Mechanisms of immune evasion by Group A Streptococcus during skin infection

A群链球菌（GAS）或化脓性链球菌感染是一个全球性的健康问题（Carapetis等人，2005年）。它们的范围从轻微的皮肤或喉咙感染到可能致命的严重侵袭性疾病。感染后并发症，如急性风湿热（ARF）、风湿性心脏病（RHD）和肾脏疾病，也会造成严重的健康问题。在社会经济上处于不利地位的群体中，包括澳大利亚土著社区，气体疾病的负担高得不成比例。没有疫苗可用的事实（Pandey等人，2012）强调需要更好地了解GAS的发病机制以及感染期间的免疫反应。在本提案中，我将重点放在NS88.2上，这是一种从北领地一位菌血症患者身上获得的临床分离物（McKay et al., 2004）。来自侵袭性感染的分离株通常在covS或covR基因中发生突变，这些基因编码毒力调节传感器激酶（covR /S）系统的控制（Maamary等人，2010）。CovR/S系统根据环境信号调节多达15%的GAS基因。NS88.2在冠状病毒中含有一个突变，Sanderson-Smith博士此前已成功修复，产生了一种等基因菌株，称为NS88.2rep，毒性降低（Sanderson-Smith et al., 2008）。因此，这对菌株是研究体内GAS发病机制的独特资源。在初步工作中发现，即使非常低剂量的NS88.2皮下注射，也会在小鼠中引起致命疾病，其特征是全身细菌传播。相反，NS88.2rep能被皮肤的先天免疫系统有效清除，因此不会引起致命疾病。体外和体内的流式细胞术和显微镜研究表明，虽然NS88.2rep被有效吞噬，但NS88.2可逃避中性粒细胞的摄取。这些结果表明，covS突变使NS88.2能够规避中性粒细胞的攻击。目的：在本应用中，我将通过分子、免疫和活体成像方法解剖NS88.2的免疫逃避特性。因此，我将获得关于这种重要的人类病原体如何逃避宿主免疫而引起疾病的基本见解。假设：NS88.2在体内皮肤感染过程中干扰中性粒细胞的摄取，使其快速传播。确定NS88.2如何逃避皮肤局部中性粒细胞反应2。确定NS88.2如何从皮肤扩散到血液

Infections by Group A Streptococcus (GAS), or Streptococcus pyogenes, represent a global health concern (Carapetis et al., 2005). They range from mild skin or throat infections to severe invasive diseases with potentially fatal outcome. Post-infectious complications such as acute rheumatic fever (ARF), rheumatic heart disease (RHD) and kidney diseases also cause serious health problems. The burden of GAS disease is disproportionately high in socio-economically disadvantaged groups, including the indigenous communities in Australia. The fact that there is no vaccine available (Pandey et al., 2012) emphasises the need to better understand GAS pathogenesis as well as immune responses during infection. In this proposal, I focus on NS88.2, a clinical isolate that was obtained from a patient with bacteraemia in the Northern Territory (McKay et al., 2004). Isolates from invasive infections often have mutations in their covS or covR genes, which encode the control of virulence regulatory sensor kinase (CovR/S) system (Maamary et al., 2010). The CovR/S system regulates up to 15% of GAS genes in response to environmental cues. NS88.2 contains a mutation in covS, which Dr. Sanderson-Smith has previously succeeded in repairing to produce an isogenic strain, termed NS88.2rep, with reduced virulence (Sanderson-Smith et al., 2008). This pair of bacterial strains is therefore a unique resource for studying GAS pathogenesis in vivo. In preliminary work, it was found that even a very low dose of NS88.2, injected intradermally, causes a fatal disease in mice, characterised by systemic bacterial dissemination. In contrast, NS88.2rep is cleared effectively by the innate immune system in the skin, and, hence, does not cause lethal disease. The flow cytometric and microscopic studies, both in vitro and in vivo, suggest that while NS88.2rep is efficiently phagocytosed, NS88.2 evades neutrophil uptake. These results suggest that the covS mutation enables NS88.2 to circumvent attack by neutrophils.Objective: In this application, I will dissect the immuno-evasive properties of NS88.2 using molecular, immunologic and intravital imaging approaches. I will thus obtain fundamental insight into how this important human pathogen evades host immunity to cause disease.Hypothesis: NS88.2 interferes with neutrophil uptake during skin infection in vivo, enabling rapid disseminationAim 1. Determine how NS88.2 evades the local neutrophil response in the skinAim 2. Determine how NS88.2 disseminates from the skin to the blood