Moreau P, Paul P, Rouas-Freiss N, Kirszenbaum M, Dausset J, Carosella E D
Département de Recherche Médicale, Hôpital Saint-Louis, Paris, France.
Am J Reprod Immunol. 1998 Sep;40(3):136-44. doi: 10.1111/j.1600-0897.1998.tb00405.x.
Human leukocyte antigen (HLA)-G is a major histocompatibility complex class I antigen, which is referred to as nonclassical because it displays a tissue-restricted distribution in the placenta, a reduced cytoplasmic domain, a limited polymorphism, and several isoforms. The HLA-G antigen is thought to play an essential role during pregnancy by protecting the semi-allogeneic fetus from recognition and destruction by maternal immune cells.
Alternative splicing of HLA-G mRNA was analyzed by Southern blot of reverse transcriptase-polymerase chain reaction products from trophoblasts of the first trimester of gestation and term placenta. The regulation of HLA-G gene expression was investigated by electrophoretic mobility shift assays using nuclear extracts from cells expressing different levels of HLA-G gene activity. Using polymerase chain reaction-single strand conformational polymorphism and sequencing, we studied HLA-G gene polymorphism in families from the Centre d'Etude du Polymorphisme Humain in Paris. To understand the function of the HLA-G molecule, cytotoxicity assays were carried out with peripheral blood mononuclear cells or polyclonal natural killer effectors cells from 30 different donors against HLA-G1 and HLA-G2 transfectants.
Four main aspects have been elucidated: 1) The primary transcript of the HLA-G gene is alternatively spliced into five main mRNA forms: HLA-G1 (full length), HLA-G2 (minus exon 3), which encodes a membrane-bound isoform associated with beta-2 microglobulin, HLA-G3 (minus exons 3 and 4), HLA-G4 (minus exon 4), and HLA-G5 (plus intron 4), which encodes a soluble form of the HLA-G antigen; 2) specific nuclear factors bind to an important regulatory element located more than 1.2 kb from the HLA-G gene. Three specific complexes are observed in cells that show HLA-G transcriptional activity and an additional factor that could correlate with the repression of HLA-G gene expression that is detected in natural killer cells; 3) we observed an important genomic polymorphism in exon 3 but a very low polymorphism at the protein level; 4) HLA-G1 and HLA-G2 transfectants clearly demonstrated that both HLA-G isoforms are capable of inhibiting natural killer lytic activity.
These results suggest that HLA-G acts as the public ligand for natural killer inhibitory receptors, thus protecting the fetus against maternal rejection.
人类白细胞抗原（HLA）-G是一种主要组织相容性复合体I类抗原，因其在胎盘中呈现组织限制性分布、细胞质结构域缩短、多态性有限以及多种异构体而被称为非经典抗原。HLA-G抗原被认为在妊娠期间发挥着重要作用，可保护半同种异体胎儿免受母体免疫细胞的识别和破坏。
通过对妊娠早期滋养层细胞和足月胎盘的逆转录聚合酶链反应产物进行Southern印迹分析，来检测HLA-G mRNA的可变剪接。利用表达不同水平HLA-G基因活性的细胞的核提取物，通过电泳迁移率变动分析来研究HLA-G基因表达的调控。使用聚合酶链反应-单链构象多态性和测序技术，我们研究了来自巴黎人类多态性研究中心家庭的HLA-G基因多态性。为了解HLA-G分子的功能，我们用来自30个不同供体的外周血单个核细胞或多克隆自然杀伤效应细胞对HLA-G1和HLA-G2转染子进行了细胞毒性试验。
已阐明四个主要方面：1）HLA-G基因的初级转录本可被可变剪接为五种主要的mRNA形式：HLA-G1（全长）、HLA-G2（缺失外显子3），其编码一种与β2微球蛋白相关的膜结合异构体、HLA-G3（缺失外显子3和4）、HLA-G4（缺失外显子4）以及HLA-G5（包含内含子4），后者编码HLA-G抗原的可溶性形式；2）特定的核因子与位于距HLA-G基因1.2 kb以上的一个重要调控元件结合。在显示HLA-G转录活性的细胞中观察到三种特定复合物，以及在自然杀伤细胞中检测到的一种可能与HLA-G基因表达抑制相关的额外因子；3）我们在外显子3中观察到重要的基因组多态性，但在蛋白质水平上多态性非常低；4）HLA-G1和HLA-G2转染子清楚地表明，这两种HLA-G异构体均能够抑制自然杀伤细胞的裂解活性。
这些结果表明，HLA-G作为自然杀伤细胞抑制性受体的公共配体，从而保护胎儿免受母体排斥。
