Allergic women have reduced sHLA-G plasma levels at delivery

SARS-CoV-2 Footprints in the Placenta: What We Know after Three Years of the Pandemic

As the COVID-19 pandemic continues into its third year, there is accumulating evidence on the consequences of maternal infection. Emerging data indicate increased obstetrics risks, including maternal complications, preterm births, impaired intrauterine fetal growth, hypertensive disorders, stillbirth, gestational diabetes, and a risk of developmental defects in neonates. Overall, controversial concerns still exist regarding the potential for vertical transmission. Histopathological examination of the placenta can represent a useful instrument for investigation and can contribute significant information regarding the possible immunohistopathological mechanisms involved in developing unfavorable perinatal outcomes. Based on current evidence, SARS-CoV-2 infection can affect placental tissue by inducing several specific changes. The level of placental involvement is considered one of the determining factors for unfavorable outcomes during pregnancy due to inflammation and vascular injuries contributing to complex cascade immunological and biological events; however, available evidence does not indicate a strong and absolute correlation between maternal infection, placental lesions, and obstetric outcomes. As existing studies are still limited, we further explore the placenta at three different levels, using histology, immunohistochemistry, and molecular genetics to understand the epidemiological and virological changes observed in the ongoing pandemic.

Effect of SARS-CoV-2 infection in pregnancy on CD147, ACE2 and HLA-G expression

INTRODUCTION

Recent studies reported a differential expression of both ACE2 and CD147 in pregnant women associated to SARS-CoV-2 placental infection. The aim of this study is to further investigate the placental SARS-CoV-2 infection and the potential effect on protein expression (ACE2, CD147, HLA-G and CD56).

METHODS

The study was on three subgroups: i) 18 subjects positive for SARS-CoV-2 swab at delivery; ii) 9 subjects that had a positive SARS-CoV-2 swab during pregnancy but resulted negative at delivery; iii) 11 control subjects with physiological pregnancy and with no previous or concomitant SARS-CoV-2 swab positivity. None of the subjects were vaccinated for SARS-CoV-2 infection. The placenta samples were analyzed for SARS-CoV-2 NP (Nucleocapsid protein) positivity and the expression of ACE2, CD147, HLA-G and CD56.

RESULTS

We observed a higher percentage of SARS-CoV-2 NP positive placenta samples in the group of SARS-CoV-2 PCR positive at delivery in comparison with SARS-CoV-2 PCR negative at delivery. The localization of SARS-CoV-2 NP positivity in placenta samples was mainly in syncytiotrophoblast (ST) of SARS-CoV-2 PCR positive at delivery group and in extra-villous trophoblast (EVT) of SARS-CoV-2 PCR negative at delivery group. CD147, HLA-G positivity was higher in ST of SARS-CoV-2 PCR positive at delivery group, while CD56-expressing immune cells were decreased in comparison with control subjects.

DISCUSSION

We confirmed the ability of SARS-CoV-2 to infect placenta tissues. The simultaneous SARS-CoV-2 swab positivity at delivery and the positivity of the placenta tissue for SARS-CoV-2 NP seems to create an environment that modifies the expression of specific molecules, as CD147 and HLA-G. These data suggest a possible impact of SARS-CoV-2 infection during pregnancy, that might be worthy to be monitored also in vaccinated subjects.

HLA-G in Allergy: Does It Play an Immunoregulatory Role?

Allergy is an inflammatory process determined by a cascade of immune events characterized by T-helper 2 lymphocytes polarization leading to interleukin-4 upregulation, IgE secretion, and mast cell and eosinophil activation. HLA-G molecules, both in membrane-bound and in soluble forms, are known to play a key immunoregulatory role and their involvement in allergic diseases is supported by increasing literature data. HLA-G expression and secretion is specifically induced in peripheral blood mononuclear cells of allergic patients after in vitro incubation with the causal allergen. Elevated levels of soluble HLA-G molecules are detected in serum of patients with allergic rhinitis correlating with allergen-specific IgE levels, clinical severity, drug consumption and response to allergen-specific immunotherapy. HLA-G genetic polymorphisms confer susceptibility to allergic asthma development and high levels of soluble HLA-G molecules are found in plasma and bronchoalveolar lavage fluid of patients with allergic asthma correlating with allergen-specific IgE levels. Interestingly, allergic pregnant women have lower plasma sHLA-G levels than non-allergic women during the 3rd trimester of pregnancy and at delivery. Finally, in allergic patients with atopic dermatitis HLA-G molecules are expressed by T cells, monocytes-macrophages and Langerhans cells infiltrating the dermis. Although at present is difficult to completely define the role of HLA-G molecules in allergic diseases, it may be suggested that they are specifically expressed and secreted by immune cells during the allergic reaction in an attempt to suppress allergic inflammation.

Evidence for a shift in placental HLA-G allelic dominance and the HLA-G isoform profile during a healthy pregnancy and pre-eclampsia

Human leukocyte antigen (HLA)-G is a non-classical class Ib major expressed by placental trophoblast cells plays a central role in establishing tolerance to the semi-allogeneic fetus and in placentation. HLA-G exists in different soluble or membrane-bound isoforms. Pre-eclampsia, a major cause of fetal and maternal morbidity and mortality, has been linked to insufficient placentation and an altered immune response in pregnancy, including altered HLA-G expression. The 14 bp insertion/deletion polymorphism in the 3' untranslated region of the gene and the isoform profile may affect HLA-G expression. The aim of the current pilot study was to characterize the expression patterns of HLAG mRNA, protein and isoform profile in uncomplicated term pregnancies and in cases of pre-eclampsia. Maternal sHLA-G mRNA and protein levels was slightly reduced in pre-eclampsia. No difference was found for placental blood, and no correlation between peripheral and placental sHLA-G levels was found. We observed no association between neither fetal nor maternal HLA-G 14 bp insertion/deletion genotypes and pre-eclampsia, nor a significant difference in isoform profiles. However, in HLA-G 14 bp insertion/deletion heterozygous placental samples, we observed abundant HLA-G1 14 bp insertion allele expression in the term placentae, which is contrary to previous findings in first trimester trophoblast. Increased HLA-G1 14 bp insertion allele expression in the placenta was associated with reduced levels of placental sHLA-G and an altered isoform profile with increased relative levels of HLA-G1 and -G5 and reduced levels of HLA-G3. The results indicate that an allelic shift in heterozygous individuals could represent a novel regulatory pathway.

HLA-G expression during hookworm infection in pregnant women

INTRODUCTION

HLA-G plays a key role on immune tolerance. Pathogens can induce soluble HLA-G (sHLA-G) production to down-regulate the host immune response, creating a tolerogenic environment favorable for their dissemination. To our knowledge, no study has yet been conducted to assess the relationship between sHLA-G and geohelminth infections.

METHODS

The study was conducted in Allada, Southeastern Benin, from 2011-2014. The study population encompassed 400 pregnant women, included before the end of the 28th week of gestation and followed-up until delivery. At two antenatal care visits and at delivery, stool and blood samples were collected. Helminths were diagnosed by means of the Kato-Katz concentration technique. We used quantile regression to analyze the association between helminth infections and sHLA-G levels during pregnancy.

RESULTS

sHLA-G levels gradually increased during pregnancy and reached maximal levels at delivery. Prevalence of helminth infections was low, with a majority of hookworm infections. We found significantly more hookworm-infected women above the 80th quantile (Q80) of the distribution of the mean sHLA-G level (p < 0.03, multivariate quantile regression). Considering only women above the Q80 percentile, the mean sHLA-G level was significantly higher in hookworm-infected compared to uninfected women (p = 0.04).

CONCLUSION

High levels of sHLA-G were associated with hookworm infection in pregnant women. This result is consistent with the potential involvement of sHLA-G in immune tolerance induced by helminths during pregnancy.

Soluble human leukocyte antigen -G during pregnancy and infancy in Benin: Mother/child resemblance and association with the risk of malaria infection and low birth weight

Human leukocyte antigen (HLA) G is a tolerogenic molecule involved in the maternal-fetal immune tolerance phenomenon. Its expression during some infectious diseases leading to immune evasion has been established. A first study conducted in Benin has shown that the production of soluble HLA-G (sHLA-G) during the first months of life is strongly correlated with the maternal level at delivery and associated with low birth weight and malaria. However sHLA-G measurements during pregnancy were not available for mothers and furthermore, to date the evolution of sHLA-G in pregnancy is not documented in African populations. To extend these previous findings, between January 2010 and June 2013, 400 pregnant women of a malaria preventive trial and their newborns were followed up in Benin until the age of 2 years. Soluble HLA-G was measured 3 times during pregnancy and repeatedly during the 2 years follow-up to explore how sHLA-G evolved and the factors associated. During pregnancy, plasma levels of sHLA-G remained stable and increased significantly at delivery (p<0.001). Multigravid women seemed to have the highest levels (p = 0.039). In infants, the level was highest in cord blood and decreased before stabilizing after 18 months (p<0.001). For children, a high level of sHLA-G was associated with malaria infection during the follow-up (p = 0.02) and low birth weight (p = 0.06). The mean level of sHLA-G during infancy was strongly correlated with the mother’s level during pregnancy (<0.001), and not only at delivery. Moreover, mothers with placental malaria infection had a higher probability of giving birth to a child with a high level of sHLA-g (p = 0.006). High sHLA-G levels during pregnancy might be associated with immune tolerance related to placental malaria. Further studies are needed but this study provides a first insight concerning the potential role of sHLA-G as a biomarker of weakness for newborns and infants.

Pregnancy and breastfeeding: a new theory for sHLA-G in breast cancer patients?

It is now widely recognized that HLA-G molecule is implicated in immune tolerance and particularly in immune subversion of tumor cells. In this study, we explored levels of soluble HLA-G (sHLA-G) in plasma samples obtained from women with breast cancer (BC). Additionally, we correlated sHLA-G concentration with pregnancy and breastfeeding history. We reported in this preliminary work significant differences in sHLA-G levels between BC patients with/without breastfeeding experience (p = 0.04). Interestingly, among women with BC, only those without previous pregnancy experience present significant increase in sHLA-G (p = 0.02). Of relevance, we demonstrated that patients without both pregnancy and breastfeeding history have advanced SBR III grade, associated with significant enhancement in tumor size compared with patients who had both experiences (p = 0.028). Taken together, our results indicate the potential implication of previous pregnancy and breastfeeding experience in sHLA-G expression during BC. We theorized that having pregnancy and breastfeeding history may protect against advanced BC stages.

Immunoregulatory Role of HLA-G in Allergic Diseases

Allergic diseases are sustained by a T-helper 2 polarization leading to interleukin-4 secretion, IgE-dependent inflammation, and mast cell and eosinophil activation. HLA-G molecules, both in membrane-bound and in soluble forms, play a central role in modulation of immune responses. Elevated levels of soluble HLA-G (sHLA-G) molecules are detected in serum of patients with allergic rhinitis to seasonal and perennial allergens and correlate with allergen-specific IgE levels, clinical severity, drug consumption, and response to allergen-specific immunotherapy. sHLA-G molecules are also found in airway epithelium of patients with allergic asthma and high levels of sHLA-G molecules are detectable in plasma and bronchoalveolar lavage of asthmatic patients correlating with allergen-specific IgE levels. Finally, HLA-G molecules are expressed by T cells, monocytes-macrophages, and Langerhans cells infiltrating the dermis of atopic dermatitis patients. Collectively, although at present it is difficult to completely define the role of HLA-G molecules in allergic diseases, it may be suggested that they are expressed and secreted by immune cells during the allergic reaction in an attempt to suppress allergic inflammation.

Human leukocyte antigen G is associated with esophageal squamous cell carcinoma progression and poor prognosis

Human leukocyte antigen G (HLA-G) is a non-classical HLA class I molecule thought to play a key role in maternal-fetal tolerance and cancer immune evasion. This study aimed to investigate the HLA-G expression in lesion sections and plasma sHLA-G levels of primary esophageal squamous cell carcinoma (ESCC) patients and its clinical significance in diagnosis and prognosis of ESCC. 60 ESCC patients and 28 healthy controls were recruited, and the positive expression of HLA-G in ESCC lesions and adjacent normal tissues were 70% (42/60) and 8.6% (5/60) (P<0.05), respectively, while no expression was found in normal controls. HLA-G1 and HLA-G5 were determined to be dominating isoforms measured by RT-PCR. There was a significant difference in plasma sHLA-G levels between patients with ESCC (15.04 U/ml, range 4.33-250.00 U/ml) and healthy controls (6.81 U/ml, range 0-29.27 U/ml) (P<0.01). The plasma IL-10 level was higher in ESCC patients than the controls (23.86 pg/ml vs. 12.81 pg/ml, P<0.01). HLA-G expression in lesion tissues was correlated with cancer cell differentiation (P=0.033), lymph node metastasis (P=0.035) of ESCC. However, no obvious correlations were demonstrated between the plasma sHLA-G levels and the clinicopathological parameters. There was a significant correlation between sHLA-G and IL-10 expression (r=0.353, P=0.006) in patients with Esophageal squamous cell carcinoma. HLA-G positive expression showed poorer prognosis of ESCC. HLA-G positive expression might serve as a potential marker in the diagnosis or prediction of ESCC.

In vitro up-regulation of HLA-G using dexamethasone and hydrocortisone in first-trimester trophoblast cells of women experiencing recurrent miscarriage

The trophoblast cells at the maternal-fetal interface express an unusual combination of human leukocyte antigen (HLA)-C, HLA-E and HLA-G. Altered expression of HLA-G on the extravillous cytotrophoblast has been implicated in the etiology of recurrent miscarriages (RMs). We have assessed HLA-G expression in extravillous cytotrophoblast in cell cultures prepared from RM patients and compared with those of first-trimester voluntarily terminated normal pregnancies (control). Glucocorticoids, dexamethasone and hydrocortisone were examined for their role in modulation of the HLA-G expression. HLA-G promoter and 3'UTR variants were investigated for their effect on the transcription of HLA-G. Cultured cytotrophoblast cells from the first-trimester RM patients were treated with dexamethasone and hydrocortisone (dose concentration 0-1000 ng/ml). HLA-G gene transcription was determined by semiquantitative and quantitative real-time polymerase chain reaction (RT-PCR), while protein expression was determined by a specific enzyme-linked immunosorbent assay (ELISA), flow cytometry and western blot analyses. HLA-G polymorphisms were detected by PCR and/or sequence-based typing. Low level of HLA-G was observed in untreated trophoblast cells obtained from RM patients as compared with controls. Upon treatment with glucocorticoids, the expression of HLA-G in these cells was up-regulated in a dose-dependent manner (P < 0.05), with no change in cellular proliferation and viability. There was no significant association between HLA-G polymorphism in RM patients and controls. HLA-G is minimally expressed in cultured trophoblast cells of RM patients. It can be up-regulated upon exposure with both dexamethasone and hydrocortisone. Glucocorticoids have the potential to modulate HLA-G expression in vitro, and can be further examined for their therapeutic applicability in RM.

The immunosuppressive molecule HLA-G and its clinical implications

Human leukocyte antigen G (HLA-G) is a non-classical major histocompatibility complex (MHC) class I molecule that, through interaction with its receptors, exerts important tolerogenic functions. Its main physiological expression occurs in placenta where it seems to participate in the maternal tolerance toward the fetus. HLA-G has been studied as a marker of pregnancy complications such as abortion or pre-eclapmsia. Although HLA-G is not expressed in most adult tissues, its ectopic expression has been observed in some diseases such as viral infections, autoimmune disorders, and especially cancer. HLA-G neo-expression in cancer is associated with the capability of tumor cells to evade the immune control. In this review, we will summarize HLA-G biology and how it participates in these physiopathological processes. Special attention will be paid to its role as a diagnostic tool and also as a therapeutic target.

Maternal soluble human leukocyte antigen-G levels in pregnancies complicated by foetal intrauterine growth restriction with and without preeclampsia

OBJECTIVE

The aim of this study was to investigate the maternal serum of soluble human leukocyte antigen-G (sHLA-G) levels in pregnant women with an isolated intrauterine growth restricted foetus (IUGR) and in preeclamptic pregnancies with and without IUGR.

PATIENTS AND METHODS

The study was conducted on 31 normotensive patients with pregnancy complicated by IUGR, 17 preeclamptic patients with appropriate-for-gestational-age foetal intrauterine growth, 21 with preeclampsia complicated by IUGR, and 32 healthy pregnant controls. Maternal serum sHLA-G levels were calculated using the enzyme-linked immunosorbent assay.

RESULTS

Maternal serum sHLA-G levels tended to be higher in both groups of preeclamptic patients, and were highest in patients with IUGR in the course of severe preeclampsia. Lower serum levels of sHLA-G were observed in the group of normotensive pregnant women with an intrauterine growth restricted foetus, but these differences were not statistically significant. The mean values were 22.759±14.151units/mL in the IUGR group, 25.948±18.888units/mL in preeclamptic patients with normal intrauterine foetal growth, 31.646±27.576units/mL in preeclamptic pregnant women with IUGR, and 24.178±24.828units/mL in the healthy controls.

CONCLUSIONS

Our findings suggest that the increased levels of sHLA-G in the maternal serum may play a significant role in the pathogenesis of preeclampsia, especially in preeclampsia complicated by intrauterine foetal growth restriction. These associations may offer a better insight into the etiology and pathogenesis of preeclampsia with and without IUGR. It seems that sHLA-G does not play a clinically significant role in the pathogenesis of isolated intrauterine foetal growth restriction in normotensive pregnancies.

The importance of HLA-G expression in embryos, trophoblast cells, and embryonic stem cells

The nonclassical HLA-G molecule is a trophoblast-specific molecule present in almost every pregnancy. It differs from classical HLA class I molecules by the low degree of allelic variants and the high diversity of protein structures. HLA-G is reported to be a tolerogenic molecule that acts on cells of both innate and adaptive immunity. At the maternal-fetal interface HLA-G seems to be responsible largely for the reprogramming of local maternal immune response. This review will focus on the HLA-G gene expression profile in pregnancy, in preimplantation embryos, and in human embryonic stem cells with emphasis on the structural diversity of the HLA-G protein and its potential functional and diagnostic implications.

Soluble human leukocyte antigen-G isoforms in maternal plasma in early and late pregnancy

PROBLEM

Human Leukocyte Antigen (HLA)-G is a class Ib gene located in the human major histocompatibility complex (MHC). Several lines of investigation indicate that the HLA-G molecule is involved in the maternal acceptance of the semi-allogenic fetus during pregnancy and in the development of tolerance. Expression of soluble HLA-G (sHLA-G) is positively correlated with successful in vitro fertilization (IVF) treatments, and aberrant expression of HLA-G in certain complications of pregnancy, such as pre-eclampsia and spontaneous abortion, has been reported. The main purpose of this study was to investigate the levels of different soluble HLA-G isoforms in maternal plasma in early and late pregnancy.

METHOD OF STUDY

Soluble HLA-G (sHLA-G) can be detected in maternal blood, and in this study, two different isoforms of sHLA-G, namely sHLA-G1 generated by shedding of membrane-bound HLA-G1 and HLA-G generated by specific HLA-G transcripts, have been investigated early [median of 16.4 weeks of gestation (GW)] and late (median: 38.9 GW) in pregnancy in an original cohort of 580 pregnant Caucasian women.

RESULTS

Lower concentrations of sHLA-G1 were found late in pregnancy (>32 GW) in a group of women with severe pre-eclampsia compared with controls with uncomplicated pregnancies (P = 0.029, P(C) = 0.09; Mann-Whitney; Logistic regression analysis: P = 0.024, OR = 0.920, 95% CI: 0.855-0.989). However, this was not the case with HLA-G5, and significantly more of the cases with severe pre-eclampsia had detectable plasma HLA-G5 compared with that of the control group (P = 0.013, P(C) = 0.04; Mann-Whitney). Similar findings were not observed in women with gestational hypertension or existing hypertension continuing into pregnancy. Furthermore, there was a trend toward lower maternal plasma sHLA-G1 in a group of women with premature birth (<37 GW) compared with that of the control group (P = 0.028, P(C) = 0.17; Mann-Whitney). On the contrary, HLA-G5 was lower in the control group compared with that in the premature group (P = 0.004, P(C) = 0.02; Mann-Whitney).

CONCLUSION

This study shows in line with other published studies that a high, detectable soluble HLA-G concentration in maternal plasma or serum is not mandatory for a successful pregnancy. However, complications during pregnancy, such as (severe) pre-eclampsia, spontaneous abortion, IUGR, and premature birth, are associated with a low or undetectable level of soluble HLA-G in the maternal blood circulation. Also, this study indicates that sHLA-G1 is the interesting soluble HLA-G isoform in pre-eclampsia, and that low or undetectable levels of HLA-G5 at the end of pregnancy seem to be associated with an uncomplicated normal pregnancy, whereas in severe pre-eclampsia and possibly other pregnancy complications, such as preterm birth and IUGR, the level of HLA-G5 is higher.