Neutrophil Accumulation in Bacterial Pneumonia

描述（由申请人提供）：细菌性肺炎是导致死亡的主要原因。中性粒细胞向肺部的募集是宿主抵抗细菌感染的最初防御中最重要的防御机制之一。然而，中性粒细胞的过度流入可引起广泛的肺损伤和ARDS，表明中性粒细胞流入受到严格调节。神经元的运输主要依赖于肺中骨髓细胞和驻留细胞产生的趋化因子。在过去，大多数的注意力都集中在髓系细胞在中性粒细胞运输中的作用。最近，我们首次报道了在LPS介导的肺部炎症中，肺泡上皮II型（AE）细胞产生嗜酸性趋化因子CXC趋化因子配体（CXCL）5。此外，我们发现CXCL 5阻断减弱了肺中LPS诱导的中性粒细胞流入。在这个建议中，我们集中在嗜肺军团菌（Lp），因为我们的初步数据表明，在体内CXCL 5的消耗，而不是其他嗜肺趋化因子，如KC和MIP-2，削弱宿主防御Lp，尽管事实上，CXCL 5，KC或MIP-2的消耗削弱宿主防御大肠杆菌。大肠杆菌感染。我们假设，脂蛋白诱导的CXCL 5是一个重要的介导的中性粒细胞流入肺和CXCL 5生产刺激脂蛋白感染涉及直接和间接级联。直接级联涉及Lp与AEII细胞的相互作用，间接级联涉及Lp与髓样细胞的相互作用，导致产生炎症介质，然后可以刺激AEII细胞。本申请的具体目的是：1）直接评估CXCL 5对Lp肺炎中中性粒细胞流入的贡献; 2）描述Lp感染后负责鼠和人AEII细胞中CXCL 5产生的直接途径（体外）;和3）描述Lp感染期间介导肺中CXCL 5产生和中性粒细胞流入的间接途径（体内）。总体而言，拟议的研究集中在负责Lp肺炎中CXCL 5产生和中性粒细胞流入的新途径上。将采用体内（小鼠，包括CXCL 5敲除）和体外（鼠AEII和树突细胞，以及人AEII细胞）系统的独特组合来解决目标。阐明肺炎中Lp诱导CXCL 5产生和中性粒细胞内流的机制将有助于更好地理解疾病的发病机制，并最终导致治疗细菌性肺炎中肺损伤和ARDS的新策略。公共卫生相关性。细菌性肺炎是成人和儿童的重要肺部疾病，仅在美国每年就影响超过100万成年人，其中30，000人死亡。尽管最近在了解细菌性肺炎方面取得了一些进展，但我们仍然没有有效的控制措施。中性粒细胞是一种白色血细胞，其向肺部的募集是对抗呼吸道细菌的重要保护机制之一;矛盾的是，响应于细菌的中性粒细胞的过度积累可显著导致肺损伤。更好地理解中性粒细胞流入的机制对于设计新颖和创新的治疗策略以最大限度地减少过度的肺部炎症至关重要。为了研究中性粒细胞被招募到肺中的机制，我们建议使用由细菌嗜肺军团菌诱导的肺部疾病（肺炎）模型。L.嗜肺菌引起称为“军团病”的严重肺炎，其特征在于广泛的嗜中性粒细胞积聚。我们最近已经表明中性粒细胞吸引分子CXCL 5在疾病（肺炎）进展中在肺部的重要性。在这个提议中，我们将确定CXCL 5在由细菌L.嗜肺菌这项研究的结果将有助于我们了解CXCL 5在细菌性疾病（肺炎）中诱导中性粒细胞在肺部积聚中所起的作用。预计这些研究将导致开发新的和创新的治疗策略，通过操纵肺中的中性粒细胞数量来治疗肺部疾病。

DESCRIPTION (provided by applicant): Bacterial pneumonia is a leading cause of death. Recruitment of neutrophils into the lungs is one of the most important defense mechanisms in the initial host defense against bacterial infection. However, excessive influx of neutrophils can cause extensive lung injury and ARDS, suggesting that neutrophil influx is tightly regulated. Neutrophil trafficking is primarily dependent on chemokine production by myeloid and resident cells in the lung. In the past, most of the attention has been focused on the role of myeloid cells in neutrophil trafficking. Recently, we reported for the first time that resident alveolar epithelial type (AE) II cells produce the neutrophilic chemokine, CXC chemokine ligand (CXCL) 5, in LPS-mediated lung inflammation. In addition, we showed that CXCL5 blockade attenuated LPS-induced neutrophil influx in the lung. In this proposal, we focus on Legionella pneumophila (Lp), as our preliminary data show that the in vivo depletion of CXCL5, but not other neutrophilic chemokines, such as KC and MIP-2, impairs host defense against Lp despite the fact that depletion of either CXCL5, KC or MIP-2 impairs host defense against E. coli infection. We hypothesize that Lp-induced CXCL5 is a critical mediator of neutrophil influx in the lung and CXCL5 production stimulated by Lp infection involves both direct and indirect cascades. The direct cascade involves interaction of Lp with AEII cells and the indirect cascade involves interaction of Lp with myeloid cells leading to the production of inflammatory mediators, which can then stimulate AEII cells. The Specific Aims of this application are: 1) To directly assess the contribution of CXCL5 to neutrophil influx in Lp pneumonia; 2) To delineate the direct pathways responsible for CXCL5 production in murine and human AEII cells (in vitro) after Lp infection; and 3) To delineate the indirect pathways (in vivo) that mediate CXCL5 production and neutrophil influx in the lung during Lp infection. Overall, the proposed studies focus on the novel pathways responsible for CXCL5 production and neutrophil influx in Lp pneumonia. A unique combination of in vivo (mouse, including CXCL5 knockout) and in vitro (murine AEII and dendritic cells, and human AEII cells) systems will be employed to address the Aims. Elucidation of the mechanisms by which Lp induces CXCL5 production and neutrophil influx in pneumonia will lead to a better understanding of disease pathogenesis and ultimately lead to new strategies to the treatment of lung injury and ARDS in bacterial pneumonia. PUBLIC HEALTH RELEVANCE. Bacterial pneumonia is an important lung disease in both adults and children, and affects more than 1 million adults with 30,000 deaths per year in the United States alone. Despite the fact that some advances have been made in the recent past in understanding bacterial pneumonia, we still do not have effective control measures. Neutrophil, a white blood cell, recruitment to the lungs is one of the important protective mechanisms against respiratory bacterial germs; paradoxically excessive accumulation of neutrophils in response to bacteria can significantly contribute to lung damage. A better understanding of the mechanisms underlying neutrophil influx is crucial to designing novel and innovative treatment strategies to minimize excessive lung inflammation. To investigate the mechanisms by which neutrophils are recruited to the lung, we propose to use a model of lung disease (pneumonia) induced by the germ, Legionella pneumophila. L. pneumophila causes severe pneumonia known as "Legionnaires disease" and is characterized by extensive neutrophil accumulation. We have recently shown the importance of a neutrophil attracting molecule, CXCL5, in the lungs in disease (pneumonia) progression. In this proposal, we will determine the role of CXCL5 in bacterial pneumonia caused by the germ, L. pneumophila. The results from this study will help us understand the role played by CXCL5 in inducing neutrophil accumulation in the lungs in bacterial disease (pneumonia). It is anticipated that these investigations will lead to the development of new and innovative treatment strategies to treat lung diseases via manipulating neutrophil numbers in the lung.