Interferons enhance HLA-G mRNA and protein in transfected mouse fibroblasts

Differentially Expressed Bone Marrow microRNAs Are Associated With Soluble HLA-G Bone Marrow Levels in Childhood Leukemia

HLA-G is a nonclassical histocompatibility class I molecule that plays a role in immune vigilance in cancer and infectious diseases. We previously reported that highly soluble HLA-G (sHLA-G) levels in the bone marrow were associated with a high blood cell count in T-acute lymphoblastic leukemia, a marker associated with a poor prognosis. To understand the posttranscriptional HLA-G gene regulation in leukemia, we evaluated the bone marrow microRNA profile associated with the HLA-G bone marrow mRNA expression and sHLA-G bone marrow levels in children exhibiting acute leukemia (B-ALL, T-ALL, and AML) using massively parallel sequencing. Ten differentially expressed miRNAs were associated with high sHLA-G bone marrow levels, and four of them (hsa-miR-4516, hsa-miR-486-5p, hsa-miR-4488, and hsa-miR-5096) targeted HLA-G, acting at distinct HLA-G gene segments. For qPCR validation, these miRNA expression levels (ΔCt) were correlated with HLA-G5 and RREB1 mRNA expressions and sHLA-G bone marrow levels according to the leukemia subtype. The hsa-miR-4488 and hsa-miR-5096 expression levels were lower in B-ALL than in AML, while that of hsa-miR-486-5p was lower in T-ALL than in AML. In T-ALL, hsa-miR-5096 correlated positively with HLA-G5 and negatively with sHLA-G. In addition, hsa-miR-4516 correlated negatively with sHLA-G levels. In AML, hsa-miR-4516 and hsa-miR-4488 correlated positively with HLA-G5 mRNA, but the HLA-G5 negatively correlated with sHLA-G. Our findings highlight the need to validate the findings of massively parallel sequencing since the experiment generally uses few individuals, and the same type of leukemia can be molecularly quite variable. We showed that miRNA’s milieu in leukemia’s bone marrow environment varies according to the type of leukemia and that the regulation of sHLA-G expression exerted by the same miRNA may act by a distinct mechanism in different types of leukemia.

Pregnancy and postpartum levels of circulating maternal sHLA-G in preeclampsia

Preeclampsia is a leading cause of maternal and offspring mortality and morbidity, and predicts increased future cardiovascular disease risk. Placental dysfunction and immune system dysregulation are likely key pathophysiological factors. Soluble human leukocyte antigen G (sHLA-G) may dampen the specific immune response towards placental trophoblasts. Previous studies have shown low sHLA-G levels in preeclampsia, but postpartum, levels are unknown. Furthermore, the relationship between sHLA-G and sFlt-1 and PlGF, placental function markers, is unknown. We hypothesized that low maternal sHLA-G during pregnancy would be associated with placental dysfunction, including preeclampsia, gestational hypertension, and dysregulated sFlt-1 and PlGF, and that sHLA-G would remain decreased following preeclampsia. We included 316 pregnant women: 58 with early-onset preeclampsia (<34 weeks' gestation), 81 with late-onset preeclampsia (≥34 weeks' gestation), 25 with gestational hypertension, and 152 normotensive controls. Postpartum (1 or 3 years), we included 321 women: 29 with early-onset preeclampsia, 98 with late-onset preeclampsia, 57 with gestational hypertension, and 137 who were normotensive during their index pregnancies. In pregnancy, plasma sHLA-G was significantly lower both in the early- and late-onset preeclampsia groups compared to controls. In women with preeclampsia or gestational hypertension, sHLA-G was inversely correlated with serum sFlt-1. Postpartum, plasma sHLA-G levels were significantly higher in women who had had early-onset preeclampsia compared to controls. Our results support that sHLA-G may be important for placental function. Unexpectedly, sHLA-G was elevated up to 3 years after early-onset preeclampsia, suggesting an excessively activated immune system following this severe preeclampsia form, potentially contributing to future cardiovascular disease risk.

HLA-G Expressing Immune Cells in Immune Mediated Diseases

HLA-G is a HLA class Ib antigen that possesses immunomodulatory properties. HLA-G-expressing CD4+ and CD8+ T lymphocytes, NK cells, monocytes, and dendritic cells with immunoregulatory functions are present in small percentages of patients with physiologic conditions. Quantitative and qualitative derangements of HLA-G+ immune cells have been detected in several conditions in which the immune system plays an important role, such as infectious, neoplastic, and autoimmune diseases as well as in complications from transplants and pregnancy. These observations strongly support the hypothesis that HLA-G+ immune cells may be implicated in the complex mechanisms underlying the pathogenesis of these disorders.

Non-classical MHC-I human leukocyte antigen (HLA-G) in hepatotropic viral infections and in hepatocellular carcinoma

The human leukocyte antigen (HLA)-G is a "nonclassical" major histocompatibility complex (MHC) class Ib gene, located at chromosome 6, in the 6p21.3 region. The HLA-G presents immunomodulatory functions essential in pregnancy for the tolerance of the semi-allogenic fetus, but an abnormal expression of HLA-G has been observed in numerous pathological conditions, such as tumors, autoimmune diseases and viral infections. In recent years, numerous studies have assessed the clinical relevance of HLA-G expression in different types of cancer: in general, a higher HLA-G expression correlates with a lower survival rate or a shorter disease-free survival. Altered expression of HLA-G has been found in both HCV and HBV infection, and some genetic polymorphisms have been associated with altered susceptibility/disease development for these infections, however, whether the biologic role of HLA-G in HCV and HBV infection is beneficial or hazardous, it is not completely clear. In the context of hepatocellular carcinoma, HLA-G has shown a potential diagnostic role, moreover a prognostic value in HCC patients has been also attributed to HLA-G molecules. We revise here the role of HLA-G in hepatotropic HBV/HCV infections and in hepatocellular carcinoma (HCC).

Transcriptional and posttranscriptional regulations of the HLA-G gene

HLA-G has a relevant role in immune response regulation. The overall structure of the HLA-G coding region has been maintained during the evolution process, in which most of its variable sites are synonymous mutations or coincide with introns, preserving major functional HLA-G properties. The HLA-G promoter region is different from the classical class I promoters, mainly because (i) it lacks regulatory responsive elements for IFN-γ and NF-κB, (ii) the proximal promoter region (within 200 bases from the first translated ATG) does not mediate transactivation by the principal HLA class I transactivation mechanisms, and (iii) the presence of identified alternative regulatory elements (heat shock, progesterone and hypoxia-responsive elements) and unidentified responsive elements for IL-10, glucocorticoids, and other transcription factors is evident. At least three variable sites in the 3' untranslated region have been studied that may influence HLA-G expression by modifying mRNA stability or microRNA binding sites, including the 14-base pair insertion/deletion, +3142C/G and +3187A/G polymorphisms. Other polymorphic sites have been described, but there are no functional studies on them. The HLA-G coding region polymorphisms might influence isoform production and at least two null alleles with premature stop codons have been described. We reviewed the structure of the HLA-G promoter region and its implication in transcriptional gene control, the structure of the HLA-G 3'UTR and the major actors of the posttranscriptional gene control, and, finally, the presence of regulatory elements in the coding region.

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

Background

Human leukocyte antigen (HLA)-G is a nonclassical class I antigen with immunomodulatory roles including up-regulation of suppressor T regulatory lymphocytes. HLA-G was recently identified as an asthma susceptibility gene, and expression of a soluble isoform, HLA-G5, has been demonstrated in human airway epithelium. Increased presence of HLA-G5 has been demonstrated in bronchoalveolar lavage fluid recovered from patients with mild asthma; this suggests a role for this isoform in modulating airway inflammation though the mechanisms by which this occurs is unclear. Airway inflammation associated with Th2 cytokines such as IL-4 and IL-13 is a principal feature of asthma, but whether these cytokines elicit expression of HLA-G is not known.

Methods

We examined gene and protein expression of both soluble (G5) and membrane-bound (G1) HLA-G isoforms in primary differentiated human airway epithelial cells collected from normal lungs and grown in air-liquid interface culture. Cells were treated with up to 10 ng/ml of either IL-4, IL-5, or IL-13, or 100 ng/ml of the immunomodulatory cytokine IL-10, or 10,000 U/ml of the Th1-associated cytokine interferon-beta, for 24 hr, after which RNA was isolated for evaluation by quantitative PCR and protein was collected for Western blot analysis.

Results

HLA-G5 but not G1 was present in dAEC as demonstrated by quantitative PCR, western blot and confocal microscopy. Neither G5 nor G1 expression was increased by the Th2-associated cytokines IL-4, IL-5 or IL-13 over 24 hr, nor after treatment with IL-10, but was increased 4.5 ± 1.4 fold after treatment with 10,000 U/ml interferon-beta.

Conclusions

These data demonstrate the constitutive expression of a T lymphocyte regulatory molecule in differentiated human airway epithelial cells that is not modulated by Th2-associated cytokines.

Macrophages at the fetal-maternal interface express markers of alternative activation and are induced by M-CSF and IL-10

During pregnancy, the maternal immune system is challenged by the presence of the fetus, which must be tolerated despite being semiallogeneic. Uterine mucosal (or decidual) macrophages (M), one of the major leukocyte populations at the fetal-maternal interface, have been implicated in fetal tolerance, but information regarding their regulation is scarce. In this study, we investigated the role of several factors potentially involved in the differentiation and polarization of decidual M with an in vitro M differentiation model. By using flow cytometry, we showed that M-CSF and IL-10 were potent inducers of M2 (immunoregulatory) M markers expressed on human decidual M (CD14, CD163, CD206, CD209). In contrast, proinflammatory stimuli, and unexpectedly also the Th2-associated IL-4 and IL-13, induced different patterns of expression, indicating that a Th2-dominated environment is not required for decidual M polarization. M-CSF/IL-10-stimulated and decidual M also showed similar cytokine secretion patterns, with production of IL-10 as well as IL-6, TNF, and CCL4. Conversely, the proinflammatory, LPS/IFN-γ-stimulated M produced significantly higher levels of TNF and no IL-10. We also used a gene array with 420 M-related genes, of which 100 were previously reported to be regulated in a global gene expression profiling of decidual M, confirming that M-CSF/IL-10-induced M are closely related to decidual M. Taken together, our results consistently point to a central role for M-CSF and in particular IL-10 in the shaping of decidual M with regulatory properties. These cytokines may therefore play an important role in supporting the homeostatic and tolerant immune milieu required for a successful pregnancy.

HLA-G in organ transplantation: towards clinical applications

HLA-G plays a particular role during pregnancy in which its expression at the feto-maternal barrier participates into the tolerance of the allogenic foetus. HLA-G has also been demonstrated to be expressed in some transplanted patients, suggesting that it regulates the allogenic response. In vitro data indicate that HLA-G modulates NK cells, T cells, and DC maturation through its interactions with various inhibitory receptors. In this paper, we will review the data reporting the HLA-G involvement of HLA-G in human organ transplantation, then factors that can modulate HLA-G, and finally the use of HLA-G as a therapeutic tool in organ transplantation.

On the role of placental Major Histocompatibility Complex and decidual leukocytes in implantation and pregnancy success using non-human primate models

While there is broad agreement that interactions of the human maternal immune system with the tissues and cells of the implanting embryo are likely to be critical contributors to pregnancy success, there remains a dearth of information which directly confirms this expectation. Although animal models of reproductive function often provide opportunities for confirming such hypotheses, progress in this area has been sporadic due to limitations of traditional laboratory or agricultural animal models, such as rodents, sheep, pigs and cattle. Many of these limitations derive from divergent modes of implantation and placentation across mammalian species. Over the past decade there has been progress in the development of the nonhuman primate as a model in which to address questions of pregnancy success in the area of immunology. The purpose of this review is to compare available model species, summarize current knowledge and recent progress with an emphasis on experimental in vivo manipulations, and suggest areas available for additional study and growth.

Non-classical transcriptional regulation of HLA-G: an update

Human leucocyte antigen-G (HLA-G) plays a key role in maternal–foetal tolerance and allotransplantation acceptance and is also implicated in tumour escape from the immune system. The modulation of HLA-G expression can prove to be very important to therapeutic goals in some pregnancy complications, transplantation, cancer and possibly autoimmune diseases. In spite of substantial similarities with classical HLA-class I genes, HLA-G is characterized by a restricted tissue-specific expression in non-pathological situations. HLA-G expression is mainly controlled at the transcriptional level by a unique gene promoter when compared with classical HLA-class I genes, and at the post-transcriptional level including alternative splicing, mRNA stability, translation and protein transport to the cell surface. We focus on the characteristics of the HLA-G gene promoter and the factors which are involved in HLA-G transcriptional modulation. They take part in epigenetic mechanisms that control key functions of the HLA-G gene in the regulation of immune tolerance.

Expression and regulation of non-classical HLA-G in renal cell carcinoma

Under physiological conditions, the non-classical major histocompatibility complex class Ib molecule human leukocyte antigen G (HLA-G) is selectively expressed in placental trophoblasts, thymus and cornea. In pathological situations, HLA-G expression was frequently found in tumour cells of distinct origin, thereby allowing these tumour cells to escape immune surveillance. Although HLA-G expression occurs at a relatively high frequency in renal cell carcinoma (RCC) of the clear cell subtype, the molecular mechanisms of its aberrant expression in RCC has not yet been determined. Therefore, the constitutive and cytokine-mediated HLA-G expression as well as its mode of regulation was investigated. In addition to HLA-G-specific mRNA expression, membrane-bound and soluble/shed HLA-G protein was determined. Eight of 14 RCC cell lines analysed (57%) exhibited HLA-G-specific transcripts, whereas only 6 of 14 RCC cell lines (43%) expressed HLA-G protein, suggesting a post-transcriptional control of HLA-G in some cases. Treatment of RCC cell lines with either interferon-gamma or interleukin-10, respectively, increased HLA-G-specific mRNA and protein in six of eight HLA-G(+) RCC lines (75%), but not in HLA-G(-) RCC cells. A 5'-aza-2-deoxycytidine (5-Aza-dC)-mediated demethylation of the HLA-G promoter DNA resulted in an enhanced HLA-G expression in four of six RCC cell lines, whereas a de novo induction of HLA-G was only observed in one HLA-G(-) RCC cell line on treatment with 5-Aza-dC. Thus, there exist multiple mechanisms controlling HLA-G expression in RCC, which might also have an impact on the development of RCC-specific immunotherapies.

Cytokine networks and the regulation of uterine function in pregnancy and parturition

Complex cytokine networks play an important role in a wide range of reproductive and pregnancy related processes. Here, we review the current knowledge concerning the impact of cytokines on uterine physiology and pathophysiology. Cytokines influence a range of uterine functions during the menstrual cycle, implantation, pregnancy and labour. The synergistic interactions between individual cytokines are intricate and dynamic, and modulated by pregnancy hormones. It is not surprising therefore, that perturbations to cytokine signalling are associated with adverse pregnancy outcomes, such as miscarriage, pre-eclampsia, preterm labour and foetal brain injury. Further insight into the complexity of cytokine networks will be required to develop novel therapeutic strategies for the treatment of cytokine imbalances in pregnancy.

Plasma soluble human leukocyte antigen G levels in asthmatic children

BACKGROUND

Human leukocyte antigen G (HLA-G) is a nonclassical major histocompatibility complex class I gene. HLA-G stimulates Th2 cytokine secretion by peripheral blood mononuclear cells. The role of soluble HLA-G (sHLA-G) in bronchial asthma is incompletely understood and the plasma level of sHLA-G in asthmatic children has not been investigated.

OBJECTIVE

It was the aim of this study to investigate the plasma level of sHLA-G in asthmatic children.

METHODS

Asthmatic (n = 53) and healthy children (n = 16) were included in the study. Levels of sHLA-G were determined in plasma using ELISA. Spirometry, total immunoglobulin E and eosinophil counts were obtained and skin testing done with a battery of 25 antigens with appropriate positive and negative controls.

RESULTS

No significant difference was observed in the plasma level of sHLA-G between the asthmatic and healthy children (p > 0.05). When we compared atopic asthmatics with healthy controls, we found significantly higher levels of sHLA-G in atopic asthmatics (p < 0.05). There was a significant difference in the peripheral blood eosinophil counts and total immunoglobulin E levels among the groups (p < 0.001).

CONCLUSION

Our study shows that plasma sHLA-G levels do not differ between asthmatic children and healthy controls. However, higher plasma levels of sHLA-G in atopic asthmatics may suggest a role for sHLA-G in atopy. Further investigations are required to better define the mechanism of the production and the role of sHLA-G molecules observed in patients with asthma.

The Effect of Interleukin-17 on the Proliferation and Invasion of JEG-3 Human Choriocarcinoma Cells

PROBLEM

As there has been a study in mice showing the expression of IL-17 by decidual cells and the status of IL-17 receptor expression in human pregnancy is not known, we hypothesized that IL-17 may regulate human trophoblast proliferation and invasion.

METHOD OF STUDY

JEG-3 cell line was used as a model for human trophoblast. Immunohistochemitry and reverse transcriptase polymerase chain reaction techniques were used to identify IL-17 receptor protein and mRNA, respectively. The effects of IL-17 on JEG-3 cell proliferation and invasion were tested using the BrdU incorporation and the Matrigel invasion assays, respectively.

RESULTS

IL-17 increased the invasive capacity of JEG-3 cells but had no effect on the proliferation and multinucleated formation of JEG-3 cells.

CONCLUSION

In this JEG-3 cell model of human trophoblast, the IL-17R and IL-17 may have a regulatory role in trophoblast invasion.

Modulation of HLA-G expression in human neural cells after neurotropic viral infections

HLA-G is a nonclassical human major histocompatibility complex class I molecule. It may promote tolerance, leading to acceptance of the semiallogeneic fetus and tumor immune escape. We show here that two viruses-herpes simplex virus type 1 (HSV-1), a neuronotropic virus inducing acute infection and neuron latency; and rabies virus (RABV), a neuronotropic virus triggering acute neuron infection-upregulate the neuronal expression of several HLA-G isoforms, including HLA-G1 and HLA-G5, the two main biologically active isoforms. RABV induces mostly HLA-G1, and HSV-1 induces mostly HLA-G3 and HLA-G5. HLA-G expression is upregulated in infected cells and neighboring uninfected cells. Soluble mediators, such as beta interferon (IFN-beta) and IFN-gamma, upregulate HLA-G expression in uninfected cells. The membrane-bound HLA-G1 isoform was detected on the surface of cultured RABV-infected neurons but not on the surface of HSV-1-infected cells. Thus, neuronotropic viruses that escape the host immune response totally (RABV) or partially (HSV-1) regulate HLA-G expression on human neuronal cells differentially. HLA-G may therefore be involved in the escape of certain viruses from the immune response in the nervous system.

HLA-G is expressed by the glandular epithelium of peritoneal endometriosis but not in eutopic endometrium

BACKGROUND

HLA-G is a major histocompatability antigen with documented immune-regulatory function. Various epithelial cancers and tissue allografts have been noted to express HLA-G, which is postulated to aid in their escape from immunosurveillance. We evaluated peritoneal endometriosis and eutopic endometrium for the expression of HLA-G protein and gene transcript.

METHODS

Two experiments were performed: (i) archived tissue blocks from peritoneal endometriotic lesions (n = 15) and eutopic endometrium (n = 12) were evaluated for extent of protein immunostaining, and (ii) eutopic endometrial biopsies from women without (n = 17) and with (n = 24) endometriosis, and peritoneal endometriotic lesions (n = 14) were evaluated for presence of RNA transcript by in situ hybridization.

RESULTS

HLA-G protein localized in the glandular epithelium of 14 of 15 (93.3%) peritoneal endometriotic lesions, but not in stromal cells. HLA-G protein staining was absent in endometrial biopsies (n = 12). HLA-G gene transcript localized to the glandular epithelium in 13 of 14 (92.8%) peritoneal endometriotic lesions. HLA-G transcript was never observed in eutopic endometrium, regardless of cycle stage or whether from women with (n = 24) or without (n = 18) endometriosis.

CONCLUSIONS

HLA-G is expressed by endometriotic glandular epithelium but not by eutopic endometrium under normal conditions. Differential expression of HLA-G suggests that peritoneal inflammation or cellular stress may up-regulate mechanisms to promote ectopic endometrial survival.

HLA-G gene activation in tumor cells involves cis-acting epigenetic changes

The tissue distribution of HLA-G molecules is broader than originally reported in trophoblastic cells. On the basis of numerous studies, HLA-G is also expressed in malignant tumors and involved in tumor immune escape. The mechanisms of HLA-G gene regulation differ from those of classical HLA class I genes and involve epigenetic processes. Here, we provide additional evidence on the influence of DNA demethylation on HLA-G activation. We also analyze the 5' regulatory region of HLA-G in 2 cellular models, melanoma (FON, M8) and choriocarcinoma (JEG-3, JAR), either expressing HLA-G transcripts or not. The data strongly suggest that HLA-G is silenced as a result of CpG site hypermethylation within a 5' regulatory region encompassing 450 bp upstream of the start codon, whereas it is activated upon demethylation. This result correlates with the acetylation status of histones within this region and the putative locus control region located at -1.2 kb. cis-acting epigenetic changes and the fact that demethylating agents activate HLA-G expression at least 5 days following treatment should be taken into account in epigenetic cancer therapies.

Potential regulatory sequences in the untranslated regions of the baboon MHC class Ib gene, Paan-AG, more closely resemble those in the human MHC class Ia genes than those in the class Ib gene, HLA-G

The baboon major histocompatibility complex (MHC) class Ib gene, Paan-AG, is structurally similar to the human MHC class Ia gene, HLA-A, but exhibits characteristics similar to those of the class Ib gene HLA-G. These include limited polymorphism, alternative splicing of a single message, and restricted tissue distribution, with high expression in the placenta. In order to determine whether regulatory elements controlling expression of Paan-AG resemble those of HLA-A or HLA-G, we cloned the 5' and 3' untranslated regions of Paan-AG. Unexpectedly, sequence comparisons showed that potential regulatory elements in Paan-AG strikingly resembled those in HLA-A and differed in major respects from those in HLA-G. Unlike HLA-G, Paan-AG contained an intact interferon-gamma stimulated response element (ISRE) in the promoter. Studies using luciferase reporter assays showed that the Paan-AG ISRE was functional. The basal activity of the Paan-AG ISRE and its response to interferon-gamma was similar to that of class Ia MHC genes. Further, we identified an ISRE in the 3' untranslated region of Paan-AG that is known to be functional in HLA-A2 but is deleted in HLA-G. These experiments predict that functional studies may demonstrate differences in regulation of expression of Paan-AG and HLA-G genes, which could restrict the use of the baboon as a primate model for studying HLA-G expression and function.

In vivo, RFX5 binds differently to the human leucocyte antigen-E, -F, and -G gene promoters and participates in HLA class I protein expression in a cell type-dependent manner

We analysed the regulation of human leucocyte antigen (HLA)-E, -F and -G genes, focusing on the SXY module, a promoter region that controls major histocompatibility complex (MHC) class II expression and participates in the expression of classical HLA class I molecules. It comprises the X1, X2 and Y boxes, bound by RFX, X2-BP/ATF/CREB and NFY factors, respectively. The complex recruits the master control factor CIITA. The SXY module is conserved in HLA-E and HLA-F gene promoters, whereas in the HLA-G promoter, the only conserved boxes are S and X1. Chromatin immunoprecipitation assays, performed on HLA-G positive and negative cell lines, demonstrated the in situ binding of RFX5 and CIITA to HLA-E and HLA-F, but not to HLA-G, promoters. In B cells from bare lymphocyte syndrome patients lacking RFX5 or CIITA, we observed lower steady-state levels of HLA-E and HLA-F transcripts but did not find any significant decrease in the cell-surface expression of HLA-E/classical HLA class I. In RFX5-deficient fibroblasts, the cell-surface expression of HLA molecules was decreased. RFX5 and CIITA are thus not involved in HLA-G expression and their importance for the surface expression of HLA-E/classical HLA class I molecules may vary depending on the cell type.

Expression of nonclassical MHC class Ib genes: comparison of regulatory elements

Peptide binding proteins of the major histocompatibility complex consist of the "classical" class Ia and "nonclassical" class Ib genes. The gene organization and structure/function relationship of the various exons comprising class I proteins are very similar among the class Ia and class Ib genes. Although the tissue-specific patterns of expression of these two gene families are overlapping, many class Ib genes are distinguished by relative low abundance and/or limited tissue distribution. Further, many of the class Ib genes serve specialized roles in immune responses. Given that the coding sequences of the class Ia and class Ib genes are highly homologous we sought to examine the promoter regions of the various class Ib genes by comparison to the well characterized promoter elements regulating expression of the class Ia genes. This analysis revealed a surprising complexity of promoter structures among all class I genes and few instances of conservation of class Ia promoter regulatory elements among the class Ib genes.

Biology and functions of human leukocyte antigen-G in health and sickness

In 1998, the first International Conference on human leukocyte antigen-G (HLA-G) was held in Paris. At that time, HLA-G was still a new HLA class I molecule, few aspects of its immunological functions were known, and its expression by tumors was just being described. In 1998, tools to properly study HLA-G were lacking, especially monoclonal antibodies, and three conclusions were drawn after the congress: (i) animal models were needed, (ii) the biology of HLA-G isoforms had to be confirmed, and (iii) HLA-G expression by tumors required clarification. Five years later, these three issues have been addressed. HLA-G is now gaining pace and is investigated for its immuno-inhibitory functions in the context of multiple pathologies. Eighty five oral presentations were given this year for more than 200 investigators working on HLA-G by speakers from over 20 countries. The success of the 3rd International Conference on HLA-G reflects the interest and tremendous work of the many research teams which, over the years, contributed to the publication of more than 500 peer-review articles. We summarize the key points that were presented and discussed during this meeting.

HLA-G Molecules: from Maternal–Fetal Tolerance to Tissue Acceptance

Over the past few years, HLA-G, the non-classical HLA class I molecule, has been the center of investigations that have led to the description of its specific structural and functional properties. Although located in the HLA class I region of chromosome six, the HLA-G gene may be distinguished from other HLA class I genes by its low polymorphism and alternative splicing that generates seven HLA-G proteins, whose tissue-distribution is restricted to normal fetal and adult tissues that display a tolerogeneic function toward both innate and acquired immune cells. We review these points, with special emphasis on the role of HLA-G in human pathologies, such as cancer, viral infection, and inflammatory diseases, as well as in organ transplantation.

Do nonhuman primates comprise appropriate experimental models for studying the function of human leukocyte antigen-G?

The expression and function of the human major histocompatibility complex (MHC) class Ia genes, human leukocyte antigen (HLA)-A, -B, and -C, is well-established; they are expressed in most nucleated cells and present endogenous peptides to CD8+ T cells. However, MHC class Ib genes are poorly characterized and have unknown functions. In humans, the best-characterized class Ib gene is HLA-G. This gene has a restricted tissue expression of the mRNA and a unique pattern of protein expression; it is expressed mainly in the extravillous cytotrophoblast cells in the placenta. The function of HLA-G is not clear, but its presence at the maternal-fetal interface suggests a role in protection of the semiallogeneic fetus. Whereas functional studies using in vitro models and transgenic mice provide useful insights regarding the potential function of this molecule, in vivo studies cannot be performed in humans. Nonhuman primates that are closely related to humans phylogenetically contain homologues of HLA-G. The MHC-G loci in nonhuman primates appear to have diverged from the human HLA-G. However, in the rhesus monkey (Macaca mulatta) and olive baboon (Papio anubis), a novel class Ia-related locus has been described. This gene encodes glycoproteins with characteristics that resemble those of HLA-G, including restricted tissue distribution, alternative splicing of mRNA, truncated cytoplasmic domain, and limited polymorphism. Thus, this molecule may be the functional homologue of HLA-G, and these two species may comprise appropriate models for elucidating the function of HLA-G.

Interferon-gamma levels are upregulated by 17-beta-estradiol and diethylstilbestrol

Gamma-interferon (IFN-gamma) plays an important role in the maintenance of immune homeostasis by regulating the functions of all key cells of the immune system. Pathologically, IFN-gamma has been implicated in several autoimmune diseases. Since estrogens affect autoimmunity, we investigated whether immunomodulatory estrogenic hormones affects IFN-gamma. Concanavalin-A-stimulated splenic lymphocytes from orchiectomized or ovariectomized C57BL/6 mice exposed to estrogen for 3-5 months secreted higher levels of IFN-gamma protein compared to controls. This increase is, in part, due to increased levels of IFN-gamma mRNA. Kinetic studies suggested that splenic lymphocytes from estrogen-treated gonadectomized mice had increased IFN-gamma mRNA and protein as early as 6-12 h of culture. Estrogen also increased the expression of co-stimulatory CD80 (B7-1) molecules on B cells. Since natural estrogen increases IFN-gamma, it became important to test whether diethylstilbestrol (DES, a synthetic estrogen which was given to millions of women) also alters IFN-gamma levels. Our initial investigatory studies show that prenatal mice exposed to DES had a normal ability to secrete IFN-gamma. However, a second exposure of these mice to DES (single dose of 1 microg/g.b.w), as late as 1-1.5 years of age, led to a pronounced increase in the number of IFN-gamma secreting cells and augmented secretion of IFN-gamma. Increased IFN-gamma secretion by splenic lymphocytes from these mice was noted even after stimulation with a submitogenic concentration of anti-CD3 antibodies with or without anti-CD28 antibodies. Cell mixing experiments suggested that the DES-induced increase in IFN-gamma secretion is due to hormonal effects on T cells but not on APC. Together our studies show that: (1) estrogens upregulate IFN-gamma secretion, a vital immunoregulatory cytokine, and (2) inappropriate exposure of developing fetus to DES may permanently alter the "cytokine programming" of lymphocytes.

Soluble human leukocyte antigen--G serum level is elevated in melanoma patients and is further increased by interferon-alpha immunotherapy

BACKGROUND

The nonclassic human major histocompatibility complex class I antigens human leukocyte antigen (HLA)--G are proposed to protect tumor cells from natural killer cell lysis. In the current study, the authors measured soluble HLA-G molecules (sHLA-G) in serum from patients with malignant melanoma.

METHODS

Soluble HLA-G was determined in serum samples of 190 melanoma patients with various stages of disease, with or without current therapy including interferon (IFN)-alpha and different cytostatics in comparison to 126 healthy controls by using a two-step enzyme-linked immunoadsorbent assay.

RESULTS

Serum sHLA-G was significantly (P < 0.0005) elevated in melanoma patients (mean +/- standard error of the mean [SEM] = 41.95 +/- 2.15 ng/mL) compared with healthy controls (mean +/- SEM = 22.92 +/- 1.51 ng/mL). Univariate analysis revealed a correlation of sHLA-G serum level with advanced stages of disease (P < 0.001) and tumor load (P < 0.05). Patients undergoing immunotherapy with IFN-alpha (n = 31) showed an increased serum sHLA-G (mean +/- SEM = 62.05 +/- 7.58 ng/mL; P < 0.0005), whereas other treatment regimens (n = 24) did not influence sHLA-G serum concentrations. Multivariate analysis revealed treatment with IFN-alpha as the only impact factor for elevated serum sHLA-G, lacking any correlation with stage of disease or tumor burden. Furthermore, IFN-alpha was found to upregulate HLA-G cell surface expression on circulating monocytes. sHLA-G serum level was not associated with recurrence free or overall survival.

CONCLUSIONS

This study shows increased sHLA-G serum concentrations in melanoma patients and additional enhancement upon treatment with IFN-alpha. The level of serum sHLA-G, however, had no negative impact on patients' prognosis.

Inhibition of antigen transport by expression of infected cell peptide 47 (ICP47) prevents cell surface expression of HLA in choriocarcinoma cell lines

Cell surface expression of HLA class I (including non-classical HLA-G) in JEG3 (choriocarcinoma cell line) was blocked by stable transfection with the sequence encoding the Herpes simplex virus protein, infected cell peptide 47 (ICP47) inserted into a vector pCEP4. Intracellular expression of ICP47 protein in ICP47-transfected cells was demonstrated. The lack of HLA cell surface expression was likely to be due to blockage of peptide transport from the cytoplasm into the endoplasmic reticulum by ICP47. ICP47 is known to block the heterodimeric transporter associated with antigen processing (formed from TAP1 and TAP2). Western blotting with a polyclonal antibody to the C-terminus of TAP1 showed high expression of TAP1 in BeWo and JEG3, but not JAR cells, expression that was strongly upregulated by gamma-interferon. Gamma-interferon also upregulated the cell surface expression of HLA class I. TAP1 was strongly expressed in MC2 and MC3 extravillous cytotrophoblast cell lines immortalised with the SV40 large T antigen. The results suggest a role for non-classical HLA in the presentation of antigenic peptides to the immune system.

A specific interferon (IFN)-stimulated response element of the distal HLA-G promoter binds IFN-regulatory factor 1 and mediates enhancement of this nonclassical class I gene by IFN-beta

Type I interferons display a broad range of immunomodulatory functions. Interferon beta increases gene expression at the transcriptional level through binding of factors to the interferon-stimulated response element (ISRE) within the promoters of interferon-inducible genes, such as HLA class I. Despite mutation of the class I ISRE sequence within the nonclassical HLA-G class I gene promoter, we show that interferon beta enhances both transcription and cell surface expression of HLA-G in trophoblasts and amniotic and thymic epithelial cells that selectively express it in vivo. Deletion and mutagenesis analysis of a putative interferon-regulatory factor (IRF)-1 binding site within the HLA-G promoter show that HLA-G transactivation is mediated through an ISRE sequence 746 base pairs upstream from ATG, which is distinct from the interferon-responsive element described within proximal classical class I gene promoters. Electrophoretic mobility shift analysis and supershift analysis further demonstrate that interferon-responsive transcription factors, including IRF-1, specifically bind to the HLA-G ISRE. Our results provide evidence that IRF-1 binding to a functional ISRE within the HLA-G promoter mediates interferon beta-induced expression of the HLA-G gene. These observations are of general interest considering the implication of HLA-G in mechanisms of immune escape involved in fetal-maternal tolerance and other immune privilege situations.

Heat shock and arsenite induce expression of the nonclassical class I histocompatibility HLA-G gene in tumor cell lines

The nonclassical histocompatibility class I gene HLA-G has a tissue-restricted expression. To explore mechanisms involved in HLA-G transcriptional regulation, we have investigated the effect of stress, including heat shock and arsenite treatment, on HLA-G expression in tumor cell lines. We show that stress induces an increase of the level of the different HLA-G alternative transcripts without affecting other MHC class I HLA-A, -B, -E, and -F transcripts. A heat shock element (HSE) that binds to heat shock factor 1 (HSF1) on stress conditions was further identified within the HLA-G promoter. Considering the ability of HLA-G to modulate the function of immunocompetent cells, we hypothesize a new feature of HLA-G as a signal regulating the immune response to stress.

Modulation of HLA-G expression in human thymic and amniotic epithelial cells

Expression of the nonclassical HLA class I antigen, HLA-G, is tightly regulated. HLA-G physiologic expression is mostly restricted to some placental and thymic cell types. Only few established cell lines express HLA-G in vitro. Cytokine-induced expression of HLA-G is hardly observed and also depends on the cell lineage. We assessed expression and cytokine regulation of HLA-G in primary cultures derived from human thymus and amnion epithelial cells, which also express HLA-G in vivo. We show that HLA-G cell surface expression is maintained, but decreases gradually, in primary cultures derived from human thymus and amnion epithelial cells. We also show that IFN-gamma re-induces HLA-G cell surface expression and upregulates classical class I gene expression in both primary cultures and in a thymus derived cell line. We further show that IFN-gamma also upregulates levels of HLA-G transcripts in TEC primary cultures. This study provides evidence that IFN-gamma induction of HLA-G expression occurs in the human amnion and the thymus, and is mediated at the transcriptional level in these tissues. These results also suggest a role for the microenvironment in regulating HLA-G in vivo gene expression in the thymus and amnion membrane.

Heat shock and arsenite induce expression of the nonclassical class I histocompatibility HLA-G gene in tumor cell lines

The nonclassical histocompatibility class I gene HLA-G has a tissue-restricted expression. To explore mechanisms involved in HLA-G transcriptional regulation, we have investigated the effect of stress, including heat shock and arsenite treatment, on HLA-G expression in tumor cell lines. We show that stress induces an increase of the level of the different HLA-G alternative transcripts without affecting other MHC class I HLA-A, -B, -E, and -F transcripts. A heat shock element (HSE) that binds to heat shock factor 1 (HSF1) on stress conditions was further identified within the HLA-G promoter. Considering the ability of HLA-G to modulate the function of immunocompetent cells, we hypothesize a new feature of HLA-G as a signal regulating the immune response to stress.

Surface expression of HLA-C antigen by human extravillous trophoblast

In this paper definitive evidence that the classical class I product, HLA-C, is expressed on the surface of normal trophoblast cells is provided. HLA-C transcripts were sequenced from cDNA isolated from first trimester trophoblast cells obtained by flow cytometric sorting. Both paternal and maternal alleles were transcribed. HLA-C proteins were demonstrated by biochemical analysis and found on the cell surface in association with beta(2)-microglobulin. Upregulation of cell surface HLA-C but not HLA-G expression after interferon (IFN)-gamma treatment was demonstrated by flow cytometric analysis. Immunohistology has confirmed HLA-C is expressed by all extravillous subpopulations in vivo. The question of whether trophoblast HLA-C molecules interact with decidual NK cells expressing killer Ig-like receptors (KIR) has also been addressed. Our results demonstrate that extravillous trophoblast expresses at least two HLA class I molecules, HLA-G and HLA-C on the cell surface.

A candidate interferon-gamma activated site (GAS element) in the HLA-G promoter does not bind nuclear proteins

The HLA-G gene is highly expressed at the maternal-fetal interface, where it is believed to participate in the generation and maintenance of maternal tolerance to the fetal semiallograft. This gene has two elements through which interferon-gamma (IFN-gamma) could act to enhance its rate of transcription, an Enhancer A/ICS region and a candidate IFN-gamma activated site (GAS). In this study we investigated functionality of this candidate HLA-G GAS. Two HLA-G-expressing cell lines were tested, the human myelomonocytic cell line, U937, and a mouse fibroblast cell line, S14/8, which is stably transfected with the full length HLA-G gene. Nuclear proteins from IFN-gamma-treated U937 and S14/8 cells bound the interferon regulatory factor-1 (IRF-1) gene GAS sequence (TTC CCCGAA) but not the HLA-G gene's candidate GAS sequence (TTTCGAGAA). Excess unlabeled HLA-G-GAS oligonucleotide failed to inhibit binding of the IRF-1-GAS using the same nuclear extracts. These data indicate that a sequence in the HLA-G gene which would normally permit cytokine enhancement of gene expression, the GAS element, is nonfunctional. This is also true of another regulatory sequence, the Enhancer A/ICS element, suggesting that defects in IFN-gamma response elements prevent inappropriate up-regulation of HLA-G gene expression at the maternal-fetal interface.