Rhead Joanne L, Letley Darren P, Mohammadi Marjan, Hussein Nawfal, Mohagheghi Mohammad A, Eshagh Hosseini Mahmoud, Atherton John C
Wolfson Digestive Diseases Centre and Institute of Infection, Immunity and Inflammation, University of Nottingham, Nottingham, England.
Gastroenterology. 2007 Sep;133(3):926-36. doi: 10.1053/j.gastro.2007.06.056. Epub 2007 Jul 3.
BACKGROUND & AIMS: Helicobacter pylori is the main cause of peptic ulceration and gastric adenocarcinoma. The vacuolating cytotoxin gene, vacA, is a major determinant of virulence. Two naturally polymorphic sites in vacA, the signal region and midregion, are well-characterized determinants of toxicity and markers of pathogenesis. The aim of this study was to characterize a new vacA polymorphic site, the intermediate (i) region.
The vacA i-region was identified and characterized by constructing isogenic vacA exchange mutants and determining their vacuolating activity on HeLa, AGS, and RK13 cell lines. The vacA i-region types of H pylori isolates from patients undergoing routine endoscopy were determined by nucleotide sequencing and allele-specific polymerase chain reaction.
Two i-region types were identified, i1 and i2, and both were common among 42 Western clinical isolates. Interestingly, only naturally occurring s1/m2 strains varied in i-type; s1/m1 and s2/m2 strains were exclusively i1 and i2, respectively. Vacuolation assays showed that i-type determined vacuolating activity among these s1/m2 strains, and exchange mutagenesis confirmed that the i-region itself was directly responsible. Using a simple i-region polymerase chain reaction-based typing system, it was shown for 73 Iranian patients that i1-type strains were strongly associated with gastric adenocarcinoma (P < 10(-3)). Finally, logistic regression analysis showed this association to be independent of, and larger than, associations of vacA s- or m-type or cag status with gastric adenocarcinoma.
Together these data show that the vacA i-region is an important determinant of H pylori toxicity and the best independent marker of VacA-associated pathogenicity.
幽门螺杆菌是消化性溃疡和胃腺癌的主要病因。空泡毒素基因（vacA）是毒力的主要决定因素。vacA中的两个天然多态性位点，即信号区和中区，是毒性的特征性决定因素和发病机制的标志物。本研究的目的是鉴定一个新的vacA多态性位点，即中间（i）区。
通过构建同基因vacA交换突变体并测定其对HeLa、AGS和RK13细胞系的空泡形成活性，对vacA i区进行鉴定和表征。通过核苷酸测序和等位基因特异性聚合酶链反应确定接受常规内镜检查患者的幽门螺杆菌分离株的vacA i区类型。
鉴定出两种i区类型，i1和i2，在42株西方临床分离株中均很常见。有趣的是，只有天然存在的s1/m2菌株在i型上有所不同；s1/m1和s2/m2菌株分别仅为i1和i2。空泡形成试验表明，i型决定了这些s1/m2菌株中的空泡形成活性，交换诱变证实i区本身直接起作用。使用基于简单i区聚合酶链反应的分型系统，对73例伊朗患者的研究表明，i1型菌株与胃腺癌密切相关（P < 10^(-3)）。最后，逻辑回归分析表明，这种关联独立于vacA s型或m型或cag状态与胃腺癌的关联，且关联程度更大。
这些数据共同表明，vacA i区是幽门螺杆菌毒性的重要决定因素，也是VacA相关致病性的最佳独立标志物。
