Re-examination of HLA-G polymorphism in African Americans
Re-examination of HLA-G polymorphism in African Americans
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DOI：
10.1007/s002510050555
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发表时间：
1999-08-01
期刊：
影响因子：
3.2
通讯作者：
Hatake, K
中科院分区：
文献类型：
--
作者：
Ishitani, A;Kishida, M;Hatake, K
非经典I类基因包括HLA-E、-F和g位点（Geraghty et al. 1987, 1990; Koller et al. 1989）。在这些基因中，HLA-G因其在胎盘滋养细胞中的特异性表达而备受关注（Ellis et al. 1990; Hirano et al. 1994; Ishitani and Geraghty 1992; Kovats et al. 1990）。先前的研究表明，膜结合HLA-G蛋白仅在侵入母体组织的外膜滋养细胞上表达，可溶性HLA-G不仅在这些细胞上表达，也在细胞滋养细胞和合胞滋养细胞上表达（Lee et al. 1995； Ishitani和同事，数据未发表）。滋养细胞位于母胎界面，不表达其他经典的I类或II类基因，可能除了HLA-C （King etal . 1996）。这些数据表明，HLA-G在人类妊娠中起着关键作用。对HLA-G基因座多态性的研究几乎一致表明等位基因多态性水平较低（Alizadeh等人1993；Kirszenbaum等人1997；Morales等人1993；Suarez等人1997；Tamaki等人1993；Yamashita等人1996）。目前，已鉴定出2个包含非同义替换的等位基因（HLA-G* 0103,* 0104）和1个包含外显子3单碱基缺失的空等位基因（* 0105N）。另外两个包含同义变化的等位基因（* 01012和* 01013）也已被表征。van der Ven和Ober（1994）的一项研究表明，与HLA-G* 01011序列相比，非洲裔美国人在HLA-G位点上存在显著的额外等位基因变异，在第3外显子上有24个非同义替换，在第2外显子上有2个非同义替换。如果这项研究得到证实，与其他类似研究相比，将表明这种高水平的多态性是非洲裔美国人所特有的。这反过来意味着，独特的选择压力可能对非洲人口起了作用。这将进一步提出这样一个问题：这种压力可能在何时起作用，是在从非洲到美洲的运动之前还是之后。表达多态性HLA-G的胎儿滋养细胞如何逃脱母体T细胞的异体识别这一重要问题也需要解释。为了解决这些问题，我们研究了HLA-G基因外显子3的等位基因多样性，在非裔美国人和纯加纳非洲人群中选择作为代表性祖先群体。作为所用方法的对照，我们还重新检查了日本人群中的HLA-G多态性。从外周血中提取基因组dna，用聚合酶链反应（PCR）扩增HLA-G基因外显子3 （Yamashita et al. 1996）。42个非裔美国人dna来自Fred Hutchinson癌症研究中心的免疫遗传学部门，42个加纳dna来自鹿儿岛大学医学院的病毒学部门，15个日本基因组dna来自兵库县血液中心（日本兵库县），26个来自当地（奈利医科大学）。HLA-G外显子3序列扩增如下：95 7C，变性9 min，变性35 cy-
The nonclassical class I genes include the HLA-E,-F, and-G loci (Geraghty et al. 1987, 1990; Koller et al. 1989). Among these genes, considerable focus has been on HLA-G because of its specific expression in trophoblast cells of the placenta (Ellis et al. 1990; Hirano et al. 1994; Ishitani and Geraghty 1992; Kovats et al. 1990). Previous work showed that membrane-bound HLA-G protein was expressed exclusively on extravillous trophoblast cells that are invading maternal tissue, and that soluble HLA-G was expressed not only on these cells but also on cytotrophoblast and syncytiotrophoblasts (Lee et al. 1995; Ishitani and co-workers, data unpublished). Trophoblasts reside at the maternal-fetal interface and express no other classical class I or class II genes, with the possible exception of HLA-C (King et al. 1996). These data have suggested that HLA-G plays a critical role in human pregnancy. Studies of polymorphism at the HLA-G locus have almost uniformly indicated a low level of allelic polymorphism (Alizadeh et al. 1993; Kirszenbaum et al. 1997; Morales et al. 1993; Suarez et al. 1997; Tamaki et al. 1993; Yamashita et al. 1996). Currently, two alleles containing nonsynonymous substitutions (HLA-G* 0103,* 0104) and 1 null allele (* 0105N) containing a single base deletion in exon 3 have been identified. Two additional alleles (* 01012 and* 01013) containing synonymous changes have also been characterized. A single study by van der Ven and Ober (1994) indicated that the African American population contains significant additional allelic variation at the HLA-G locus with 24 nonsynonymous substitutions in exon 3 and two in exon 2 when compared with the HLA-G* 01011 sequence. If confirmed, this study, when contrasted with other similar studies, would indicate that this high level of polymorphism is unique to the African American population. This would in turn imply that unique selective pressures might have operated on the African population. It would further raise the question of when such pressures might have been in play, before or after the movement from Africa to America. The important issue of how fetal trophoblast cells expressing polymorphic HLA-G could escape from allorecognition by maternal T cells would also demand explanation. In order to address these issues, we investigated the allelic diversity in exon 3 of the HLA-G gene in a population of African Americans and a pure Ghanaian African population chosen as a representative ancestral group. As a control for the methodology used, we also reexamined HLA-G polymorphism in a Japanese population.Genomic DNAs were extracted from peripheral blood and used in a polymerase chain reaction (PCR) to amplify exon 3 of the HLA-G gene as described (Yamashita et al. 1996). Forty-two DNAs from individuals of African American descent were obtained from the Department of Immunogenetics, Fred Hutchinson Cancer Research Center, 42 Ghanaian DNAs were obtained from the Dept. of Virology, Kagoshima University School of Medicine, 15 Japanese genomic DNAs were obtained from the Hyogo Blood Center (Hyogo, Japan), and 26 were obtained locally (Nara Medical University). HLA-G exon 3 sequences were amplified as follows: 95 7C, 9 min denaturation followed by 35 cy-