High plasma levels of HLA-G are associated with low birth weight and with an increased risk of malaria in infancy

Placental Malaria is Associated with Higher LILRB2 Expression in Monocyte Subsets and Lower Anti-Malarial IgG Antibodies During Infancy

Background

Placental malaria (PM) is associated with a higher susceptibility of infants to Plasmodium falciparum (Pf) malaria. A hypothesis of immune tolerance has been suggested but no clear explanation has been provided so far. Our goal was to investigate the involvement of inhibitory receptors LILRB1 and LILRB2, known to drive immune evasion upon ligation with pathogen and/or host ligands, in PM-induced immune tolerance.

Method

Infants of women with or without PM were enrolled in Allada, southern Benin, and followed-up for 24 months. Antibodies with specificity for five blood stage parasite antigens were quantified by ELISA, and the frequency of immune cell subsets was quantified by flow cytometry. LILRB1 or LILRB2 expression was assessed on cells collected at 18 and 24 months of age.

Findings

Infants born to women with PM had a higher risk of developing symptomatic malaria than those born to women without PM (IRR=1.53, p=0.040), and such infants displayed a lower frequency of non-classical monocytes (OR=0.74, p=0.01) that overexpressed LILRB2 (OR=1.36, p=0.002). Moreover, infants born to women with PM had lower levels of cytophilic IgG and higher levels of IL-10 during active infection.

Interpretation

Modulation of IgG and IL-10 levels could impair monocyte functions (opsonisation/phagocytosis) in infants born to women with PM, possibly contributing to their higher susceptibility to malaria. The long-lasting effect of PM on infants’ monocytes was notable, raising questions about the capacity of ligands such as Rifins or HLA-I molecules to bind to LILRB1 and LILRB2 and to modulate immune responses, and about the reprogramming of neonatal monocytes/macrophages.

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 3^rd 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.

Immunomodulatory Potential of Non-Classical HLA-G in Infections including COVID-19 and Parasitic Diseases

Human Leukocyte Antigen-G (HLA-G), a polymorphic non-classical HLA (HLA-Ib) with immune-regulatory properties in cancers and infectious diseases, presents both membrane-bound and soluble (sHLA-G) isoforms. Polymorphism has implications in host responses to pathogen infections and in pathogenesis. Differential expression patterns of HLA-G/sHLA-G or its polymorphism seem to be related to different pathological conditions, potentially acting as a disease progression biomarker. Pathogen antigens might be involved in the regulation of both membrane-bound and sHLA-G levels and impact immune responses during co-infections. The upregulation of HLA-G in viral and bacterial infections induce tolerance to infection. Recently, sHLA-G was found useful to identify the prognosis of Coronavirus disease 2019 (COVID-19) among patients and it was observed that the high levels of sHLA-G are associated with worse prognosis. The use of pathogens, such as Plasmodium falciparum, as immune modulators for other infections could be extended for the modulation of membrane-bound HLA-G in COVID-19-infected tissues. Overall, such information might open new avenues concerning the effect of some pathogens such as parasites in decreasing the expression level of HLA-G to restrict pathogenesis in some infections or to influence the immune responses after vaccination among others.

Maternal risk factors and neonatal outcomes associated with low birth weight in a secondary referral hospital in Ghana

INTRODUCTION

Over the past decade, the incidence of low birth weight (LBW) in sub-Saharan Africa has not seen any decline and this is a matter of grave concern for healthcare providers, policymakers, and researchers. Therefore, this study aimed to assess the incidence of LBW and related maternal risk factors (during pregnancy or delivery) as well as neonatal outcomes.

METHODS

An institutional-based retrospective cross-sectional study design was employed to select 1,017 mothers who delivered in the study hospital from January to December 2017 with singleton newborn babies without congenital diseases. Data were analysed using STATA version 14.1 (StataCorp. 2015. Stata Statistical Software: Release 14. College Station, TX: Stata Corp LP). Chi-square test of independence was used to test the association between the dependent variable (LBW) and risk factors of LBW. Bivariate and multivariable unconditional logistic regression was used to determine the factors associated with LBW.

RESULTS

The incidence of LBW was 23.7%. The findings show that being married has a protective effect on LBW [AOR = 0.60 (95%CI: 0.40-0.90), p = 0.013] compared to single mothers. Neonates born between gestational age of 37-42 weeks had 85% lower odds of LBW [AOR = 0.15, (95%CI: 0.10-0.24), p < 0.001)]. Neonates with LBW had a higher risk of low Apgar score in the first minute compared to neonates with normal birth weight [AOR = 0.52 (95%CI: 0.37-0.73), p < 0.001]. Female neonates had 64% higher odds of LBW compared to their male counterparts [AOR = 1.64 (95%CI: 1.19-2.24), p = 0.002].

CONCLUSION

This study revealed a high incidence of LBW. Women's marital status (single mothers), gestational age (<37 weeks), neonatal sex (female), are independent risk factors associated with LBW, while a higher risk of an Apgar score of less than 7 in the first minute was an independent outcome of low birth weight births. The current study findings contribute to the growing literature on the influence of maternal and neonatal factors on LBW in resource-constrained settings. These findings could guide healthcare providers, hospital administrators, stakeholders, and policymakers to develop and implement appropriate clinical and public health strategies aimed at reducing LBW.

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.

Evaluation of the Level of Salivary sHLA-G in Children Aged 3-5 Years with or without Dental Caries

Methods and Materials

This analytic cross-sectional study was carried out on 83 healthy children aged 3 to 5 years of both genders, who were divided into three groups based on decayed dental surfaces (ds): group 1, caries-free children (CF, n = 29); group 2, children with 1 ≤ ds ≤ 3, 1 ≤ ds ≤ 4, and 1 ≤ ds ≤ 5 for age 3, 4, and 5 years, respectively (ECC, n = 20); and group 3, children with ds ≥ 4, ds ≥ 5, and ds ≥ 6 for age 3, 4, and 5 years, respectively (S-ECC, n = 34). The unstimulated saliva samples were collected, and the salivary sHLA-G concentration was measured by the ELISA kit. The SPSS Statistics v17.0 software and Mann–Whitney, Kruskal–Wallis, chi-square, and Spearman's rank correlation tests were used for statistical analysis. The level of significance was considered at p < 0.05.

Results

The mean concentrations of salivary sHLA-G in CF, ECC, and S-ECC groups were 3.18 ± 2.28, 5.64 ± 5.51, and 6.21 ± 6.03 ng/l, respectively (p = 0.047), and the mean salivary sHLA-G level was comparatively higher in children with dental caries than that of the CF group (p = 0.02), but there is no significant difference between ECC and S-ECC groups (p > 0.05). Spearman's rank correlation test showed a weak positive correlation (p = 0.039, r = 0.22), between the level of salivary sHLA-G and dental caries.

Conclusion

The present study provides some preliminary evidences on relationship between sHLA-G and dental caries in children.

Effect of immune regulatory pathways after immunization with GMZ2 malaria vaccine candidate in healthy lifelong malaria-exposed adults

BACKGROUND

Despite appreciable immunogenicity in malaria-naive populations, many candidate malaria vaccines are considerably less immunogenic in malaria-exposed populations. This could reflect induction of immune regulatory mechanisms involving Human Leukocyte Antigen G (HLA-G), regulatory T (Treg), and regulatory B (Breg) cells. Here, we addressed the question whether there is correlation between these immune regulatory pathways and both plasmablast frequencies and vaccine-specific IgG concentrations.

METHODS

Fifty Gabonese adults with lifelong exposure to Plasmodium spp were randomized to receive three doses of either 30 µg or 100 µg GMZ2-CAF01, or 100 µg GMZ2-alum, or control vaccine (rabies vaccine) at 4-week intervals. Only plasma and peripheral blood mononuclear cells isolated from blood samples collected before (D0) and 28 days after the third vaccination (D84) of 35 participants were used to measure sHLA-G levels and anti-GMZ2 IgG concentrations, and to quantify Treg, Breg and plasmablast cells. Vaccine efficacy was assessed using controlled human malaria infection (CHMI) by direct venous inoculation of Plasmodium falciparum sporozoites (PfSPZ Challenge).

RESULTS

The sHLA-G concentration increased from D0 to D84 in all GMZ2 vaccinated participants and in the control group, whereas Treg frequencies increased only in those receiving 30 µg or 100 µg GMZ2-CAF01. The sHLA-G level on D84 was associated with a decrease of the anti-GMZ2 IgG concentration, whereas Treg frequencies on D0 or on D84, and Breg frequency on D84 were associated with lower plasmablast frequencies. Importantly, having a D84:D0 ratio of sHLA-G above the median was associated with an increased risk of P. falciparum infection after sporozoites injection.

CONCLUSION

Regulatory immune responses are induced following immunization. Stronger sHLA-G and Treg immune responses may suppress vaccine induced immune responses, and the magnitude of the sHLA-G response increased the risk of Plasmodium falciparum infection after CHMI. These findings could have implications for the design and testing of malaria vaccine candidates in semi-immune individuals.

Schistosoma haematobium infection modulates Plasmodium falciparum parasite density and antimalarial antibody responses

AIMS

Schistosomiasis and malaria are endemic in sub-Saharan Africa where Schistosoma haematobium (Sh) and Plasmodium falciparum (Pf) coinfections are thus frequent. We explored the effect of Sh infection on antibody responses directed to Pf merozoite antigens and on malaria susceptibility in Beninese children.

METHODS AND RESULTS

A total of 268 children were followed during a malaria transmission season. Detection of Pf infection was performed by microscopy and rapid diagnostic tests. Sh infection was determined in urine by microscopy. Antimalarial antibody, cytokine and HLA-G concentrations were quantified by ELISA. The expression of HLA-G receptors by immune cells was assessed by flow cytometry. Children infected by Sh had higher concentrations of IgG1 directed to MSP3 and GLURP_R0 , IgG2 directed to GLURP_R0 and IgG3 directed to MSP3, GLURP_R0 and GLURP_R2 and have lower Pf densities than those uninfected by Sh. No difference in cytokine and HLA-G concentrations was observed between Sh egg carriers and non-carriers.

CONCLUSION

Schistosoma haematobium modulates host immune responses directed to Pf antigens. The absence of immune downregulation usually observed during helminth infections is surprising in our study. We hypothesize that the stage of Sh development could partly explain the immune pathways leading to increased antibody levels that favour better control of Pf parasitemia.

Increased Risk of Malaria During the First Year of Life in Small-for-Gestational-Age Infants: A Longitudinal Study in Benin

BACKGROUND

According to the Developmental Origins of Health and Diseases paradigm, the fetal period is highly vulnerable and may have profound effects on later health. Few studies assessed the effect of small-for-gestational age (SGA), a proxy for fetal growth impairment, on risk of malaria during infancy in Africa.

METHODS

We used data from a cohort of 398 mother-child pairs, followed from early pregnancy to age 1 year in Benin. Malaria was actively and passively screened using thick blood smear. We assessed the effect of SGA on risk of malaria infection and clinical malaria from birth to 12 months, after stratifying on the infant's age using a logistic mixed regression model.

RESULTS

After adjustment for potential confounding factors and infant's exposure to mosquitoes, SGA was associated with a 2-times higher risk of malaria infection (adjusted odds ratio [aOR] = 2.16; 95% confidence interval [CI], 1.04-4.51; P = .039) and clinical malaria (aOR = 2.33; 95% CI, 1.09-4.98; P = .030) after age 6 months.

CONCLUSION

Results suggest higher risk of malaria during the second semester of life in SGA infants, and argue for better follow-up of these infants after birth, as currently for preterm babies.

Human leukocyte antigen-G 3' untranslated region polymorphism +3142G/C (rs1063320) and haplotypes are associated with manifestations of the American Tegumentary Leishmaniasis in a Northeastern Brazilian population

While the role of cytokine genes has been well documented in the context of Leishmania (Viannia) braziliensis infection, no studies have addressed the influence of human leukocyte antigen-G (HLA-G) in susceptibility/resistance to American Tegumentary Leishmaniasis (ATL). Here, we evaluated the influences of HLA-G, IL-10, TNF-A and IFN-G in the susceptibility and clinical manifestations of ATL. DNA of 114 ATL patients and 346 healthy individuals were sequenced for well-documented polymorphisms in HLA-G 3' untranslated region (UTR), in IL-10 and TNF-A promoters and in IFN-G intron 1. Soluble HLA-G (sHLA-G) and cytokine levels were evaluated by ELISA and flow cytometry, respectively. Analyses were performed using GraphPad and R-package software. Individuals bearing HLA-G +3142G/G showed an association with increased risk for ATL, whereas those carrying the HLA-G +3142C/G and one copy of UTR6 haplotype, showed an association with decreased risk for ATL. sHLA-G was overexpressed in "susceptible" patients compared to the "resistant'' one, and also in patients bearing +3142G/G genotype. From these results, HLA-G +3142G/G may be considered as genotype of susceptibility and UTR6 as marker of protection to ATL. Our findings showed a participation of HLA-G in the pathogenesis of the ATL.

Congenital Transmission of Trypanosoma cruzi: A Review About the Interactions Between the Parasite, the Placenta, the Maternal and the Fetal/Neonatal Immune Responses

Chagas disease (CD), caused by the protozoan parasite Trypanosoma cruzi, is considered a neglected tropical disease by the World Health Organization. Congenital transmission of CD is an increasingly relevant public health problem. It progressively becomes the main transmission route over others and can occur in both endemic and non-endemic countries. Though most congenitally infected newborns are asymptomatic at birth, they display higher frequencies of prematurity, low birth weight, and lower Apgar scores compared to uninfected ones, and some suffer from severe symptoms. If not diagnosed and treated, infected newborns are at risk of developing disabling and life-threatening chronic pathologies later in life. The success or failure of congenital transmission depends on interactions between the parasite, the placenta, the mother, and the fetus. We review and discuss here the current knowledge about these parameters, including parasite virulence factors such as exovesicles, placental tropism, potential placental defense mechanisms, the placental transcriptome of infected women, gene polymorphism, and the maternal and fetal/neonatal immune responses, that might modulate the risk of T. cruzi congenital transmission.

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.

High level of soluble human leukocyte antigen (HLA)-G at beginning of pregnancy as predictor of risk of malaria during infancy

Placental malaria has been associated with an immune tolerance phenomenon and a higher susceptibility to malaria infection during infancy. HLA-G is involved in fetal maternal immune tolerance by inhibiting maternal immunity. During infections HLA-G can be involved in immune escape of pathogens by creating a tolerogenic environment. Recent studies have shown an association between the risk of malaria and HLA-G at both genetic and protein levels. Moreover, women with placental malaria have a higher probability of giving birth to children exhibiting high sHLA-G, independently of their own level during pregnancy. Our aim was to explore the association between the level of maternal soluble HLA-G and the risk of malaria infection in their newborns. Here, 400 pregnant women and their children were actively followed-up during 24 months. The results show a significant association between the level of sHLA-G at the first antenatal visit and the time to first malaria infection during infancy adjusted to the risk of exposure to vector bites (aHR = 1.02, 95%CI [1.01–1.03], p = 0.014). The level of sHLA-G is a significant predictor of the occurrence of malaria infection during infancy consistent with the hypothesis that mother sHLA-G could be a biomarker of malaria susceptibility in children.

HLA-G, -E and -F regulatory and coding region variability and haplotypes in the Beninese Toffin population sample

HLA-G/E/F genes exhibit immunomodulatory properties and are expressed in placenta. Little attention has been devoted to the study of these genes in sub-Saharan African populations, which are yet the most diverse. To fill this gap, we evaluated the complete gene variability, approximately 5.1 kb for HLA-G (n = 149), 7.7 kb for HLA-E (n = 150) and 6.2 kb for HLA-F (n = 152) in the remote Beninese Toffin population, using massive parallel sequencing. Overall, 96, 37 and 68 variable sites were detected along the entire HLA-G, -E and -F, respectively, arranged into region-specific haplotypes; i.e., promoter haplotypes (16, 19, and 15 respectively), coding haplotypes (19, 15, and 29 respectively), 3' untranslated region (3'UTR) haplotypes (12, 7 and 2, respectively) and extended haplotypes (33, 31 and 32 respectively). All promoter/coding/3'UTR haplotypes followed the patterns already described in worldwide populations. HLA-E was the most conserved, exhibiting mainly two full-length encoded-molecules (E*01:01 and E*01:03), followed by HLA-F, three full-length proteins (F*01:01, F*01:02 and F*01:03) and HLA-G, four proteins: three full-length (G*01:01, G*01:03 and G*01:04) and one truncated (G*01:05N). Although HLA-G/E/F alleles in the Toffin population were the most frequently observed worldwide, the frequencies of the coding haplotypes were closely similar to those described for other African populations (Guinea-Conakry and Burkina-Faso), when compared to non-African ones (Brazilian), indicating that variable sites along these genes were present in Africa before human dispersion.

Low birth weight and its associated factors in Ethiopia: a systematic review and meta-analysis

Background

Different primary studies in Ethiopia showed the burden of low birth weight. However, variation among those studies was seen. This study was aimed to estimate the national prevalence and associated factors of low birth weight in Ethiopia.

Methods

PubMed, Web of Science, Cochrane library, and Google Scholar were searched. A funnel plot and Egger’s regression test were used to see publication bias. I-squared statistic was applied to check heterogeneity of studies. A weighted inverse variance random-effects model was applied to estimate the national prevalence and the effect size of associated factors. The subgroup analysis was conducted by region, study design, and year of publication.

Result

A total of 30 studies with 55,085 participants were used for prevalence estimation. The pooled prevalence of LBW was 17.3% (95% CI: 14.1–20.4). Maternal age < 20 years (AOR = 1.7; 95% CI:1.5–2.0), pregnancy interval < 24 months (AOR = 2.8; 95%CI: 1.4–4.2), BMI < 18.5 kg/m² (AOR = 5.6; 95% CI: 1.7–9.4), and gestational age < 37 weeks at birth (AOR = 6.4; 95% CI: 2.5–10.3) were identified factors of LBW.

Conclusions

The prevalence of low birth weight in Ethiopia remains high. This review may help policy-makers and program officers to design low birth weight preventive interventions.

Alterations in Placental Gene Expression of Pregnant Women with Chronic Chagas Disease

Trypanosoma cruzi infection in women of reproductive age is associated with congenital transmission and adverse pregnancy outcomes. The placenta is a key barrier to infection. Gene expression profiles of term placental environment from T. cruzi-seropositive (SP) and -seronegative (SN) mothers were characterized by RNA-Seq. Nine pools of placental RNA paired samples were used: three from SN and six from SP tissues. Each pool consisted of female/male newborns and vaginal/cesarean delivery binomials. No newborn was congenitally infected. T. cruzi satellite DNA quantitative PCR in placental tissues and maternal and neonatal blood, and parasite 18S quantitative RT-PCR from placental RNA were negative, except in three SP women's bloodstream. To identify pathways associated with maternal T. cruzi infection, a gene-set association analysis was implemented: SP placental samples showed overexpression of inflammatory response and lymphocytic activation, whereas numerous biosynthetic processes were down-regulated. About 42 genes showed a significant fold-change between SP and SN groups. KISS1 and CGB5 were down-regulated, whereas KIF12, HLA-G, PRG2, TAC3, FN1, and ATXN3L were up-regulated. Several expressed genes in SP placentas encode proteins associated with preeclampsia and miscarriage. This first transcriptomics study in human term placental environment shows a placental response that may affect the fetus while protecting it from parasite infection; this host response could be responsible for the low rate of congenital transmission in chronic Chagas disease.

Inhibiting HLA-G restores IFN-γ and TNF-α producing T cell in pleural Tuberculosis

Human Leukocyte Antigen-G (HLA-G), a non-classical, class Ib molecule, has been shown to mediate immunoregulatory functions by inducing apoptosis, inhibits cytotoxicity and differentiation by modulating cytokine secretion. Due to its immune-suppressive function, it facilitates tolerance in feto-maternal interface and transplantation. In contrary, it favours immune evasion of microbes and tumors by inhibiting immune and inflammatory responses. In Tuberculosis (TB), we previously reported differential expression of HLA-G and its receptor Ig-like transcript -2 (ILT-2) in disseminated vs. localized Tuberculosis. The present study explores the impact of HLA-G inhibition on the function of T cells and monocytes, in TB Pleural Effusion (PE), a localized form of TB. Blocking of HLA-G resulted in significant increase in IFN-γ and TNF-α production by CD3⁺ T cells. Additionally, we observed that HLA-G influences the apoptosis and cytotoxic effect of T cells from TB- PE patients. Next, we checked the impact of interaction between HLA-G and ILT-4 receptor in monocytes derived from TB-PE patients upon blocking and observed significant increase in IFN-γ production. The present study reveals for the first time HLA-G mediated suppression of Th1 cytokines, especially, IFN-γ and TNF-α in TB-PE patients.

The role of HLA-G in parasitic diseases

Little attention has been devoted to the role of HLA-G gene and molecule on parasitic disorders, and the available studies have focused on malaria, African and American trypanosomiasis, leishmaniosis, toxoplasmosis and echinococcosis. After reporting a brief description regarding the role of the cells of innate and adaptive immune system against parasites, we reviewed the major features of the HLA-G gene and molecule and the role of HLA-G on the major cells of immune system. Increased levels of soluble HLA-G (sHLA-G) have been observed in patients presenting toxoplasmosis and in the active phase of echinococcosis. In addition, increased sHLA-G has also been associated with increased susceptibility to malaria and increased susceptibility to develop human African trypanosomiasis (HAT). In contrast, decreased membrane-bound HLA-G has been reported in placenta of patients infected with Plasmodium falciparum and in heart and colon of patients presenting Chagas disease. The 3' untranslated region of the HLA-G gene has been the main focus of studies on malaria, HAT and Chagas disease, exhibiting distinct patterns of associations. Considering that HLA-G is an immune checkpoint molecule, inhibiting the activity of several cells of the immune system, the excessive neoexpression and the increased sHLA-G levels together with the decreased constitutive tissue expression of membrane-bound HLA-G may be detrimental to the host infected with parasite agents.

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.

Recent Advances in Our Understanding of HLA-G Biology: Lessons from a Wide Spectrum of Human Diseases

HLA-G is a HLA-class Ib molecule with potent immunomodulatory activities, which is expressed in physiological conditions, where modulation of the immune response is required to avoid allograft recognition (i.e., maternal-fetal interface or transplanted patients). However, HLA-G can be expressed de novo at high levels in several pathological conditions, including solid and hematological tumors and during microbial or viral infections, leading to the impairment of the immune response against tumor cells or pathogens, respectively. On the other hand, the loss of HLA-G mediated control of the immune responses may lead to the onset of autoimmune/inflammatory diseases, caused by an uncontrolled activation of the immune effector cells. Here, we have reviewed novel findings on HLA-G functions in different physiological and pathological settings, which have been published in the last two years. These studies further confirmed the important role of this molecule in the modulation of the immune system.

Human Leukocyte Antigen-G: A Promising Prognostic Marker of Disease Progression to Improve the Control of Human African Trypanosomiasis

BACKGROUND

Human African trypanosomiasis (HAT) caused by Trypanosoma brucei gambiense can be diagnosed in the early hemolymphatic stage (stage 1 [S1]) or meningoencephalitic stage (stage 2 [S2]). Importantly, individuals harbouring high and specific antibody responses to Tbg antigens but negative parasitology are also diagnosed in the field (seropositive [SERO]). Whereas some develop the disease in the months following their initial diagnosis (SERO/HAT), others remain parasitologically negative for long periods (SERO) and are apparently able to control infection. Human leucocyte antigen (HLA)-G, an immunosuppressive molecule, could play a critical role in this variability of progression between infection and disease.

METHODS

Soluble HLA-G (sHLA-G) was measured in plasma for patients in the SERO (n = 65), SERO/HAT (n = 14), or HAT (n = 268) group and in cerebrospinal fluid for patients in S1 (n = 55), early S2 (n = 93), or late S2 (n = 110). Associations between these different statuses and the soluble level or genetic polymorphisms of HLA-G were explored.

RESULTS

Plasma sHLA-G levels were significantly higher in HAT (P = 6 × 10^-7) and SERO/HAT (P = .007) than SERO patients. No difference was observed between the SERO/HAT and HAT groups. Within the HAT group, specific haplotypes (HG010102 and HG0103) displayed increased frequencies in S1 (P = .013) and late S2 (P = .036), respectively.

CONCLUSIONS

These results strongly suggest the involvement of HLA-G in HAT disease progression. Importantly, high plasma sHLA-G levels in SERO patients could be predictive of subsequent disease development and could represent a serological marker to help guide therapeutic decision making. Further studies are necessary to assess the predictive nature of HLA-G and to estimate both sensitivity and specificity.

HLA-G 14-bp Ins/Ins Genotype in Patients Harbouring Helicobacter pylori Infection: A Potential Risk Factor?

H. pylori is a potent pathogen due to its capacity to successfully evade host defence mechanisms. Despite inducing immune responses in infected individuals, sometimes these responses fail to clear the infection and the bacterium establishes a persistent infection leading to chronic inflammation. In this context, we hypothesized that human leucocyte antigen G (HLA-G), a non-classical major histocompatibility complex molecule that has the ability to regulate immune responses both in physiological and in pathological conditions, may play an important role in promoting tolerance and helping H. pylori to subvert host defence and consequently establish a chronic infection. Therefore, we evaluated the expression of HLA-G 14-bp Ins/Del polymorphism in patients harbouring H. pylori infection, as well as their relationship with histological and demographic variables, to gain a better understanding of the actual role of HLA-G and its genetic polymorphisms in bacterial infection. Sixty-eight patients with clinical symptoms suggestive of H. pylori infection were enrolled to assess HLA-G 14-bp Ins/Del polymorphism allele and genotype frequencies. After adjustment for covariates (age and gender), the odds of having the genotype Ins/Ins, compared to Del/Del, were 3.77 times greater among HP+ cases than among controls. These findings suggest that the 14-bp Ins/Ins genotype, already associated with inflammatory and autoimmune diseases as well as some viral and parasitic infections, could confer a greater risk of developing H. pylori infection.

Evolution of the levels of human leukocyte antigen G (HLA-G) in Beninese infant during the first year of life in a malaria endemic area: using latent class analysis

Background

HLA-G, a non-classical HLA class I antigen, is of crucial interest during pregnancy by inhibiting maternal immune response. Its role during infections is discussed, and it has been described that high levels of soluble HLA-G during childhood increase the risk of malaria. To explore more precisely interactions between soluble HLA-G and malaria, latent class analysis was used to test whether distinct sub-populations of children, each with distinctive soluble HLA-G evolutions may suggest the existence of groups presenting variable malaria susceptibility.

Method

A study was conducted in Benin from 2010 to 2013 and 165 children were followed from birth to 12 months. Evolution of soluble HLA-G was studied by the latent class method.

Results

Three groups of children were identified: one with consistently low levels of soluble HLA-G during follow-up, a second with very high levels and a last intermediate group. In all groups, low birth weight, high number of malaria infections and high exposure to malaria transmission were associated with high level of soluble HLA-G. Placental malaria was not. Presence of soluble HLA-G in cord blood increased the probability of belonging to the highest trajectory.

Conclusion

These results, together with previous ones, confirm the important role of HLA-G in the individual susceptibility to malaria. Assaying soluble HLA-G at birth could be a good indicator of newborns more fragile and at risk of infections during childhood.

Differential expression of HLA-G and ILT-2 receptor in human tuberculosis: Localized versus disseminated disease

Human leukocyte antigen-G (HLA-G) is an anti-inflammatory and immunosuppressive molecule that can modulate immune cell activation. The role of HLA-G in tuberculosis, an immune-mediated and chronic bacterial disease remains to be elucidated. We investigated the expression profile of soluble and membrane bound HLA-G in pulmonary TB (PTB), TB pleural effusion (TB-PE, localized disease) and Miliary TB (disseminated form). The expression of HLA-G receptor, ILT-2 was also determined on the immune cells. We observed that the plasma sHLA-G levels were significantly increased in Miliary TB than in TB-PE patients. In contrast, immunophenotyping revealed that the percent frequency of CD3(+) T cells expressing HLA-G was significantly reduced in Miliary TB as compared to TB-PE, whereas frequency of CD14(+) monocytes expressing HLA-G was significantly higher in TB-PE patients. Strikingly in the TB-PE cases, comparison of disease site, i.e. pleural effusion with peripheral blood showed increased expression of both soluble and surface HLA-G, whereas ILT-2 expressing cells were reduced at the local disease site. Furthermore, we demonstrated that in TB-PE cases, HLA-G expression on CD3(+) T cells was influenced by broad spectrum MMP inhibitor. Thus, differential expression of HLA-G could potentially be a useful biomarker to distinguish different states of TB disease.

The Role of HLA-G Molecule and HLA-G Gene Polymorphisms in Tumors, Viral Hepatitis, and Parasitic Diseases

Considering that the non-classical HLA-G molecule has well-recognized tolerogenic properties, HLA-G expression is expected to be deleterious when present in tumor cells and in cells chronically infected by viruses, whereas HLA-G expression is expected to be advantageous in autoimmune disorders. The expression of HLA-G on tissue or peripheral blood cells, the levels of soluble HLA-G and polymorphic sites along the gene have been studied in several disorders. In this study, we revised the role of the molecule and polymorphic sites along the HLA-G gene in tumors, viral hepatitis, and parasitic disorders. Overall, several lines of evidence clearly show that the induction of HLA-G expression in tumors has been associated with worse disease outcome and disease spread. In addition, the few studies conducted on hepatitis and parasitic disorders indicate that HLA-G may contribute to disease pathogenesis. Few isolated polymorphic sites, primarily located at the coding or 3′ untranslated HLA-G region, have been evaluated in these disorders, and a complete HLA-G typing together with the study of gene regulatory elements may further help on the understanding of the influence of the genetic background on disease susceptibility.