Environment, innate immunity and type 1 diabetes

描述(申请人提供)：1型糖尿病(T1D)是遗传和环境因素相互作用的结果。最近的全基因组扫描提供了许多关于易患疾病的基因的信息，但对导致易感个体患T1D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)中产生的证据表明，通过先天免疫适配器MyD88介导的先天免疫反应可能在影响疾病的发展中发挥关键作用。我们发现，MyD88基因缺陷的小鼠在无特定病原体(SPF)的环境中饲养时不会患上糖尿病。有证据表明，这些MyD88-/-小鼠的胰腺淋巴结中T调节细胞活性增加。然而，当小鼠被重新衍生到无菌设施时，它们在相同条件下患糖尿病的几率与野生型小鼠一样高。重新引入一组受限的肠道共生细菌(改变了舍德勒菌群)，再次降低了糖尿病的发病率。这表明，内部共生环境正在影响疾病的发展。了解共生体如何与内部粘膜相互作用来塑造我们的免疫系统，包括先天免疫和获得性免疫，对于解释包括自身免疫性疾病在内的慢性炎症性疾病是如何发展至关重要的。在这个项目中，我们将1)研究肠道菌群暴露影响疾病发展和相关免疫发育变化的关键时间窗口；2)测试MyD88在肠道树突状细胞中作为最强大的抗原提呈细胞的重要性，以及天然和获得性免疫反应之间的关键联系；3)研究MyD88在肠道上皮细胞中表达在响应和感知共生菌群中的重要性。我们的研究将加强我们对内部环境如何塑造免疫反应并导致遗传易感自身免疫性糖尿病模型的自身免疫的理解。反过来，这可能有助于指导对糖尿病遗传易感性人群的研究，并有助于开发预防和治疗1型糖尿病的新策略。 公共卫生相关性：1型糖尿病(T1D)发生在遗传易感的人中，多年来人们已经知道，环境因素在决定这些人是否患上糖尿病方面发挥着重要作用。然而，这些环境因素的识别及其在诱发自身免疫性糖尿病中的机制仍不清楚。病毒、毒素、饮食因素都被认为是临床疾病的诱因。生物与环境之间的相互作用主要是通过粘膜表面来调节的。先天免疫系统是一种进化上保守的系统，代表着抵御环境侮辱的第一道防线。先天免疫主要通过识别病原体关键模式序列的Toll样受体(TLRs)来介导。已经在老鼠身上发现了11种TLR，其中大多数在人类身上也表达了。作为我们更广泛研究计划的一部分，我们已经在非肥胖糖尿病(NOD)背景下培育了几个单一TLR缺陷小鼠品系。NOD小鼠是目前应用最广泛的1型糖尿病实验模型。我们使用这些动物产生的数据表明，在每个TLR缺陷的NOD小鼠品系中，TLR对疾病表达具有特异性影响。大多数TLR下游的一个常见的关键信号分子是MyD88。为了阐明TLRs在糖尿病表达中的作用，我们产生了MyD88缺陷的NOD小鼠。令人惊讶的是，这些小鼠被发现在传统的无特定病原体(SPF)环境中饲养时，对糖尿病的发展完全具有抵抗力。最引人注目的是，当这些动物被饲养在无菌(GF)条件下时，糖尿病抵抗力减弱。当GF MyD88-/-NOD小鼠与共生菌群重新克隆时，糖尿病的发生率降低。这表明，接触共生菌是MyD88缺陷NOD小鼠免受T1D发病保护的重要机制之一。在这一应用中，我们将检验这一假设，即接触共生非致病细菌的时机对于保护易感个体免受糖尿病发展是重要的，而MyD88在树突状细胞和肠上皮细胞中的表达塑造了共生细菌的组成，而共生细菌又影响疾病的发展。为了检验我们的假设，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.