HLA-G genotype and HLA-G expression in systemic lupus erythematosus: HLA-G as a putative susceptibility gene in systemic lupus erythematosus

Association of HLA-G 3' untranslated region indel polymorphism and its serum expression with susceptibility to colorectal cancer

Background: Colorectal cancer (CRC) is a significant global health challenge with increasing incidence and mortality rates in developing countries. Genome-wide association studies have identified new low-penetrance genetic variants linked to CRC. This study aimed to explore the relationship between HLA-G polymorphism and serum expression with CRC. Methodology: In a case-control configuration, standard PCR was used for genotyping HLA-G 3' indel polymorphism and ELISA for quantifying soluble HLA-G in plasma. Results: The study revealed a significant association between the rs371194629 deletion allele and CRC, as well as higher soluble HLA-G levels in CRC patients. Conclusion: These findings suggest that HLA-G could be a promising biomarker for CRC, and further research could lead to improved screening and treatment for more personalized care.

Evidence for Epistatic Interaction between HLA-G and LILRB1 in the Pathogenesis of Nonsegmental Vitiligo

Vitiligo is the most frequent cause of depigmentation worldwide. Genetic association studies have discovered about 50 loci associated with disease, many with immunological functions. Among them is HLA-G, which modulates immunity by interacting with specific inhibitory receptors, mainly LILRB1 and LILRB2. Here we investigated the LILRB1 and LILRB2 association with vitiligo risk and evaluated the possible role of interactions between HLA-G and its receptors in this pathogenesis. We tested the association of the polymorphisms of HLA-G, LILRB1, and LILRB2 with vitiligo using logistic regression along with adjustment by ancestry. Further, methods based on the multifactor dimensionality reduction (MDR) approach (MDR v.3.0.2, GMDR v.0.9, and MB-MDR) were used to detect potential epistatic interactions between polymorphisms from the three genes. An interaction involving rs9380142 and rs2114511 polymorphisms was identified by all methods used. The polymorphism rs9380142 is an HLA-G 3'UTR variant (+3187) with a well-established role in mRNA stability. The polymorphism rs2114511 is located in the exonic region of LILRB1. Although no association involving this SNP has been reported, ChIP-Seq experiments have identified this position as an EBF1 binding site. These results highlight the role of an epistatic interaction between HLA-G and LILRB1 in vitiligo pathogenesis.

CD83 Regulates the Immune Responses in Inflammatory Disorders

Activating the immune system plays an important role in maintaining physiological homeostasis and defending the body against harmful infections. However, abnormalities in the immune response can lead to various immunopathological responses and severe inflammation. The activation of dendritic cells (DCs) can influence immunological responses by promoting the differentiation of T cells into various functional subtypes crucial for the eradication of pathogens. CD83 is a molecule known to be expressed on mature DCs, activated B cells, and T cells. Two isotypes of CD83, a membrane-bound form and a soluble form, are subjects of extensive scientific research. It has been suggested that CD83 is not only a ubiquitous co-stimulatory molecule but also a crucial player in monitoring and resolving inflammatory reactions. Although CD83 has been involved in immunological responses, its functions in autoimmune diseases and effects on pathogen immune evasion remain unclear. Herein, we outline current immunological findings and the proposed function of CD83 in inflammatory disorders.

The double-sided of human leukocyte antigen-G molecules in type 1 autoimmune hepatitis

The immunomodulatory effects of HLA-G expression and its role in cancers, human liver infections and liver transplantation are well documented, but so far, there are only a few reports addressing autoimmune liver diseases, particularly autoimmune hepatitis (AIH).

3'UTR-HLA-G polymorphisms and circulating sHLA-G are associated with breast cancer: Evidence from a meta-analysis

BACKGROUND

Human leukocyte antigen-G (HLA-G) gene polymorphisms and circulating sHLA-G have often been linked to the risk of breast cancer (BC). However, the results remain controversial. To resolve this issue, we performed a meta-analysis of HLA-G gene polymorphisms and sHLA-G levels in BC.

METHODS

We performed a meta-analysis on the association of HLA-G 14-bp Insertion/Deletion (Ins/Del) and HLA-G +3142 C/G polymorphisms with BC as well as the relationship between sHLA-G and the disease outcome.

RESULTS

Pooled analysis showed a statistically significant association between the HLA-G 14-bp Ins/Del polymorphism and BC susceptibility for the overall population and for Caucasians. The Del allele and genotypes with at least one copy of the Del allele presented significant risks for BC. For HLA-G +3142 C/G polymorphism, the G allele significantly decreased the risk of BC for the overall population and for Caucasians, indicating that the G allele was a protective factor against BC and that the C allele was a significant risk factor for BC. The meta-analysis revealed a significantly increased level of sHLA-G patients with BC compared to the control group for the overall population, Caucasians and Asians.

CONCLUSION

The present meta-analysis showed a major association of both HLA-G 14-bp Ins/Del and +3142 C/G polymorphisms with BC susceptibility, suggesting Del and C variants as highly significant risk factors for BC. The present study also showed significantly higher sHLA-G levels in patients with BC compared to healthy controls. Our pooled results suggested a critical role of HLA-G in BC, thereby providing evidence to use HLA-G as a biomarker and a therapeutic tool.

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.

Association between exonic polymorphisms of human leukocyte antigen-G gene and non-segmental vitiligo in the Korean population

BACKGROUND

Vitiligo is a pigmentary skin disorder characterised by a chronic and progressive loss of melanocytes. Although several theories have been suggested to the pathogenesis of vitiligo, an autoimmune process leading to melanocyte destruction appears most likely. Human leukocyte antigen-G is a non-classic, major histocompatibility complex Class I molecule that plays an important role in the suppression of the immune response. Several recent studies have provided evidences that polymorphisms in the human leukocyte antigen-G gene might be related with autoimmune diseases.

OBJECTIVES

The aim of this study was to decide whether exonic single nucleotide polymorphisms in human leukocyte antigen-G contribute to the risk of developing non-segmental vitiligo in the Korean population.

METHODS

To evaluate the associations between exonic single nucleotide polymorphisms (rs1630223 [Ala5Ala] and rs12722477 [Leu134Ile]) of human leukocyte antigen-G and vitiligo, 244 patients with vitiligo and 398 healthy controls were recruited. Genotyping was performed using Fluidigm 192.24 Dynamic Array with EP1 (Fluidigm Corp., CA). The SNP type assay (Fluidigm Corp., CA), which employs allele-specifically designed fluorescences (FAM or VIC) primers and a common reverse primer was applied and the data were analysed using the EP1 single nucleotide polymorphisms genotyping analysis software to obtain genotype calls.

RESULTS

Two exonic single nucleotide polymorphisms (rs1630223 and rs12722477) exhibited significant associations with susceptibility and remained a statistically significant association following Bonferroni correction. These two single nucleotide polymorphisms were located within a block of linkage disequilibrium. Haplotypes G-C and A-A comprising rs1630223 and rs12722477 demonstrated a significant association with non-segmental vitiligo.

LIMITATIONS

The protein expression level of patients with vitiligo and controls was not studied and a replication study of the genetic association in an independent group was not managed.

CONCLUSION

Our results suggest that exonic human leukocyte antigen-G polymorphisms (rs1630223 and rs12722477) are associated with the development of non-segmental vitiligo.

HLA-G: Too Much or Too Little? Role in Cancer and Autoimmune Disease

HLA-G is a non-classical HLA class I molecule with immunomodulatory properties. It was initially described at the maternal-fetal interface, and it was later found that this molecule was constitutively expressed on certain immuneprivileged tissues, such as cornea, endothelial and erythroid precursors, and thymus. The immunosuppressive effect of HLA-G is exerted through the interaction with its cognate receptors, expressed on immunocompetent cells, like ILT2, expressed on NK, B, T cells and APCs; ILT4, on APCs; KIR, found on the surface of NK cells; and finally, the co-receptor CD8. Because of these immunomodulatory functions, HLA-G has been involved in several processes, amongst which organ transplantation, viral infections, cancer progression, and autoimmunity. HLA-G neo-expression on tumors has been recently described in several types of malignancies. In fact, tumor progression is tightly linked to the presence of the molecule, as it exerts its tolerogenic function, inhibiting the cells of the immune system and favoring tumor escape. Several polymorphisms in the 3’UTR region condition changes in HLA-G expression (14bp and +3142C/G, among others), which have been associated with both the development and outcome of patients with different tumor types. Also, in recent years, several studies have shown that HLA-G plays an important role in the control of autoimmune diseases. The ability of HLA-G to limit the progression of these diseases has been confirmed and, in fact, levels of the molecule and several of its polymorphisms have been associated with increased susceptibility to the development of autoimmune diseases, as well as increased disease severity. Thus, modulating HLA-G expression in target tissues of oncology patients or patients with autoimmune diseases may be potential therapeutic approaches to treat these pathological conditions.

Serum levels of soluble HLA-G correlate with disease activity in pediatric patients with Crohn's disease

BACKGROUND

Human leukocyte antigen (HLA)-G, a member of the HLA family, is crucial for fetomaternal tolerance. Transmembrane or circulating/soluble HLA-G (sHLA-G) is elevated in autoimmune conditions and the tumor microenvironment. Circulating sHLA-G levels and their association with disease activity have not yet been assessed in pediatric patients with inflammatory bowel disease (IBD). This study aimed to quantify the serum sHLA-G levels of pediatric patients with IBD and assess the association of serum sHLA-G with disease activity.

METHODS

: We enrolled 24 pediatric IBD patients Crohn's disease (CD) and ulcerative colitis (UC), n = 12 each] and 24 healthy controls. Based on the disease activity index, five and seven of the CD patients had mild and moderate/severe disease, respectively, whereas six of the UC patients were in remission and six had mild disease. Serum was collected and sHLA-G levels were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

: Pediatric patients with CD had significantly higher sHLA-G levels compared with patients with UC and healthy controls. Notably, serum sHLA-G levels were significantly higher in patients with moderate/severe CD than in those with mild CD.

CONCLUSIONS

: Serum sHLA-G levels correlate with disease activity in pediatric patients with CD and are higher in CD patients than in UC patients. Thus, sHLA-G is a potential biomarker for disease activity in CD.

Immunogenetic Relationship of HLA-G 14 bp Insertion/Deletion Polymorphism and Toll-Like Receptor 9 with Systemic Lupus Erythematosus in Egyptian Patients: A Case-Control Study

Introduction

The level of expression of the immunoregulatory human leukocyte antigen-G (HLA-G) has been suggested to play a role in the immunopathogenesis of systemic lupus erythematosus (SLE). A 14 bp insertion/deletion (ins/del) polymorphism in the 3ˊuntranslated region of HLA-G gene may influence the level of expression. The role of Toll-like receptor 9 (TLR9) in the pathogenesis of SLE has been highlighted. Data among Egyptian patients are quite limited.

Purpose

To detect the association of HLA-G 14 bp ins/del gene polymorphism with the susceptibility to SLE and to correlate TLR9 serum level with disease activity among Egyptian patients.

Patients and Methods

A case-control study that included 102 SLE female patients and 102 healthy matched volunteers as controls was carried out. Disease activity in patients was determined using the modified Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). HLA-G 14 bp ins/del genotype was detected by polymerase chain reaction (PCR). TLR9 serum level was estimated using enzyme-linked immunosorbent assay (ELISA) technique.

Results

The ins/ins genotype was significantly increased among SLE patients compared to healthy subjects (58.8% vs 9.8%; odds ratio [OR] = 11.79, P < 0.001). The 14 bp ins allele was significantly more frequent in SLE patients than in healthy subjects (65.7% vs 27.9%, respectively) and significantly associated with an increased risk of SLE (OR 4.94, P < 0.001). The mean TLR9 serum level showed a significant increase in SLE patients compared to healthy subjects (397.04±137.86 vs 195.22±45.14 ng/L, p < 0.001) and was significantly associated with disease activity as well as to patients’ HLA-G genotypes (p < 0.001).

Conclusion

Among Egyptian population, HLA-G 14 bp ins/ins homozygous genotype and ins allele may constitute a potential risk for SLE susceptibility, while TLR9 serum level is significantly associated with disease activity.

The HLA-G Immune Checkpoint Plays a Pivotal Role in the Regulation of Immune Response in Autoimmune Diseases

The human G-leukocyte antigen (HLA-G) molecule is a non-classical major histocompatibility complex (MHC) class I molecule. The pertinence of HLA-G has been investigated in numerous studies which have sought to elucidate the relevance of HLA-G in pathologic conditions, such as autoimmune diseases, cancers, and hematologic malignancies. One of the main goals of the current research on HLA-G is to use this molecule in clinical practice, either in diagnostics or as a therapeutic target. Since HLA-G antigens are currently considered as immunomodulatory molecules that are involved in reducing inflammatory and immune responses, in this review, we decided to focus on this group of antigens as potential determinants of progression in autoimmune diseases. This article highlights what we consider as recent pivotal findings on the immunomodulatory function of HLA-G, not only to establish the role of HLA-G in the human body, but also to explain how these proteins mediate the immune response.

Association of HLA-G polymorphisms with systemic lupus erythematosus and correlation between soluble HLA‑G levels and the disease: a meta-analysis

OBJECTIVE

To investigate the association between HLA‑G polymorphisms and systemic lupus erythematosus (SLE) susceptibility as well as the relationship between circulating soluble HLA‑G (sHLA‑G) levels and SLE.

METHODS

A meta-analysis was performed to investigate the relationships between HLA‑G 14-bp insertion (I)/deletion (D), +3142 G/C, +3035 T/C, and +3003 C/T polymorphisms and SLE as well as the relationship between sHLA‑G serum/plasma levels in SLE patients and controls.

RESULTS

Eleven publications fulfilled our inclusion criteria. Meta-analysis under the dominant model showed an association in the overall group between the II+ID genotype of HLA‑G 14-bp I/D polymorphism and SLE (OR = 1.213, 95%CI = 1.077-1.365, P = 0.001). Ethnicity-specific meta-analysis showed an association between II+ID and SLE in Asians but not in South American and European populations. No correlation was observed using the allele contrast between HLA‑G +3142 G/C polymorphisms and SLE. Contrastingly, +3035 T/C and +3003 C/T meta-analysis showed a significant allelic association between SLE and HLA‑G polymorphisms (OR = 1.378, 95%CI = 1.109-1.713, P = 0.004; OR = 1.834, 95%CI = 1.112-3.022, P = 0.017; respectively). sHLA‑G levels were significantly higher in the SLE group than in the controls (SMD = 0.637, 95%CI = 0.382-0.892, P < 0.001).

CONCLUSION

We showed association of HLA‑G 14-bp I/D, +3035 T/C, and +3003 C/T polymorphisms with SLE susceptibility and significantly higher circulating sHLA‑G levels in SLE patients.

Analysis of key markers: IL-10/sHLA-G in psoriasis patients and the identification of 14-bp INDEL in the HLA-G gene

BACKGROUND

Psoriasis is a chronic inflammation resulting from interactions between immunological and genetic factors. An important tolerogenic role in this autoimmunological disease is played by HLA-G, which is modulated by IL-10. Therefore, this study (N.=80) aimed to evaluate changes in the serum sHLA-G and IL-10 levels in active psoriasis vulgaris and in the early stages of treatment with Methotrexate (MTX) compared to healthy controls. The 14-bp INDEL of the HLA-G gene was evaluated to find possible associations with clinical and laboratory variables.

METHODS

The level of sHLA-G and IL-10 in serum was evaluated (ELISA tests) in patients before the first dose of MTX and at week 12 of treatment, compared to healthy control donors. The 14-bp INDEL in 3'UTR of the HLA-G gene was identified using gDNA templates isolated from full blood. HLA-G amplicons were obtained by PCR, separated by electrophoresis and sequenced.

RESULTS

The mean serum IL-10 level was 4.653±3.33 pg/mL in psoriatic patients, 13.3±9.64 pg/mL after short MTX treatment, compared to 6.23 pg/mL in healthy controls. In addition, the serum level of sHLA-G was 0.275±0.03 ng/mL and 0.332±0.06 ng/mL in patients before and after MTX treatment, respectively, and 0.302±0.08 ng/mL in the control group. A correlation was found (r=-0.43; P<0.005) between the IL-10 and BSA serum levels in psoriasis patients after MTX treatment, indicating health improvement. The three genotypes identified in the 3'UTR of the HLA-G revealed no association with sHLA-G level in serum.

CONCLUSIONS

The mean levels of sHLA-G and the key anti-inflammatory cytokine IL-10 in the blood of pretreatment psoriasis patients are low and indicate that the immunotolerance mechanisms have failed. Treatment of psoriasis patients with low systemic levels of sHLA-G and IL-10 brings them to the same or higher protein levels, respectively, as in healthy donors. Higher sHLA-G levels in healthy donors and after MTX treatment, compared to the sHLA-G levels in the acute phase of psoriasis, indicates its immune system surveillance function.

Susceptibility role of soluble HLA-G and HLA-G 14-bp insertion/deletion polymorphism in inflammatory bowel disease

Background

Inflammatory bowel disease (IBD) is a group of chronic inflammatory disorders of the gastrointestinal tract. It is fundamentally related to a dysregulated immune response in the intestinal mucosa against microbiota in genetically predisposed individuals. Among the genetic and immunological factors that are suggested to have role in etiology and pathogenesis of IBD are human leukocyte antigen (HLA)-G molecules. Therefore, soluble HLA-G (sHLA-G) serum level and genetic association with HLA-G 14-bp insertion (Ins)/deletion (Del) polymorphism was analyzed in 100 IBD patients; 50 ulcerative colitis (UC) and 50 Crohn’s disease (CD), and 100 controls.

Results

sHLA-G level was significantly elevated in IBD patients compared to controls (174.7 ± 27.1 vs. 126.8 ± 15.1; corrected probability [pc] < 0.001). The level was also elevated in UC patients compared to CD patients but the difference was not significant (180.5 ± 27.1 vs. 168.9 ± 26.3; p = 0.059). Receiver operating characteristic analysis confirmed the significance of sHLA-G in total IBD, UC, and CD patients (area under curve = 0.944, 0.961, and 0.927, respectively). The genetic association was analyzed under five genetic models (allele, recessive, dominant, overdominant, and codominant). At the allele level, Del allele frequency was significantly increased in total IBD patients (Odds ratio [OR] = 1.93; 95% confidence interval [CI] = 1.27–2.94; pc = 0.018) and CD patients (OR = 2.08; 95% CI = 1.23–3.54; pc = 0.042) compared to controls. Among UC patients, a similar increased frequency was observed, but the pc value was not significance (OR = 1.79; 95% CI = 1.07–3.00; p = 0.031). At the genotypic level, Del/Del genotype was associated with a significantly increased IBD-risk in total patients under codominant model (OR = 4.06; 95% CI = 1.56–10.56; pc = 0.024). sHLA-G level was not influenced by the Ins/Del polymorphism.

Conclusions

This study demonstrated a significant increase in serum level of sHLA-G in UC and CD patients. Further, HLA-G 14-bp Ins/Del polymorphism may be associated with susceptibility to IBD, particularly CD.

The potential role of HLA-G in the pathogenesis of HBV infection: Immunosuppressive or immunoprotective?

The non-classical human leukocyte antigens (HLA)-G could be generally considered as a potent tolerogenic molecule, which modulates immune responses. HLA-G due to the immunosuppressive properties may play an important role in the pathogenesis of infections related to the liver. HLA-G may display two distinct activities in the pathological conditions so that it could be protective in the autoimmune and inflammatory diseases or could be suppressive of the immune system in the infections or cancers. HLA-G might be used as a novel therapeutic target for liver diseases in the future. Indeed, new therapeutic agents targeting HLA-G expression or antibodies which block HLA-G activity are being developed and tested. However, further consideration of the HLA-G function in liver disease is required. This review aims to summarize the role of HLA-G in the liver of patients with HBV infection.

The Role of HLA-G in Human Papillomavirus Infections and Cervical Carcinogenesis

Human leukocyte antigen (HLA)-G, a non-classical HLA-class I molecule, has a low polymorphism frequency, restricted tissue distribution and immunoinhibitory property. HLA-G expression in tumor cells and cells chronically infected with virus may enable them to escape from host immune surveillance. It is well-known that the HLA-G molecule is a novel biomarker and potential therapeutic target that is relevant in various types of cancers, but its role in cervical cancer has not been fully explored. In this review, we aim to summarize and discuss the immunologic role of the HLA-G molecule in the context of HPV infections and the process of cervical cancer carcinogenesis. A better understanding of the potential impact of HLA-G on the clinical course of persistent HPV infections, cervical epithelial cell transformation, tumor growth, recurrence and metastasis is needed to identify a novel diagnostic/prognostic biomarker for cervical cancer, which is critical for cervical cancer risk screening. In addition, it is also necessary to identify HLA-G-driven immune mechanisms involved in the interactions between host and virus to explore novel immunotherapy strategies that target HLA-G/immunoglobulin-like transcript (ILT) immune checkpoints.

Human leukocyte antigen-G polymorphisms in periodontitis

Objective: This study evaluated human leucocyte antigen-G gene polymorphisms in patients with periodontitis and healthy controls.Material and methods: The insertion/deletion polymorphism of 14 bp and a single nucleotide polymorphism (SNP) C > G on the position +3142 of the 3' untranslated region of the gene were analyzed in chronic periodontitis (n = 62), aggressive periodontitis (n = 24) patients and healthy individuals (n = 47).Results: Considering the 14 bp insertion/deletion, a significant deviation from Hardy-Weinberg expectations in the chronic periodontitis group was observed, but not in the other groups. No significant deviations were observed in patients and control groups considering the +3142 C > G SNP. A significant increased frequency of homozygotes for the 14 bp deletion allele was observed in the chronic periodontitis group as compared to controls. This group also presented a higher frequency of the deletion allele, which was marginally not significant. Concerning this polymorphism, no significant differences were observed between the aggressive periodontitis and healthy control groups. In addition, no significant differences were seen amongst patients and controls when considering the +3142 C > G frequencies.Conclusion: No differences were found amongst patients and controls when considering the +3142 C > G SNP haplotypes frequencies, but a significant increased frequency of homozygotes for the 14 bp deletion allele was observed in chronic periodontitis patients compared to healthy controls, suggesting a susceptibility role of this polymorphism in the pathogenesis of this condition.

IDO activation, inflammation and musculoskeletal disease

The IDO/kynurenine pathway is now established as a major regulator of immune system function. The initial enzyme, indoleamine 2,3-dioxygenase (IDO1) is induced by IFNγ, while tryptophan-2,3-dioxygenase (TDO) is induced by corticosteroids. The pathway is therefore positioned to mediate the effects of systemic inflammation or stress-induced steroids on tissue function and its expression increases with age. Disorders of the musculoskeletal system are a common feature of ageing and many of these conditions are characterized by an inflammatory state. In inflammatory arthritis and related disorders, kynurenine protects against the development of disease, while inhibition or deletion of IDO1 increases its severity. The long-term regulation of autoimmune disorders may be influenced by the epigenetic modulation of kynurenine pathway genes, with recent data suggesting that methylation of IDO may be involved. Osteoporosis is also associated with abnormalities of the kynurenine pathway, reflected in an inversion of the ratio between blood levels of the metabolites anthranilic acid and 3-hydroxy-anthranilic acid. This review discusses evidence to date on the role of the IDO/kynurenine pathway and the highly prevalent age-related disorders of osteoporosis and rheumatoid arthritis and identifies key areas that require further research.

Expression of membrane-bound human leucocyte antigen-G in systemic sclerosis and systemic lupus erythematosus

Human leucocyte antigen-G (HLA-G) is a nonclassical class I major histocompatibility complex (MHC) molecule characterized by complex immunoregulatory and tolerogenic functions. Membrane-bound HLA-G is expressed on the surface of different cell populations in both physiological and pathological conditions. Systemic sclerosis (SSc) is a multisystem autoimmune disease characterized by widespread tissue fibrosis, vascular lesions and immunological alterations. Systemic lupus erythematosus is the prototypic systemic autoimmune disease affecting virtually any organ system, such as skin, joints, central nervous system, or kidneys. In SSc and SLE patients, the membrane expression of HLA-G on monocytes (0.88 ± 1.54 and 0.43 ± 0.75, respectively), CD4+ (0.42 ± 0.78 and 0.63 ± 0.48, respectively), CD8+ (2.65 ± 3.47 and 1.29 ± 1.34, respectively) and CD4+ CD8+ double-positive cells (13.87 ± 15.97 and 3.79 ± 3.11, respectively) was significantly higher than in healthy controls (0.12 ± 0.07; 0.01 ± 0.01; 0.14 ± 0.20 and 0.32 ± 0.38, respectively) (p < 0.0001). Our results show that in SSc and SLE the membrane expression of HLA-G by different subpopulations of peripheral blood mononuclear cells (PBMC) is increased, suggesting a potential role of HLA-G molecules in the complex immunological pathogenesis of these two autoimmune disorders.

Analysis of HLA-G expression in renal tissue in lupus nephritis: a pilot study

BACKGROUND

The study aimed to investigate whether HLA-G antigen is expressed in the kidneys of patients affected by lupus nephritis (LN) and whether its detection in renal biopsies could be adopted as a marker of treatment response and prognosis.

METHODS

Thirty renal biopsies from patients with LN were selected and analyzed through immunohistochemistry. Laboratory and clinical data were retrospectively collected at baseline, 6 and 12 months and at the latest clinical appointment. A number of patients (63.3%) were treated with rituximab (RTX) +/- methylprednisolone in the induction phase. The expression of HLA-G in glomeruli, tubules and infiltrating cells was examined and compared between lupus patients who achieved either complete or partial renal response and those who did not respond to treatment.

RESULTS

HLA-G staining was observed in the glomeruli of 20 of 30 samples from patients with LN. The expression of the antigen was detected in podocytes, along glomerular capillary walls, on parietal glomerular epithelial cells and within the juxtaglomerular apparatus. Seventy per cent of patients whose glomeruli expressed HLA-G achieved partial or complete response at 6 months and 75% at the latest available follow up compared with 30% and 40%, respectively, of those who did not show any expression. The pattern of staining in tubules and infiltrating cells was highly variable precluding any clinical correlation.

CONCLUSION

This study demonstrates that HLA-G is expressed in renal tissue in LN. Our retrospective data suggest that its expression could correlate with response to treatment.

The Impact of HLA-G 3'UTR Polymorphisms in Breast Cancer in a Tunisian Population

Human leukocyte antigens G and E (HLA-G and HLA-E) are nonclassical major histocompatibility complex (MHC) class I molecules. These molecules play an important role in immune surveillance by inhibiting natural killer and cytotoxic T cells responsible for immune escape. The expression of HLA-G and HLA-E has been associated with several diseases including tumor. The main objective of the study is to evaluate the impact of three HLA-G 3'UTR potential polymorphisms: +3187 A > G (rs9380142), +3142 G > C (rs1063320), +2960 14-base pair (bp) Insertion/Deletion (Ins/Del) (rs66554220), and the HLA-E*01:01/01:03 A > G (rs1264457) polymorphism in Tunisian breast cancer population. A total of 355 patients and 381 controls were genotyping for HLA-G and HLA-E polymorphisms using a Taq Man assay. +3142 C allele and +3142 C/C genotype were significantly associated with increased risk of breast cancer (p = 0.00002; OR = 1.58; 95% CI = 27-1.97) (49% versus 35%; p = 0.0001; OR = 1.79; 95% CI = 1.32-2.44). In addition, Del allele and the homozygous state for Del/Del genotype confer a risk for breast cancer (52% versus 45%, p = 0.006; OR = 1.33, 95% CI = 1.08-1.64) (28% versus 22%, p = 0.039; OR = 1.43, 95% CI = 0.90-2.25). However, no statistical significant differences were reported for HLA-G + 3187 A > G and HLA-E variations and breast cancer in a Tunisian population. The found results indicate that HLA-G may play an important role in the breast cancer.

The HLA-G 14 bp insertion/deletion polymorphism and its association with soluble HLA-G levels in women with recurrent miscarriages

HLA-G, a nonclassical class-Ib gene is mainly expressed on extravillous trophoblasts at the fetal-maternal interface. HLA-G molecule is considered to play an important role in maternal immune suppression during pregnancy. The 14 bp insertion/deletion polymorphism (rs66554220) in exon eight of the HLA-G gene influences HLA-G mRNA stability and isoform splicing patterns. In this study, 202 recurrent miscarriage (RM) women with two or more than two consecutive miscarriages, their 202 partners and 204 fertile control women with at least one live birth and no miscarriages were analyzed for 14 bp insertion/deletion polymorphism. Soluble HLA-G (sHLA-G) levels were also determined and compared between randomly selected 111 RM women and 111 control women using QAYEE-Bio ELISA kits. Student's t test and χ² test were used to depict the statistical differences. The results showed no significant differences for 14 bp allele and genotype frequencies between the study groups. However, our study showed a significant difference (P = .0107) for sHLA-G levels in RM women and control women. Furthermore, a significant difference (P = .0135) for sHLA-G levels in relation to +/-14 bp heterozygous genotype was seen between the two groups. The 14 bp allele sharing between the partners did not show any significant association with the number of miscarriages in RM couples. The association of 14 bp polymorphism and recurrent miscarriages was not significant in our study.

Genetic Polymorphism of HLA-G 14-bp Insertion/Deletion in Pancreas Transplant Recipients and Its Association With Type 1 Diabetes Mellitus

OBJECTIVES

Human leukocyte antigen-G is an immuno-modulatory factor that affects acute allograft rejection and autoimmune diseases such as type 1 diabetes mellitus. In this study, possible associations between human leukocyte antigen-G 14-bp insertion/deletion polymorphism and acute pancreas rejection were investigated.

MATERIALS AND METHODS

Human leukocyte antigen-G genotyping was assessed in 102 Iranian pancreas transplant recipients (including 41 with acute rejection and 61 with nonacute rejection). Results were compared with 100 individuals in a normal control group.

RESULTS

No significant differences in genotype frequencies of human leukocyte antigen-G 14-bp insertion / deletion were observed in recipients who had acute rejection episodes. On the other hand, the insertion / insertion genotype was a risk factor for susceptibility to type 1 diabetes mellitus (odds ratio = 3.82, 95% confidence interval, 1.37- 11.22; P = .005).

CONCLUSIONS

Our results provided evidence revealing that the human leukocyte antigen-G insertion / insertion genotype might be involved in the pathogenesis of type 1 diabetes mellitus.

Association of HLA-G 3' UTR polymorphism and expression with the progression of cervical lesions in human papillomavirus 18 infections

Background

Human leukocyte antigen (HLA)-G is an immune checkpoint molecule, which expression in cervical cancer cells enables them to escape immunosurveillance. To date, limited information has been published on the association of HLA-G genetic background in malignant cells with levels of HLA-G expression and the clinical outcome of patients.

Methods

We investigated the influence of the HLA-G 14 bp In/Del (rs66554220) and + 3142C/G (rs1063320) polymorphisms in 130 cases of HPV16 infection, 130 cases of HPV18 infection and 185 age-matched, unrelated, HPV-negative, and cytologically normal Chinese Han women. Case-matched cervical biopsy tissues were evaluated by immunohistochemistry.

Results

Our findings show that the frequency of alleles, 14 bp In (38.5% vs 29.2%, OR = 1.52, P < 0.05) and + 3142G (72.7% vs 57.0%, OR = 2.01, P < 0.05), were significantly increased in the HPV18-infected group compared with the control group. The HLA-G polymorphisms (alleles 14 bp In and + 3142G) are also associated with the progression of HPV18-related cervical lesions. Moreover, HLA-G expression increased from CIN1 to CIN2/3 lesions and was highest in patients with adenocarcinoma; however, a significant association between these characteristics and the HLA-G polymorphisms was not observed.

Conclusion

Our results support that the HLA-G 14 bp In and + 3142G alleles are risk factors for HPV18 infections and influence the progression of HPV18-related cervical lesions. This suggests that HLA-G-driven immune mechanisms play an important role in cervical carcinogenesis.

Genetic association between HLA-G 14-bp polymorphism and diseases: A systematic review and meta-analysis

BACKGROUND

HLA-G is an immune checkpoint molecule. Since a differential molecule expression has been reported even for healthy individuals, many studies have focused on polymorphisms at HLA-G regulatory regions, particularly the 3' untranslated region (3'UTR). The presence/absence of a 14-bp sequence was the first polymorphism described and it is the most studied in association between HLA-G and disorders.

METHODS

In this study, we performed a systematic review and meta-analysis of all association studies published regarding the HLA-G 14-bp.

RESULTS

We verified association between 14-bp alleles and diseases in the following situations: (1) presence of 14-bp (insertion) conferred susceptibility to preeclampsia (child alleles evaluated) and systemic lupus erythematosus (OR = 1.42; 95%CI = 1.04-1.93; p = 0.026 and OR = 1.13; 95%CI = 1.01-1.27, p = 0.028); (2) 14-bp absence (deletion) was associated with increased risk to breast cancer (OR = 1.23; 95%CI = 1.06-1.43; p = 0.006) and human Cytomegalovirus infection (OR = 2.06; 95%CI = 1.60-2.64; p < 0.0001); and (3) a risk association was observed between the group of reproductive disorders and the 14-bp insertion (OR = 1.12; 95%CI = 1.01-1.24; p = 0.034).

CONCLUSIONS

Considering that others 14-bp associations were inconclusive and that other variation sites observed at HLA-G 3'UTR exhibit a proven role on post-transcriptional regulation of HLA-G expression, the complete 3'UTR segment should be analyzed in terms of disease susceptibility, instead of a single polymorphism.

Meta-analysis of correlationship between HLA-G 3'UTR 14-bp Ins/Del polymorphism and virus susceptibility

BACKGROUND

There is a considerable amount of literature on the potential relationship between human leukocyte antigen-G 14-bp Ins/Del polymorphism and virus infection; however, results from these studies were inconclusive.

OBJECTIVES

A meta-analysis was carried out to determine whether the 14-bp Ins/Del polymorphism is a susceptible factor for virus infection.

METHODS

Data were extracted from PubMed and Web of Science databases, and included 10 case-control studies (1835 patients and 2357 controls).

RESULTS

A total of 177 records from 10 studies were retrieved. Overall, no significant correlation was found between HLA-G 14-bp Ins/Del polymorphism and total viruses under all genetic models (dominant model: OR = 0.93, 95% CI = 0.68-1.29; recessive model: OR = 1.12, 95% CI = 0.84-1.48; deletion/deletion (DD) vs insertion/insertion (II): OR = 1.03, 95% CI = 0.71-1.49; deletion (D) vs insertion (I): OR = 1.01, 95% CI = 0.81-1.25). However, further subgroup analyses by virus type and ethnicity revealed that HLA-G 14-bp Ins/Del polymorphism was significantly associated with HTLV-1 infection in mixed population under the dominant model.

CONCLUSIONS

Our study demonstrated that HLA-G 14-bp Ins/Del polymorphism may not have any effect on susceptibility to viruses.

10-Year Experience with HLA-G in Heart Transplantation

The Human Leukocyte Antigen-G (HLA-G) is a MHC-class Ib molecule with robust immunomodulatory properties; in transplant, it inhibits cytotoxic activity of immune cells and thus has a pivotal role in protecting the allograft from immune attack. The present review details a 10-year experience investigating the influence of HLA-G on heart transplantation, allograft rejection and cardiac allograft vasculopathy development. Exploration of HLA-G in transplantation began with the initial findings of its increased expression in allograft hearts. Since then, HLA-G has been recognized as an important factor in transplant immunology. We discuss inducers of HLA-G expression, and the importance of HLA-G as a potential biomarker in allograft rejection and heart failure. We also highlight the importance of polymorphisms and how they may influence both HLA-G expression and clinical outcomes. There remains much to be done in this field, however we hope that findings from our group and other groups will ignite interest and facilitate further expansion of HLA-G research in transplantation.

The HLA-G Genetic Contribution to Bipolar Disorder: A Trans-Ethnic Replication

Bipolar disorder (BD) is frequently associated with immune dysfunctions. Studying the genetic diversity of the immuno-modulatory human leukocyte antigen (HLA)-G locus in a French BD cohort, we previously reported an association between a functionally relevant 14 bp Ins/Del polymorphism and BD risk. The present study investigated the genetic and expression diversities of HLA-G in a geographically distinct South Indian population-group BD patients, as well as the influence of exposure to the neurotropic Toxoplasma gondii pathogen. Three functionally relevant HLA-G polymorphisms, i.e. HLA-G 14 bp Ins/Del (rs66554220), +3142G>C (rs1063320) and +3187A>G (rs9380142) were genotyped by polymerase chain reaction (PCR) and real-time PCR. Sub-samples of BD patients and healthy controls (HC) were investigated for plasma levels of soluble HLA-G (sHLA-G) isoforms, as well as circulating stigma of T. gondii infection. Findings indicate: (i) the frequency of the HLA-G 14 bp Del/Del genotype was higher in BD cases, as compared to HC; (ii) the HLA-G + 3142 C allele and CC genotype were more prevalent in BD patients than in HC; (iii) sHLA-G levels were significantly higher in BD cases, especially in females and in the early onset sub-group; and (iv) the InsGA haplotype was more prevalent in HC. Our findings further support the genetic contribution of HLA-G to BD risk, as well as indicate relevant expression profiles. Such data may also indicate a potential developmental role in BD etiology, given that HLA-G is an important immune regulator from the intrauterine period and across development.

The Immunosignature of Mother/Fetus Couples in Gestational Diabetes Mellitus: Role of HLA-G 14 bp ins/del and PAPP-A A/C Polymorphisms in the Uterine Inflammatory Milieu

We enrolled 151 healthy mother/newborn couples and 26 with gestational diabetes mellitus (GDM). HLA-G and PAPP-A plasma levels were measured by ELISA at first and second trimesters, at delivery, and in cord blood. HLA-G 14 bp ins/del and PAPP-A A/C polymorphisms were genotyped. HLA-G del/del and PAPP-A C/C genotypes were more frequent among GDM mothers than controls. We observed a genetic epistasis between the two polymorphisms: the HLA-G del/del and PAPP-A C/C combination was carried by 8% of GDM mothers and 1.3% of controls (OR = 9.5, 95% CI = 0.8-109, p = 0.07). GDM mothers showed increased sHLA-G levels compared to controls (p = 0.004), and those carrying the HLA-G del/del genotype produced more sHLA-G at the second trimester and at delivery (p = 0.014). A genetic pressure by fetal genotype on maternal sHLA-G production was observed in GDM mothers with heterozygous HLA-G del/ins newborns (p = 0.02). Babies born to GDM mothers showed higher sHLA-G concentrations compared to those born to healthy mothers, and those carrying HLA-G del/del showed the highest sHLA-G levels (p = 0.013). PAPP-A amounts significantly increased along pregnancy (p < 0.001), but the median levels at the first and second trimesters were significantly lower in GDM (p = 0.03). Our findings first suggest an involvement of HLA-G and PAPP-A gene-protein interaction in GDM and highlight a possible contribution of the fetus in balancing maternal inflammation.

Role of major histocompatibility complex variation in graft-versus-host disease after hematopoietic cell transplantation

Graft-versus-host disease (GVHD) remains a significant potentially life-threatening complication of allogeneic hematopoietic cell transplantation (HCT). Since the discovery of the human leukocyte antigen (HLA) system over 50 years ago, significant advances have clarified the nature of HLA variation between transplant recipients and donors as a chief etiology of GVHD. New information on coding and non-coding gene variation and GVHD risk provides clinicians with options to consider selected mismatched donors when matched donors are not available. These advances have increased the availability of unrelated donors for patients in need of a transplant and have lowered the overall morbidity and mortality of HCT.

"HLA-G 3'UTR gene polymorphisms and rheumatic heart disease: a familial study among South Indian population"

BACKGROUND

Rheumatic heart disease (RHD) is an autoimmune disease where cross reactive CD4⁺ T cells are involved in the pathogenesis of valvular damage. Human Leukocyte Antigen-G (HLA-G), an immunosuppressive molecule playing a crucial role in the inhibition of T cell response is associated with the pathogenesis of various autoimmune and inflammatory diseases. Genetic polymorphisms within the 3'untranslated region (UTR) of HLA-G influences its expression and thus disease pathogenesis. Hence, the present study aims to unravel the association of 14 bp Ins/Del (rs66554220) and +3142 C/G (rs1063320) polymorphisms in 3' UTR of HLA-G with RHD.

METHODS

This familial study consists of 99 RHD families (99 RHD patients, 140 parents and 126 healthy siblings). The 14 bp Ins/Del and +3142 C/G polymorphisms were evaluated by PCR using sequence specific primers and its transmission disequilibrium (TD) was tested by TD test in 70 trio families.

RESULTS

The frequency of +3142 C/C genotype was high in patients with combined valvular lesions (CVL) (OR = 5.88; p_c = 0.012) and pooled RHD patients (P: OR = 2.76; p = 0.043; p_c = 0.076) when compared to healthy siblings. Under the additive (OR = 5.50; p_c = 0.026) and recessive genetic model (OR = 5.88; p_c = 0.012), the +3142 C/C genotype was significantly associated with CVL in patients.

CONCLUSION

The results suggest that the +3142 C/C genotype may be associated with minor risk for the development of RHD and is more likely to influence the severity of the disease.

Mesenchymal stem cells upregulate Treg cells via sHLA-G in SLE patients

BACKGROUND

Soluble human leukocyte antigen-G (sHLA-G) is a non-classical HLA class I molecule, exhibiting strong immunosuppressive properties by inducing the differentiation of T regulatory cells (Treg). Mesenchymal stem cells (MSCs) transplantation alleviates disease progression in systemic lupus erythematosus (SLE) patients. However, the underlying mechanisms are largely unknown.

OBJECTIVES

To explore whether sHLA-G is involved in upregulating effects of MSCs on Treg, which contributes to therapeutic effects of MSCs transplantation in SLE.

METHODS

The serum sHLA-G levels of SLE patients and healthy controls were detected by ELISA. The percentages of peripheral blood CD4+ILT2+, CD8+ILT2+, CD19+ILT2+ cells and Treg cells were examined by flow cytometry. Ten patients with active SLE, refractory to conventional therapies, were infused with umbilical cord derived MSCs (UC-MSCs) and serum sHLA-G was measured 24h and 1month after infusion. The mice were divided into three groups: C57BL/6 mice, B6.MRL-Fas^lpr mice infused with phosphate buffer saline (PBS), and B6.MRL-Fas^lpr mice infused with bone marrow MSCs (BM-MSCs). Then, the concentrations of serum Qa-2 were detected. Peripheral blood mononuclear cells (PBMCs) were isolated from SLE patients and co-cultured with UC-MSCs for 3days at different ratios (50:1, 10:1, and 2:1) with or without HLA-G antibody, and the frequencies of CD4+CD25+Foxp3+ T cells were then determined by flow cytometry.

RESULTS

The concentrations of serum sHLA-G were comparable between SLE patients and healthy controls. However, there was a negative correlation between sHLA-G levels and SLE disease activity index (SLEDAI) scores in active SLE patients (SLEDAI>4). We found that serum sHLA-G levels were negatively correlated with blood urea nitrogen, serum creatinine and 24-hour urine protein in SLE patients. The sHLA-G levels were significantly lower in SLE patients with renal involvement than those without renal involvement. The expression of ILT2 on CD4+ T cells from SLE patients decreased significantly compared to that of healthy controls. A positive correlation between the frequencies of Treg and CD4+ILT2+ T cells was found in SLE patients. The levels of sHLA-G increased 24h post UC-MSCs transplantation. The concentrations of Qa-2 in BM-MSCs transplanted mice were significantly higher than those of control group. In vitro studies showed that MSCs increased the frequency of Treg cells in SLE patients in a dose-dependent manner, which was partly abrogated by the anti-HLA-G antibody.

CONCLUSIONS

Our results suggested that MSCs may alleviate SLE through upregulating Treg cells, which was partly dependent on sHLA-G.

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

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

Soluble monomers, dimers and HLA-G-expressing extracellular vesicles: the three dimensions of structural complexity to use HLA-G as a clinical biomarker

The HLA-G molecule belongs to the family of nonclassical human leukocyte antigen (HLA) class I. At variance to classical HLA class I, HLA-G displays (i) a low number of nucleotide variations within the coding region, (ii) a high structural diversity, (iii) a restricted peptide repertoire, (iv) a limited tissue distribution and (v) strong immune-suppressive properties. The physiological HLA-G surface expression is restricted to the maternal-fetal interface and to immune-privileged adult tissues. Soluble forms of HLA-G (sHLA-G) are detectable in various body fluids. Cellular activation and pathological processes are associated with an aberrant or a neo-expression of HLA-G/sHLA-G. Functionally, HLA-G and its secreted forms are considered to be key players in the induction of short- and long-term tolerance. Thus, its unique expression profile and tolerance-inducing functions render HLA-G/sHLA-G an attractive biomarker to monitor the systemic health/disease status and disease activity/progression for clinical approaches in disease management and treatments. Here, we place emphasis on (i) the current status of the tolerance-inducing functions by HLA-G/sHLA-G, (ii) the current complexity to implement this molecule as a meaningful clinical biomarker regarding the three dimensions of structural diversity (monomers, dimers and HLA-G-expressing extracellular vesicles) with its functional implications, and (iii) novel and future approaches to detect and quantify sHLA-G structures and functions.

Association of genetic variants in the 3'UTR of HLA-G with Recurrent Pregnancy Loss

Human Leukocyte Antigen (HLA)-G is involved in reprogramming immune responses at fetal-maternal interface during pregnancy. We evaluated the genetic diversity of the 3′ Un-Translated Region (UTR) of HLA-G, previously associated with HLA-G mRNA post-transcriptional regulation, in women with unexplained Recurrent Pregnancy Loss (RPL), with 2 pregnancy losses (RPL-2, n = 28), or 3 or more pregnancy losses (RPL-3, n = 24), and in 30 women with a history of successful pregnancy. Results showed in RPL-2, but not in RPL-3, women compared to controls: i) higher frequency of the 14 bp Ins allele, in single and in double copy; ii) significantly lower frequency of DelG/X genotype, iii) reduced frequency of the UTR-2, and UTR-3 haplotypes; iv) higher frequencies of the UTR-5, UTR-7, and UTR-8 haplotypes. This pilot study supports the relevance of performing 3′UTR HLA-G genetic screening, not limited to a specific polymorphism, but considering the extended haplotypes, as a possible predictor of pregnancy outcome.

Association of HLA-G 3' Untranslated Region Polymorphisms with Systemic Lupus Erythematosus in a Japanese Population: A Case-Control Association Study

HLA-G plays a role in fetal-maternal tolerance as well as immunoregulation, and has been suggested to be involved in autoimmune diseases and cancers. HLA-G encodes two potentially functional polymorphisms in the 3' untranslated region, 14bp insertion/deletion (14bp indel, rs371194629) and a single nucleotide polymorphism rs1063320, previously reported to affect HLA-G expression level or splicing isoform and to be associated with susceptibility to systemic lupus erythematosus (SLE). However, the results of SLE association studies are inconsistent, probably due to the small sample size of each study and lack of consideration of linkage disequilibrium (LD) with HLA-class II haplotypes in each population. In this study, we performed association studies of these polymorphisms on 843 patients with SLE and 778 healthy controls in a Japanese population, in many of whom HLA-DRB1 alleles have been genotyped at the four-digit level. LD was detected between DRB1*13:02, protective against multiple autoimmune diseases in the Japanese, and the rs1063320 G (D' = 0.86, r2 = 0.02) and with 14bp del (D' = 0.62, r2 = 0.01), but not between SLE-susceptible DRB1*15:01 and HLA-G. Although significant association with overall SLE was not detected, 14bp ins allele was significantly associated with SLE with the age of onset <20 years, when compared with healthy controls (P = 0.0067, PFDR = 0.039, OR 1.44, additive model) or with SLE patients with the age of onset ≥20 (P = 0.033, PFDR = 0.0495, OR 2.09, additive model). This association remained significant after conditioning on DRB1*13:02 or DRB1*15:01. On the other hand, significant association was detected between rs1063320 C and anti-RNP antibody and anti-Sm antibody positive SLE, which was dependent on negative LD with DRB1*13:02. eQTL analysis showed reduced HLA-G mRNA level in 14bp ins/ins individuals. In conclusion, our observations showed that HLA-G 14bp ins allele represents a genetic contribution on early-onset SLE independent of DRB1.

The Potential of HLA-G-Bearing Extracellular Vesicles as a Future Element in HLA-G Immune Biology

The HLA-G molecule is a member of the non-classical HLA class I family. Its surface expression is physiologically restricted to the maternal–fetal interface and to immune privileged adult tissues. Despite the restricted tissue expression, HLA-G is detectable in body fluids as secreted soluble molecules. A unique feature of HLA-G is the structural diversity as surface expressed and as secreted molecules. Secreted HLA-G can be found in various body fluids either as free soluble HLA-G or as part of extracellular vesicles (EVs), which are composed of various antigens/ligands/receptors, bioactive lipids, cytokines, growth factors, and genetic information, such as mRNA and microRNA. Functionally, HLA-G and its secreted forms are considered to play a crucial role in the network of immune-regulatory tolerance mechanisms, preferentially interacting with the cognate inhibitory receptors LILRB1 and LILRB2. The HLA-G mediated tolerance is described in processes of pregnancy, inflammation, and cancer. However, almost all functional and clinical implications of HLA-G in vivo and in vitro have been established based on simple single ligand/receptor interactions at the cell surface, whereas HLA-G-bearing EVs were in minor research focus. Indeed, cytotrophoblast cells, mesenchymal stem cells, and cancer cells were recently described to secrete HLA-G-bearing EVs, displaying immunosuppressive effects and modulating the tumor microenvironment. However, numerous functional and clinical open questions persist. Here, we (i) introduce basic aspects of EVs biology, (ii) summarize the functional knowledge, clinical implications and open questions of HLA-G-bearing EVs, and (iii) discuss HLA-G-bearing EVs as a future element in HLA-G biology.

HLA-G 14-bp polymorphism affects the age of onset in Type I Diabetes Mellitus

Type I diabetes mellitus (T1DM) is an organ-specific autoimmune disorder affecting the insulin-producing pancreatic cells. T1DM genetic association studies have so far revealed the involvement of more than 40 loci, with particularly strong associations for the human leucocyte antigens (HLA). Further to the well-established HLA class II associations, the immunomodulatory elements in the telomeric major histocompatibility complex locus, specifically nonclassical HLA class I, were also associated with T1DM, either in conferring susceptibility or by contributing to the overall pathogenesis. This study investigates the involvement of a 14-bp deletion polymorphism (rs371194629) at the 3' untranslated region of HLA-G in the context of T1DM and age of onset. The frequency of the polymorphism was determined in unrelated T1DM Cypriot patients and findings that emerge from this study show a strong association between the HLA-G 14-bp polymorphism and T1DM with respect to the age of onset. Specifically, the deletion/deletion (DEL/DEL) genotype was found to be associated with an early age of onset (P = 0.001), while the presence of the insertion allele (INS) was associated to a later age of onset (P = 0.0001), portraying a possible dominant effect over the deletion allele, a role in delaying disease onset and an overall involvement of HLA-G in the pathogenesis of type I diabetes mellitus.

Association of an HLA-G 14-bp Insertion/Deletion polymorphism with high HBV replication in chronic hepatitis

Identification of an HLA-G 14-bp Insertion/Deletion (Ins/Del) polymorphism at the 3' untranslated region of HLA-G revealed its importance in HLA-G mRNA stability and HLA-G protein level variation. We evaluated the association between the HLA-G 14-bp Ins/Del polymorphism in patients with chronic Hepatitis B virus (HBV) infection in a case-control study. Genomic DNA was extracted from 263 patients with chronic HBV hepatitis and 246 control subjects and was examined for the HLA-G 14-bp Ins/Del polymorphism by PCR. The polymorphic variants were genotyped in chronic HBV seropositive cases stratified according to HBV DNA levels, fibrosis stages and in a control population. There was no statistical significant association between the 14-bp Ins/Del polymorphism and increased susceptibility to HBV infection neither for alleles (P = 0.09) nor for genotypes (P = 0.18). The stratification of HBV patients based on HBV DNA levels revealed an association between the 14-bp Ins/Del polymorphism and an enhanced HBV activity with high HBV DNA levels. In particular, the Ins allele was significantly associated with high HBV DNA levels (P = 0.0024, OR = 1.71, 95% CI 1.2-2.4). The genotype Ins/Ins was associated with a 2.5-fold (95% CI, 1.29-4.88) increased risk of susceptibility to high HBV replication compared with the Del/Del and Ins/Del genotypes. This susceptibility is linked to the presence of two Ins alleles. No association was observed between the 14-bp Ins/Del polymorphism and fibrosis stage of HBV infection. We observed an association between the 14-bp Ins/Del polymorphism and high HBV replication characterized by high HBV DNA levels in chronic HBV patients. These results suggest a potential prognostic value for disease outcome evaluation.