Immunological Mechanisms Underlying T1dm Pathogenesis

1型糖尿病（T1DM）是一种自身免疫性疾病，由T细胞介导的胰腺中产生胰岛素的β细胞的破坏引起。目前的治疗包括注射胰岛素替代、频繁血糖监测和饮食/运动纪律，可以防止因激素不足而死亡，但不能治愈，也不能完全预防长期并发症，包括神经损伤和大血管和小血管损伤。血管损伤反过来会导致各种器官的损伤，包括心脏、大脑、肾脏和眼睛。与没有糖尿病的人相比，糖尿病患者的预期寿命缩短了约三分之一。这项工作始于20世纪90年代中期的海军医学研究所，并在德国乌尔姆大学进一步发展，随后在过去的两年里在美国国立卫生研究院利用大鼠胰岛素启动子(RIP)-CD80转基因小鼠（RIP-CD80小鼠）建立了一种独特的自身免疫性糖尿病小鼠模型。基于它们的共刺激分子CD80的β细胞特异性表达，这些动物倾向于免疫介导的β细胞破坏。虽然RIP-CD80小鼠很少发生自发性糖尿病（发病率为6.7%，与野生型小鼠相比没有），但我们已经观察到并初步描述了这些小鼠在用β细胞自身抗原（即由这些小鼠的胰腺β细胞特异性表达的蛋白质分子）免疫后表现出的发展进行性胰岛浸润和最终胰岛素依赖型糖尿病（IDDM）的深刻易感性。例如，这些动物，与非转基因的同伴不同，在胰岛素前体免疫后，一致发生胰岛细胞破坏和胰岛素依赖性糖尿病（IDDM），胰岛素前体是一种强烈怀疑参与人类T1DM发病机制的β细胞自身抗原。我们已经证明，成熟胰岛素分子中至少存在一个相关的自身抗原CTL表位（H-2b），这与目前基于算法的表位预测模型形成对比。此外，到目前为止，我们的模型比非肥胖糖尿病小鼠（NOD）更能预测对治疗药物的免疫反应，NOD是一种最广泛用于研究自身免疫性糖尿病的模型。我们使用RIP-CD80小鼠模型的目的可以概括如下：(1)确定重要的自身抗原（Ag）和ctl表位，作为发展自身免疫反应的初始靶点。我们将探索几种候选自身抗原的免疫途径，包括肽免疫、dna疫苗和逆转录病毒转导的树突状细胞（DC），因为它们能够引发MHC I类限制性T细胞反应、胰岛素和糖尿病。(2)在过继转移模型中研究β细胞特异性T细胞反应，其中主要的自身反应性T细胞敏化将在体外或通过体内免疫进行，如上文(1)所述。这些研究将集中于发展中的β细胞破坏性免疫反应的机制，并将试图确定新的治疗方法来干扰正在进行的免疫反应。(3)继续探索我们的初步数据，表明非专业抗原呈递细胞（APC），如胰腺β细胞或成纤维细胞，可以在体内启动初始前体CTL，并刺激慢性自身免疫反应。非专业APC诱导的免疫反应与专业APC（即来自造血谱系的APC，如树突状细胞）诱导的免疫反应形成对比，因为专业APC诱导的是一致的暴发性胰岛破坏和糖尿病。重要的是要认识到，在人类T1DM中观察到的胰岛破坏通常不是暴发性的，而是与我们观察到的慢性过程更一致。(4)在小鼠模型中测试正在考虑用于新发T1DM患者试验的潜在免疫治疗药物的预防疾病的能力。RIP-CD80模型中的糖尿病诱导可能偏向于几乎完全依赖CD8+ T细胞的诱导（抗原脉冲成纤维细胞免疫），或者使用不同的免疫策略（例如DNA疫苗接种）偏向于同时依赖CD4+和CD8+ T细胞的诱导。(5)我们已经将RIP-CD80模型作为一个体内系统，能够测试β细胞的祖细胞，因为它们有能力产生功能性胰岛素产生细胞。

Type 1 diabetes mellitus (T1DM) is an autoimmune disease resulting from the T cell mediated destruction of insulin-producing beta cells located in the pancreas. Current treatment, which includes insulin replacement by injection, frequent blood glucose monitoring, and dietary/exercise discipline, can prevent death from hormonal insufficiency, but is not curative and does not completely prevent the long-term complications including nerve damage, and vascular damage to both large and small blood vessels. The blood vessel damage in turn results in injury to various organs, including the heart, brain, kidneys, and eyes. Life expectancy is shortened by an estimated one-third compared to individuals without T1DM. This work, initiated in the mid 1990's at the Naval Medical Research Institute and further developed at the University of Ulm in Germany and subsequently for the past 2 years at the NIH has characterized a unique murine model of autoimmune diabetes using rat-insulin promoter (RIP)-CD80 transgenic mice (RIP-CD80 mice). These animals are predisposed to immune mediated beta cell destruction based on their beta cell-specific expression of the costimulatory molecule CD80. While RIP-CD80 mice rarely develop spontaneous diabetes (incidence 6.7%, compared to none of wild type mice), we've observed and have initially characterized the profound susceptibility these mice display to develop progressive islet infiltration and eventually insulin dependent diabetes mellitus (IDDM) following immunization with beta cell autoantigens (i.e. protein molecules that are expressed specifically by the pancreatic beta cells of these mice). For instance, these animals, unlike non-transgenic littermates, uniformly develop islet cell destruction and insulin dependent diabetes mellitus (IDDM) upon immunization with an insulin precursor, a beta cell autoantigen strongly suspected to be involved in the pathogenesis of human T1DM. We have shown that at least one relevant autoantigenic CTL epitope (H-2b) must be present in the mature insulin molecule, which contrasts with current algorhythm-based epitope prediction models. Moreover, our model has so far been more predictive of immune responses to therapeutic agents than the non-obese diabetic (NOD) mouse, a model most widely used to study autoimmune diabetes. Our objectives using the RIP-CD80 mouse model can be summarized as follows: (1) Identify important self-antigens (Ag) and CTL-epitopes serving as the initial targets for the developing autoimmune response. We will explore several routes to immunize with candidate auto-antigens, including peptide immunizations, DNA-vaccines, and retrovirally transduced dendritic cells (DC), for their ability to elicit MHC class I restricted T cell responses, insulitis, and diabetes. (2) Study beta cell specific T cell responses in an adoptive transfer model where the primary autoreactive T cell sensitization will take place either in vitro, or by immunizing in vivo, as proposed above in (1). These studies will focus on the mechanisms of the developing beta cell destructive immune responses, and will attempt to identify novel therapeutic approaches to interfere with the ongoing immune responses. (3) Continue to explore our preliminary data suggesting that non-professional antigen-presenting cells (APC), such pancreatic beta cells or fibroblastoid cells, can prime naive precursor CTL in vivo, and stimulate a chronic autoimmune response. The immune response induced by the non-professional APCs contrasts with that produced by professional APC (i.e. those derived from the hematopoetic lineage, such as dendritic cells) in that professional APCs induce a uniform and fulminant islet destruction and diabetes. It is important to recognized that the islet destruction observed in human T1DM is typically not fulminant but is more consistent with the chronic process we've observed. (4) Test potential immunotherapeutic agents being considered for trials in patients with new onset T1DM for their ability to prevent disease in the mouse model. Diabetes induction in the RIP-CD80 model can be biased toward one dependent almost exclusively on CD8+ T cells (antigen pulsed fibroblast immunization) or using different immunization strategies (e.g. DNA vaccination) toward one dependent upon both CD4+ and CD8+ T cells. (5) We have adapted the RIP-CD80 model as an in vivo system capable of testing cells felt to represent progenitors for beta cells for their capacity to generate functional insulin producing cells.