Virulence mechanisms of group A streptococcal toxins

描述（由申请人提供）：化脓性链球菌或A群链球菌（GAS）是链球菌性咽炎，皮肤和软组织感染以及危及生命的侵袭性感染的病原体。除发病率和经济损失外，气体感染和感染后后遗症，主要以风湿性心脏病的形式，每年造成50万人死亡。目前还没有疫苗，在10%到20%的咽炎病例中，抗生素治疗失败或复发。GAS感染的难治性可能反映了GAS与人类的共同进化，以及它在人类咽部（其主要的环境生态位）中对生存的微妙适应。我们和其他人已经在体外观察到GAS进入人上皮细胞。虽然细胞内细菌最终被杀死，但我们发现GAS共毒素溶血素O和NADase抑制GAS内化并延长细胞内存活，这些作用可能导致抗生素治疗失败、复发和长时间携带。本提案的目的是确定SLO和NADase如何阻断咽上皮细胞对GAS的内化并阻止有效的细胞内杀伤。具体目的是：(1)表征咽部上皮细胞对GAS的内化，(2)确定SLO和NADase在阻断其内化中的具体作用，以及(3)确定GAS避免或逃避细胞内杀伤的分子机制。在初步研究中，我们发现SLO和NADase在与角质形成细胞相互作用过程中对GAS的命运有显著的影响。我们已经组装了必要的分子工具、细胞培养模型和成像技术，以解读这些毒素和宿主细胞机制如何决定咽上皮中这种关键病原体-宿主相互作用的结果。研究结果将为预防和治疗气体感染提供新的途径。

DESCRIPTION (provided by applicant): Streptococcus pyogenes or group A Streptococcus (GAS) is the agent of streptococcal pharyngitis, infections of the skin and soft tissue, and life-threatening invasive infections. GAS infections and post-infectious sequelae, primarily in the form of rheumatic heart disease, account for 500,000 deaths annually in addition to morbidity and economic losses. A vaccine is not yet available and antibiotic treatment fails or is followed by relapse in 10 to 20 percent of pharyngitis cases. The refractory nature of GAS infection may reflect the co-evolution of GAS with human beings and its exquisite adaptation for survival in the human pharynx, its primary environmental niche. We and others have observed entry of GAS into human epithelial cells in vitro. While intracellular bacteria are eventually killed, we have found that GAS co-toxins streptolysin O and NADase inhibit GAS internalization and prolong intracellular survival, effects that may contribute to antibiotic treatment failure, relapse, and prolonged carriage. The goal of this proposal is to determine how SLO and NADase block internalization of GAS by pharyngeal epithelial cells and prevent effective intracellular killing. Specific aims are (1) to characterize internalization of GAS by pharyngeal epithelial cells, (2) to determine the specific roles of SLO and NADase in blocking internalization, and (3) to define the molecular mechanisms by which GAS avoids or escapes intracellular killing. In preliminary studies, we have found striking effects of SLO and NADase on the fate of GAS during interaction with keratinocytes. We have assembled the necessary molecular tools, cell culture models, and imaging techniques to decipher how these toxins and host cellular mechanisms determine the outcome of this critical pathogen-host interaction at the pharyngeal epithelium. The results will inform new approaches to prevention and treatment of GAS infection. Project Narrative: Group A Streptococcus or GAS is responsible for millions of cases of streptococcal sore throat and approximately 10,000 cases of life-threatening invasive infections annually in the United States, and rheumatic fever, a complication of GAS infection, is a leading cause of often fatal heart disease in developing countries. The objective of this project is determine how cells lining the human throat ingest and kill GAS, thereby blocking GAS infection, and how two GAS toxins act to counteract this host defense mechanism. Understanding these interactions may lead to novel strategies for prevention or treatment of GAS infections.