Environment, innate immunity and type 1 diabetes

描述（由申请人提供）：1型糖尿病（T1 D）是遗传和环境因素相互作用的结果。最近的全基因组扫描已经提供了许多关于易患疾病的基因的信息，但对导致易感个体发展为T1 D的环境相互作用知之甚少。我们最近在非肥胖糖尿病小鼠（NOD）中获得的证据表明，通过先天免疫适配器MyD 88介导的先天免疫应答可能对疾病的发展起着关键作用。我们发现，MyD 88缺陷的小鼠在无特定病原体（SPF）环境中繁殖时不会发生糖尿病。在这些MyD 88-/-小鼠的胰腺淋巴结中存在增加的T调节细胞活性的证据。然而，当小鼠被重新衍生到无菌设施中时，它们在相同条件下与野生型小鼠一样患上了糖尿病。重新引入一组有限的肠道细菌（改变的Schaedler植物群）再次减少了糖尿病。这表明，内环境影响疾病的发展。了解肠道如何与内部粘膜相互作用以塑造我们的免疫系统，包括先天性和适应性免疫，对于解释慢性炎症性疾病（包括自身免疫性疾病）如何发展至关重要。本课题将1）研究肠道植物群暴露对疾病发生和相关免疫发育变化的影响的关键时间窗; 2）检测MyD 88在肠道树突状细胞中表达的重要性，MyD 88是最有效的抗原呈递细胞，也是先天性和获得性免疫应答之间的关键联系;（3）探讨MyD 88在肠上皮细胞中的表达在响应和感受肠道植物群中的作用。我们的研究将增强我们对内部环境如何塑造免疫反应并导致遗传易感的自身免疫性糖尿病模型中的自身免疫性的理解。反过来，这可能有助于直接调查遗传上易患糖尿病的人群，并有助于制定预防和治疗1型糖尿病的新策略。 公共卫生相关性：1型糖尿病（T1 D）发生在遗传易感个体中，多年来人们已经知道环境因素在决定这些个体是否患糖尿病方面起着重要作用。然而，这些环境因素及其诱导自身免疫性糖尿病的机制仍不清楚。病毒、毒素、饮食因素都被认为是临床疾病的触发因素。生物体与环境之间的相互作用主要通过粘膜表面介导。先天免疫系统是一种进化上保守的系统，代表了抵御环境侵害的第一道防线。天然免疫主要通过Toll样受体（TLR）介导，其识别病原体的关键模式序列。在小鼠中发现了11种TLR，其中大多数也在人类中表达。作为我们更广泛的研究计划的一部分，我们已经在非肥胖糖尿病（NOD）背景下产生了几种单一TLR缺陷小鼠。NOD小鼠是1型糖尿病最广泛使用的实验模型。我们使用这些动物产生的数据表明，在每个TLR缺陷型NOD小鼠品系中，TLR对疾病表达具有特异性作用。大多数TLR下游的一种常见关键信号分子是MyD 88。为了阐明TLR在介导糖尿病表达中的作用，我们产生了MyD 88缺陷型NOD小鼠。令人惊讶的是，这些小鼠被发现在常规的无特定病原体（SPF）环境中饲养时完全抵抗糖尿病的发展。最引人注目的是，当这些动物被关在无菌（GF）条件下时，糖尿病抵抗力减弱。当GF MyD 88-/-NOD小鼠用植物植物群接种时，糖尿病的发病率降低。这表明暴露于肠道细菌是MyD 88缺陷型NOD小鼠免受T1 D发展的机制的重要组成部分。在本申请中，我们将测试以下假设：暴露于肠道非致病性细菌的时间对于保护易感个体免于糖尿病发展是重要的，并且MyD 88在树突状细胞和肠上皮细胞中的表达塑造了肠道细菌的组成，这反过来影响疾病的发展。为了验证我们的假设，我们提出了三个具体目标。

DESCRIPTION (provided by applicant): Type 1 diabetes (T1D) occurs as a result of interplay of genetic and environmental factors. Recent genome-wide scans have given much information about the genes that predispose to disease but much less is known of the environmental interaction that causes susceptible individuals to develop T1D. We have recently generated evidence in the Non Obese Diabetic mouse (NOD) that the innate immune response, mediated through the innate immune adaptor MyD88, may plays a critical role influencing development of disease. We showed that mice deficient in MyD88 did not develop diabetes when bred in a Specific Pathogen free (SPF) environment. There was evidence of increased T regulatory cell activity in the pancreatic lymph nodes of these MyD88-/- mice. However, when the mice were rederived into a germ free facility, they developed the same high incidence of diabetes as wild type mice in the same conditions. Re-introduction of a restricted set of gut commensal bacteria (Altered Schaedler's flora) again reduced diabetes. This indicated that the internal commensal environment was influencing the development of disease. Understanding how commensals interact with the internal mucosa to shape our immune system, both innate and adaptive immunity, is critical to explain how chronic inflammatory diseases, including autoimmune diseases, develop. In this project we will 1) investigate the critical time windows for the exposure to intestinal flora in influencing whether disease develops and the associated immune developmental changes; 2) test the importance of expression of MyD88 in intestinal dendritic cells as the most potent antigen presenting cells and the critical link between innate and adaptive immune responses; 3) investigate the importance of expression of MyD88 in intestinal epithelial cells in responding to and sensing the commensal flora. Our studies will enhance our understanding of how the internal environment may shape the immune response and lead to autoimmunity in a genetically susceptible autoimmune diabetes model. In turn, this may help to direct investigation in people genetically susceptible to diabetes and aid development of new strategies for prevention and treatment of type 1 diabetes. PUBLIC HEALTH RELEVANCE: Type 1 diabetes (T1D) occurs in genetically susceptible individuals and it has been known for many years that environmental factors play an important role in determining whether these individuals develop diabetes. However, the identification of these environmental factors and their mechanisms in induction of autoimmune diabetes remains unclear. Viruses, toxins, dietary factors have all been implicated as triggers for clinical disease. The interaction between the organisms and environment is mediated principally through mucosal surfaces. The innate immune system is an evolutionarily conserved system that represents the first line of defense against environmental insults. Innate immunity is mediated primarily through Toll-like receptors (TLRs) that recognize the key pattern sequences of pathogens. Eleven TLRs have been found in mice and most of them are also expressed in humans. As part of our broader research program, we have generated several lines of single TLR deficient mice on the non-obese diabetic (NOD) background. NOD mice are the most widely used experimental model for type 1 diabetes. Our data generated using these animals suggest a TLR specific effect on disease expression in each TLR deficient NOD mouse strain. A common critical signaling molecule downstream of most TLRs is MyD88. In an attempt to clarify the role of TLRs in mediating the expression of diabetes, we have generated MyD88 deficient NOD mice. Surprisingly, these mice were found to be completely resistant to the development of diabetes when raised in a conventional specific pathogen free (SPF) environment. Most strikingly, when these animals were housed in germ free (GF) conditions, diabetes resistance was diminished. When the GF MyD88-/-NOD mice were recolonized with commensal flora, the incidence of diabetes was reduced. This suggests that exposure to commensal bacteria was an important part of the mechanism by which MyD88 deficient NOD mice were protected from development of T1D. In this application, we will test the hypothesis that the timing of exposure to commensal, non-pathogenic bacteria is important in protecting susceptible individuals from diabetes development and the expression of MyD88 in dendritic cells and gut epithelial cells shapes the composition of the commensal bacteria which in turn affects disease development. To test our hypothesis, we propose three specific aims.