Virulence mechanisms of group A streptococcal toxins

描述（由申请方提供）：化脓性链球菌或A组链球菌（GAS）是链球菌性咽炎、皮肤和软组织感染以及危及生命的侵入性感染的病原体。除发病率和经济损失外，GAS感染和感染后后遗症（主要以风湿性心脏病的形式）每年导致50万人死亡。目前还没有疫苗，抗生素治疗失败或在10%至20%的咽炎病例中复发。GAS感染的难治性可能反映了GAS与人类的共同进化及其对人类咽部生存的精致适应，咽部是GAS的主要环境生态位。我们和其他人已经观察到GAS在体外进入人上皮细胞。虽然细胞内细菌最终被杀死，但我们发现GAS辅毒素链球菌溶血素O和NAD酶抑制GAS内化并延长细胞内存活，这可能导致抗生素治疗失败、复发和携带时间延长。本提案的目的是确定SLO和NAD酶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）表征咽上皮细胞对GAS的内化，（2）确定SLO和NAD酶在阻断内化中的特定作用，以及（3）确定GAS避免或逃避细胞内杀伤的分子机制。在初步的研究中，我们发现SLO和NADase在与角质形成细胞相互作用期间对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，以破译这些毒素和宿主细胞机制如何决定咽上皮这种关键的病原体-宿主相互作用的结果。研究结果将为预防和治疗GAS感染提供新的方法。 项目叙述：在美国，A组链球菌或GAS每年造成数百万例链球菌性咽喉炎和约10，000例危及生命的侵入性感染，而风湿热是GAS感染的并发症，是发展中国家经常致命的心脏病的主要原因。该项目的目标是确定人类喉咙内衬细胞如何摄取和杀死GAS，从而阻止GAS感染，以及两种GAS毒素如何抵消这种宿主防御机制。了解这些相互作用可能会导致预防或治疗GAS感染的新策略。

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.