HLA-G remains a mystery

Prognostic significance of high circulating sHLA-G in ovarian carcinoma

HLA-G is a non-classical major histocompatibility complex class Ib molecule. Its expression has been described in various cancer types, including ovarian cancer. HLA-G molecule has been implicated in immune escape and in progression of ovarian tumor cells. Our goal was to assess if total soluble (s)HLA-G molecules or HLA-G5 and sHLA-G1 isoforms could be considered as circulating ovarian tumor biomarkers, we measured the concentration of these molecules in ovarian carcinoma patients stratified according with their clinicopathological parameters. sHLA-G, sHLA-G1 and HLA-G5 concentrations were dosed in plasma samples by sandwich-ELISA. The sHLA-G dimerization was analyzed after immunoprecipitation and SDS-PAGE migration. Total sHLA-G and sHLA-G1 levels were significantly represented in plasma of ovarian carcinoma patients compared to healthy controls. sHLA-G1 isoform concentration was highly represented in ovarian carcinoma compared to HLA-G5 isoforms. Additionally, high sHLA-G molecules have been found in aged patients, as well as in patients with advanced stages, and those with metastatic lymph nodes and those with distant metastasis. Elsewhere, sHLA-G monomers were highly represented in ovarian carcinoma patients compared to controls. sHLA-G plasmatic protein was highly represented in ovarian carcinoma. In effect, HLA-G might be considered as a new checkpoint molecule that could be used to assess progression and recurrence of the disease, thus placing it as a potential biomarker for advanced and complicated ovarian carcinoma.

Predicting the most deleterious missense nsSNPs of the protein isoforms of the human HLA-G gene and in silico evaluation of their structural and functional consequences

BACKGROUND

The Human Leukocyte Antigen G (HLA-G) protein is an immune tolerogenic molecule with 7 isoforms. The change of expression level and some polymorphisms of the HLA-G gene are involved in various pathologies. Therefore, this study aimed to predict the most deleterious missense non-synonymous single nucleotide polymorphisms (nsSNPs) in HLA-G isoforms via in silico analyses and to examine structural and functional effects of the predicted nsSNPs on HLA-G isoforms.

RESULTS

Out of 301 reported SNPs in dbSNP, 35 missense SNPs in isoform 1, 35 missense SNPs in isoform 5, 8 missense SNPs in all membrane-bound HLA-G isoforms and 8 missense SNPs in all soluble HLA-G isoforms were predicted as deleterious by all eight servers (SIFT, PROVEAN, PolyPhen-2, I-Mutant 3.0, SNPs&GO, PhD-SNP, SNAP2, and MUpro). The Structural and functional effects of the predicted nsSNPs on HLA-G isoforms were determined by MutPred2 and HOPE servers, respectively. Consurf analyses showed that the majority of the predicted nsSNPs occur in conserved sites. I-TASSER and Chimera were used for modeling of the predicted nsSNPs. rs182801644 and rs771111444 were related to creating functional patterns in 5'UTR. 5 SNPs in 3'UTR of the HLA-G gene were predicted to affect the miRNA target sites. Kaplan-Meier analysis showed the HLA-G deregulation can serve as a prognostic marker for some cancers.

CONCLUSIONS

The implementation of in silico SNP prioritization methods provides a great framework for the recognition of functional SNPs. The results obtained from the current study would be called laboratory investigations.

O-GlcNAcylation and its role in the immune system

O-linked-N-acetylglucosaminylation (O-GlcNAcylation) is a type of glycosylation that occurs when a monosaccharide, O-GlcNAc, is added onto serine or threonine residues of nuclear or cytoplasmic proteins by O-GlcNAc transferase (OGT) and which can be reversibly removed by O-GlcNAcase (OGA). O-GlcNAcylation couples the processes of nutrient sensing, metabolism, signal transduction and transcription, and plays important roles in development, normal physiology and physiopathology. Cumulative studies have indicated that O-GlcNAcylation affects the functions of protein substrates in a number of ways, including protein cellular localization, protein stability and protein/protein interaction. Particularly, O-GlcNAcylation has been shown to have intricate crosstalk with phosphorylation as they both modify serine or threonine residues. Aberrant O-GlcNAcylation on various protein substrates has been implicated in many diseases, including neurodegenerative diseases, diabetes and cancers. However, the role of protein O-GlcNAcylation in immune cell lineages has been less explored. This review summarizes the current understanding of the fundamental biochemistry of O-GlcNAcylation, and discusses the molecular mechanisms by which O-GlcNAcylation regulates the development, maturation and functions of immune cells. In brief, O-GlcNAcylation promotes the development, proliferation, and activation of T and B cells. O-GlcNAcylation regulates inflammatory and antiviral responses of macrophages. O-GlcNAcylation promotes the function of activated neutrophils, but inhibits the activity of nature killer cells.

Natural Killer Cell Interactions with Classical and Non-Classical Human Leukocyte Antigen Class I in HIV-1 Infection

Natural killer (NK) cells are effector lymphocytes of the innate immune system that are able to mount a multifaceted antiviral response within hours following infection. This is achieved through an array of cell surface receptors surveilling host cells for alterations in human leukocyte antigen class I (HLA-I) expression and other ligands as signs of viral infection, malignant transformation, and cellular stress. This interaction between HLA-I ligands and NK-cell receptor is not only important for recognition of diseased cells but also mediates tuning of NK-cell-effector functions. HIV-1 alters the expression of HLA-I ligands on infected cells, rendering them susceptible to NK cell-mediated killing. However, over the past years, various HIV-1 evasion strategies have been discovered to target NK-cell-receptor ligands and allow the virus to escape from NK cell-mediated immunity. While studies have been mainly focusing on the role of polymorphic HLA-A, -B, and -C molecules, less is known about how HIV-1 affects the more conserved, non-classical HLA-I molecules HLA-E, -G, and -F. In this review, we will focus on the recent progress in understanding the role of non-classical HLA-I ligands in NK cell-mediated recognition of HIV-1-infected cells.

Plasma human leukocyte antigen-G (HLA-G) in patients with thyroid cancer

Background/aim: A number of tumor markers detected in the serum or pathological specimens using immunohistochemical methods are used for early detection of malignancies and postoperative follow-up. Human leukocyte antigen-G (HLA-G) is a nonclassic HLA class I molecule. Recent studies suggested a relationship between HLA-G positivity and the stage or the phenotype of the malignancy. In this study, the relationship between serum HLA-G positivity and thyroid cancer was investigated. Materials and methods: Fifty patients with thyroid cancer and 45 healthy volunteers were included in this study. Serum HLA-G levels were measured using ELISA. Results: HLA-G was positive in only 3 out of 50 patients with thyroid cancer (2 papillary, 1 follicular type). On the other hand, HLA-G was positive in 20 out of 45 healthy subjects (P < 0.001). The prevalence of detectable levels of serum HLA-G was independent of sex and age in the whole study population. No correlation was found between serum HLA-G value and thyroid hormone profile, neither in papillary thyroid cancer nor follicular thyroid cancer patients. Conclusion: In this study, serum HLA-G was significantly less common in patients with thyroid cancer than in healthy controls.

Overexpression of HLA-G Is positively associated with Kazakh esophageal squamous cell carcinoma in Xinjiang, China

HLA-G is a class I HLA that has gained much attention due to its multiple functions in the immune system. More important, some studies found HLA-G may be detrimental in tumors and viral infections, and the detection of HLA-G expression might serve as a clinical marker in the prediction of clinical outcomes for certain types of carcinoma. We assessed the association between the development of Kazakh esophageal squamous cell carcinoma (ESCC) harboring high-risk HPV infection and the expression of HLA-G. The expression of HLA-G was detected by S-P immunohistochemical staining in 60 cases of Kazakh ESCC tissues and 40 cases of Kazakh tumor adjacent normal tissues. HPV16 infection in ESCC was detected by genotype-specific polymerase chain reaction. HPV16 infection rate in Kazakh ESCC was 35.0%, significantly higher than that of the infection rate of the adjacent normal tissues 15% (p<0.05, OR=3.051; 95% CI: 1.103-8.438). The expression of HLA-G in Kazakh ESCC was 75.0% (45/60), significantly higher than that of tumor adjacent normal tissues (17.5%; p<0.05); expression of HLA-G was slightly higher in HPV16-positive than HPV16-negative ESCC, but the difference was not statistically significant (p>0.05). The positive expression rate of HLA-G was closely related to depth of invasion and clinical stage (p<0.05 for all), but was not related to age, sex, tumor location, histologic grade, and nodal status (p>0.05 for all). Overexpression of HLA-G was a characteristic feature of Kazakh ESCC; HLA-G may be involved in Kazakh ESCC carcinogenesis and HPV infection.

Quantified colocalization reveals heterotypic histocompatibility class I antigen associations on trophoblast cell membranes: relevance for human pregnancy

Human placental syncytiotrophoblasts lack expression of most types of human leukocyte antigen (HLA) class I and class II molecules; this is thought to contribute to a successful pregnancy. However, the HLA class Ib antigens HLA-G, -E, and -F and the HLA class Ia antigen HLA-C are selectively expressed on extravillous trophoblast cells, and they are thought to play a major role in controlling feto-maternal tolerance. We have hypothesized that selective expression, coupled with the preferential physical association of pairs of HLA molecules, contribute to the function of HLA at the feto-maternal interface and the maternal recognition of the fetus. We have developed a unique analytical model that allows detection and quantification of the heterotypic physical associations of HLA class I molecules expressed on the membrane of human trophoblast choriocarcinoma cells, ACH-3P and JEG-3. Automated image analysis was used to estimate the degree of overlap of HLA molecules labeled with different fluorochromes. This approach yields an accurate measurement of the degree of colocalization. In both JEG-3 and ACH-3P cells, HLA-C, -E, and -G were detected on the cell membrane, while the expression of HLA-F was restricted to the cytoplasm. Progesterone treatment alone induced a significant increase in the expression level of the HLA-G/HLA-E association, suggesting that this heterotypic association is modulated by this hormone. Our data shows that the cell-surface HLA class I molecules HLA-G, -E, and -C colocalize with each other and have the potential to form preferential heterotypic associations.

HLA class I expression in the human placenta

Placental trophoblast cells of the semi-allogenic human conceptus invade deeply into maternal uterine tissue. From a classical immunoiogic point of view this invasion and the following growth and development of the fetus in the uterus have to be tolerated by a pregnant woman's immune system. Among the various possible protective mechanisms that may be involved, the unique expression pattern of HLA class I molecules seems to be relevant. Besides many other differences between placentation and organ transplantation, this extraordinary HLA class I expression on trophoblast explains why pregnancy should not be considered an immunologic paradox but rather a fascinating example of a very special challenge for the female immune system.

Alternative spliced CD1d transcripts in human bronchial epithelial cells

CD1d is a MHC I like molecule which presents glycolipid to natural killer T (NKT) cells, a group of cells with diverse but critical immune regulatory functions in the immune system. These cells are required for optimal defence against bacterial, viral, protozoan, and fungal infections, and control of immune-pathology and autoimmune diseases. CD1d is expressed on antigen presenting cells but also found on some non-haematopoietic cells. However, it has not been observed on bronchial epithelium, a site of active host defence in the lungs. Here, we identify for the first time, CD1D mRNA variants and CD1d protein expression on human bronchial epithelial cells, describe six alternatively spliced transcripts of this gene in these cells; and show that these variants are specific to epithelial cells. These findings provide the basis for investigations into a role for CD1d in lung mucosal immunity.

Complement activation and pregnancy failure

Pregnancy represents a physiologic condition where maternal immune system tolerates the semi-allogenic fetus. The fetal tissues are directly exposed to the maternal blood with potential attacks from maternal immune system, including the activation of complement cascade. Small amounts, of both early and late components, of complement are physiologically found in the placenta, maybe in relation to the vascular remodeling process. A significant increase of complement activation was associated with different pathologic pregnancy outcomes, namely pre-eclampsia, recurrent spontaneous abortions, intra-uterine growth retardation, and anti-phospholipid syndrome (APS). In some, but not in all, mice models of APS, complement activation plays a major role in pregnancy loss, with a massive accumulation of C3 in the placenta, while C3 deficient mice didn't show fetal resorption. Basing on these findings, anti-phospholipid antibodies and complement activation (via C3a, C5a, and MAC) may cooperate in triggering a local inflammatory process, eventually leading to placental thrombosis, hypoxia, and neutrophil infiltration. However, histological analysis of human placenta tissues from APS women shows small rather than widespread inflammation. In a similar manner, complement activation can be detected in human APS placentas but without any relationship with pregnancy outcome and therapy. Further studies are necessary to investigate whether complement activation and inflammatory processes found in animal models are really taking place in APS.

A major histocompatibility Class I locus contributes to multiple sclerosis susceptibility independently from HLA-DRB1*15:01

Background

In Northern European descended populations, genetic susceptibility for multiple sclerosis (MS) is associated with alleles of the human leukocyte antigen (HLA) Class II gene DRB1. Whether other major histocompatibility complex (MHC) genes contribute to MS susceptibility is controversial.

Methodology/Principal Findings

A case control analysis was performed using 958 single nucleotide polymorphisms (SNPs) spanning the MHC assayed in two independent datasets. The discovery dataset consisted of 1,018 cases and 1,795 controls and the replication dataset was composed of 1,343 cases and 1,379 controls. The most significantly MS-associated SNP in the discovery dataset was rs3135391, a Class II SNP known to tag the HLA-DRB1*15:01 allele, the primary MS susceptibility allele in the MHC (O.R. = 3.04, p<1×10⁻⁷⁸). To control for the effects of the HLA-DRB1*15:01 haplotype, case control analysis was performed adjusting for this HLA-DRB1*15:01 tagging SNP. After correction for multiple comparisons (false discovery rate = .05) 52 SNPs in the Class I, II and III regions were significantly associated with MS susceptibility in both datasets using the Cochran Armitage trend test. The discovery and replication datasets were merged and subjects carrying the HLA-DRB1*15:01 tagging SNP were excluded. Association tests showed that 48 of the 52 replicated SNPs retained significant associations with MS susceptibility independently of the HLA-DRB1*15:01 as defined by the tagging SNP. 20 Class I SNPs were associated with MS susceptibility with p-values ≤1×10⁻⁸. The most significantly associated SNP was rs4959039, a SNP in the downstream un-translated region of the non-classical HLA-G gene (Odds ratio 1.59, 95% CI 1.40, 1.81, p = 8.45×10⁻¹³) and is in linkage disequilibrium with several nearby SNPs. Logistic regression modeling showed that this SNP's contribution to MS susceptibility was independent of the Class II and Class III SNPs identified in this screen.

Conclusions

A MHC Class I locus contributes to MS susceptibility independently of the HLA-DRB1*15:01 haplotype.

Distinct effects of human glioblastoma immunoregulatory molecules programmed cell death ligand-1 (PDL-1) and indoleamine 2,3-dioxygenase (IDO) on tumour-specific T cell functions

Immunotherapy is a promising new treatment for patients suffering from glioma, in particular glioblastoma multiforme (GBM). However, tumour cells use different mechanisms to escape the immune responses induced by the treatment. As many other tumours, gliomas express or secrete several immunosuppressive molecules that regulate immune cell functions. In this study, we first analysed FasL, HLA-G, IDO, PDL-1 and TGF-beta1, -beta2 and -beta3 expression by transcriptomic microarray analysis in a series of 20 GBM samples and found respectively 15%, 60%, 85%, 30%, 70%, 80% and 35% of positive specimens. mRNA expression was then confirmed in 10 GBM primary cell lines and 2 immortalised cell lines U251 and U87MG. Furthermore, the protein expression of PDL-1, IDO activity and TGF-beta2 secretion were found on most of the untreated GBM primary cell lines. Remarkably, treatment with IFN-gamma increased the PDL-1 cell surface expression and the IDO activity, but reduced the TGF-beta2 secretion of GBM cell lines. We finally analysed the immunosuppressive effects of IDO, PDL-1 and TGF-beta1-3 by measuring IFN-gamma production and cell cytotoxicity activity of tumour antigen-specific T cells. PDL-1 partially affected the IFN-gamma production of antigen-specific T cells in response to GBM primary cell lines, and IDO inhibited lymphocyte proliferation induced by lectins. None of these molecules directly affected the T cell cytotoxicity function. Due to the functional role of PDL-1 and IDO molecules expressed by GBM cells, one could expect that blocking these molecules in the immunotherapy strategies would reinforce the efficiency of these treatments of GBM patients.

A genomic and proteomic investigation of the impact of preimplantation factor on human decidual cells

OBJECTIVE

Preimplantation factor (PIF) is a novel, 15 amino acid peptide, secreted by viable embryos. This study aims to elucidate PIF's effects in human endometrial stromal cells (HESC) decidualized by estrogen and progestin, which mimics the preimplantation milieu, and in first-trimester decidua cultures (FTDC).

STUDY DESIGN

HESC or FTDC were incubated with 100 nmol/L synthetic PIF or vehicle control. Global gene expression was analyzed using microarray and pathway analysis. Proteins were analyzed using quantitative mass spectrometry, and PIF binding by protein array.

RESULTS

Gene and proteomic analysis demonstrate that PIF affects immune, adhesion, and apoptotic pathways. Significant up-regulation in HESC (fold change) include: nuclear factor-k-beta activation via interleukin-1 receptor-associated kinase binding protein 1 (53); Toll-like receptor 5 (9); FK506 binding protein 15, 133kDa protein (2.3); and Down syndrome cell adhesion molecule like 1 (16). B-cell lymphoma protein 2 was down-regulated in HESC (21.1) and FTDC (27.1). Protein array demonstrates PIF interaction with intracellular targets insulin-degrading enzyme and beta-K+ channels.

CONCLUSION

PIF displays essential multitargeted effects, of regulating immunity, promoting embryo-decidual adhesion, and regulating adaptive apoptotic processes.

Regulation of a bovine nonclassical major histocompatibility complex class I gene promoter

Studies have shown in humans and other species that the major histocompatibility complex class I (MHC-I) region is involved at a number of levels in the establishment and maintenance of pregnancy. The aim of this study was to characterize how a bovine nonclassical MHC-I gene (NC1) is regulated. Initial serial deletion experiments of a 2-kb fragment of the NC1 promoter identified regions with positive regulatory elements in the proximal promoter and evidence for a silencer module(s) further upstream that cooperatively contributed to constitutive NC1 expression. The cytokines interferon tau (IFNT), interferon gamma (IFNG), and interleukin 4 (IL4) significantly increased luciferase expression in NC1 promoter reporter constructs and endogenous NC1 mRNA levels in a bovine endometrial cell line. In addition, IFNG, IL3, IL4, and progesterone significantly increased Day 7 bovine blastocyst NC1 mRNA expression when supplemented during in vitro embryo culture. Site-directed mutagenesis analysis identified a STAT6 binding site that conferred IL4 responsiveness in the NC1 proximal promoter. Furthermore, methylation treatment of the proximal promoter, which contains a CpG island, completely abrogated constitutive NC1 expression. Overall, the findings presented here suggest that constitutive NC1 expression is regulated positively by elements in the proximal promoter, which are further controlled by upstream silencer modules. The promoter is responsive to IFNT, IFNG, and IL4, suggesting possible roles for these cytokines in bovine preimplantation embryo survival and/or maternal-fetal tolerance. Our studies also suggest that methylation of the proximal promoter, in particular, could play a significant role in regulating NC1 expression.

Immunotherapeutic approaches for glioma

The development of effective immunotherapy strategies for glioma requires adequate understanding of the unique immunological microenvironment in the central nervous system (CNS) and CNS tumors. Although the CNS is often considered to be an immunologically privileged site and poses unique challenges for the delivery of effector cells and molecules, recent advances in technology and discoveries in CNS immunology suggest novel mechanisms that may significantly improve the efficacy of immunotherapy against gliomas. In this review, we first summarize recent advances in the CNS and CNS tumor immunology. We address factors that may promote immune escape of gliomas. We also review advances in passive and active immunotherapy strategies for glioma, with an emphasis on lessons learned from recent early-phase clinical trials. We also discuss novel immunotherapy strategies that have been recently tested in non-CNS tumors and show great potential for application to gliomas. Finally, we discuss how each of these promising strategies can be combined to achieve clinical benefit for patients with gliomas.

A Study of Soluble HLA-G1 Protecting Porcine Endothelial Cells Against Human Natural Killer Cell-Mediated Cytotoxicity

Human natural killer (NK) cells, which can mediate direct lysis of porcine endothelial cells, play an important role in xenograft rejection. HLA-G, which is a critical molecule in maintaining maternal immune tolerance of semi-allogenic fetus, is able to protect susceptible target cells from lysis induced by NK cells. In this study, we investigated whether soluble HLA-G1 (sHLA-G1) protected porcine xenogeneic cells against human NK cell-mediated lysis.

METHODS

The human sHLA-G1 genomic DNA (pcDNA3-sHLA-G1) was transfected into a B lymphoblastoid cell line 721.221 (LCL721.221) by nucleofector. The sHLA-G1 expression of the transfected LCL721.221 cells was identified by RT-PCR and Dot-ELISA. The sHLA-G1 protein was purified by affinity chromatography on anti-HLA-ImAb W6/32 coupled to cyanogen-bromide-activated Sepharose 4B from culture supernates of transfectants. Various concentrations of sHLA-G(1) protein (0, 2, 4, 6, or 8 microg/mL) were added to a NK cell-mediated xenogenic cell lysis system with either NK92 cells or fresh human peripheral blood mononuclear cells (PBMCs) cocultured with the porcine endothelial cells line. A LDH release assay was used to evaluate NK cell-mediated cytotoxicity.

RESULTS

sHLA-G1 provided significant protection of porcine endothelial cells against human NK-mediated cytotoxicity in a dose-dependent manner. The rates of NK92 cell-mediated cytotoxicity were reduced to 83.4 +/- 5.7% (2 microg/mL), 56.6 +/- 9.3% (4 microg/mL), 39.3 +/- 10.2% (6 microg/mL), and 31.2 +/- 4.9% (8 microg/mL) versus 96.9 +/- 3.0% in the control group (P < .01). Similarly, adding 6 microg/mL sHLA-G1 reduced the mean rate of PBMC-mediated cytotoxicity (n = 4) to 5.8 +/- 1.6% from 23.9 +/- 1.3% in the control group (P < .01).

CONCLUSIONS

These results indicated that sHLA-G1 protected xenogeneic porcine endothelial cells against attack by human NK cells, thus providing a new approach to overcome NK-mediated immunity to xenografts.

Activation of NK cells by an endocytosed receptor for soluble HLA-G

Signaling from endosomes is emerging as a mechanism by which selected receptors provide sustained signals distinct from those generated at the plasma membrane. The activity of natural killer (NK) cells, which are important effectors of innate immunity and regulators of adaptive immunity, is controlled primarily by receptors that are at the cell surface. Here we show that cytokine secretion by resting human NK cells is induced by soluble, but not solid-phase, antibodies to the killer cell immunoglobulin-like receptor (KIR) 2DL4, a receptor for human leukocyte antigen (HLA)-G. KIR2DL4 was constitutively internalized into Rab5-positive compartments via a dynamin-dependent process. Soluble HLA-G was endocytosed into KIR2DL4–containing compartments in NK cells and in 293T cells transfected with KIR2DL4. Chemokine secretion induced by KIR2DL4 transfection into 293T cells occurred only with recombinant forms of KIR2DL4 that trafficked to endosomes. The profile of genes up-regulated by KIR2DL4 engagement on resting NK cells revealed a proinflammatory/proangiogenic response. Soluble HLA-G induced secretion of a similar set of cytokines and chemokines. This unique stimulation of resting NK cells by soluble HLA-G, which is endocytosed by KIR2DL4, implies that NK cells may provide useful functions at sites of HLA-G expression, such as promotion of vascularization in maternal decidua during early pregnancy.

KIR2DL4, a human killer cell immunoglobulin receptor expressed on natural killer cells, can be stimulated by soluble antibody or the soluble version of its natural ligand (HLA-G), and may signal from within endosomes.

The complement system in the pathophysiology of pregnancy

A fully active complement system deriving from the maternal circulation as well as from local production by various cell source is present in the placenta. The role of this system at the placental level, as in any other tissue in the body, is to protect both the fetus and the mother against infectious and other toxic agents. As fetal tissues are semi-allogeneic and alloantibodies commonly develop in the mother, the placenta is potentially subject to complement-mediated immune attack at the feto-maternal interface with the potential risk of fetal loss. Uncontrolled complement activation is prevented in successful pregnancy by the three regulatory proteins DAF, MCP and CD59 positioned on the surface of trophoblasts. The critical role played by these complement regulators is supported by the embryonic lethality observed in mice deficient in the complement regulator Crry. Excessive complement activation in the placenta places the fetus at risk for growth restriction or death. The role played by the complement system in the fetal damage induced by anti-phospholipid antibodies in a mouse model will be examined.

Evidence for Expression of Both Classical and Non-Classical Major Histocompatibility Complex Class I Genes in Bovine Trophoblast Cells

PROBLEM

During the third trimester of pregnancy bovine trophoblast cells in the interplacentomal and arcade regions of the placenta express major histocompatibility complex class I (MHC-I) antigens. At parturition immunological recognition of MHC-I antigens appears to contribute to normal placental release. Therefore, we hypothesized that during late pregnancy bovine trophoblast cells express polymorphic, classical MHC-I antigens.

METHOD OF STUDY

Cloning, microarray screening and sequencing of cDNA were used to study transcription of MHC-I genes in peripheral blood mononuclear cells (PBMC) and interplacentomal, trophoblast cells. Real-time reverse transcription, polymerase chain reaction (RT-PCR) was used to compare the abundance of MHC-I transcripts in PBMC and trophoblast cells.

RESULTS

Screening of cloned MHC-I cDNA on MHC-I microarrays indicated that in PBMC 90-98% of MHC-I transcripts were encoded by classical MHC-I genes with the remainder encoded by non-classical MHC-I genes. In contrast, 21-66% of MHC-I transcripts from interplacentomal trophoblast cells were from classical genes and 34-79% were from non-classical genes. Transcripts from four non-classical MHC-I loci were identified by sequence analysis. Real-time RT-PCR indicated that the overall levels of MHC-I gene expression in PBMC and trophoblast were similar.

CONCLUSION

Bovine interplacentomal trophoblast cells express both classical and non-classical MHC-I genes, but the relative level of expression varies considerably.

The production, purification and crystallization of a soluble form of the nonclassical MHC HLA-G: the essential role of cobalt

HLA-G is a nonclassical class I major histocompatibility complex (MHC) molecule that is primarily expressed at the foetal-maternal interface. Although the role of HLA-G has not been fully elucidated, current evidence suggests it protects the foetus from the maternal immune response. In this report, HLA-G (44 kDa) is characterized by expression in Escherichia coli. The inclusion bodies were refolded in complex with a peptide derived from histone H2A (RIIPRHLQL), purified and subsequently crystallized. Correct refolding was determined using two conformation-dependent antibodies. Cobalt ions were shown to be an essential ingredient for obtaining diffraction-quality crystals. The crystals, which diffracted to 1.9 A resolution, belonged to space group P3(2)2(1), with unit-cell parameters a = b = 77.15, c = 151.72 A.

The CD85J/leukocyte inhibitory receptor-1 distinguishes between conformed and beta 2-microglobulin-free HLA-G molecules

For a proper development of the placenta, maternal NK cells should not attack the fetal extravillous cytotrophoblast cells. This inhibition of maternal NK cells is partially mediated via the nonclassical MHC class I molecule HLA-G. Recently, we demonstrated that HLA-G forms disulfide-linked high molecular complexes on the surface of transfected cells. In the present study, we demonstrate that HLA-G must associate with beta(2)m for its interaction with CD85J/leukocyte Ig-like receptor-1 (LIR-1). Although HLA-G free H chain complexes are expressed on the surface, they are not recognized and possibly interfere with CD85J/LIR-1 and HLA-G interaction. The formation of these complexes on the cell surface might represent a novel mechanism developed specifically by the HLA-G protein aimed to control the efficiency of the CD85J/LIR-1-mediated inhibition. We also show that endogenous HLA-G complexes are expressed on the cell surface. These findings provide novel insights into the delicate interaction between extravillous cytotrophoblast cells and NK cells in the decidua.

Differential Expression of Alternatively Spliced Transcripts of HLA-G in Human Preimplantation Embryos and Inner Cell Masses

It has been reported that preimplantation human embryos secrete HLA-G, and the levels may be predictive of their ability to implant. However, it is not known which of the membrane-bound (HLA-G 1-4) and soluble (HLA-G 5-6) alternatively spliced forms are present, nor the developmental stage at which they appear. Therefore, we have investigated HLA-G mRNA isoform expression on single embryos at the two-, four-, six-, and eight-cell, morula, and blastocyst stages. The percentage of embryos expressing each HLA-G isoform mRNA increased with developmental stage, but contrary to expectation, HLA-G5 mRNA was not detected in single two- to eight-cell embryos and was only expressed by 20% of morulae and blastocysts. Similarly, soluble HLA-G6 mRNA was not detected until the blastocyst stage and then in only one-third of embryos. In contrast, labeling with MEM G/9 Ab (specific for HLA-G1 and -G5) was observed in 15 of 20 two- to eight-cell embryos and 5 of 5 blastocysts. This disparity between mRNA and protein may be due to HLA-G protein remaining from maternal oocyte stores produced before embryonic genome activation and brings into question the measurement of soluble HLA-G for clinical evaluation of embryo quality. Although HLA-G is expressed in the preimplantation embryo, later it is primarily expressed in the invasive trophoblast of the placenta rather than the fetus. Therefore, we have investigated whether down-regulation of HLA-G first occurs in the inner cell mass (precursor fetal cells) of the blastocyst and, in support of this concept, have shown the absence HLA-G1 and -G5 protein and mRNA.

A novel sandwich ELISA for alpha1 domain based detection of soluble HLA-G heavy chains

The detection of soluble human leukocyte antigen G (HLA-G) has been a technically demanding task for several years now and various enzyme linked immunosorbent assay (ELISA) formats have been designed. However, no ELISA test has been described so far which is able to detect all possible kinds of soluble HLA-G (sHLA-G) molecules that might occur in bio fluids. Here we describe a new ELISA approach able to recognize soluble alpha1 domain containing heavy chains of all HLA-G isoforms. The detection limit is shown to be at about 150 pg soluble recombinant HLA-G1 heavy chain per milliliters. Detectable HLA-G fragments are shown to occur in the supernatants of different HLA-G transfected cell lines and appear to be particularly abundant in supernatant of trophoblast derived choriocarcinoma cell lines. The novel ELISA employs the well characterized HLA-G mAbs 4H84 and MEM-G1 which ensure high HLA-G specificity. A negative control ELISA format, designed against non-existing analytes, has been established to reveal non-specific signal interference.

Less HLA-G expression in Plasmodium falciparum-infected third trimester placentas is associated with more natural killer cells

During pregnancy, maternal immune tolerance of the fetal semi-allogeneic graft is partly the consequence of extravillous trophoblast HLA-G expression and its interaction with natural killer (NK) cells. Plasmodium falciparum malaria is frequently associated with maternal and fetal complications. Local HLA-G expression and the number of NK cells were evaluated immunohistochemically in P. falciparum-infected and uninfected placentas (15 each) collected in a seasonal malaria-hypoendemic area. In control placentas, HLA-G was almost always expressed in extravillous trophoblast whereas, in infected placentas, it was significantly more weakly expressed in extravillous trophoblast but was also detected in intervillous space macrophages. NK cells were evaluated in intervillous and intravillous spaces and in basal plate. NK cells were always more abundant in basal plate than in intervillous and intravillous spaces in infected or control placentas. For each area, more NK cells were seen in infected than control placentas. These data suggest that HLA-G down-regulation and more NK cells in placentas may be among the mechanisms involved in poor birth outcome associated with P. falciparum infection.

β2-Microglobulin required for cell surface expression of blastocyst MHC

Blastocyst MHC is a mouse MHC class Ib gene that is selectively expressed in blastocysts and placenta like human HLA-G, which protect fetal trophoblasts and some tumor cells from NK cell attack, and in TAP-dependent expression on the cell surface. We expressed blastocyst MHC cDNA in beta2-deficient EL-4 S3 or beta2m-transfected EL-4 S3 cells. In parental EL-4 S3 cells, only 47-kDa blastocyst MHC protein was expressed and retained in the cytoplasm. However, additional 51-kDa blastocyst MHC protein was expressed on the surface of beta2m-transfected EL-4 S3 cells. The 51-kDa protein was resistant to Endo-H, whereas the 47-kDa protein was sensitive for Endo-H. The results suggested that beta2m as well as TAP was necessary for the transportation of blastocyst MHC from endoplasmic reticulum to cell surfaces through the Golgi apparatus, similar to other MHC class I molecules.

Lack of Histocompatibility Leukocyte Antigen-G expression in early embryos is not related to germinal defects or impairment of interleukin-10 production by embryos

The expression of Histocompatibility Leukocyte Antigen (HLA)-G molecules is a mandatory prerequisite for the development of pregnancy but no hypotheses have yet been advanced regarding the lack of HLA-G modulation expression in a percentage of early embryos obtained by in vitro fertilization (IVF). One possible hypothetical model assumes that the absence of regulation of HLA-G or impaired interleukin (IL)-10 secretion could be related to germinal defects. We investigated the presence of soluble HLA-G antigens in supernatants of single embryo cultures from couples admitted to a second fertilization procedure; these couples showed a complete absence of HLA-G modulation in the first cycle's embryo supernatants (0/31). The results obtained in the second IVF cycle showed embryo supernatants positive for HLA-G (14/40), suggesting that the previous lack of antigen modulation is independent of germinal defects. Furthermore, since it has been reported that oocytes and early embryos can secrete IL-10, an anti-inflammatory cytokine produced by type 2 helper T cells that induces upregulation of HLA-G expression in monocytes and trophoblasts, we investigated the levels of IL-10 and soluble HLA-G in 40 embryo culture supernatants from 21 IVF cycles. No associations were observed between the presence of IL-10 and the production and concentrations of soluble HLA-G, or between IL-10 levels and pregnancy outcome. These results indicate that the lack of HLA-G production in early embryos is not related to germinal defects or to impairment in embryo IL-10 secretion but could be ascribed to possible uncorrected fertilization processes.

Crystal structure of HLA-G: a nonclassical MHC class I molecule expressed at the fetal-maternal interface

HLA-G is a nonclassical major histocompatibility complex class I (MHC-I) molecule that is primarily expressed at the fetal-maternal interface, where it is thought to play a role in protecting the fetus from the maternal immune response. HLA-G binds a limited repertoire of peptides and interacts with the inhibitory leukocyte Ig-like receptors LIR-1 and LIR-2 and possibly with certain natural killer cell receptors. To gain further insights into HLA-G function, we determined the 1.9-A structure of a monomeric HLA-G complexed to a natural endogenous peptide ligand from histone H2A (RIIPRHLQL). An extensive network of contacts between the peptide and the antigen-binding cleft reveal a constrained mode of binding reminiscent of the nonclassical HLA-E molecule, thereby providing a structural basis for the limited peptide repertoire of HLA-G. The alpha3 domain of HLA-G, a candidate binding site for the LIR-1 and -2 inhibitory receptors, is structurally distinct from the alpha3 domains of classical MHC-I molecules, providing a rationale for the observed affinity differences for these ligands. The structural data suggest a head-to-tail mode of dimerization, mediated by an intermolecular disulfide bond, that is consistent with the observation of HLA-G dimers on the cell surface.

The 4H84 monoclonal antibody detecting beta2m free nonclassical HLA-G molecules also binds to free heavy chains of classical HLA class I antigens present on activated lymphocytes

We have found that 4H84 monoclonal antibody (mAb) used for detection of beta2m free HLA-G molecules also binds to free heavy chains of classical HLA class I antigens generated on the cell surface by mild acid treatment. Here we demonstrate that beta2m free classical HLA class I molecules induced on the surface of activated lymphocytes not expressing HLA-G also bind 4H84 mAb. These results demonstrate that 4H84 mAb should be used for detection of HLA-G in cells and tissues with backing by other HLA-G specific mAbs.

Inhibition of the activating signals in NK92 cells by recombinant GST-sHLA-G1a chain

The soluble HLA-G1 (sHLA-G1) isoform was found to be secreted by trophoblast cells at the materno-fetal interface, which suggests that it may act as an immunomodulator during pregnancy. In this paper, we reported that GST-sHLA-G1a chain could bind to its receptor ILT-2 on NK92 cells and then the latter recruited Src homology 2 domain-containing tyrosine phosphatase-1 (SHP-1), which consequently dephosphorylated some important protein tyrosine kinases and blocked the activation of downstream molecules such as MEK and ERK so that the cytotoxicity of natural killer (NK) cells was inhibited. These results indicated that GST-sHLA-G1a chain might be exploited in new immunotherapy strategies aiming at inducing immunotolerance during allograft, xenograft and autoimmune situations. In addition, we found that modification of O-linked b-N-acetylglucosamine (O-GlcNAc) was involved in NK cells' activating and inhibitory signals. This may provide a novel molecular target for inducing immunotolerance but needs further study.

Intrahepatic gene expression during chronic hepatitis C virus infection in chimpanzees

Hepatitis C virus (HCV) infections represent a global health problem and are a major contributor to end-stage liver disease including cirrhosis and hepatocellular carcinoma. An improved understanding of the parameters involved in disease progression is needed to develop better therapies and diagnostic markers of disease manifestation. To better understand the dynamics of host gene expression resulting from persistent virus infection, DNA microarray analyses were conducted on livers from 10 chimpanzees persistently infected with HCV. A total of 162 genes were differentially regulated in chronically infected animals compared to uninfected controls. Many genes exhibited a remarkable consistency in changes in expression in the 10 chronically infected animals. A second method of analysis identified 971 genes altered in expression during chronic infection at a 99% confidence level. As with acute-resolving HCV infections, many interferon (IFN)-stimulated genes (ISGs) were transcriptionally elevated, suggesting an ongoing response to IFN and/or double-stranded RNA which is amplified in downstream ISG expression. Thus, persistent infection with HCV results in a complex and partially predictable pattern of gene expression, although the underlying mechanisms regulating the different pathways are not well defined. A single genotype 3-infected animal was available for analysis, and this animal exhibited reduced levels of ISG expression compared to levels of expression with genotype 1 infections and increased expression of a number of genes potentially involved in steatosis. Gene expression data in concert with other observations from HCV infections permit speculation on the regulation of specific aspects of HCV infection.

Evidence that HLA-G is the functional homolog of mouse Qa-2, the Ped gene product

Qa-2, a murine class Ib major histocompatibility complex (MHC) molecule, is a possible functional homolog of human leukocyte antigen G (HLA-G). Both molecules have been implicated in immunoregulation and embryonic development and both occur in membrane-bound and soluble isoforms that arise by alternative splicing. Soluble splice variants have been implicated in the reproductive functions of HLA-G. While soluble variants of Qa-2 have been previously detected in T lymphocytes, we now demonstrate the presence of mRNA for one of the two known soluble forms of Qa-2 in eight-cell embryos and in blastocysts. Qa-2 is glycosylphosphatidylinositol (GPI) linked in the outer leaflet of the cell membrane and is found in lipid raft microdomains where other raft-associated proteins transduce signals into the cell. In contrast, HLA-G has a truncated six amino acid cytoplasmic tail. By fluorescence co-localization in JEG-3 cells, using fluorescent cholera toxin beta subunit (a lipid raft marker) and anti-HLA-G antibody, we have demonstrated that membrane-bound HLA-G also localizes to lipid rafts, consistent with functional homology between the two molecules. Finally, our experiments in which we have purified Qa-2 and transferred it via a process known as protein painting to Qa-2 negative cells represent a model for potential therapy involving HLA-G.

Major histocompatibility antigen expression on the bovine placenta: its relationship to abnormal pregnancies and retained placenta

In viviparous animals, regulation of expression of major histocompatibility complex (MHC) class I antigens by the trophoblast cells, which constitute the outermost layer of the placenta, seems to be critical for maternal immunological acceptance of an allogeneic fetus. Cattle are unusual in this regard, since the bovine trophoblast cells, in specific regions of the uterine/placental interface, normally express MHC class I antigens during the third trimester of gestation. This expression appears to be biologically relevant as MHC class I compatibility between a cow and her fetus has been associated with an increased incidence of placental retention. We have found significant differences in lymphocyte populations, cytokine production, and trophoblast cell apoptosis in the placentomes of MHC-compatible and -incompatible pregnancies at parturition. This suggests that maternal immunological recognition of fetal MHC class I proteins triggers an immune/inflammatory response that contributes to placental separation at parturition in cattle. Early in pregnancy, a complete shutdown of MHC class I expression by trophoblast cells appears to be critical for normal placental development and fetal survival. In bovine somatic cell nuclear transfer (SCNT) pregnancies, there is an extremely high rate of fetal loss between days 30 and 90 of pregnancy. We have shown that in bovine SCNT pregnancies, between days 34 and 63 of gestation, there is both abnormal expression of MHC class I antigens by trophoblast cells and an abnormal accumulation of lymphocytes within the uterine stroma. Consequently, it is likely that activation of the maternal mucosal immune system, within the uterus at the same time when placentomes are being established, interferes with the process of placentome development and leads to immune-mediated abortion. Our data suggest that bovine MHC-compatible pregnancies provide a unique model for studying regulation of the uterine immune system, as well as immune-mediated placental rejection.

Cytokines, implantation and early abortion: re-examining the Th1/Th2 paradigm leads to question the single pathway, single therapy concept

PROBLEM

Human in vitro fertilization (IVF) embryo transfer is accompanied by a low implantation rate even after a very successful IVF, and there are a certain number of 'idiopathic sterilities' which are due to repeated implantation failures. In the very same vein, the question of improving implantation rates is of prime importance in agricultural research to improve the management of livestock. Preimplantation prenatal diagnosis cannot be accomplished in individuals who have a high rate of implantation failure, whether women undergoing IVF, or animals, during genetic cloning. Implantation cytokine networks need to be known in such a perspective.

METHODS

We review the evolution and theories in reproductive immunology, briefly deal with the complexity of implantation as a step by step developmental event, and then present some of our recent data in mice and human.

CONCLUSIONS

We conclude that the T helper cell type 1/2 (Th1/ Th2) paradigm, as useful as it has been to explain pregnancy, is no longer sufficient in view of the emerging complexity of the cytokine network at the materno-fetal interface. This is peculiarly true for implantation, which, as a step by step developmentally regulated process, involving inflammatory molecules, cannot fit into such a scheme.

Human cytomegalovirus-encoded US2 differentially affects surface expression of MHC class I locus products and targets membrane-bound, but not soluble HLA-G1 for degradation

Human CMV (HCMV) can elude CTL as well as NK cells by modulating surface expression of MHC class I molecules. This strategy would be most efficient if the virus would selectively down-regulate viral Ag-presenting alleles, while at the same time preserving other alleles to act as inhibitors of NK cell activation. We focused on the HCMV unique short (US) region encoded protein US2, which binds to newly synthesized MHC class I H chains and supports their dislocation to the cytosol for subsequent degradation by proteasomes. We studied the effect of US2 on surface expression of individual class I locus products using flow cytometry. Our results were combined with crystal structure data of complexed US2/HLA-A2/beta(2)-microglobulin and alignments of 948 HLA class I database sequences of the endoplasmic reticulum lumenal region inplicated in US2 binding. This study suggests that surface expression of all HLA-A and -G and most HLA-B alleles will be affected by US2. Several HLA-B alleles and all HLA-C and -E alleles are likely to be insensitive to US2-mediated degradation. We also found that the MHC class I endoplasmic reticulum-lumenal domain alone is not sufficient for degradation by US2, as illustrated by the stability of soluble HLA-G1 in the presence of US2. Furthermore, we showed that the membrane-bound HLA-G1 isoform, but also tailless HLA-A2, are targeted for degradation. This indicates that the cytoplasmic tail of the MHC class I H chain is not required for its dislocation to the cytosol by US2.

Down-regulation of HLA-G1 cell surface expression in human cytomegalovirus infected cells

PROBLEM

Down-modulation of human leukocyte antigen (HLA)-G1 cell surface expression by human cytomegalovirus (HCMV) has only been studied in cellular models expressing independent unique short (US) recombinant proteins, but not in the context of viral infection. To explore the level of HLA-G1 cell surface expression after HCMV infection and to investigate the influence of US viral proteins, we infected HLA-G1 expressing cells by HCMV laboratory strains.

METHOD OF STUDY

Human U373-MG astrocytoma cells were transfected with HLA-G1 cDNA. Following HCMV infection, HLA-G1 cell surface expression of these transfectants was evaluated by flow cytometry and confocal microscopy, using an HLA-G specific monoclonal antibody, and compared with that of uninfected cells. US-deleted viruses were then used to evaluate the implication of US proteins.

RESULTS

Using flow cytometry, it was found that HCMV infection of U373-G1 cells decreased HLA-G1 cell surface expression. Similar results were obtained with two different HCMV strains, namely Towne and AD169. Two color confocal microscopy staining further confirmed such HLA-G down-modulation in HCMV-infected cells stained for immediate early (IE1/2) nuclear proteins expression. Infection of U373-G1 cells with US-deleted HCMV strain had no effect on the level of cell surface HLA-G1 expression, thus demonstrating the US dependency of the HCMV-mediated down-regulation of HLA-G1.

CONCLUSION

HCMV infection down-modulates HLA-G1 expression at the cell surface. This is likely to have functional consequences in case of HCMV uterine infection during pregnancy.

Presence of detectable levels of soluble HLA-G molecules in CSF of relapsing-remitting multiple sclerosis: relationship with CSF soluble HLA-I and IL-10 concentrations and MRI findings

We have investigated the presence of non-classical soluble HLA-G molecules (sHLA-G) in cerebrospinal fluid (CSF) of multiple sclerosis (MS) patients and the possible relationships between CSF levels of sHLA-G, classical soluble HLA-I (sHLA-I) molecules, IL-10 amounts and Magnetic Resonance Imaging (MRI) findings were evaluated. We studied by ELISA technique the sHLA-I, sHLA-G and IL-10 levels in CSF of 50 relapsing-remitting (RR) MS patients stratified according to clinical and MRI evidence of disease activity. Thirty-six patients with other inflammatory neurological disorders (OIND) and 41 with non-inflammatory neurological disorders (NIND) were used as controls. CSF mean levels were significantly higher in MS and OIND than in NIND for sHLA-I (p<0.001) and in MS than in controls for sHLA-G (p<0.001), with no differences among the various groups for IL-10 mean concentrations. An increase in CSF sHLA-I was found in MS patients with Gd-enhancing lesions (p<0.01), while sHLA-G and IL-10 were more represented in MS patients without lesional activity on MRI scans (p<0.02). In MRI-inactive MS, CSF IL-10 mean concentrations were significantly greater in patients with CSF-detectable levels of sHLA-G than in those without any evidence of CSF sHLA-G expression (p<0.05). Our findings suggest that CSF classical sHLA-I and non-classical sHLA-G levels may modulate MS activity as assessed by MRI acting in opposite directions. The association observed between sHLA-G and IL-10 when Gd-enhancing lesion resolved indicates a potential immunoregulatory role for IL-10 in the control of MS disease activity by shifting the sHLA-I/sHLA-G balance towards sHLA-G response.

Tolerance of the fetus by the maternal immune system: role of inflammatory mediators at the feto-maternal interface

The adaptive immune system of placental mammals has evolved to tolerate the fetus. Rejection of the fetus by adaptive immune responses is therefore a rare event, with abortion being caused more frequently by inflammation in the placenta. This review will cover recent aspects of immune privilege and the innate immune system at the feto-maternal interface, citing examples of the role played by microbial infections in fetal demise.

A subclass of soluble HLA-G1 modulates the release of cytokines from mononuclear cells present in the decidua additively to membrane-bound HLA-G1

PROBLEM

Our previous studies have demonstrated that a subclass of soluble human leukocyte antigen-G1 protein (sub-sHLA-G1), that has alpha1 to alpha3 extra-cellular portion but lacks C-terminus of authentic soluble HLA-G1 secreted by trophoblasts, fine-tunes the release of cytokines from peripheral blood mononuclear cells (PBMCs) chiefly by counterbalancing membrane-bound HLA-G1 (mHLA-G1), and thereby may play a role in maintaining pregnancy. In this study, we investigated whether the presence of sHLA-G1 protein altered the release of cytokines from decidual mononuclear cells (DMCs) which are localized at the interface of feto-maternal interaction and whose cell population is completely different from PBMCs.

METHOD OF STUDY

We cultured peripheral DMCs with either HLA-A and -B lacking B lymphoblast cell line (721.221 cells) or the cells transfected with mHLA-G1 (721.221-G1 cells) with or without sub-sHLA-G1. Cytokines concentrations in the culture media were determined by an enzyme-linked immunosorbent assay.

RESULTS

Regardless of the presence of mHLA-G1 expressing cells, the addition of the recombinant sub-sHLA-G1 protein in the DMC culture media decreased the amounts of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma, with the release of IL-4 from DMCs being unchanged.

CONCLUSION

The sub-sHLA-G1 protein modulates the release of cytokines from DMCs additively to mHLA-G1 expressing cells. In view of the distinct fetomaternal interaction during implantation, it appears that sHLA-G1 might play a role in the establishment of pregnancy by regulating cytokine release in concert with mHLA-G1.