HLA-G expression in trophoblast cells is independent of embryonic development

HLA-G is a nonclassical major histocompatibility complex class I molecule that is selectively expressed on cytotrophoblasts at the feto-maternal interface where it may play a major role in maternal-fetal tolerance. In this study, we compared HLA-G expression in trophoblasts from normal and pathologic pregnancies by immunohistochemical analysis. First, we found a defective HLA-G expression in miscarriages associated with hypotrophic but normal eggs. Conversely, by studying molar pregnancies, we observed a high HLA-G expression in complete and partial hydatidiform moles. Finally, HLA-G expression could be visualized in extravillous trophoblasts that develop outside of their normal environment, as reported here in ectopic pregnancies. Taken together, these results suggest that HLA-G expression in extravillous trophoblasts is induced in an autonomous manner, independently of embryonic development, and may be an integral part of placental development allowing its tolerance from maternal immune system.     

The expression of human leukocyte antigen-G on trophoblasts abolishes the growth-suppressing effect of interleukin-2 towards them

PROBLEM: We have shown the attenuated human leukocyte antigen (HLA)-G expression on trophoblasts and an aberrant expression of interleukin (IL)-2, a cytotoxic cytokine, in decidual tissue in preeclampsia, where deteriorated trophoblastic invasion into decidual layers may constitute a crucial pathogenesis. We hypothesized that the absence of HLA-G might make trophoblasts susceptible to compromise by IL-2. METHOD OF STUDY: We analyzed the growth of HLA-G-negative and positive cell lines, all of which possessed IL-2 receptors, in the culture with or without IL-2 supplementation. RESULTS: The proliferation of HLA-G positive trophoblastic cell lines (BeWo and JEG-3) was not influenced by the addition of IL-2, whereas a HLA-G-negative trophoblastic cell line (JAR) exhibited significantly decreased proliferation when cultured with IL-2. Interestingly, the transfection of JAR cells with HLA-G completely eliminates the growth-inhibitory effect of IL-2. CONCLUSION: The expression of HLA-G may commit trophoblasts to evade cell damage by IL-2, which may be relevant to maternal tolerance of the fetus during pregnancy and its derangement as exemplified by preeclampsia.     

Expression and Functional Role of HLA-G in Immune Cells from Patients with Systemic Lupus Erythematosus

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

Linkage disequilibrium between human leukocyte antigen (HLA) class II and HLA-G--possible implications for human reproduction and autoimmune disease

A line of investigation indicates that one or several genes in the human major histocompatibility complex (MHC) influences reproductive success. Studies have revealed associations between human leukocyte antigen (HLA) class II genes and risk of recurrent spontaneous abortion (RSA) and pre-eclampsia. However, these genes are not expressed at the feto-maternal interface. Furthermore, associations between polymorphisms in the nonclassical HLA class Ib gene, HLA-G, and reproductive outcome have been demonstrated. HLA-G is expressed by extravillous trophoblast during pregnancy, making it a more obvious candidate gene for a possible influence on pregnancy outcome. HLA-G has immunomodulatory functions. We have studied linkage disequilibrium between HLA class II genes, primarily HLA-DRB1 alleles, and HLA-G alleles in women with RSA and their partners (n = 103) and in control women and their partners (n = 92). We found a significant linkage disequilibrium between HLA-DR3 and HLA-G*010102 in both the RSA and control populations. For all four studied HLA loci, the alleles in the haplotype HLA-DRB1*03.DQA1*05.DQB1*02.G*010102 was in clear linkage disequilibrium. This HLA haplotype has repeatedly been associated with different autoimmune diseases but also with RSA. The G*010102 allele includes a 14-bp sequence polymorphism in the 3' untranslated region of the gene, which has been associated with differences in HLA-G mRNA alternative splicing and stability. This 14-bp polymorphism has also been associated with RSA, pre-eclampsia, and outcome of in vitro fertilization. Implications of HLA polymorphism--and other polymorphic genes in the MHC for pregnancy outcome--and for autoimmune diseases during pregnancy are discussed.     

Differential expression of major histocompatibility complex class Ia, Ib, and II molecules on monocytes-derived dendritic and macrophagic cells.

Blood monocyte derived antigen presenting cells (APC) such as dendritic cells and macrophages are considered as major promising tools for antitumoral immunotherapy. In order to contribute to their phenotype characterization, we have precisely investigated their levels of expression of MHC class Ia, Ib (HLA-G) and II molecules using mainly flow cytometry quantification assays. APC were generated from monocytes cultured for 7 days in the presence of GM-CSF and IL-4 or M-CSF. These cells, which exhibited known morphological and immunological features of dendritic cells and macrophages respectively, were evidenced to display high expression of MHC class Ia and class II antigens in comparison to that found in monocytes. Dendritic cells and macrophages thus expressed 2-fold more and 4-fold more MHC class Ia molecules and 5-fold and 3-fold more MHC class II DR molecules than parental monocytes. In addition, expression of MHC class II DP and DQ molecules, not or only barely detected in monocytes, was clearly demonstrated in the two kinds of APC. In contrast, monocytes, dendritic cells and macrophages failed to express MHC class Ib HLA-G antigen. The up-regulation in monocyte-derived APC of MHC class Ia and II molecules mediating the presentation of antigen peptides to lymphocytes fully supports the interest of such APC in antitumoral immunotherapy.     

Defective production of soluble HLA-G molecules by peripheral blood monocytes in patients with asthma

BACKGROUND: HLA-G, a human nonclassic MHC class I molecule, is responsible for complex immunoinhibitory functions. HLA-G is expressed as membrane-bound and is secreted as soluble molecules by the peripheral blood CD14+ monocytes activated by IL-10. OBJECTIVE: It has been reported that LPS stimulation induces IL-10 production by PBMCs and that IL-10 levels are reduced in patients with severe asthma compared with patients with mild asthma and healthy subjects. The study was designed to investigate whether this impaired IL-10 production can affect the expression and the secretion of soluble HLA-G (sHLA-G)-1/HLA-G5 molecules. METHODS: We investigated the production of sHLA-G1/HLA-G5 and IL-10 by specific ELISAs in the culture supernatants of LPS-activated PBMCs from 24 healthy subjects and 20 patients with moderate to severe persistent asthma. RESULTS: LPS stimulation induced the secretion of IL-10 and sHLA-G1/HLA-G5 molecules in all healthy subjects, whereas in patients with asthma, the levels of IL-10 were significantly lower (P < .001) and the number of cultures exhibiting detectable sHLA-G1/HLA-G5 was reduced (7/20; P < .001). The addition of exogenous IL-10 to LPS-stimulated PBMCs from patients with asthma restored normal sHLA-G1/HLA-G5 production. CONCLUSION: Our data suggest that a specific deficit of IL-10 secretion in patients with asthma could prevent the normal production of sHLA-G1/HLA-G5 molecules. The reduction of immunosuppressive activity mediated by HLA-G could in turn contribute to the persistence of chronic airway inflammation in asthma.     

人类白细胞抗原-G与肝炎病毒感染的相关性研究进展

人类白细胞抗原-G(human leukocyte antigen G,HLA-G)属于非经典主要组织相容性复合体Ⅰ类分子,选择性表达在母胎交界面的细胞滋养层细胞使得妊娠期间形成母体对胎儿的免疫耐受。但是,HLA-G的有限多态性和异常表达与多种病理改变有关,例如肿瘤、自身免疫病和感染性疾病等。近来有研究表明,乙型肝炎病毒和丙型肝炎病毒感染过程中HLA-G的表达均会发生改变,而且HLA-G的表型与病毒的易感性相关。但是,至于HLA-G分子在乙型肝炎和丙型肝炎疾病发展中的作用目前仍不完全清楚。HLA-G与病毒性肝炎的相关性仍需深入研究。     

Pseudomonas aeruginosa Quorum Sensing Molecule N-(3-Oxododecanoyl)-l-Homoserine-Lactone Induces HLA-G Expression in Human Immune Cells

HLA-G is a nonclassical class I human leukocyte antigen (HLA) involved in mechanisms of immune tolerance. The objective of this study was to determine whether N-(3-oxododecanoyl)-l-homoserine lactone (3O-C₁₂-HSL), a quorum sensing molecule produced by Pseudomonas aeruginosa, could modify HLA-G expression to control the host immune response. We evaluated the ability of 3O-C₁₂-HSL to induce HLA-G expression in primary immune cells, monocytes (U937 and THP1), and T-cell lines (Jurkat) in vitro and analyzed the cellular pathway responsible for HLA-G expression. We studied the HLA-G promoter with a luciferase assay and interleukin-10 (IL-10) and p38/CREB signaling with enzyme-linked immunosorbent assay and immunofluorescence, respectively. We observed that 3O-C₁₂-HSL is able to induce HLA-G expression in human monocytes and T cells. We showed that the induction of HLA-G by 3O-C₁₂-HSL is p38/CREB and IL-10 dependent. 3O-C₁₂-HSL treatment is able to arrest only the U937 cell cycle, possibly due to the peculiar expression of the ILT2 receptor in the U937 cell line. Our observations suggest HLA-G as a mechanism to create a protected niche for the bacterial reservoir, similar to the role of HLA-G molecules during viral infections.     

Maternal-fetal tolerance is maintained despite transgene-driven trophoblast expression of MHC class I,and defects in Fas and its ligand

During mammalian pregnancy, one or more semiallogeneic fetuses gestate in direct contact with the maternal circulation and uterine tissue. However, a damaging maternal immune response is not normally provoked. We studied two possible mechanisms for this maternal-fetal tolerance, alone and in combination. First, we directly tested the hypothesis that the striking absence of MHC class I molecules on most placenta trophoblasts protects the fetus from maternal immune attack, by creating transgenic mice which express L^d in giant cell trophoblasts. Second, because Fas ligand (FasL) may contribute to immune privilege, we tested whether functional FasL expression by the fetus, or Fas expression by the mother, contributes to successful reproduction in a fully allogeneic breeding. Our data indicate that neither abnormal expression of MHC class I in giant cells, nor disruption of the Fas-FasL system, nor a combination of these two defects, has an adverse effect on pregnancy outcome. These results suggest that during healthy allogeneic pregnancy, down-regulation of MHC class I and expression of FasL on placenta are not critical events, and other factors must prevent a harmful maternal immune response.     

HLA-G gene polymorphism segregation within CEPH reference families

HLA-G, a nonclassical HLA class I antigen, presents tissue-restricted expression on human trophoblasts and may play an important role in immune tolerance of mother-versus-fetus. In this work we have demonstrated extensive HLA-G genomic polymorphism within three CEPH reference families, by PCR-SSCP analysis and direct sequencing. Among six unrelated parents we assigned eight HLA-G alleles, seven of which are new. We observed the segregation of HLA-G alleles of heterozygous parents among their offspring that matched the segregation of the HLA class I haplotypes. Only one of the mutations observed was found to be nonsynonymous indicating low polymorphism of the HLA-G molecule.     

The X1 box of HLA-G promoter is a target site for RFX and Sp1 factors

HLA-G gene regulation was investigated with regards to homologies among the pathways regulating both classical MHC class I and MHC class II gene expression. They include four conserved cis-acting regulatory elements located in the proximal promoter region referred to as the W/S/Z box, the X box that is comprised of the X1 and X2 halves, and the Y box with an inverted CCAAT site. The X1 box is the binding site for the ubiquitous RFX complex consisting of three subunits; the X2 box is bound by the X2BP/ATF/CREB family factors. The basic S-X-Y regulatory module interacts with CIITA, which is expressed constitutively in APCs, but may be inducible in others cell types by IFN-gamma. Within HLA-G gene promoter the only conserved motifs are S and X1 boxes. We thus investigated the binding capacity of the HLA-G X box in comparison to that of HLA-DRA and HLA-E. We demonstrate that X2 box mutations in HLA-G promoter affect the binding of ATF/CREB family factors and may privilege the X2 box to access by other shared factors. The X1 box is the target for RFX complex and an additional factor we identified as Sp1. We propose that the X region in the HLA-G gene promoter might participate to the combination of factors which play a role in HLA-G gene activation.     

Human leukocyte antigen F protein is expressed in the extra-villous trophoblasts but not on the cell surface of them

PROBLEM: Human leukocyte antigen (HLA)-F together with other class 1b HLAs may play a pivotal role in immunological interaction at feto-maternal interface. However, it is not elucidated whether HLA-F is expressed on cell surface of extra-villous trophoblasts (EVTs). METHOD OF STUDY: The localization of HLA-F in placenta of each trimester was investigated by immunohistochemistry. The expression modality of HLA-F molecule was compared with that of HLA-G in cultured EVTs using flowcytometry. RESULTS AND CONCLUSION: In immunohistochemical study, remarkable staining for HLA-F was confirmed in EVTs throughout gestation. HLA-F expression was restricted to be intracellular in cultured EVTs. HLA-F expression was increased with time in culture, which was accompanied by the increase of cell surface HLA-G. Consequently, HLA-F lacking in cell surface expression on EVTs may not contribute to the direct cell-to-cell immune reaction but might work supportively modifying the function of HLA-G.