Kahlmann Daniel, Davalos-Misslitz Ana Clara Marques, Ohl Lars, Stanke Frauke, Witte Torsten, Förster Reinhold
Institute of Immunology, Hannover Medical School, Hannover, Germany.
BMC Genet. 2007 Jun 22;8:33. doi: 10.1186/1471-2156-8-33.
The chemokine receptor CCR7 is a key organizer of the immune system. Gene targeting in mice revealed that Ccr7-deficient animals are severely impaired in the induction of central and peripheral tolerance. Due to these defects, Ccr7-deficient mice spontaneously develop multi-organ autoimmunity showing symptoms similar to those observed in humans suffering from connective tissue autoimmune diseases. However, it is unknown whether mutations of CCR7 are linked to autoimmunity in humans.
DNA samples were collected from 160 patients suffering from connective tissue autoimmune disease (Sjogren's syndrome, n = 40; systemic lupus erythematosus, SLE, n = 20 and systemic sclerosis, n = 100) and 40 health subjects (n = 40). All participants in this study were of German descent. Samples were screened for single nucleotide polymorphisms (SNP) by sequencing the coding region of the CCR7 gene as well asthe exon flaking intron sites and parts of the regions encoding for the 5'- and 3'-UTR. CCR7 variants were rare. We identified six different sequence variants, which occurred in heterozygosis. The identified SNP were observed at position -60 C/T (observed 1x), +6,476 A/G (7x), +6,555 C/T (15x), +6,560 C/T (6x), +10,440 A/G (3x) and +11,475 C/A (1x). Four of these variants (+6,476 A/G, +6,555 C/T, +6,560 C/T and +10,440 A/G) display allelic frequencies between 1% and 5 % and were present in both patients and control groups. The variants +6,476 A/G, +6,555 C/T, +6,560 C/T are located in the intron 2, while the +10,440 A/G variant corresponds to a silent mutation in exon 3. The variants -60 C/T and +11,475 C/A which are located at the 5'-UTR and 3-UTR respectively, display allelic frequencies below 1%. No correlation between these variants and the autoimmune diseases investigated could be observed. However, reporter gene expression assay demonstrated that the mutation at the -60 C/T position in homozygosis leads to reduced luciferase activity.
These results suggest that variants of CCR7 gene occur at an extremely low frequency in the German population and that neither Sjogren's syndrome, systemic lupus erythematosus, nor systemic sclerosis are associated with these variants. Nevertheless, the decreased luciferase activity observed in cells transfected with the promoter region bearing the -60 C/T mutation suggests that this CCR7 variant could potentially lead to increased susceptibility to autoimmunity.
趋化因子受体CCR7是免疫系统的关键组织者。对小鼠进行基因靶向研究发现，缺乏Ccr7的动物在诱导中枢和外周耐受性方面严重受损。由于这些缺陷，缺乏Ccr7的小鼠会自发发展出多器官自身免疫，表现出与结缔组织自身免疫疾病患者相似的症状。然而，尚不清楚CCR7突变是否与人类自身免疫有关。
从160例结缔组织自身免疫疾病患者（干燥综合征，n = 40；系统性红斑狼疮，SLE，n = 20；系统性硬化症，n = 100）和40名健康受试者（n = 40）中收集DNA样本。本研究的所有参与者均为德国血统。通过对CCR7基因的编码区、外显子侧翼内含子位点以及部分5'-和3'-UTR编码区进行测序，筛选样本中的单核苷酸多态性（SNP）。CCR7变体很少见。我们鉴定出六个不同的序列变体，均为杂合状态。所鉴定的SNP分别位于-60 C/T（观察到1次）、+6,476 A/G（7次）、+6,555 C/T（15次）、+6,560 C/T（6次）、+10,440 A/G（3次）和+11,475 C/A（1次）位置。其中四个变体（+6,476 A/G、+6,555 C/T、+6,560 C/T和+10,440 A/G）的等位基因频率在1%至5%之间，且在患者组和对照组中均有出现。变体+6,476 A/G、+6,555 C/T、+6,560 C/T位于内含子2中，而+10,440 A/G变体对应于外显子3中的一个沉默突变。分别位于5'-UTR和3'-UTR的变体-60 C/T和+11,475 C/A，其等位基因频率低于1%。未观察到这些变体与所研究的自身免疫疾病之间存在相关性。然而，报告基因表达分析表明，纯合状态下-60 C/T位置的突变会导致荧光素酶活性降低。
这些结果表明，CCR7基因变体在德国人群中出现的频率极低，干燥综合征、系统性红斑狼疮和系统性硬化症均与这些变体无关。尽管如此，在转染了带有-60 C/T突变的启动子区域的细胞中观察到荧光素酶活性降低，这表明该CCR7变体可能会增加自身免疫易感性。
