ULCER-ASSOCIATED MAJOR ANTIGEN OF HELICOBACTER PYLORI

幽门螺杆菌是一种弯曲的、微需氧的革兰氏阴性细菌。 这是人类慢性胃炎的主要原因。虽然大多数人 感染者仍然没有症状，感染这种病原体是一种 消化性溃疡疾病发生的重要危险因素 胃癌。拟议工作的主要目标是 鉴定131 kDa免疫优势抗原(CagA； 细胞毒素相关基因产物)在幽门螺杆菌致病机制中的作用 十二指肠溃疡相关疾病。大约50%-60%的幽门螺杆菌分离株 产生CagA抗原，几乎所有感染幽门螺杆菌的患者 十二指肠溃疡患者对CagA产生血清学反应。上一首 研究表明，粘膜中性粒细胞的浸润和上皮 局部皮肤退变的患者明显更严重 对CagA的胃免疫反应明显高于无CagA反应的患者。 此前的研究也表明，产生CagA的幽门螺杆菌菌株 胃液诱导显著增加IL-8的合成 与CagA阴性菌株相比，CagA阴性菌株具有更强的抗性。此外，最近的研究 已经表明，感染CagA+菌株的患者会诱导一种特殊的 IL-1α和IL-1α在胃组织中的细胞因子表达模式 IL-1β。编码CagA的基因现已克隆并重组 CagA蛋白被幽门螺杆菌感染患者的血清识别。 幽门螺杆菌可以改变CagA的大小，这种大小的变化与 带有重复序列的缺失或插入。基因的序列分析 CagA上游区域，这在CagA菌株中不存在， 鉴定出三个基因(cagB、CAGC和cagD)。推导出的CAGC序列 被发现与百日咳波氏杆菌毒素有显著的同源性 分泌蛋白(PtIC)。这项研究的假设是CagA 幽门螺杆菌抗原与十二指肠溃疡疾病有关，是一种 重要的毒力因素。具体目标是：1)研究 CagA的产生与幽门螺杆菌感染相关十二指肠的关系 溃疡疾病，2)确定CagA在胃炎症中的作用， 3)研究CagA+和CagA H.Pylori的遗传差异 为了实现第一个目标，从幽门螺杆菌中获得天然的CagA 84-183菌株的纯化及其结构和生化特性 特征已确定。接下来，对CagA的粘膜免疫反应将是 单纯性胃炎与十二指肠炎组的比较 溃疡。随后，从胃炎患者中分离出幽门螺杆菌 单独和十二指肠溃疡将测试CagA大小并确定 CagA基因表达类型与临床预后的关系 CagA+和CagA菌株的同基因对将被用来确定 CagA在细胞因子诱导和中性粒细胞激活中起作用 胃组织。CagA是唯一存在的邻近基因 在CagA+菌株中，将通过插入 突变，并将对突变体进行细胞毒素分泌和/或 细胞因子诱导。理解CagA及其致病因子的致病作用 幽门螺杆菌感染的邻近基因产物可能有助于幽门螺杆菌的发展 制定策略，以减少与并发症相关的发病率 幽门螺杆菌感染。

Helicobacter pylori is a curved, microaerophilic, gram-negative bacterium that is the major cause of chronic gastritis in humans. While most infected persons remain asymptomatic, infection with this pathogen is a significant risk factor for the development of peptic ulcer disease and gastric carcinoma. The major objective of the proposed work is to characterize the role of the 131 kDa immunodominant antigen (CagA; cytotoxin-associated gene product) in the pathogenesis of H.pylori- associated duodenal ulcer disease. About 50-60% of H.pylori isolates produce the CagA antigen, and virtually all H. pylori-infected patients with duodenal ulceration develop a serologic response to CagA. Previous studies have shown that mucosal neutrophil infiltration and epithelial surface degeneration are significantly greater in patients with a local gastric immune response to CagA than in those without such a response. Previous studies have also shown that CagA-producing H. pylori strains induce significantly more interleukin-8 (lL-8) synthesis by gastric epithelial cells than do CagA-negative strains. In addition,recent studies have shown that patients infected with CagA+ strains induce a specific pattern of cytokine expression in gastric tissue involving IL-1 alpha and IL-1 beta. The gene encoding CagA has now been cloned, and recombinant CagA protein is recognized by sera from an H.pylori-infected patients. H.pylori can vary the size of CagA and the size variation is associated with deletion or insertion of repeat sequences. Sequence analysis of the region upstream from cagA, which is not present in CagA strains, identified three genes (cagB, cagC, and cagD ). The deduced CagC sequence was found to have significant homology with the Bordetella pertussis toxin secretion protein (PtIC). The hypothesis of this study is that the CagA antigen of H.pylori is associated with duodenal ulcer disease, and is an important virulence factor. The specific aims are 1) to study the relationship between CagA production and H.pylori-associated duodenal ulcer disease, 2) to determine the role of CagA in gastric inflammation, 3) to characterize the genetic differences between CagA+ and CagA H.pylori strains.To accomplish the first objective, native CagA from H.pylori strain 84-183 will be purified and its structural and biochemical characteristics determined. Next, mucosal immune responses to CagA will be compared in patients with gastritis alone and those with duodenal ulceration. Subsequently, H.pylori isolates from patients with gastritis alone and duodenal ulcer will be tested for CagA size and determine the relationship between the type of CagA expressed and clinical outcome. Isogenic pairs of CagA+ and CagA strains will be used to determine whether CagA plays a role in cytokine induction and neutrophil activation within gastric tissues. The cagA neighboring genes that are present exclusively in CagA+ strains will be characterized and disrupted by insertional mutagenesis, and the mutants will be tested for cytotoxin secretion and/or cytokine induction. Understanding the pathogenic role of CagA and its neighboring gene products in H.pylori infection may aid in the development of strategies to decrease the morbidity associated with complications of H.pylori infection.