Human neutrophils and Staphylcoccus aureus: microbial targets and responses

描述（由申请人提供）： 金黄色葡萄球菌（SA）感染仍然是一个重要的临床挑战，尽管有效的抗生素。新的治疗进展等待阐明的分子基础的持久性，慢性和转移性扩散-即SA感染的标志。SA产生严重和慢性人类疾病的显著倾向部分反映了其表达的毒力因子阵列，包括在其对数生长期晚期分泌的磷酸肌醇特异性磷脂酶C（PI-PLC）。PI-PLC在感染期间分泌并且具有免疫原性，使其成为毒力因子的候选者。 人多形核白细胞（PMN）是细胞先天免疫介导的宿主防御SA感染的前线，PMN对吞噬体内的SA发挥其全部抗菌作用。在PMN吞噬过程中，与吞噬细胞NADPH氧化酶的激活同时，颗粒与新生吞噬体融合并将其内容物释放到吞噬体中，从而将摄入的微生物暴露于一系列毒性试剂和氧化剂流中，这些试剂和氧化剂流协同杀死吞噬体中的微生物。然而，尽管存在这种有效的PMN抗微生物系统，但10-20%的摄入SA在PMN中保持活力，但不复制。作为对吞噬体中PMN毒素的反应，持续存在的SA刺激PMN启动决定PMN命运的转录程序。 SA负载的PMN有两种潜在的命运：它们可能从非典型凋亡进展到坏死，释放活性SA，或者可以被巨噬细胞（Mf）摄取，从而触发促进进一步炎症的表型反应。而MF吸收典型的凋亡中性粒细胞发生不触发促炎级联反应（即非炎症反应），我们最近已经证明，MF摄入的SA-PMN促进异常细胞因子反应。SA在吞噬细胞内的持续存在具有深远的临床后果，因为SA感染的特征是复发、转移和SA敏感的抗生素的失效。在小鼠感染模型中，从脓肿中回收的PMN相关SA可以将感染传播给未处理小鼠，表明PMN可以作为“特洛伊木马”，秘密进入巨噬细胞（Mf），然后传播引起转移性感染。 鉴于我们的初步数据，我们提出的研究，以测试的总体假设，SA PI-PLC作为毒力因子SA凭借其破坏吞噬细胞先天宿主防御的能力。我们假设PI-PLC可能在两个不同的阶段参与SA感染：（1）感染早期，在有效的细胞宿主防御和生物体摄入之前，细胞外PI-PLC将攻击脆弱的底物，包括招募的吞噬细胞上的底物，并破坏其正常反应的能力（目的1）;和（2）随后，在吞噬细胞摄取后，在吞噬体内表达PI PLC的SA将改变PMN-Mf相互作用，干扰炎症的正常消退，并促进感染和传播（目的2）。我们的具体目标包括：目标1。确定细胞外SA PI-PLC对吞噬细胞功能和固有宿主防御的影响-重点关注PMN NADPH氧化酶的引发和直接激动剂效应吞噬细胞，以及Aim 2。确定PMN内表达的PI-PLC对SA感染的启动和促进的贡献-关注体外PMN和Mf的命运以及体内感染的后果。 我们已经产生的分析工具和开发的实验模型，研究PI-PLC对吞噬细胞反应的影响，我们正在进行的研究PMN含有可行的SA和MF之间的相互作用提供了一个框架，在体外模型的命运SA负载PMN可能发生感染。

DESCRIPTION (provided by applicant): Infection with Staphylococcus aureus (SA) remains an important clinical challenge despite potent antibiotics. Novel therapeutic advances await elucidation of the molecular bases for persistence, chronicity, and metastatic spread - i.e. the hallmarks of SA infection. The remarkable proclivity of SA to produce severe and chronic human disease reflects, in part, the array of virulence factors it expresses, including a phosphoinositol-specific phospholipase C (PI-PLC) that is secreted during its late logarithmic growth phase. PI-PLC is secreted during infection and is immunogenic, making it a candidate as a virulence factor. Human polymorphonuclear leukocytes (PMN) are at the front-line of cellular innate immune-mediated host defense against SA infection, and PMN exert ~ all of their antimicrobial effort against SA internalized within phagosomes. During PMN phagocytosis and coincident with activation of the phagocyte NADPH oxidase, granules fuse with nascent phagosomes and release their contents into the phagosome, thereby exposing the ingested microbe to an array of toxic agents and a flux of oxidants that collaborate to kill microbes in phagosomes. However, despite the presence of this potent PMN antimicrobial system, 10-20% of ingested SA remain viable, but not replicating, in PMN. In response to PMN toxins in phagosomes, persisting viable SA stimulate PMN to initiate transcriptional programs that dictate the fate of PMN. SA-laden PMN have two potential fates: they may progress from atypical apoptosis to necrosis, with release of viable SA, or can be ingested by macrophages (Mf), thereby triggering phenotypic responses that promote further inflammation. Whereas Mf uptake of typical apoptotic PMN occurs without triggering proinflammatory cascades (i.e. a non phlogistic response), we have recently demonstrated that Mf ingestion of SA-PMN promoted aberrant cytokine responses. Persistence of SA within phagocytes has profound clinical consequences, as signature features of SA infection are relapse, metastases, and failure of antibiotics to which SA are susceptible. In murine infection models, PMN-associated SA recovered from an abscess can transmit infection to na¿ve mice, demonstrating that PMN can serve as a "Trojan horse", covertly entering macrophages (Mf) and then disseminating to cause metastatic infection. Given our preliminary data, we propose studies to test the overall hypothesis that SA PI-PLC serves as a virulence factor for SA by virtue of its ability to undermine phagocyte innate host defense. We hypothesize that PI-PLC may contribute to SA infection at two distinct stages: (1) early in infection, before effective cellular host defenses have been engaged and organisms ingested, extracellular PI-PLC will attack vulnerable substrates, including those on recruited phagocytes, and undermine their capacity to respond normally (Aim 1); and (2) later, after ingestion by phagocytes PI-PLC-expressing SA within phagosomes will alter PMN-Mf interactions, interfere with normal resolution of inflammation, and promote infection and dissemination (Aim 2). Our Specific Aims include: Aim 1. To determine the impact of extracellular SA PI-PLC on phagocyte function and innate host defense - focusing on priming of PMN NADPH oxidase and direct agonist effects phagocytes, and Aim 2. To determine the contribution of PI-PLC expressed within PMN on initiation and promotion of SA infection - focusing on PMN and Mf fate in vitro and consequences in infection in vivo. We have generated the analytical tools and developed experimental models necessary to study the effects of PI-PLC on phagocyte responses, and our ongoing studies of interactions between PMN containing viable SA and Mf provide a framework to model in vitro the fate of SA-laden PMN as might occur in infection.