Role of Cytokines in the Developing Immune System

有人认为，小岛屿发展中国家可能是在发育中的免疫系统更容易受到炎症介质影响的时候，由微生物产物和/或其他环境因素(如环境烟草烟雾)的组合引起的病理生理反应。我们已经开发了一种模拟双重感染的动物模型，使用了一种非致命性的甲型流感病毒株和亚致死量的内毒素。在该模型中，在10日龄接种流感疫苗，然后在流感后第2天接种内毒素0.2 mg/kg，死亡率最低。这些元素成为模型的定义参数。只有当满足特定的标准，如感染侮辱和幼崽发育年龄之间的时间间隔，并且年龄是模型中的关键风险因素时，才会发生死亡。我们定义了人类婴儿SID病理与该模型中所见的相似之处，并检查了与双重挑战相关的基本免疫因素。这些研究表明，发育中的免疫系统可以做好准备，以一种夸张的方式对导致意外死亡的第二次免疫挑战做出反应。为了研究这种死亡率的机制，在内毒素注射后2-8小时进行了一系列实验来评估免疫参数。由于病理发现提示了全身免疫的调节，而不是肺的特异性损伤，我们评估了与全身休克和氧化应激相关的细胞因子反应。在双重攻击的幼鼠中，观察到血清和脾干扰素-γ水平的显著变化，以及脾和肺中特定免疫细胞群的变化。在双重挑战的动物中，炎性细胞因子基因在肺和肝脏中的表达更早达到峰值。由于一氧化氮是细菌和病毒感染免疫反应的一个重要方面，因此检测了目标组织中一氧化氮合酶mRNA的表达。与只接受内毒素的动物相比，双重攻击动物的肝脏(iNOS、eNOS和nNOS)和肺(iNOS、eNOS)的基因表达增加。我们还调查了鼻腔内注射内毒素是否会显示出类似的免疫学变化模式，内毒素将更接近于潜在的人类暴露。在以这种方式挑战的动物中没有观察到死亡。我们正在与杜克大学的布拉德-齐格弗里德博士合作，利用这一模型研究环境烟草烟雾在小岛屿发展中国家发展中的作用。尼古丁暴露似乎以类似于流感暴露的方式启动免疫系统，因为暴露于尼古丁的动物似乎对特定发育窗口中的细菌产品暴露敏感。

It has been suggested that SIDS may be a patho-physiological response elicited by combinations of microbial products and/or other environmental factors such as environmental tobacco smoke (ETS) at a time when the developing immune system is more vulnerable to the effects of inflammatory mediators. We have developed an animal model to mimic dual infection, using a non-lethal strain of Influenza A virus and a sub-lethal dose of endotoxin. In this model inoculation with influenza at 10 days of age followed by endotoxin 0.2 mg/kg 2 days post influenza caused mortality with the lowest morbidity. These elements became the defining parameters of the model. Mortality only occurred when specific criteria such as timing between infectious insults and developmental age of the pup were met and age was a key risk factor in the model. We have defined similarities of SIDS pathology in human infants and that seen in this model and examined basic immune factors associated with dual challenge. These studies suggest that the developing immune system can be primed to respond in an exaggerated way to a second immune challenge resulting in unexpected death. To examine the mechanisms underlying this mortality, a series of experiments were conducted to evaluate immune parameters 2-8 hours following endotoxin administration. As the pathologic findings a suggested modulation of systemic immunity rather than lung-specific damage, we evaluated cytokine responses related to systemic shock and oxidative stress. Significant alterations in serum and spleen IFN gamma levels were observed in dually challenged pups, as well as changes in specific immune cell populations in the spleen and lung. Inflammatory cytokine gene expression peaked earlier in dually challenged animals in both the lung and liver. As nitric oxide is an important aspect of the immune response to both bacterial and viral infection, nitric oxide synthase mRNA expression was examined in the target tissues. Increased gene expression was observed in the liver (iNOS, eNOS and nNOS) and the lung (iNOS, eNOS) in dually challenged animals as compared to animal receiving only endotoxin. We also investigated whether intranasal administration of endotoxin, which would more closely mimic potential human exposure, would show similar patterns of immunologic changes. No mortality was observed in animals challenged in this fashion. We are collaborating with Dr. Blood-Siegfried at Duke University to examine the role of environmental tobacco smoke in the development of SIDS using this model. Nicotine exposure appears to prime the immune system in a manner similar to influenza exposure in that nicotine-exposed animals appear to be sensitive to the exposure to bacterial products during a specific developmental window.