Environment, innate immunity and type 1 diabetes

描述（由申请人提供）：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已经提供了很多关于易患病基因的信息，但对导致易感个体患上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）中获得的证据表明，先天免疫反应，通过先天免疫受体MyD88介导，可能在影响疾病发展中起关键作用。我们发现缺乏MyD88的小鼠在特定无病原体（SPF）环境中繁殖时不会发生糖尿病。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，当这些小鼠被重新培育到无菌环境中时，在相同的条件下，它们与野生型小鼠出现了同样高的糖尿病发病率。重新引入一组受限制的肠道共生细菌（改变的舍德勒菌群）再次降低了糖尿病。这表明内部共生环境影响着疾病的发展。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。在这个项目中，我们将1)研究暴露于肠道菌群对疾病是否发展和相关免疫发育变化的影响的关键时间窗；2)验证MyD88在肠道树突状细胞中作为最有效的抗原呈递细胞的表达，以及在先天免疫和适应性免疫应答之间的关键联系的重要性；3)研究MyD88在肠道上皮细胞中表达对共生菌群的响应和感知的重要性。我们的研究将增强我们对内部环境如何影响免疫反应的理解，并在遗传易感的自身免疫性糖尿病模型中导致自身免疫。反过来，这可能有助于对糖尿病遗传易感人群的直接调查，并有助于开发预防和治疗1型糖尿病的新策略。

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.