Toxemia and systemic disease in Clostridium difficile infection

描述（申请人提供）：艰难梭菌是最重要的医院内肠道病原体之一。艰难梭菌感染（CDI）的发病率和死亡率在过去十年中急剧增加，使CDI成为美国和欧洲致命感染性腹泻的最常见原因。暴发性或严重复杂性CDI （SCCDI）患者常发展为全身性疾病，这是死亡的前奏。发生全身性并发症的原因尚不清楚，但我们和其他人的临床观察以及动物模型研究表明，艰难梭菌外毒素TcdA和TcdB可能是促成因素。我们的中心假设是，TcdA和/或TcdB的全身传播是导致全身并发症的主要因素，而SCCDI可以通过中和针对这两种毒素的抗体来预防。为了验证这一假设，我们将利用本实验室开发的超灵敏免疫细胞毒性试验来测量循环毒素，并确定它们与CDI患者全身并发症的关系。此外，我们将研究导致TcdA和/或TcdB全身传播的事件的时间和顺序，组织和器官的趋向性以及与个体毒素相关的异常。最后，我们建议开发一种针对SCCDI的新疗法，通过产生多价单域（或VHH）抗体，增强对两种毒素的中和活性。在完成我们提出的研究后，我们希望对SCCDI的发病机制有更多的了解，并有可能开发出急需的治疗方法。为了实现这些目标，我们将使用来自几家医院的CDI患者的临床标本，以及我们在本实验室开发的独特研究工具/方法和动物模型。

DESCRIPTION (provided by applicant): Clostridium difficile is one of the most important, resurging nosocomial enteric pathogens. Incidence and mortality rates for C. difficile infection (CDI) have increased dramatically over the past decade making CDI by far the most common cause of fatal infectious diarrhea in the United States and in Europe. Patients with fulminant or severe complicated CDI (SCCDI) often develop systemic disease which is a prelude to fatality. The causes for the development of systemic complications remain poorly understood, but clinical observations by us and by others and studies using animal models suggest that C. difficile exotoxins TcdA and TcdB are likely contributing factors. Our central hypothesis is that systemic dissemination of TcdA and/or TcdB is a major factor leading to systemic complications and SCCDI is preventable by neutralizing antibodies against the two toxins. To test this hypothesis, we will exploit an ultrasensitive immunocytotoxicity assay developed at this lab to measure circulating toxins and determine their association with systemic complications in CDI patients. In addition, we will investigate the time and sequence of events leading to systemic dissemination of TcdA and/or TcdB, the tissue and organ tropism and abnormalities associated with the individual toxins. Finally, we propose to develop a novel therapeutics against SCCDI by generating multivalent single-domain (or VHH) antibodies with enhanced neutralizing activity against each of the two toxins. Upon completion of our proposed studies, we expect to gain more understandings of the pathogenesis of SCCDI and potentially lead to a development of much needed treatments against the disease. To accomplish these objectives we will use clinical specimens of CDI patients from several hospitals, as well as unique research tools/methods and animal models we have developed at this laboratory.