Differential expression of HLA-E, HLA-F, and HLA-G transcripts in human tissue

The data presented here demonstrate that the HLA-G class I gene is unique among the members of the human class I gene family in that its expression is restricted to extraembryonic tissues during gestation. Furthermore, the pattern of HLA-G expression in these tissues changes as gestation proceeds. During first trimester HLA-G is expressed within the placenta and not within the extravillous membrane. At term, the pattern of the HLA-G expression is reversed, extravillous membrane expresses HLA-G while placenta does not. Another non-HLA-A, -B, -C class I gene, HLA-E, is also expressed by extraembryonic tissues. Unlike HLA-G, HLA-E is expressed by both placenta and extravillous membrane at first trimester and at term. These results raise the intriguing possibility that the HLA-G-encoded molecule has a role in embryonic development and/or the fetal-maternal immune response.     

HLA-G and classical HLA class I expression in primary colorectal cancer and associated liver metastases

De novo expression of HLA-G has been demonstrated in colorectal cancer. HLA-G, amongst others, inhibits natural killer cell function, contributing to host immune defense evasion. Another mechanism to escape anti-tumor immunity is loss of HLA class I. Therefore, we determined HLA-G and HLA class I expression on primary colorectal tumors and associated liver metastases, in order to get insight in the metastasizing process regarding escaping anti-tumor immunity. HLA-G expression was evaluated using three mAbs; 4H84, MEM-G/1 and MEM-G/2. In total 81 colorectal cancer patients were evaluated. Formalin-fixed paraffin-embedded tissue sections of primary tumors and associated liver metastases, were immunohistochemically stained. A concordance between expression or loss/downregulation in the primary tumor and associated liver metastasis regarding HLA class I expression was observed in 80% of the cases. In contrast with the hypothesis of escaping NK cell-killing, we demonstrated for each HLA-G detecting mAbs used in this study, that the majority of the primary tumors that positively stained for HLA-G did not express HLA-G in the associated liver metastasis. Furthermore, we revealed the existence of non-specific binding and in addition we found that the different epitopes of HLA-G detected by 4H84, MEM-G/1 and MEM-G/2 mAbs were expressed differentially in colorectal tumor tissues.     

Comparative reactivity of different HLA-G monoclonal antibodies to soluble HLA-G molecules

Different HLA-G monoclonal antibodies (mAbs) were first evaluated for their capability to identify soluble HLA-G (sHLA-G) in ELISA. Three of them, namely 87G, BFL.1 and MEM-G/9, when used as coating mAbs together with W6/32 capture mAb, identified beta2-microglobulin (beta2m)-associated-sHLA-G but not soluble HLA-B7 (sHLA-B7) in cell culture supernatants from transfected cells. By comparison, the anti-HLA class I mAb 90 did recognize both sHLA-G and sHLA-B7. By using these HLA-G mAbs, sHLA-G was identified in amniotic fluids as well as in culture supernatants of first trimester and term placental explants but not in cord blood. Intron 4-retaining sHLA-G isoforms were identified in some amniotic fluids by the use of an intron 4-specific mAb (16G1). Reactivity of these different HLA-G mAbs was then compared to determine their respective binding sites on soluble and membrane-bound HLA-G. Using both ELISA and flow cytometry analysis, we showed that they did not compete with each other, which suggested that they did not recognize the same determinants. Finally, we report that two mAbs directed against the alpha1 domain of HLA class I heavy chain (mAb 90 and YTH 862) did compete with 87G, therefore demonstrating that this latter mAb recognized an epitope localized on this external domain of HLA-G.     

Impaired spontaneous endocytosis of HLA-G

HLA-G is a class Ib (non-classical) major histocompatibility complex (MHC) protein expressed at the maternal-fetal interface that inhibits natural killer (NK) cell-mediated lysis in an allotype-independent manner. Here we report that the spontaneous endocytosis of HLA-G is severely reduced because of its short cytoplasmic tail. Class I (classical) MHC proteins on the surface of B cell trans-fectants detected by primary and secondary antibodies underwent endocytosis at a moderate rate, whereas HLA-G, chimeric proteins consisting of the extracellular domains of HLA-C with the C-terminal sequence of HLA-G, or glycophosphatidylinositol-tailed HLA-C proteins, were not efficiently internalized. In addition, a mutant of β2-microglobulin (Ser88Cys) that could be specifically labeled with Texas red (or other fluorescent probes) and exchanged into class I or class Ib MHC proteins was employed to study spontaneous internalization of MHC proteins by a non-perturbative method independent of an antibody ligand. These data are discussed in terms of both the role of HLA-G expressed on the fetal trophoblast and the function of the cytoplasmic tail in class I MHC proteins.     

Association between HLA-G genotype and risk of pre-eclampsia: a case-control study using family triads

Pre-eclampsia affects 2-7% of all pregnancies with varying severity and is a leading cause of maternal and fetal mortality and morbidity. The aetiology involves almost certainly a combination of genetic predisposition with maternal and fetal contributions and environmental factors. Research points towards pathologies in the placenta as the triggering factor which leads to systemic endothelial dysfunction in the mother, probably as the result of interaction with released placental factors circulating in the maternal blood. One prominent hypothesis regarding the aetiology of pre-eclampsia suggests that it is caused by immune- maladaptation. The MHC class Ib gene, HLA-G, is expressed in the placenta and seems to have immunomodulatory functions. Aberrant HLA-G mRNA and protein expression in pre-eclamptic placentas have been reported. Here, we have investigated detailed HLA-G genotypes in a case-control study of 155 family triads of mother, father and newborn. Among primiparas, an overrepresentation of a homozygous HLA-G genotype was detected in the 40 pre-eclamptic offspring compared to the 70 controls [P = 0.002, Fisher's exact test; odds ratio 5.57 (95% CI 1.79-17.31)]. Further analyses suggested that the differences between pre-eclamptic cases and controls primarily were accomplished by a different transmission from the father of a 14 bp deletion/insertion polymorphism in exon 8 (P = 0.006, Fisher's exact test), which previously has been linked to differences in the levels of HLA-G expression and in HLA-G mRNA splicing. The results may also indicate that combined mother-child HLA-G genotypes could influence the risk of developing pre-eclampsia. Overall, the study suggests that HLA-G genotypes and expression might have a significant influence on development of pre-eclampsia.     

HLA-G1 co-expression boosts the HLA class I-mediated NK lysis inhibition

It is now acknowledged that the pattern of HLA-G expression is not restricted to extravillous cytotrophoblast cells, as several studies described HLA-G in HLA class I+ cells, such as thymic epithelial cells, cytokine-activated monocytes and some tumors. In these situations, HLA-G may provide an additional inhibitory signal to escape from NK cell-mediated cytotoxicity. Accordingly, the aim of this study was to define the behavior of HLA-G once it is co-expressed into an HLA-A, -B, -C and -E+ cell line. For this purpose, HLA-G1 cDNA was transfected into an HLA class I+ melanoma cell line which was used as a target towards freshly isolated peripheral blood NK cells. Cytotoxic experiments using either anti-HLA-G1 or anti-HLA-G1 inhibitory receptor mAb show that HLA-G1 boosts the HLA class I-mediated inhibition of polyclonal NK cells through interaction with ILT-2, which appears as the major HLA-G1 inhibitory receptor involved. Nevertheless, HLA-G1 is also able to inhibit the cytolytic activity of an ILT-2- NK clone which otherwise expresses another HLA-G1 inhibitory receptor belonging to the KIR103 gene family. In order to more precisely define the relative role exerted by HLA-G1 versus -E on polyclonal NK cells, antibody-blocking assays were carried out using either anti-HLA class I or anti-CD94/NKG2A. Results demonstrate that in the absence of HLA-G1, the naturally expressed HLA class I-mediated NK inhibition is predominantly exerted by HLA-E through binding with CD94/NKG2A. In contrast, once HLA-G1 is expressed, it becomes the major NK inhibitory ligand.     

Role of 14-bp deletion in the HLA-G gene in the maintenance of pregnancy

Differential expression of human leukocyte antigens (HLAs) on trophoblast has been the focus of many studies, specially on extravillous cytotrophoblast cells, which migrates into the maternal uterine tissues. These invading cells do not express classical major histocompatibility complex class I (-A and -B) and class II molecules, along with low expression of HLA-C. HLA-G is the predominantly expressed antigen along with HLA-E. Hence, it is believed that expressed antigens may be involved in materno-fetal tolerance. In the present study, we have studied 14-bp deletion polymorphism in the exon-8 of the non-classical HLA-G antigen. There was no difference in the frequency of deletion/insertion polymorphism in fertile normal women and recurrent spontaneous abortion (RSA) women. However, the number of heterozygotes (-14b/+14b) were increased in RSA women. The probable mechanism for the increase of heterozygotes in recurrent fetal loss is discussed in light of soluble HLA-G.     

HLA-G的遗传、功能及临床意义

HLA－G属非经典的HLA Ⅰ类分子，与经典的HLA Ⅰ类分子相比它有3个特点：（1）多态性水平低；（2）体内分布局限于特定组织；（3）由于内含子和外显子间的剪接位点改变可形成4种膜结合型和两种可溶型HLA－G异构体。过去几年大量研究结果表明，HLA－G是一种免疫耐受分子。在此将系统地介绍HLA－G的遗传多态性、表达、功能、对免疫相关疾病的影响、演变及HLA－G的临床应用前景。     

Analysis of HLA-G gene polymorphism and protein expression in invasive breast ductal carcinoma

The human leukocyte antigen G (HLA-G) is a non-classical HLA class I molecule predominantly expressed in trophoblastic placental cells to protect the fetus during pregnancy. However, evidence has shown that this molecule may be implicated in the immune escape mechanism of tumor cells. Thus, the aim of this study was to evaluate the frequency of 14-bp insertion/deletion HLA-G polymorphism, as well as the expression of this molecule in patients with invasive breast ductal carcinoma (IDC). A significant association between the expression of HLA-G and the presence of metastasis in lymph nodes (p = 0.01) was observed and the expression of HLA-G was significantly higher in patients with shorter survival time (p = 0.03). The analysis suggests that the polymorphism observed in patients with IDC may be inducing a higher expression of the HLA-G molecule, which may possibly contribute to shorter survival time and a worse clinical prognosis for such patients.     

白纹伊蚊T7噬茵体展示cDNA文库的构建

为筛选白纹伊蚊与相关蚊媒病毒相互作用的基因,本文构建了白纹伊蚊Aedes albopictusT7噬菌体展示eDNA文库,分离与纯化白纹伊蚊mRNA,所得mRNA经反转录合成双链cDNA后,在双链cDNA末端加上定向EcoRI／HindIn接头使其两端分别带EcoRI和Hind11I黏性末端;接着用MiniColumn纯化收集300bp以上的双链cDNA片段连接于T7 Select 10—3b载体;经体外包装后,以BLT5403为受体菌构建1v7噬菌体展示cDNA文库。所建文库的库容量经测定为1．7×10’pfu／mL,扩增后文库滴度为2．5×10^（15）pfu／mL。对从原始文库中随机挑取的50个噬菌斑进行PCR鉴定,重组率为95％以上;阳性克隆片段长度分布在200～2000bp,其中有90％的插入片段大于300bp。本文所构建的白纹伊蚊T7噬菌体展示cDNA文库,满足cDNA文库的基本要求,可以用于筛选白纹伊蚊与相关蚊病毒相互作用的基因。