Mechanisms of Interleukin-17 Inflammation Induced by Bacteroides fragilis

描述(申请人提供)：脆弱类杆菌是一种常见的结肠共生菌，已知在结肠中占据粘膜生态位，是人类疾病中最主要的厌氧菌。脆性肠毒素杆菌(ETBF)是近年来发现的一种炎症性腹泻的病原菌，可诱发活动性炎症性肠病。然而，多达30%的个人可能会被ETBF殖民，似乎没有任何症状。ETBF的主要毒力因子是一种20 kDa的依赖锌的金属蛋白酶毒素，称为脆性芽孢杆菌毒素(BFT)。我们的新的ETBF感染常规C57BL/6小鼠模型显示，ETBF定植的小鼠在1至2周内迅速出现症状性结肠炎，并出现明显的结肠炎。1周时的结肠炎性浸润物由增加的产生IL-17(IL-17)的CD4+T细胞组成，但不产生干扰素或IL-4。结肠上皮细胞和粘膜炎症细胞亚群均表达磷酸化信号转导和转录激活因子-3(STAT3)。随着时间的推移，ETBF急性结肠炎消退，产生慢性结肠炎，持续至少8个月。使用匹配的同基因脆弱芽孢杆菌菌株，只有在分泌生物活性BFT方面不同，结肠炎可以至少部分归因于BFT。在体外，BFT增加肠上皮通透性至少部分是通过切割黏附蛋白E-钙粘素，并激活核因子-？B信号从而分泌促炎细胞因子--白介素8。我们的数据支持这样的假设，即ETBF定植通过诱导先天反应来刺激急性结肠炎，先天反应沿着依赖STAT3信号的Th17途径引导适应性反应。我们推测，ETBF诱导了一系列人类病理过程，从可能与结肠增生和炎症(肿瘤转化的前驱条件)相关的无症状的定植，到炎症性腹泻和结肠炎。该建议的目的是确定与ETBF诱导的C57BL/6小鼠结肠炎的启动和持续相关的先天和适应性宿主免疫机制。我们将确定Th17效应细胞和STAT信号在ETBF诱导的结肠炎的炎症反应中的作用。我们的结果使我们能够使用一种常见的人类结肠细菌ETBF来开始了解新发现的依赖Th17的结肠炎，这可能为临床常见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(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。第一种是传染性腹泻疾病，这是与儿童营养不良和认知发育迟缓有关的全球发病率和死亡率的原因；第二种是结直肠癌，这是美国与癌症相关的死亡的第二大原因。了解结肠炎症也有助于确定对患有炎症性肠病(克罗恩病和溃疡性结肠炎)和肠易激综合征的患者的治疗方法，肠易激综合征是一种对女性影响不成比例的疾病。

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.