Antigen Presentation By Class I Major Histocompatibility Complex Molecules: A Context for Thinking About HLA-G

PROBLEM: There is substantial data that support the efficacy of paternal leukocyte immunization (PLI) for the treatment of alloimmune mediated miscarriage; however, there is confusion regarding the laboratory test that should be performed to determine levels of maternal anti-paternal leukocyte antibodies (MAPLA). METHOD: Popular methodologies employed include: 1) microcytotoxicity (MCX), 2) mixed lymphocyte culture (MLC), and 3) cell flow cytometry crossmatch (FCXM). Cell flow cytometry crossmatch correlates well with the more difficult MLC assay although the former proves the more sensitive study. This work compares the MCX assays with FCXM. The study group consisted of ten women who had a history of three or more spontaneous abortions (SABs). All ten had very low levels (<10%) of MAPLA as measured by FCXM. Following PLI all subjects demonstrated elevated levels (>50%) of MAPLA by FCXM. At 12 weeks gestation, sera were simultaneously measured for MAPLA by MCX and FCXM. RESULTS: Although all ten patients had very high levels of MAPLA by FCXM during pregnancy, five of ten had antibodies to HLA Class I and two of ten had antibodies to HLA Class II paternal antigens by MCX. Furthermore, all patients who were positive by MCX to paternal Class I antigens were also positive to Class I antigens not seen in either parent. Both patients who were positive by MCX to paternal Class II antigens were also positive to maternal Class II antigens. Notable is that all ten women eventually delivered healthy infants. CONCLUSION: Based on this preliminary study, the MCX assay is neither sensitive or reliable enough to determine the need and/or to monitor the effectiveness of PLI. Flow cytometry should be the modality of choice when determining the need for alloimmunotherapy and to monitor the effectiveness of treatment.     

Evaluation of trophoblast HLA-G antigen with a specific monoclonal antibody

A monoclonal antibody to HLA-G has been generated by immunizing HLA-A2.1/human β²-microglobulin (β²m) double transgenic mice with murine L cells transfected with both human β²m and HLA-G. This monoclonal antibody, designated as G233, has been found not to cross-react with other HLA class I antigens when tested on numerous cell lines by flow cytometry. With immunohistology, all populations of extravillous trophoblast (cell columns, interstitial trophoblast, endovascular trophoblast, placental bed giant cells) were stained. An extensive range of adult and fetal tissues was also tested but none reacted with monoclonal antibody G233, including those previously reported to express HLA-G mRNA, indicating that the protein has a highly restricted distribution. Failure to detect HLA-G in the fetal thymus raises the question as to how T-cell tolerance to this antigen is induced. Immunoprecipitation of trophoblast surface proteins with monoclonal antibody G233 revealed a heavy chain of 39 kDa and a light chain of 12 kDa, indicating that HLA-G expressed on the surface of trophoblast is complexed with p2m. However, sequential immunoprecipitation with monoclonal antibody W6/32 followed by monoclonal antibody G233 continued to detect a residual band of 39 kDa, suggesting that trophoblast surface HLA-G may also occur as free heavy chains not associated with p2m. Immunoprecipitation followed by two dimensional gel electrophoresis showed that monoclonal antibody G233 recognizes several iso-forms of HLA-G from trophoblast similar to the characteristic spot array previously described for HLA-G. This monoclonal antibody G233 will be highly useful in future experiments to elucidate the function of HLA-G.     

Placental site trophoblastic tumor of the mediastinum

Choriocarcinoma has been described as the most frequent subtype of mediastinal germ cell tumors showing trophoblastic differentiation. We report a unique case of a placental site trophoblastic tumor, which developed in the mediastinum of a 14-year-old boy 2 years after the resection of a mature teratoma. The recurrent tumor was composed of a grossly hemorrhagic and necrotic mass. Histologically, diffusely infiltrating large polygonal cells with focal nodular growth and a teratomatous part containing mature intestinal, respiratory, and squamous epithelium with adjacent cutaneous adnexal structures were found. The typical morphologic features included vessel wall infiltration by the neoplastic cells with fibrinoid deposits and geographic necroses within the tumor masses. Characteristic diffuse positivity for melanoma cell adhesion molecule and human leucocyte antigen G was found on immunohistochemical investigation, confirming the diagnosis of placental site trophoblastic tumor. The patient died 1 year later after polychemotherapy. The outcome of this rare tumor is similar to the reported poor clinical outcome in patients with mediastinal choriocarcinomas.     

人白细胞抗原G1及G5在重度子痫前期患者胎盘组织中的表达

目的 探讨重度子痫前期(sPE)患者胎盘组织中人白细胞抗原(HLA)G1及G5表达的变化.方法 选取早发型及晚发型sPE患者各10例、早产及正常足月妊娠产妇各10例,通过蛋白印迹法及免疫组化方法检测胎盘组织中HLA-G1及G5蛋白的表达.结果 与早产产妇相比,HLA-G1蛋白在早发型sPE患者的胎盘组织中表达量明显减少,分别为2.9±1.1、2.4±0.6,两者比较,差异有统计学意义(P＜0.05);与正常足月妊娠产妇相比,晚发型sPE患者的胎盘组织中HLA-G1蛋白的表 达量明显减少,分别为4.2±2.4、3.5±2.1,两者比较,差异有统计学意义(P＜0.05).与正常足月妊娠产妇相比,HLA-G5蛋白在晚发型sPE患者的胎盘组织中表达量增加,分别为1.1±0.9、1.8±1.1,两者比较,差异有统计学意义(P＜0.05);与早产产妇相比,HLA-G5蛋白在早发型sPE患者胎盘组织中的表达量无明显变化(分别为1.4±0.7、1.6±0.9,P＞0.05).HLA-G1蛋白在早产产妇胎盘组织中的表达量较正常足月妊娠者减少(P＜0.05);HLA-G5蛋白在早产及正常足月妊娠产妇胎盘组织中的表达量无明显差异(P＞0.05).HLA-G1及G5蛋白主要在胎盘的绒毛外细胞滋养细胞中有表达,在血管周围及胚外中胚层中也有高表达.结论(1)HLA-G1在早发型及晚发型sPE患者胎盘组织中的表达均减少.(2)HLA-G5在早发型及晚发型sPE患者胎盘组织中的表达均增加,这一增加趋势在晚发型sPE患者中更为明显.(3)在妊娠晚期,HLA-G1在早产产妇胎盘组织中的表达较少.(4)胎盘组织中能够检测到HLA-G1及G5的表达,其主要位于胎盘的绒毛外细胞滋养细胞中.     

HLA-G haplotype structure shows good conservation between different populations and good correlation with high,normal and low soluble HLA-G expression

HLA-G molecule has considerable impact in various clinical fields, therefore many studies attempted to predict its expression based on HLA-G genotype. These studies have focused on polymorphisms in either the coding region or in one of the two untranslated regions (UTR) of the gene. The aim of our study was to determine if HLA-G haplotype defined based on SNPs 5′ and 3′UTR could be used to predict soluble HLA-G expression in unstimulated individuals. Our findings showed that HLA-G haplotype structure was well conserved between distant populations and that the defined haplotypes were correlated with high, normal and low HLA-G soluble secretors. In conclusion, we showed that this genotyping strategy based on the use of a few selected SNPs rather than isolated SNP analysis allows reliable HLA-G expression in all populations. This strategy could be useful in a number of clinical settings, e.g., predicting graft compatibility immunogenetic laboratories.     

贵州省3个少数民族 HLA-G基因14 bp插入/缺失的多态性研究

目的：了解贵州省3个少数民族（布依族、水族、苗族）群体人类白细胞抗原-G（ HLA-G）基因14 bp插入/缺失多态性的分布规律及其与遗传背景之间的关系。方法：采用PCR扩增、电泳及测序的方法对来自贵州地区的布依族、水族、苗族共344例健康个体DNA进行HLA-G基因14 bp插入/缺失多态性检测,并与文献报道的仡佬族、壮族等13个民族群体的HLA-G基因14 bp插入/缺失多态性分布数据进行对比。结果：布依族、水族和苗族人群的+14 bp 等位基因频率分别为23.7%、26.0%和38.1%,+14 bp/+14 bp 基因型频率分别为9.40%、10.4%和15.9%,14 bp插入频率比较示布依族和苗族差异有统计学意义（χ2=11.345,P=0.001）,苗族与水族差异有统计学意义（χ2=6.125,P=0.009）而布依族和水族间比较差异无统计学意义（ P>0.017）;与其他人群数据比较,苗族群体的14 bp插入/缺失分布与其他人群相似,而作为壮侗语族的布依族、水族则有自己独特的14 bp插入/缺失分布规律。结论：布依族、水族人群的14 bp插入/缺失分布相似,但是与苗族人群的分布存在一定的差异。     

Proteomic analysis of knock-down HLA-G in invasion of human trophoblast cell line JEG-3

Previous studies showed that aberrant HLA-G expression in trophoblast cells plays important roles in trophoblast invasion; however, the mechanisms remain to be explored. In this study, we found that suppressed HLA-G expression could dramatically decrease the mRNA and protein expression levels of matrix metalloproteinase 2 and matrix metalloproteinase 9, and in the proteome assay, there were 3 identified proteins namely, prefoldin 1, eukaryotic translation elongation factor 2 and malate dehydrogenase 2, which were verified by Western blot and known to be associated with invasion, cell cycle and cell metabolism, respectively. Collectively, our study indicated a potential involvement of HLA-G in autocrine networks that may regulate prefoldin, MMPs and trophoblast invasion at the maternal-fetal interface in human pregnancy.     

Human amnion epithelial cells expressing HLA-G as novel cell-based treatment for liver disease

Despite routine liver transplantation and supporting medical therapies, thousands of patients currently wait for an organ and there is an unmet need for more refined and widely available regenerative strategies to treat liver diseases. Cell transplants attempt to maximize the potential for repair and/or regeneration in liver and other organs. Over 40 years of laboratory pre-clinical research and 25 years of clinical procedures have shown that certain liver diseases can be treated by the infusion of isolated cells (hepatocyte transplant). However, like organ transplants, hepatocyte transplant suffers from a paucity of tissues useful for cell production. Alternative sources have been investigated, yet with limited success. The tumorigenic potential of pluripotent stem cells together with their primitive level of hepatic differentiation, have limited the use of stem cell populations.Stem cell sources from human placenta, and the amnion tissue in particular are receiving renewed interest in the field of regenerative medicine. Unlike pluripotent stem cells, human amnion epithelial (AE) cells are easily available without ethical or religious concerns; they do not express telomerase and are not immortal or tumorigenic when transplanted. In addition, AE cells have been reported to express genes normally expressed in mature liver, when transplanted into the liver. Moreover, because of the possibility of an immune-privileged status related to their expression of HLA-G, it might be possible to transplant human AE cells without immunosuppression of the recipient.