Role of human leukocyte antigen-G in the induction of adaptive type 1 regulatory T cells

Structural Characterization of the Interaction of Hypoxia Inducible Factor-1 with Its Hypoxia Responsive Element at the -964G > A Variation Site of the HLA-G Promoter Region

Human Antigen Leukocyte-G (HLA-G) gene encodes an immune checkpoint molecule that has restricted tissue expression in physiological conditions; however, the gene may be induced in hypoxic conditions by the interaction with the hypoxia inducible factor-1 (HIF1). Hypoxia regulatory elements (HRE) located at the HLA-G promoter region and at exon 2 are the major HIF1 target sites. Since the G allele of the −964G > A transversion induces higher HLA-G expression when compared to the A allele in hypoxic conditions, here we analyzed HIF1-HRE complex interaction at the pair-atom level considering both −964G > A polymorphism alleles. Mouse HIF2 dimer crystal (Protein Data Bank ID: 4ZPK) was used as template to perform homology modelling of human HIF1 quaternary structure using MODELLER v9.14. Two 3D DNA structures were built from 5′GCRTG’3 HRE sequence containing the −964G/A alleles using x3DNA. Protein-DNA docking was performed using the HADDOCK v2.4 server, and non-covalent bonds were computed by DNAproDB server. Molecular dynamic simulation was carried out per 200 ns, using Gromacs v.2019. HIF1 binding in the HRE containing −964G allele results in more hydrogen bonds and van der Waals contact formation than HRE with −964A allele. Protein-DNA complex trajectory analysis revealed that HIF1-HRE-964G complex is more stable. In conclusion, HIF1 binds in a more stable and specific manner at the HRE with G allele.

Three Types of Functional Regulatory T Cells Control T Cell Responses at the Human Maternal-Fetal Interface

During pregnancy, maternal regulatory T cells (Tregs) are important in establishing immune tolerance to invading fetal extravillous trophoblasts (EVTs). CD25^HIFOXP3+ Tregs are found at high levels in decidual tissues and have been shown to suppress fetus-specific and nonspecific responses. However, limited data are available on additional decidual Treg types and the mechanisms by which they are induced. This study investigated three distinct decidual CD4+ Treg types in healthy pregnancies with a regulatory phenotype and the ability to suppress T cell responses: CD25^HIFOXP3+, PD1^HIIL-10+, and TIGIT+FOXP3^dim. Moreover, co-culture of HLA-G+ EVTs or decidual macrophages with blood CD4+ T cells directly increased the proportions of CD25^HIFOXP3+ Tregs compared to T cells cultured alone. EVTs also increased PD1^HI Tregs that could be inhibited by HLA-C and CD3 antibodies, suggesting an antigen-specific induction. The presence of distinct Treg types may allow for the modulation of a variety of inflammatory responses in the placenta.

Regulatory T Cells in Pregnancy: It Is Not All About FoxP3

In pregnancy, the semi-allogeneic fetus needs to be tolerated by the mother's immune system. Regulatory T cells (Tregs) play a prominent role in this process. Novel technologies allow for in-depth phenotyping of previously unidentified immune cell subsets, which has resulted in the appreciation of a vast heterogeneity of Treg subsets. Similar to other immunological events, there appears to be great diversity within the Treg population during pregnancy, both at the maternal-fetal interface as in the peripheral blood. Different Treg subsets have distinct phenotypes and various ways of functioning. Furthermore, the frequency of individual Treg subsets varies throughout gestation and is altered in aberrant pregnancies. This suggests that distinct Treg subsets play a role at different time points of gestation and that their role in maintaining healthy pregnancy is crucial, as reflected for instance by their reduced frequency in women with recurrent pregnancy loss. Since pregnancy is essential for the existence of mankind, multiple immune regulatory mechanisms and cell types are likely at play to assure successful pregnancy. Therefore, it is important to understand the complete microenvironment of the decidua, preferably in the context of the whole immune cell repertoire of the pregnant woman. So far, most studies have focused on a single mechanism or cell type, which often is the FoxP3 positive regulatory T cell when studying immune regulation. In this review, we instead focus on the contribution of FoxP3 negative Treg subsets to the decidual microenvironment and their possible role in pregnancy complications. Their phenotype, function, and effect in pregnancy are discussed.

Induction of CD4+CD25+FOXP3+ regulatory T cells by mesenchymal stem cells is associated with modulation of ubiquitination factors and TSDR demethylation

Background

Mesenchymal stem cells (MSCs) are known for their ability to induce the conversion of conventional T cells (Tconvs) into induced regulatory T cells (iTregs) in specific inflammatory contexts. Stable Foxp3 expression plays a major role in the phenotypic and functional stability of iTregs. However, how MSCs induce stable Foxp3 expression remains unknown.

Methods

We first investigated the role of cell–cell contact and cytokine secretion by bone marrow-derived MSCs (BM-MSCs) on the induction, stability, and suppressive functions of Tregs under various experimental conditions that lead to Foxp3 generation by flow cytometry and ELISA respectively. Second, we studied the effect of MSCs on TRAF6, GRAIL, USP7, STUB1, and UBC13 mRNA expression in CD4⁺ T cells in correlation with the suppressive function of iTregs by real-time PCR; also, we investigated Foxp3 Treg-specific demethylated region (TSDR) methylation in correlation with Foxp3 stability by the high-resolution melting technique. Third, we studied the effect of ex-vivo-expanded BM-MSCs on the induction of transplant tolerance in a model of fully allogeneic skin transplantation. We further analyzed the cytokine secretion patterns in grafted mice as well as the mRNA expression of ubiquitination genes in CD4⁺ T cells collected from the spleens of protected mice.

Results

We found that in-vitro MSC-induced Tregs express high mRNA levels of ubiquitination genes such as TRAF6, GRAIL, and USP7 and low levels of STUB1. Moreover, they have enhanced TSDR demethylation. Infusion of MSCs in a murine model of allogeneic skin transplantation prolonged allograft survival. When CD4⁺ T cells were harvested from the spleens of grafted mice, we observed that mRNA expression of the Foxp3 gene was elevated. Furthermore, Foxp3 mRNA expression was associated with increased TRAF6, GRAIL, UBC13, and USP7 and decreased STUB1 mRNA levels compared with the levels observed in vitro.

Conclusions

Our data suggest a possible ubiquitination mechanism by which MSCs convert Tconvs to suppressive and stable iTregs.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0991-1) contains supplementary material, which is available to authorized users.

ERAP1 deficient mice have reduced Type 1 regulatory T cells and develop skeletal and intestinal features of Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a prototypical sero-negative autoimmune disease that affects millions worldwide. Single nucleotide polymorphisms in the Endoplasmic Reticulum Aminopeptidase 1 (ERAP1) gene have been linked to AS via GWAS studies, however, the exact mechanism as to how ERAP1 contributes to pathogenesis of AS is not understood. We undertook µCT imaging and histologic analysis to evaluate bone morphology of the axial skeletons of ERAP1-/- mice and discovered the hallmark skeletal features of AS in these mice, including spinal ankylosis, osteoporosis, and spinal inflammation. We also confirmed the presence of spontaneous intestinal dysbiosis and increased susceptibility to Dextran Sodium Sulfate (DSS)-induced colitis in ERAP1-/- mice, however the transfer of healthy microbiota from wild type mice via cross-fostering experiments did not resolve the skeletal phenotypes of ERAP1-/- mice. Immunological analysis demonstrated that while ERAP1-/- mice had normal numbers of peripheral Foxp3+ Tregs, they had reduced numbers of both "Tr1-like" regulatory T cells and tolerogenic dendritic cells, which are important for Tr1 cell differentiation. Together, our data suggests that ERAP1-/- mice may serve as a useful animal model for studying pathogenesis of intestinal, skeletal, and immunological manifestations of Ankylosing Spondylitis.

Correlation of serum sHLA-G levels with cyst stage in patients with cystic echinococcosis: is it an immune evasion strategy?

Patients with cystic echinococcosis (CE) can harbour cysts for years or even decades, apparently without effect of the immune system on the metacestode. Although several immune evasion mechanisms by echinococcal cysts have been described, it is unclear whether the human leucocyte antigen (HLA) system plays a role in the susceptibility or resistance to CE in humans. HLA-G molecules are known to exert a suppressive action on dendritic cells maturation and on natural killer (NK) cells functions, therefore hampering T-cell responses and NK cytolysis. HLA-G plays an important role in immune tolerance, is involved in foetus and in allotransplant tolerance, and may be involved in tumoral and viral immune evasion. In this study, we assessed the presence and levels of soluble HLA-G (sHLA-G) in patients with CE using a commercial ELISA kit to determine whether host's HLA-G may have a role in the course of human CE.

Immune regulatory network in successful pregnancy and reproductive failures

Maternal immune system must tolerate semiallogenic fetus to establish and maintain a successful pregnancy. Despite the existence of several strategies of trophoblast to avoid recognition by maternal leukocytes, maternal immune system may react against paternal alloantigenes. Leukocytes are important components in decidua. Not only T helper (Th)1/Th2 balance, but also regulatory T (Treg) cells play an important role in pregnancy. Although the frequency of Tregs is elevated during normal pregnancies, their frequency and function are reduced in reproductive defects such as recurrent miscarriage and preeclampsia. Tregs are not the sole population of suppressive cells in the decidua. It has recently been shown that regulatory B10 (Breg) cells participate in pregnancy through secretion of IL-10 cytokine. Myeloid derived suppressor cells (MDSCs) are immature developing precursors of innate myeloid cells that are increased in pregnant women, implying their possible function in pregnancy. Natural killer T (NKT) cells are also detected in mouse and human decidua. They can also affect the fetomaternal tolerance. In this review, we will discuss on the role of different immune regulatory cells including Treg, γd T cell, Breg, MDSC, and NKT cells in pregnancy outcome.

Lesion HLA-G5/-G6 isoforms expression in patients with ovarian cancer

HLA-G is an immune tolerant with seven isoforms. HLA-G expression was observed to be associated with tumor cell immune escaping, invasion and metastasis, and with poor prognosis in cancer patients. Different types of HLA-G isoforms could be expressed in clinical settings when meet different cellular and environmental conditions. Lesion total HLA-G expression detected by the monoclonal antibody (mAb) 4H84 was widely investigated in previous studies, while specific HLA-G isoforms such as HLA-G5/-G6 remains to be clarified. In this study, 118 primary ovarian cancer lesions were probed with mAb 5A6G7 which recognizes HLA-G5/-G6 was performed by immunohistochemistry. Data showed that HLA-G5/-G6 was expressed in 79.7% (94/118) of these ovarian cancer lesions, where HLA-G5/-G6 expression was observed in 75.7% (53/70) serous, 63.6% (7/11) mucinous cystadenocarcinoma and in 100% (11/11) endometrioid adenocarcinoma, in 85.7% (6/7) clear cell carcinoma, 100% (10/10) sex cord-stromal tumor and 77.8% (7/9) germ cell tumors. However, lesion HLA-G5/-G6 expression was unrelated to histological type, patient age, FIGO stage and patient survival. Unlike total HLA-G expression, no clinical significance of HLA-G5/-G6 expression in ovarian cancer lesion was observed in this study. Our findings indicated that different HLA-G isoforms might have different biological functions in malignancies.

Down-expression of miR-152 lead to impaired anti-tumor effect of NK via upregulation of HLA-G

It is known that chronic HBV infection (CHB) is the major risk factor for hepatocellular carcinoma (HCC) because CHB could not only cause liver tumorigenesis but also lead to change of local microenviroment and lower immune response to infected and cancerous cells (immune tolerance). Human leucocyte antigen-G (HLA-G) belongs to a non-classic MHC-I family and was considered to be an immune tolerance molecule, which could bind to immunosuppressive receptors of natural killer cell (NK) and T cells and trigger immunosuppressive signaling. Recently, numerous studies highlighted that microRNAs (miRNAs) were significantly differentially expressed in HCC tumorigenesis, and the expression was tissue-specific, indicating that miRNAs may cause great epigenetic changes in HCC tumorigenesis. In this study, we found that the expression of HLA-G was upregulated by hepatitis B virus (HBV) infection and miR-152; a HLA-G-targeting miRNA was downregulated by HBV infection. And high expression of HLA-G further suppressed NK against cancer cells, providing a new concept that miR-152 was involved in HBV-induced hepatocellular carcinoma.

Budesonide increases TLR4 and TLR2 expression in Treg lymphocytes of allergic asthmatics

BACKGROUND

Reduced innate immunity responses as well as reduced T regulatory activities characterise bronchial asthma.

OBJECTIVES

In this study the effect of budesonide on the expression of TLR4 and TLR2 in T regulatory lymphocyte sub-population was assessed.

METHODS

TLR4 and TLR2 expression in total peripheral blood mononuclear cells (PBMC), in CD4+/CD25+ and in CD4+/CD25- was evaluated, by flow cytometric analysis, in mild intermittent asthmatics (n = 14) and in controls (n = 11). The in vitro effects of budesonide in modulating: TLR4 and TLR2 expression in controls and in asthmatics; IL-10 expression and cytokine release (IL-6 and TNF-α selected by a multiplex assay) in asthmatics were also explored.

RESULTS

TLR4 and TLR2 were reduced in total PBMC from asthmatics in comparison to PBMC from controls. CD4+CD25+ cells expressed at higher extent TLR2 and TLR4 in comparison to CD4+CD25- cells. Budesonide was able to increase the expression of TLR4, TLR2 and IL-10 in CD4+/CD25 highly+ cells from asthmatics. TLR4 ligand, LPS induced Foxp3 expression. Budesonide was also able to reduce the release of IL-6 and TNF-α by PBMC of asthmatics.

CONCLUSIONS

Budesonide potentiates the activity of Treg by increasing TLR4, TLR2 and IL-10 expression. This event is associated to the decreased release of IL-6 and TNF-α in PBMC treated with budesonide. These findings shed light on new mechanisms by which corticosteroids, drugs widely used for the clinical management of bronchial asthma, control T lymphocyte activation.

HLA-G expression levels influence the tolerogenic activity of human DC-10

Human leukocyte antigen (HLA)-G is a non-classical HLA class I molecule with known immune-modulatory functions. Our group identified a subset of human dendritic cells, named DC-10, that induce adaptive interleukin-10-producing T regulatory type 1 (Tr1) cells via the interleukin-10-dependent HLA-G/ILT4 pathway. In this study we aimed at defining the role of HLA-G in DC-10-mediated Tr1 cell differentiation. We analyzed phenotype, functions, and genetic variations in the 3' untranslated region of the HLA-G locus of in vitro-differentiated DC-10 from 67 healthy donors. We showed that HLA-G expression on DC-10 is donor-dependent. Functional studies demonstrated that DC-10, independently of HLA-G expression, secrete interleukin-10 and negligible levels of interleukin-12. Interestingly, DC-10 with high HLA-G promote allo-specific anergic T cells that contain a significantly higher frequency of Tr1 cells, defined as interleukin-10-producing (P=0.0121) or CD49b(+)LAG-3(+) (P=0.0031) T cells, compared to DC-10 with low HLA-G. We found that the HLA-G expression on DC-10 is genetically imprinted, being associated with specific variations in the 3' untranslated region of the gene, and it may be finely tuned by microRNA-mediated post-transcriptional regulation. These data highlight the important role of HLA-G in boosting DC-10 tolerogenic activity and confirm that interleukin-10 production by DC-10 is necessary but not sufficient to promote Tr1 cells at high frequency. These new insights into the role of HLA-G in DC-10-mediated induction of Tr1 cells provide additional information for clinical use in Tr1- or DC-10-based cell therapy approaches.

Regulatory T cells and immune regulation of allergic diseases: roles of IL-10 and TGF-β

The prevalence of allergic diseases has significantly increased in industrialized countries. Allergen-specific immunotherapy (AIT) remains as the only curative treatment. The knowledge about the mechanisms underlying healthy immune responses to allergens, the development of allergic reactions and restoration of appropriate immune responses to allergens has significantly improved over the last decades. It is now well-accepted that the generation and maintenance of functional allergen-specific regulatory T (Treg) cells and regulatory B (Breg) cells are essential for healthy immune responses to environmental proteins and successful AIT. Treg cells comprise different subsets of T cells with suppressive capacity, which control the development and maintenance of allergic diseases by various ways of action. Molecular mechanisms of generation of Treg cells, the identification of novel immunological organs, where this might occur in vivo, such as tonsils, and related epigenetic mechanisms are starting to be deciphered. The key role played by the suppressor cytokines interleukin (IL)-10 and transforming growth factor (TGF)-β produced by functional Treg cells during the generation of immune tolerance to allergens is now well established. Treg and Breg cells together have a role in suppression of IgE and induction of IgG4 isotype allergen-specific antibodies particularly mediated by IL-10. Other cell types such as subsets of dendritic cells, NK-T cells and natural killer cells producing high levels of IL-10 may also contribute to the generation of healthy immune responses to allergens. In conclusion, better understanding of the immune regulatory mechanisms operating at different stages of allergic diseases will significantly help the development of better diagnostic and predictive biomarkers and therapeutic interventions.

HLA-G as a tolerogenic molecule in transplantation and pregnancy

HLA-G is a nonclassical HLA class I molecule. In allogeneic situations such as pregnancy or allograft transplantation, the expression of HLA-G has been related to a better acceptance of the fetus or the allograft. Thus, it seems that HLA-G is crucially involved in mechanisms shaping an allogeneic immune response into tolerance. In this contribution we focus on (i) how HLA-G is involved in transplantation and human reproduction, (ii) how HLA-G is regulated by genetic and microenvironmental factors, and (iii) how HLA-G can offer novel perspectives with respect to therapy.

Immune-monitoring in Kawasaki disease patients treated with infliximab and intravenous immunoglobulin

The expansion of regulatory T cells (Treg ) controls inflammation in children with acute Kawasaki disease (KD). Blockade of tumour necrosis factor (TNF)-α is an emerging therapy for KD patients with refractory inflammation, but there is concern that this therapy could impede the host immune regulation. To define the effect of TNF-α blockade, we conducted ex-vivo immune-monitoring in KD subjects who participated in a randomized, double-blind, placebo-controlled clinical trial of the addition of infliximab to standard intravenous immunoglobulin (IVIG) therapy. We enumerated circulating myeloid and plasmocytoid dendritic cells (DC), regulatory T cells (Treg ) and memory T cells (Tmem ) in 14 consecutive, unselected KD patients (seven treated with IVIG, seven with IVIG + infliximab) at three time-points: (i) acute phase prior to treatment, (ii) subacute phase and (iii) convalescent phase. Myeloid DC (mDC), but not plasmacytoid DC (pDC), were numerous in the peripheral blood in acute KD subjects and decreased in the subacute phase in both IVIG(-) and IVIG (+)  infliximab-treated groups. The co-stimulatory molecule for antigen presentation to T cells and CD86 decreased in mDC from acute to subacute time-points in both treatment groups, but not in the single patient who developed coronary artery aneurysms. We also defined tolerogenic mDC that expand in the subacute phase of KD not impaired by infliximab treatment. Treg and Tmem expanded after treatment with no significant differences between the two groups. Treatment of KD patients with infliximab does not adversely affect generation of tolerogenic mDC or the development of T cell regulation and memory.

Elevation of human leukocyte antigen-G expression is associated with the severe encephalitis associated with neurogenic pulmonary edema caused by Enterovirus 71

Enterovirus 71 (EV71) infection can develop devastating clinical outcomes such as brain stem encephalitis (BE) and pulmonary edema (PE). Alteration of human leukocyte antigen-G (HLA-G) expression or cytokine production was considered playing important roles in virus-related pathogenesis. However, clinical relevance of HLA-G in EV71 infection remains unknown. In the current study, patients were stratified by disease severity as BE (n = 107) and PE (n = 18). HLA-G expression on peripheral blood monocytes from patients with BE (n = 15), patients with PE (n = 15) and control subjects (n = 31) was analyzed with flow cytometry. Plasma soluble HLA-G (sHLA-G) (in 67 BE, 18 PE and 120 control subjects), IL-6 and IL-10 (in 50 patients with BE, 18 patients with PE and 45 control subjects) were determined with enzyme-linked immunosorbent assay. Data showed that the percentage of HLA-G-positive monocytes (mean 7.76 vs 3.68 %, p < 0.001), levels for sHLA-G (median 129.2 vs 70.6 U/ml, p < 0.001), IL-10 (median 160.5 vs 29.5 pg/ml, p < 0.001) and IL-6 (median 20.50 vs 5.21 pg/ml, p = 0.002) was significantly higher in patients with PE than in patients with BE. Taken together, our findings indicated that elevation of HLA-G expression on monocytes, plasma sHLA-G, IL-10 and IL-6 levels was associated with PE in patients infected with EV71.

Multiple in vitro and in vivo regulatory effects of budesonide in CD4+ T lymphocyte subpopulations of allergic asthmatics

Background

Increased activation and increased survival of T lymphocytes characterise bronchial asthma.

Objectives

In this study the effect of budesonide on T cell survival, on inducible co-stimulator T cells (ICOS), on Foxp3 and on IL-10 molecules in T lymphocyte sub-populations was assessed.

Methods

Cell survival (by annexin V binding) and ICOS in total lymphocytes, in CD4+/CD25+ and in CD4+/CD25- and Foxp3 and IL-10 in CD4+/CD25+ and in CD4+/CD25-cells was evaluated, by cytofluorimetric analysis, in mild intermittent asthmatics (n = 19) and in controls (n = 15). Allergen induced T lymphocyte proliferation and the in vivo effects of budesonide in mild persistent asthmatics (n = 6) were also explored.

Results

Foxp3 was reduced in CD4+/CD25- and in CD4+/CD25+ cells and ICOS was reduced in CD4+/CD25+ cells but it was increased in CD4+CD25-in asthmatics when compared to controls. In asthmatics, in vitro, budesonide was able to: 1) increase annexin V binding and to reduce ICOS in total lymphocytes; 2) increase annexin V binding and Foxp3 and to reduce ICOS in CD4+/CD25- cells; 3) reduce annexin V binding and to increase IL-10 and ICOS in CD4+/CD25+ cells; 4) reduce cell allergen induced proliferation. In vivo, budesonide increased ICOS in CD4+/CD25+ while it increased Foxp3 and IL-10 in CD4+/CD25+ and in CD4+/CD25- cells.

Conclusions

Budesonide modulates T cell survival, ICOS, Foxp3 and IL-10 molecules differently in T lymphocyte sub-populations. The findings provided shed light on new mechanisms by which corticosteroids, drugs widely used for the clinical management of bronchial asthma, control T lymphocyte activation.

Induction of antigen-specific human T suppressor cells by membrane and soluble ILT3

Antigen-specific CD8 suppressor T cells (CD8(+) Ts) are adaptive regulatory T cells that are induced in vivo and in vitro by chronic antigenic stimulation of human T cells. CD8(+) Ts induce the upregulation of the inhibitory receptors ILT3 and ILT4 on monocytes and dendritic cells rendering these antigen presenting cells (APCs) tolerogenic. Tolerogenic APCs induce CD4(+) T helper anergy and elicit the differentiation of CD4(+) and CD8(+) T regulatory/suppressor cells. Overexpression of membrane ILT3 in APC results in inhibition of NF-κB activation, transcription of inflammatory cytokines and costimulatory molecules. Soluble ILT3-Fc which contains only the extracellular, Ig-like domain linked to mutated IgG1 Fc, is strongly immunosuppressive. ILT3-Fc, induces the differentiation of human CD8(+) Ts which inhibit CD4(+) Th and CD8(+) CTL effector function both in vitro and in vivo. The acquisition of Ts' function by primed CD8(+) T cells treated with ILT3-Fc was demonstrated to be the effect of the significant upregulation of BCL6, a transcriptional repressor of IL-2, IFN-gamma, IL-5 and granzyme B. The upregulated expression of BCL6, SOCS1 and DUSP10 is integral to the signature of ILT3-Fc-induced CD8(+) Ts. These genes are known inhibitors of cytokine production and TCR signaling and are targeted by miRNAs which are suppressed by ILT3-Fc. ILT3-Fc induces tolerance to allogeneic human islets and reverses rejection after its onset in a humanized NOD/SCID mouse model. Based on these findings we postulate that ILT3-Fc may become an important new agent for treatment of autoimmunity and transplant rejection.

Analysis of immunoglobulin-like transcripts (ILTs) in lymphocytes with sHLA-G and IL10 from SLE patients

The aim of this work was to study the expression of human leukocyte antigen G (HLA-G) and interleukin 10 (IL-10) in conjunction with expression of HLA-G killer-cell inhibitory receptor ligand immunoglobulin-like transcript 2 (ILT2) in CD3+, CD19+, CD56+ lymphomas, and ILT4 in CD14+ cells from patients with systemic lupus erythematosus (SLE). Thirty-one SLE patients and 36 healthy controls were studied. ILTs expression was analyzed by flow cytometry in peripheral blood mononuclear cells (PBMCs). The plasma sHLA-G and IL10 were evaluated by enzyme-linked immunosorbent assay (ELISA). We found a significant increased expression of ILT2 by lymphocytes in SLE patients. When the expression of this receptor was assessed in cell subsets, significantly higher ILT2 MRFI levels were detected in CD3+ cells, CD19+ cells, CD56+ cells (P < 0.05), but no change with ILT4 MRFI in CD14+ cells, neither did the percentages of ILT2/4+ lymphocytes change in SLE patients compared with healthy controls (P > 0.05). The upregulation of ILT2 expression was related to IL10 and anti-ds-DNA antibodies (P < 0.05), but not sHLA-G and steroid therapy (P > 0.05). IL-10 and sHLA-G were increased, but did not change remarkably (P > 0.05); however, they were quite related (P < 0.05). ILT2 might be one of the factors accounting for the evasion of immunosurveillance, thus participate in the pathogenesis of SLE, and the upregulation of ILT2 may be associated with its disease activity.

Human leucocyte antigen-G: expression and function in airway allergic disease

Human leucocyte antigen-G (HLA-G) is a non-classical HLA class I molecule demonstrated originally in placental trophoblast cells. Recognition of the importance of HLA-G to the maternal immune accommodation of the semi-allogeneic fetus has led to investigations of its role in the suppression of immune responses and induction of tolerance. More recently, HLA-G has been shown to have increased expression in several immunological diseases including asthma and allergic rhinitis. The focus of this review is the potential role of HLA-G in immunological airway diseases.

The tolerogenic interplay(s) among HLA-G, myeloid APCs, and regulatory cells

Myeloid antigen-presenting cells (APCs), regulatory cells, and the HLA-G molecule are involved in modulating immune responses and promoting tolerance. APCs are known to induce regulatory cells and to express HLA-G as well as 2 of its receptors; regulatory T cells can express and act through HLA-G; and HLA-G has been directly involved in the generation of regulatory cells. Thus, interplay(s) among HLA-G, APCs, and regulatory cells can be easily envisaged. However, despite a large body of evidence on the tolerogenic properties of HLA-G, APCs, and regulatory cells, little is known on how these tolerogenic players cooperate. In this review, we first focus on key aspects of the individual relationships between HLA-G, myeloid APCs, and regulatory cells. In its second part, we highlight recent work that gathers individual effects and demonstrates how intertwined the HLA-G/myeloid APCs/regulatory cell relationship is.

HLA-G expression is associated with metastasis and poor survival in the Balb/c nu/nu murine tumor model with ovarian cancer

Aberrant HLA-G expression is associated with tumor invasiveness and poor clinical prognosis; however, there is a lack of preclinical animal model to address whether HLA-G plays a causal role in the unfavorable prognosis of malignancies. In the current study, ovarian carcinoma cell lines (HO-8910 and Ovcar-3) were transfected with HLA-G gene. HLA-G expression was analyzed with western blot and flow cytometry. Transwell experiment was performed to analyze the cell migration and invasion capability and/or multicellular spheroid formation was investigated with the 3D culture assay in vitro. The effects of HLA-G expression for tumor cell organ metastasis and for mouse survival was analyzed with the Balb/c nu/nu mouse model. Our data showed that HO-8910-G and Ovcar-3-G cells are of higher invasion potential compared with the parental HO-8910 and Ovcar-3 cells. Multicellular spheroid formation exists only in HO-8910-G cells in a 3D culture assay. In Balb/c nu/nu mouse model, widespread metastasis was observed in mice xenografted with HO-8910-G cells, but not in the group with parental cells. Mouse survival was dramatically decreased in HO-8910-G and Ovcar-3-G xenografted mice than that with HO-8910 and Ovcar-3 cells, respectively. In summary, our study provided the first evidence that HLA-G expression is associated with tumor metastasis and with poor survival in an animal model with ovarian cancer.

Clinical tolerance in allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) has been a curative therapeutic option for a wide range of immune hematologic malignant and non-malignant disorders including genetic diseases and inborn errors. Once in the host, allogeneic transplanted cells have not only to ensure myeloid repopulation and immunological reconstitution but also to acquire tolerance to host human leukocyte antigens via central or peripheral mechanisms. Peripheral tolerance after allogeneic HSCT depends on several regulatory mechanisms aimed at blocking alloimmune reactivity while preserving immune responses to pathogens and tumor antigens. Patients transplanted with HSCT represent an ideal model system in humans to identify and characterize the key cellular and molecular players underlying these mechanisms. The knowledge gained from these studies has allowed the development of novel therapeutic strategies aimed at inducing long-term peripheral tolerance, which can be applicable not only in allogeneic HSCT but also in autoimmune diseases and solid-organ transplantation. In the present review, we describe Type 1 regulatory T cells, initially discovered and characterized in chimeric patients transplanted with human leukocyte antigen-mismatched HSCT, and how their presence correlates to tolerance induction and maintenance. Furthermore, we summarize different cell therapy approaches with regulatory T cells, designed to facilitate tolerance induction, minimizing pharmaceutical interventions.

HLA-G level on monocytoid dendritic cells correlates with regulatory T-cell Foxp3 expression in liver transplant tolerance

BACKGROUND

Human leukocyte antigen (HLA)-G is a nonclassical HLA class I molecule expressed as membrane-bound and soluble isoforms. Interaction of HLA-G with its receptor, immunoglobulin-like transcript 4 on dendritic cells (DCs) down-regulates their T-cell stimulatory ability.

METHODS

We examined expression of HLA-G, immunoglobulin-like transcript 4, other immune regulatory molecules (inducible costimulator ligand and glucocorticoid-induced tumor necrosis factor-related receptor ligand), and the activation marker CMRF44 on circulating monocytoid dendritic cell (mDC) and plasmacytoid dendritic cell by monoclonal antibody staining and flow cytometry. Three groups of stable liver transplant recipients: operationally tolerant (TOL), prospective immunosuppressive drug weaning, and maintenance immunosuppression (MI) were studied, together with healthy controls (HC). Serum HLA-G levels were measured by enzyme-linked immunosorbent assay.

RESULTS

In TOL patients, monocytoid dendritic cell (mDC) but not plasmacytoid dendritic cell expressed higher HLA-G than in MI patients or HC. In TOL patients, the incidence of CD4(+)CD25(hi)CD127(-) regulatory T cells (Treg) and the intensity of Treg forkhead box p3 (Foxp3) expression were significantly higher than in the MI group. HLA-G expression on circulating mDC correlated significantly with that of Foxp3 in the TOL group. There was no correlation between immunosuppressive drug (tacrolimus) dose or trough level and HLA-G expression or Treg frequency or Foxp3 expression. The incidence of patients with circulating HLA-G levels more than 100 ng/mL was highest in the TOL group, although statistical significance was not achieved.

CONCLUSIONS

Higher HLA-G expression on circulating mDC in TOL recipients compared with MI or HC, suggests a possible role of HLA-G in immune regulation possibly mediated by enhanced host Treg Foxp3 expression.

Expression and functional role of HLA-G in immune cells from patients with systemic lupus erythematosus

Human leukocyte antigen (HLA)-G is a class I non-classical HLA molecule with an important regulatory role on the immune response. The possible role of this molecule in the pathogenesis of SLE has not been explored. In this work, we evaluated the expression and function of HLA-G in SLE patients. We studied 37 SLE patients as well as 25 healthy donors. Peripheral blood monocytes and in vitro-generated dendritic cells (DCs) were analyzed for HLA-G expression by flow cytometry. We found that monocytes from SLE patients as well as mature CD83+ DCs showed a diminished expression of HLA-G compared with healthy controls. In addition, monocytes from SLE patients showed a diminished induction of HLA-G expression in response to stimulation with IL-10. Furthermore, functional assays showed that these monocytes pre-treated with IFN-γ exhibited a diminished capability to inhibit the proliferation of autologous lymphocytes. Finally, lymphocytes from SLE patients tended to display a lower acquisition of HLA-G (by trogocytosis) from autologous monocytes compared to controls. Our results might have implications for the immune abnormalities observed in patients with SLE.

A balancing act: mechanisms by which the fetus avoids rejection by the maternal immune system

Successful pregnancy requires strict temporal regulation of maternal immune function to accommodate the growing fetus. Early implantation is facilitated by inflammatory processes that ensure adequate vascular remodeling and placental invasion. To prevent rejection of the fetus, this inflammation must be curtailed; reproductive immunologists are discovering that this process is orchestrated by the fetal unit and, in particular, the extravillous trophoblast. Soluble and particulate factors produced by the trophoblast regulate maternal immune cells within the decidua, as well as in the periphery. The aim of this review is to discuss the action of recently discovered immunomodulatory factors and mechanisms, and the potential effects of dysregulation of such mechanisms on the maternal immune response that may result in pregnancy loss or preeclampsia.

Role of dendritic cells in the induction of regulatory T cells

Dendritic cells (DCs) play a key role in initiating immune responses and maintaining immune tolerance. In addition to playing a role in thymic selection, DCs play an active role in tolerance under steady state conditions through several mechanisms which are dependent on IL-10, TGF-β, retinoic acid, indoleamine-2,3,-dioxygenase along with vitamin D. Several of these mechanisms are employed by DCs in induction of regulatory T cells which are comprised of Tr1 regulatory T cells, natural and inducible foxp3⁺ regulatory T cells, Th3 regulatory T cells and double negative regulatory T cells. It appears that certain DC subsets are highly specialized in inducing regulatory T cell differentiation and in some tissues the local microenvironment plays a role in driving DCs towards a tolerogenic response. In this review we discuss the recent advances in our understanding of the mechanisms underlying DC driven regulatory T cell induction.

Human leukocyte antigen-G expression is associated with a poor prognosis in patients with esophageal squamous cell carcinoma

Human leukocyte antigen (HLA)-G inhibits functions of immune component cells and promotes malignant cells evading from antitumor immunity. We investigated the clinical relevance of HLA-G expression in esophageal squamous cell carcinoma (ESCC). In our study, HLA-G expression in 79 primary ESCC lesions and corresponding adjacent normal tissues were analyzed with immunohistochemistry. Soluble HLA-G (sHLA-G) in plasma was detected with enzyme-linked immunosorbent assay (ELISA) in 41 ESCC patients (including 19 case-matched lesions and plasma samples) and in 153 normal healthy controls. HLA-G expression was observed in 65.8% (52/79) of the ESCC lesions but not in adjacent normal esophageal tissues. HLA-G expression was more frequently observed in patients with advanced disease stage (III/IV vs. I/II, p = 0.01). Patients with HLA-G expression had a significantly worse survival, and HLA-G could be an independent prognostic factor. sHLA-G levels in plasma were significantly increased in patients compared to normal controls (median: 152.4 U/ml vs. 8.9 U/ml, p < 0.001). The area under receiver-operating characteristic (ROC) curve for sHLA-G in plasma was 0.992. However, no significant correlation was found between sHLA-G in plasma and clinical parameters studied. In conclusion, our findings indicated that HLA-G expression in ESCC is associated with poor survival and could be a prognostic indicator. Furthermore, increased levels of sHLA-G in plasma might be a useful preoperative biomarker for diagnosis.

The role of HLA-G in immunity and hematopoiesis

The non-classical HLA class I molecule HLA-G was initially shown to play a major role in feto-maternal tolerance. Since this discovery, it has been established that HLA-G is a tolerogenic molecule which participates to the control of the immune response. In this review, we summarize the recent advances on (1) the multiple structures of HLA-G, which are closely associated with their role in the inhibition of NK cell cytotoxicity, (2) the factors that regulate the expression of HLA-G and its receptors, (3) the mechanism of action of HLA-G at the immunological synapse and through trogocytosis, and (4) the generation of suppressive cells through HLA-G. Moreover, we also review recent findings on the non-immunological functions of HLA-G in erythropoiesis and angiogenesis.

Granulocyte-colony stimulating factor drives the in vitro differentiation of human dendritic cells that induce anergy in naïve T cells

G-CSF is a modulator of T-cell and DC functions. Previous reports show that monocytes from G-CSF-treated (post-G) healthy donors differentiate into tolerogenic DC in vitro in the presence of autologous serum, containing high levels of IL-10 and IFN-α, and in turn induce type 1 Treg (Tr1) cells. However, the direct effect of G-CSF on DC differentiation was not investigated. Here, we show that monocytes differentiated in the presence of exogenous G-CSF (G-DC) remain CD14(+) CD1a(-) , but acquire a DC-like morphology, express CD83 and CD86 and low levels of the tolerogenic markers Ig-like transcript (ILT)4 and HLA-G. G-DC spontaneously produce IL-10 and, upon stimulation, low levels of IL-12. G-DC display low stimulatory capacity and induce anergy in naïve T cells, but do not confer suppressive function. Therefore, in vitro differentiation of monocyte-derived DC in the presence of G-CSF can replicate some but not all features of post-G DC. These findings indicate that the tolerogenic properties of G-CSF do not exclusively reside in its direct effect on DC, which in turn induce T-cell anergy, but also in its ability to generate a tolerogenic milieu in vivo, which is necessary for Tr1 cell induction and cannot be replicated in vitro.

How tolerogenic dendritic cells induce regulatory T cells

Since their discovery by Steinman and Cohn in 1973, dendritic cells (DCs) have become increasingly recognized for their crucial role as regulators of innate and adaptive immunity. DCs are exquisitely adept at acquiring, processing, and presenting antigens to T cells. They also adjust the context (and hence the outcome) of antigen presentation in response to a plethora of environmental inputs that signal the occurrence of pathogens or tissue damage. Such signals generally boost DC maturation, which promotes their migration from peripheral tissues into and within secondary lymphoid organs and their capacity to induce and regulate effector T cell responses. Conversely, more recent observations indicate that DCs are also crucial to ensure immunological peace. Indeed, DCs constantly present innocuous self- and nonself-antigens in a fashion that promotes tolerance, at least in part, through the control of regulatory T cells (Tregs). Tregs are specialized T cells that exert their immunosuppressive function through a variety of mechanisms affecting both DCs and effector cells. Here, we review recent advances in our understanding of the relationship between tolerogenic DCs and Tregs.