Mechanisms of Interleukin-17 Inflammation Induced by Bacteroides fragilis

描述（由申请人提供）：脆弱拟杆菌是常见的结肠共生体，已知在结肠中占据粘膜生态位，是人类疾病的主要厌氧菌。一类脆弱杆菌，肠产毒素脆弱拟杆菌（ETBF），最近被认为是炎症性腹泻病的病因之一，并可能引发活动性炎症性肠病。然而，高达30%的个体可能在看似无症状的情况下被ETBF定植。ETBF的主要毒力因子是一种20 kDa的锌依赖性金属蛋白酶毒素，称为脆弱芽孢杆菌毒素（BFT）。我们新的ETBF感染的传统C57BL/6小鼠模型显示，被ETBF定植的小鼠在3天内出现快速发作的症状性结肠炎，并在1至2周内出现明显的结肠炎。1周的结肠炎性浸润由CD4+ T细胞增加组成，这些细胞产生白细胞介素-17 (IL-17)，但不产生白细胞介素-17。-干扰素或IL-4结肠上皮细胞和一部分粘膜炎症细胞都表现出磷酸化的信号换能器和转录激活因子-3 （Stat3）。随着时间的推移，ETBF急性结肠炎消退，产生持续至少8个月的慢性结肠炎。使用匹配的等基因脆弱杆菌菌株，仅在其生物活性BFT的分泌上不同，结肠炎可以归因于，至少部分归因于BFT。在体外，BFT至少部分地通过分裂小带粘附蛋白（E-cadherin）增加肠上皮通透性，并激活核因子-？B信号导致促炎细胞因子，白细胞介素-8的分泌。我们的数据支持这样的假设，即ETBF定殖通过诱导先天反应刺激急性结肠炎，先天反应沿着依赖于Stat3信号的Th17途径指导适应性反应。我们假设ETBF诱导了一系列人类病理，从“无症状”定植，可能与结肠增生和炎症（肿瘤转化的前兆条件）相关，到炎症性腹泻和结肠炎。本研究的目的是确定与C57BL/6小鼠中etbf诱导结肠炎发生和持续相关的先天和适应性宿主免疫机制。我们将定义Th17效应细胞和Stat信号在etbf诱导的结肠炎炎症反应中的作用。我们的研究结果使我们能够使用一种常见的人类结肠细菌，ETBF，开始了解新发现的th17依赖性结肠炎症，可能为常见的临床问题结肠炎的治疗方法提供见解。与公共卫生相关的结肠炎症（结肠炎）造成了很大的疾病负担，包括两个主要的公共卫生问题。首先是传染性腹泻病，这是一种全球性的发病和死亡原因，与儿童营养不良和认知发育迟缓有关；第二个是结肠直肠癌，这是美国癌症相关死亡率的第二大原因。了解结肠炎症也可能有助于确定对患有炎症性肠病（克罗恩病和溃疡性结肠炎）和肠易激综合征的个体的治疗方法，这种疾病对女性的影响尤其大。

DESCRIPTION (provided by applicant): Bacteroides fragilis are common colonic commensals, known to occupy a mucosal niche in the colon and the leading anaerobe in human disease. One class of B. fragilis, enterotoxigenic Bacteroides fragilis (ETBF), is recently recognized as an etiology of inflammatory diarrheal disease and may incite active inflammatory bowel disease. Up to 30% of individuals, however, may be colonized, seemingly asymptomatically, with ETBF. The primary virulence factor of ETBF is a 20 kDa zinc-dependent metalloprotease toxin termed B. fragilis toxin (BFT). Our new ETBF-infected conventional C57BL/6 mouse model reveals that mice colonized with ETBF develop rapid onset symptomatic colitis (within 3 days) with marked colitis at 1 to 2 weeks. The colonic inflammatory infiltrates at 1 week are composed of increased CD4+ T cells that produce interleukin-17 (IL-17) but not ?-interferon or IL-4. Both the colonic epithelial cells and a subset of mucosal inflammatory cells display phosphorylated signal transducer and activator of transcription-3 (Stat3). Over time ETBF acute colitis subsides yielding chronic colitis that persists at least 8 months. Using matched isogenic B. fragilis strains differing only in their secretion of biologically active BFT, the colitis can be ascribed, at least in part, to BFT. In vitro BFT increases intestinal epithelial permeability at least, in part, by cleavage of the zonula adherens protein, E-cadherin, and activates Nuclear Factor-?B signaling resulting in secretion of the proinflammatory cytokine, interleukin-8. Our data support the hypothesis that ETBF colonization stimulates acute colitis mediated by induction of innate responses that direct adaptive responses along a Th17 pathway dependent on Stat3 signaling. We postulate that ETBF induce a continuum of human pathology from `asymptomatic' colonization, potentially associated with colonic hyperplasia and inflammation (precursor conditions to neoplastic transformation), to inflammatory diarrhea and colitis. The goals of this proposal are to identify the innate and adaptive host immune mechanisms associated with initiation and persistence of ETBF-induced colitis in C57BL/6 mice. We will define the contribution of Th17 effector cells and Stat signaling to the inflammatory response in ETBF-induced colitis. Our results allow us to use a common human colonic bacterium, ETBF, to begin to understand the newly recognized Th17-dependent colonic inflammation, potentially providing insights into therapeutic approaches for a common clinical problem, colitis. PUBLIC HEALTH RELEVANCE Colonic inflammation (colitis) contributes to a large burden of disease including two major public health concerns. The first is infectious diarrheal diseases, a global cause of morbidity and mortality that is associated with malnutrition and delayed cognitive development in children; and the second is colorectal cancer, the second leading cause of cancer-related mortality in the United States. Understanding colonic inflammation may also help in identifying treatments for individuals afflicted by inflammatory bowel disease (Crohn's disease and ulcerative colitis) and irritable bowel syndrome, an illness disproportionately affecting women.