independently of clinical subtypes, autoantibody profiles, disease duration, or treatments. Moreover, sHLA-G levels were inversely correlated to FMc quantities (Spearman correlation, p < 0.01). Finally, women with SSc had lower sHLA-G independently of the eight HLA-G 5'URR/3'UTR polymorphisms, although they were statistically more often homozygous than heterozygous for HLA-G polymorphism genotypes -716 (G/T), -201 (G/A), 14 bp (ins/del), and +3,142 (G/A) than healthy women. In conclusion, women with SSc display less sHLA-G expression independently of the eight HLA-G polymorphisms tested. This decreased production correlates with higher quantities of persisting FMc commonly observed in blood from SSc women. These results shed some lights on the contribution of the maternal HLA-G protein to long-term persistent fetal Mc and initiate new perspectives in this field.