Human leukocyte antigen-G expression in differentiated human airway epithelial cells: lack of modulation by Th2-associated cytokines

HLA-G in asthma and its potential as an effective therapeutic agent

OBJECTIVE

Asthma is a heterogeneous disease. Severity of asthma and sensitivity to medications vary across asthma subtypes. Human leukocyte antigen (HLA)-G has a wide range of functions in normal and pathological physiology. Due to its powerful immune function, HLA-G participates in the pathogenesis of different asthma phenotypes by regulating the activity and function of various immune cells. The mechanism of HLA-G in asthma is not fully clear, and there is no consensus on its mechanism in asthma. Further studies are needed to explore the role of HLA-G in different phenotypes of human asthma.

METHODS

Observational study.

RESULTS

HLA-G is an important immunomodulatory factor in asthma. Studies have found different levels of HLA-G in patients with different asthma subtypes and healthy controls, but other studies have come to the opposite conclusion.

CONCLUSION

We speculate that further study on the mechanism of HLA-G in asthma pheno-types may explain some of the contradictions in current studies. Findings should provide information regarding the potential of HLA-G as a novel target for asthma diagnosis and treatment.

Induction of pulmonary HLA-G expression by SARS-CoV-2 infection

The non-classical human leukocyte antigen (HLA)-G exerts immune-suppressive properties modulating both NK and T cell responses. While it is physiologically expressed at the maternal-fetal interface and in immune-privileged organs, HLA-G expression is found in tumors and in virus-infected cells. So far, there exists little information about the role of HLA-G and its interplay with immune cells in biopsies, surgical specimen or autopsy tissues of lung, kidney and/or heart muscle from SARS-CoV-2-infected patients compared to control tissues. Heterogeneous, but higher HLA-G protein expression levels were detected in lung alveolar epithelial cells of SARS-CoV-2-infected patients compared to lung epithelial cells from influenza-infected patients, but not in other organs or lung epithelia from non-viral-infected patients, which was not accompanied by high levels of SARS-CoV-2 nucleocapsid antigen and spike protein, but inversely correlated to the HLA-G-specific miRNA expression. High HLA-G expression levels not only in SARS-CoV-2-, but also in influenza-infected lung tissues were associated with a high frequency of tissue-infiltrating immune cells, but low numbers of CD8+ cells and an altered expression of hyperactivation and exhaustion markers in the lung epithelia combined with changes in the spatial distribution of macrophages and T cells. Thus, our data provide evidence for an involvement of HLA-G and HLA-G-specific miRNAs in immune escape and as suitable therapeutic targets for the treatment of SARS-CoV-2 infections.

Mobilisation of HLA-F on the surface of bronchial epithelial cells and platelets in asthmatic patients

Uncontrolled inflammation of the airways in chronic obstructive lung diseases leads to exacerbation, accelerated lung dysfunction and respiratory insufficiency. Among these diseases, asthma affects 358 million people worldwide. Human bronchial epithelium cells (HBEC) express both anti-inflammatory and activating molecules, and their deregulated expression contribute to immune cell recruitment and activation, especially platelets (PLT) particularly involved in lung tissue inflammation in asthma context. Previous results supported that HLA-G dysregulation in lung tissue is associated with immune cell activation. We investigated here HLA-F expression, reported to be mobilised on immune cell surface upon activation and displaying its highest affinity for the KIR3DS1-activating NK receptor. We explored HLA-F transcriptional expression in HBEC; HLA-F total expression in PBMC and HBEC collected from healthy individuals at rest and upon chemical activation and HLA-F membrane expression in PBMC, HBEC and PLT collected from healthy individuals at rest and upon chemical activation. We compared HLA-F transcriptional expression in HBEC from healthy individuals and asthmatic patients and its surface expression in HBEC and PLT from healthy individuals and asthmatic patients. Our results support that HLA-F is expressed by HBEC and PLT under healthy physiological conditions and is retained in cytoplasm, barely expressed on the surface, as previously reported in immune cells. In both cell types, HLA-F reaches the surface in the inflammatory asthma context whereas no effect is observed at the transcriptional level. Our study suggests that HLA-F surface expression is a ubiquitous post-transcriptional process in activated cells. It may be of therapeutic interest in controlling lung inflammation.

Aberrant Expression of Immune-related MicroRNAs in Pediatric Patients with Asthma

MicroRNAs (miRNAs) have been implicated as regulatory molecules that could play a considerable role in the pathogenesis of different diseases including asthma. This work aims at exploring the role of miR-146a and miR- 106b in the pathogenesis of asthma and their association with asthma severity, IgE, and inflammatory cytokines in asthmatic children. Thirty asthmatic children and twenty age-matched healthy children aged 4-17 years old were enrolled. Expression of plasma miR-146a and miR-106b was measured using quantitative real-time PCR. Plasma levels of interleukin-5 (IL-5) and interleukin-13 (IL-13) were assessed using ELISA. Lung functions were measured by Spirometry. MiR-146a and miR-106b were significantly over-expressed in asthmatic children compared to healthy children. A significant positive correlation between total IgE and both miR-146a and miR-106b was found while no significant correlation could be detected between these miRNAs and asthma severity in asthmatic children. Plasma levels of IL-5 and IL-13 were non-significantly higher in asthmatic children compared to healthy children, and there was no significant correlation between them and both miR-146a and miR-106b expressions in the asthmatic children. The aberrant expression of immune-related miRNAs (miR-146a and miR-106b) and inflammatory cytokines (IL-5 and IL-13) among asthmatic children suggest their probable role in asthma pathogenesis.

Human Amnion Epithelial Cells Impair T Cell Proliferation: The Role of HLA-G and HLA-E Molecules

The immunoprivilege status characteristic of human amnion epithelial cells (hAECs) has been recently highlighted in the context of xenogenic transplantation. However, the mechanism(s) involved in such regulatory functions have been so far only partially been clarified. Here, we have analyzed the expression of HLA-Ib molecules in isolated hAEC obtained from full term placentae. Moreover, we asked whether these molecules are involved in the immunoregulatory functions of hAEC. Human amnion-derived cells expressed surface HLA-G and HLA-F at high levels, whereas the commonly expressed HLA-E molecule has been measured at a very low level or null on freshly isolated cells. HLA-Ib molecules can be expressed as membrane-bound and soluble forms, and in all hAEC batches analyzed we measured high levels of sHLA-G and sHLA-E when hAEC were maintained in culture, and such a release was time-dependent. Moreover, HLA-G was present in extracellular vesicles (EVs) released by hAEC. hAEC suppressed T cell proliferation in vitro at different hAEC:T cell ratios, as previously reported. Moreover, inhibition of T cell proliferation was partially reverted by pretreating hAEC with anti-HLA-G, anti-HLA-E and anti-β2 microglobulin, thus suggesting that HLA-G and -E molecules are involved in hAEC-mediated suppression of T cell proliferation. Finally, either large-size EV (lsEV) or small-size EV (ssEV) derived from hAEC significantly modulated T-cell proliferation. In conclusion, we have here characterized one of the mechanism(s) underlying immunomodulatory functions of hAEC, related to the expression and release of HLA-Ib molecules.

HLA-G Neo-Expression on Tumors

HLA-G is known to modulate the immune system activity in tissues where physiological immune-tolerance is necessary (i.e., maternal-fetal interface, thymus, and cornea). However, the frequent neo-expression of HLA-G in many cancer types has been previously and extensively described and is correlated with a bad prognosis. Despite being an MHC class I molecule, HLA-G is highly present in tumor context and shows unique characteristics of tissue restriction of a Tumor Associated Antigen (TAA), and potent immunosuppressive activity of an Immune CheckPoint (ICP). Consequently, HLA-G appears to be an excellent molecular target for immunotherapy. Although the relevance of HLA-G in cancer incidence and development has been proven in numerous tumors, its neo-expression pattern is still difficult to determine. Indeed, the estimation of HLA-G's actual expression in tumor tissue is limited, particularly concerning the presence and percentage of the new non-canonical isoforms, for which detection antibodies are scarce or inexistent. Here, we summarize the current knowledge about HLA-G neo-expression and implication in various tumor types, pointing out the need for the development of new tools to analyze in-depth the HLA-G neo-expression patterns, opening the way for the generation of new monoclonal antibodies and cell-based immunotherapies.

Human PZP and common marmoset A2ML1 as pregnancy related proteins

While pregnancy-related proteins (PRP) are known to contribute to immunotolerance during pregnancy, their significance to development of invasive placenta is unclear. We compared PRP expression in humans and the common marmoset (Callithrix jacchus), a new-world monkey. Invasive placenta was observed at the maternal-foetal interface of marmoset placenta from green fluorescent protein (GFP)-expressing foetus and wild type mother. The pregnancy zone protein (PZP) and alpha-2 macroglobulin-like 1 (A2ML1) proteins exhibited the most prominent increase in expression during the second trimester in humans and marmoset, respectively. In humans, PZP accumulated at the maternal-foetal interface and A2ML1 accumulated in the amnion. Similarly, A2ML1 mRNA was detected in marmoset placenta. These proteins belong to the A2M family of protease inhibitors, and both PZP and A2ML1 share around 90% homology between human and marmoset and have highly conserved structures. However, the protease-reacting bait regions of the proteins had lower homology (56.8–60.7% in proteins) relative to the rest of the sequence. Notably, the cleavage site of a proinflammatory proline-endopeptidase was preserved in human PZP and marmoset A2ML1. These proteins contain multiple sites that are cleaved by proteases involving proline-endopeptidase. Systemic regulation of these A2M family proteins may be important in animals with invasive placenta.

Changes in circulating microRNA-126 levels are associated with immune imbalance in children with acute asthma

Regulation of the immune response in asthma is complex. MicroRNA-126 (miR-126) expression has been implicated in this response, so we sought to determine the clinical significance of miR-126 measured in the peripheral blood. A total of 80 children with acute asthma were selected to participate in the study and were compared to 80 healthy children. The relative circulating miR-126 levels, interleukin (IL)-4 levels, and the Th17 cell percentage in the peripheral blood of children in the case group were significantly higher than those in the control group, while the interferon (IFN)-γ levels and the CD4⁺CD25⁺Treg cell percentage were significantly lower than those in the control group. Along with the aggravation of the disease, the relative levels of miR-126 and IL-4 and the percentage of Th17 cells increased gradually, while the IFN-γ levels and the CD4⁺CD25⁺Treg cell percentage decreased. The relative level of miR-126 in the peripheral blood of children with asthma was positively correlated with IL-4 and the Th17 cell percentage and was negatively correlated with IFN-γ levels, CD4⁺CD25⁺Treg cell percentage and lung function indicators. The relative level of miR-126 was correlated with the Th17 cell percentage in the peripheral blood, forced vital capacity (FVC), and forced expiratory flow (FEF)_75% of the children with asthma. The relative levels of miR-126 and IL-4 and the Th17 cell percentage were positively correlated with the severity of the asthma, while IFN-γ levels and the CD4⁺CD25⁺Treg cell percentage were negatively correlated with the severity of the asthma. CD4⁺CD25⁺Treg cell percentage and relative miR-126 levels were of the most predictive value in the diagnosis of asthma. Our findings show that the overexpression of miR-126 in acute asthma is correlated with signs of immune imbalance and is predictive of the severity of the disease, suggesting that it could be used as a potential serological marker for asthma diagnosis and evaluation.

The Clinical Significance of Changes in the Expression Levels of MicroRNA-1 and Inflammatory Factors in the Peripheral Blood of Children with Acute-Stage Asthma

This study assessed the changes and clinical significance of microRNA-1 (miR-1) and inflammatory factors in the peripheral blood of children with acute-stage asthma. 100 children with acute-stage asthma (study group) and 100 healthy children (control group) were enrolled. For all enrolled children, the peripheral blood levels of miR-1, interleukin-4 (IL-4), IL-5, IL-8, tumor necrosis factor-alpha (TNF-α), and interferon-γ (IFN-γ) were measured. The relative expression levels of miR-1 and IFN-γ in the peripheral blood of children in the study group were significantly lower than those in the control group, whereas expression levels of IL-4, IL-5, IL-8, and TNF-α were significantly higher. Moreover, these levels changed to a greater extent in patients with severe disease (P < 0.05). Further analyses showed that the miR-1 expression level positively correlated with IFN-γ and negatively correlated with IL-4, IL-5, IL-8, and TNF-α expression levels (P < 0.05). ROC curve analysis to identify diagnostic specificity and sensitivity showed that, for diagnosing exacerbation in asthma, the area under the curve (AUC) for miR-1 was the highest (AUC = 0.900, P < 0.05) of all tested markers; this held true for diagnosing severe asthma as well (AUC = 0.977, P < 0.05). Compared to healthy children, children with acute-stage asthma had a low miR-1 expression level and a Th1/Th2 imbalance in their peripheral blood. The changes were closely related, became more exaggerated with an increase in disease severity, and could be used as auxiliary variables for diagnosing asthma exacerbation and evaluating disease severity.

Bronchial Epithelial Cells from Asthmatic Patients Display Less Functional HLA-G Isoform Expression

Not all asthmatic patients adequately respond to current available treatments, such as inhaled corticosteroids or omalizumab^®. New treatments will aim to target the bronchial epithelium-immune response interaction using different pathways. HLA-G is involved in immunomodulation and may promote epithelial cell differentiation and proliferation. HLA-G protein has several isoforms generated by alternative splicing that might have differential functionalities. HLA-G protein expression and genetic polymorphisms have been reported to be associated with asthma. Our hypothesis is that bronchial epithelium from asthmatic patients displays less functional HLA-G isoforms. HLA-G transcriptional isoforms were quantified by real-time PCR in human bronchial epithelium cells (HBEC) grown in air-liquid interface culture obtained from five healthy controls (HC), seven patients with mild asthma (MA), and seven patients with severe asthma (SA). They were re-differentiated, and IL-13 exposure was used as a proxy for a pro-inflammatory cytokine. HLA-G protein expression was assessed by western blot analysis. HLA-G allele was typed by direct sequencing. Our results showed that both MA and SA display less functional HLA-G isoforms than HC (p < 0.05); in vitro HBEC re-differentiation from SA displays a particular isoform expression profile compared to MA and HC (p = 0.03); HLA-G*01:06 frequency in MA and SA was significantly higher than in the healthy population (p = 0.03 and p < 0.001, respectively); and IL-13 exposure had no impact on HLA-G expression. Our results support that an impaired expression of HLA-G isoforms in asthmatic patients could contribute to the loss of inflammation control and epithelium structural remodeling. Therefore, HLA-G might be an interesting alternative target for asthmatic patients not adequately responding to current drugs.

HLA-G expression and regulation during Pseudomonas aeruginosa infection in cystic fibrosis patients

BACKGROUND

Deregulated immune response fails to control biofilm-forming bacteria, as Pseudomonas aeruginosa, in the lungs of cystic fibrosis (CF) patients. HLA-G is an immune-modulatory molecule involved in respiratory diseases and infections.

MATERIALS & METHODS

HLA-G mRNA and protein were analyzed in plasma and exhaled breath condensate from CF patients undergoing intravenous antibiotic treatment, CF cell line and murine model.

RESULTS

Therapy normalizes HLA-G plasmatic in CF patients suggesting a systemic anti-inflammatory role while in CF airway system, higher expression of HLA-G is associated with P. aeruginosa infection. CF cell line and murine model expressed higher HLA-G molecules in the presence of P. aeruginosa.

CONCLUSION

Plasmatic and lung HLA-G expression suggest a role in reducing systemic inflammation and supporting P. aeruginosa infection.

Peripheral blood NK cells expressing HLA-G, IL-10 and TGF-β in healthy donors and breast cancer patients

Human natural killer (NK) cells are not only professional cytotoxic cells integrated into effector branch of innate immunity, but they are also regulatory cells, managing different immune processes. Immunoregulatory NK cells, expressing HLA-G and IL-10, have been generated in vitro from human hematopoietic progenitors and found in vivo among decidual NK cells of pregnant women. Human peripheral blood NK cells have been shown to acquire suppressive properties after HLA-G uptake during trogocytosis. Moreover, it has been shown that circulating NK cells contain a trace amount of cells producing TGF-β and IL-10, which exert a suppressive influence upon innate and adaptive immunity. In this study, we report on a minor subset of peripheral blood HLA-G(+) NK cells possessing suppressive activity toward effector functions of NK cells. Further we demonstrate an increased number of circulating HLA-G(+), IL-10(+), and TGF-β(+) NK cells in breast cancer patients which might impair efficiency of anti-tumor immunity.

Role of HLA-G as a predictive marker of low risk of chronic rejection in lung transplant recipients: a clinical prospective study

Human leukocyte antigen G (HLA-G) expression is thought to be associated with a tolerance state following solid organ transplantation. In a lung transplant (LTx) recipient cohort, we assessed (1) the role of HLA-G expression as a predictor of graft acceptance, and (2) the relationship between (i) graft and peripheral HLA-G expression, (ii) HLA-G expression and humoral immunity and (iii) HLA-G expression and lung microenvironment. We prospectively enrolled 63 LTx recipients (median follow-up 3.26 years [min: 0.44-max: 5.03]). At 3 and 12 months post-LTx, we analyzed graft HLA-G expression by immunohistochemistry, plasma soluble HLA-G (sHLA-G) level by enzyme-linked immunosorbent assay, bronchoalveolar lavage fluid (BALF) levels of cytokines involved in chronic lung allograft dysfunction (CLAD) and anti-HLA antibodies (Abs) in serum. In a time-dependent Cox model, lung HLA-G expression had a protective effect on CLAD occurrence (hazard ratio: 0.13 [0.03-0.58]; p = 0.008). The same results were found when computing 3-month and 1-year conditional freedom from CLAD (p = 0.03 and 0.04, respectively [log-rank test]). Presence of anti-HLA Abs was inversely associated with graft HLA-G expression (p = 0.02). Increased BALF level of transforming growth factor-β was associated with high plasma sHLA-G level (p = 0.02). In conclusion, early graft HLA-G expression in LTx recipients with a stable condition was associated with graft acceptance in the long term.

Increased IL-4 mRNA expression and poly-aromatic hydrocarbon concentrations from children with asthma

Background

Asthma is the most common chronic childhood disease. Imbalance of cytokines released from T helper cells and environmental factors, such as exposure to poly-aromatic hydrocarbon (PAH), play pivotal roles in the pathogenesis of asthma. The aim of this study was to compare the mRNA expression patterns of Interleukin (IL)-4, interferon (IFN)-γ and Acyl Co A long chain 3 (ACSL3) in peripheral blood leukocytes of children with and without asthma. To correlate the obtained mRNA data with serum IL-4, IFN-γ and PAH levels. Further, to determine the effect of in vivo exposure to PAH on mRNA expression of IL-4, IFN-γ and ACSL3 genes in a rat model.

Methods

A total of 170 children below 16 years (85 pediatric asthma patients and 85 matched healthy controls) were randomly selected from the Riyadh Cohort, Saudi Arabia. Gene expression analysis was performed using qRTPCR. Serum IL-4, IFN-γ and PAH were measured using LINCOplex (human multiplex immunoassay kit) and HPLC respectively.

Results

IL-4 mRNA expression was significantly increased (P < 0.05) in children with asthma compared to healthy control group whereas no differences were observed for either IFN-γ or ACSL3 mRNA. Similarly, serum IL- 4 and PAHs concentration was significantly higher as well in children with asthma in whom IFN-γ was also significantly lower. Results obtained in rats showed that exposure to the benzopyrene prototype PAH resulted in a 2.6 fold (P < 0.001) increased IL-4 mRNA expression in blood.

Conclusion

Peripheral blood IL-4 mRNA levels, serum concentration of this cytokine are elevated in children with asthma. Also, elevated levels of PAH were observed in children with asthma. Additionally, PAH administration in rodents resulted in an increased IL-4 mRNA which is supposed to partly mediate the inflammatory response noted in asthma.