An Anthrax Lethal Toxin Model Of Sepsis

吸入性炭疽感染是当今生物恐怖主义的主要威胁。需要模拟这种疾病的模型来研究发病机制和治疗。炭疽感染开始于肺泡孢子的局部聚集，然后以入侵细菌的形式传播到纵隔结构。从那里，感染通过血管内传播系统地传播。血管内扩散导致毒素释放增加，直接导致死亡。炭疽杆菌产生两种不同的毒力因子，包括一种多谷氨酸胶囊和一种3种成分的外毒素。胶囊抵抗吞噬作用，而毒素能够损伤和杀死它所结合的细胞。这种毒素对巨噬细胞的杀伤在疾病的传播中起着重要作用。这种感染被描述为产毒感染，其大部分发病机制直接与毒素有关，或与毒素对潜在有害宿主介体的影响有关。因此，仅基于毒素的动物模型就能够模拟与感染本身相关的许多关键致病事件。这一点很重要，因为可以比细菌本身更安全地操纵毒素。 到目前为止，所有使用毒素挑战的小动物模型都使用了单一的快速推注。在这些模型中，死亡相对较快，从攻击后1小时到3小时不等，具体取决于毒素的剂量。然而，这样的挑战与这种感染的自然过程并不一致，这种感染过程可能包括宿主正在处理的毒素数量逐渐增加。这种增加反映在随着时间的推移观察到的血液细菌浓度的变化中。因此，模拟这种毒素进行性增加的动物模型将更好地模拟临床遇到的情况。这反过来将提供与毒素相关的不断演变的致病事件的更准确的评估，更重要的是，将提供一个更好的模型来测试旨在抑制毒素或其效果的疗法的影响。 到目前为止，该项目正在进行的研究表明，与类似的重量推注剂量相比，在Spraogue-Dawley大鼠中，24小时输注炭疽毒素会产生更长且显著不同的致死时间过程。这一延长的时间进程使我们能够更准确地评估模型中发生的心肺损伤和细胞宿主反应。与类似致死性脓毒症内毒素模型相比，炭疽毒素感染早期(6h)和晚期(24h)血清硝酸盐和亚硝酸盐水平均未升高。目前正在分析细胞因子小组，以更好地确定宿主对致命炭疽毒素攻击的炎症反应。与文献中描述的费舍尔大鼠对炭疽毒素具有独特的敏感性不同，在我们现在完成的对照实验中，Spraogue-Dawley大鼠表现出与费舍尔动物相同的毒素反应模式，使我们的模型更适用于其他实验室。鉴于巨噬细胞被认为在炭疽感染的发病机制中起着核心作用，作为该项目的一部分，目前正在进行实验，以调查在长期输注毒素期间粒细胞-巨噬细胞集落刺激因子治疗的影响。

Inhaled anthrax infection is a major bioterrorism threat today. Models that simulate this disease for the study of pathogenesis and treatment are needed. Anthrax infection begins as a local collection of alveolar spores, which then spread as invasive bacteria to the mediastinal structures. From there the infection is disseminated systemically by intravascular spread. Intravascular spread results in a increasing toxin release that contributes directly to death. Anthrax bacilli produce two different virulence factors including a polyglutamate capsule and a 3 components exotoxin. The capsule resists phagocytosis while the toxin is capable of injuring and killing the cells, which it binds to. Macrophage killing by the toxin is important in the spread of the disease. The infection is described as a toxigenic one with most of its pathogenesis relating directly to the toxin or to the toxin's influence on potentially harmful host mediators. Therefore, animal models based on the toxin alone are capable of simulating many of the key pathogenic events associated with the infection itself. This is important because the toxin can be manipulated far more safely than the bacteria itself. All small animal models to date using toxin challenge, have employed a single rapid bolus. Death in these models is relatively rapid extending from 1 to 3 hours after challenge depending on the dose of toxin. However, such a challenge is not consistent with the natural course of this infection which likely includes a gradual increase in the amount of toxin the host is dealing with. Such increases are reflected in the changes in blood bacteria concentrations that have been observed over time. Thus, an animal model simulating this progressive increase in toxin would better simulate conditions encountered clinically. This in turn would provide a more accurate assessment of evolving pathogenic events associated with toxin and, more importantly, would provide a better model to test the influence of therapies directed at inhibiting the toxin or its effects. The research underway for this project has so far shown that anthrax toxin administered as a 24 h infusion in Sprague-Dawley rats produces a prolonged and significantly different time course in lethality compared to a similar weight based bolus dose. This prolonged time course has permitted a more accurate assessment of the cardiopulmonary injury and cellular host response occurring in the model. In marked contrast to similarly lethal endotoxin models of sepsis, serum nitrate and nitrite levels were not increased either early (6h) or late (24h) following anthrax \toxin. Cytokine panels are now under analysis to better define the host inflammatory response to lethal anthrax toxin challenge in the model. In contrast to the unique sensitivity to anthrax toxin that Fischer rats are described as having in the literature, in controlled experiments we have now completed, Sprague-Dawley rats show the same pattern of response to toxin as Fischer animals, making our model even more applicable for laboratories elsewhere. Given the central role the macrophage is believed to have in the pathogenesis of anthrax infection, as part of this project experiments are now underway to investigate the influence of granulocyte-macrophage colony stimulating factor treatment during prolonged toxin infusion.