HOST DEFENSES AGAINST PATHOGENIC E. coli

致病性（腹泻性）大肠杆菌是美国和发展中国家食源性疾病的重要原因。大多数致病性大肠杆菌菌株，如EPEC和EHEC，可引起粘膜炎症和疾病，但不会深入肠黏膜或全身扩散。尽管在了解致病性大肠杆菌致病的机制（如毒素）方面取得了很大进展，但对宿主对这些病原体的防御知之甚少。基于缺乏深层组织侵袭，我们假设在肠腔或粘膜表面操作的宿主防御是控制和根除大多数致病性大肠杆菌感染的关键。我们的初步数据强烈支持这一观点，因为我们发现B细胞是清除感染小鼠模型中的EPEC菌株所绝对需要的。拟开展的研究将建立在这一观察的基础上，并利用小鼠感染模型确定B细胞依赖性宿主防御致病性大肠杆菌的机制。我们将特别关注分泌抗体作为B细胞免疫效应器的重要性。这些特异性免疫效应机制的研究将辅以对黏膜免疫防御对致病性大肠杆菌的调节功能的研究，特别是对免疫调节细胞因子IL-6的功能的研究。此外，我们将开始确定肠上皮在协调对致病性大肠杆菌的免疫防御中的重要性，因为上皮细胞是宿主和大多数致病性大肠杆菌菌株相互作用的焦点。这些实验将特别关注转录因子NF-kappaB在肠上皮中的生理功能，使用我们开发的一种新型小鼠模型，其中NF-kB信号通路的关键成分从肠上皮细胞中选择性地删除。拟议的研究有以下具体目标：目标1。明确B细胞依赖性宿主对致病性大肠杆菌的防御机制。目标2。探讨IL-6在宿主防御致病性大肠杆菌中的作用。目标3。目的探讨上皮细胞NF-kappaB在宿主防御致病性大肠杆菌中的作用。总之，这些研究将为宿主根除致病性大肠杆菌感染的关键宿主防御提供重要的新见解，从而为设计针对这些病原体的免疫策略提供重要依据。

DESCRIPTION (provided by applicant): Pathogenic (diarrheagenic) Escherichia coli are an important cause of food-borne disease in the U.S. and developing countries. Most pathogenic E. coli strains, e.g. EPEC and EHEC, cause mucosal inflammation and disease without deep invasion into the intestinal mucosa or systemic spread. Although much progress has been made in understanding the mechanisms by which pathogenic E. coli cause disease (e.g. toxins), relatively little is known about the host defenses against these pathogens. Based on the lack of deep tissue invasion, we hypothesize that host defenses that operate in the intestinal lumen or at the mucosal surface are key for controlling and eradicating infections with most strains of pathogenic E. coil. Our preliminary data strongly support this notion since we found that B cells are absolutely required for clearance of an EPEC strain in a mouse model of infection. The proposed studies will build on this observation and define the mechanisms of B cell-dependent host defense against pathogenic E. coli, using murine infection models. We will focus specifically on the importance of secretory antibodies as immune effectors of B cells. These studies on specific immune effector mechanisms will be complemented with functional investigations on the regulation of mucosal immune defenses against pathogenic E. coli, with a particular focus on the functions of the immunoregulatory cytokine, IL-6. In addition, we will begin to determine the importance of the intestinal epithelium in orchestrating immune defenses against pathogenic E. coli, as epithelial cells are a focal point of interaction between host and most strains of pathogenic E. coll. These experiments will focus particularly on the physiologic functions of the transcription factor, NF-kappaB, in the intestinal epithelium, using a novel murine model we have developed in which a key component of the NF-kB signaling pathway is deleted selectively from intestinal epithelial cells. The proposed studies have the following Specific Aims: AIM 1. To define the mechanisms of B cell-dependent host defense against pathogenic E. coli. AIM 2. To determine the functions of IL-6 in host defense against pathogenic E. coli. AIM 3. To define the importance of epithelial cell NF-kappaB in host defense against pathogenic E. coll. Together, these studies will provide significant new insights into the key host defenses by which the host can eradicate infection with pathogenic E. coli, thus providing an important basis for designing immunization strategies against these pathogens.