Neutrophil Accumulation in Bacterial Pneumonia

描述(申请人提供)：细菌性肺炎是导致死亡的主要原因。中性粒细胞在肺部的募集是宿主抵抗细菌感染的最重要的防御机制之一。然而，中性粒细胞的过度流入可导致广泛的肺损伤和ARDS，这表明中性粒细胞的流入受到严格的调控。中性粒细胞的运输主要依赖于肺内髓系细胞和常驻细胞产生趋化因子。过去，人们的注意力主要集中在髓系细胞在中性粒细胞运输中的作用。最近，我们首次报道了肺泡上皮型(AE)II细胞在内毒素介导的肺部炎症中产生中性粒细胞趋化因子CXC趋化因子配体(CXCL)5。此外，我们还发现CXCL5受体拮抗剂可以减少内毒素诱导的中性粒细胞进入肺内。在这个建议中，我们关注嗜肺军团菌，因为我们的初步数据表明，体内CXCL5的缺失，而不是其他中性趋化因子，如KC和MIP-2，会损害宿主对LP的防御，尽管CXCL5、KC或MIP-2的缺失会损害宿主对大肠杆菌感染的防御。我们假设Lp诱导的CXCL5是中性粒细胞进入肺的关键介质，Lp感染刺激的CXCL5的产生包括直接和间接级联反应。直接级联涉及LP与AEII细胞的相互作用，间接级联涉及LP与髓系细胞的相互作用，导致炎症介质的产生，从而刺激AEII细胞。这项应用的具体目的是：1)直接评估CXCL5在LP肺炎中性粒细胞内流中的作用；2)描述LP感染后小鼠和人AEII细胞(体外)产生CXCL5的直接途径；以及3)描述在LP感染过程中介导CXCL5产生和中性粒细胞内流的间接途径(体内)。总体而言，建议的研究集中于在LP肺炎中导致CXCL5产生和中性粒细胞流入的新途径。体内(小鼠，包括CXCL5基因敲除)和体外(小鼠AEII和树突状细胞，以及人AEII细胞)系统的独特组合将被用于解决这些目标。阐明LP在肺炎中诱导CXCL5产生和中性粒细胞内流的机制将有助于更好地了解疾病的发病机制，并最终为细菌性肺炎的肺损伤和ARDS的治疗提供新的策略。与公共卫生相关。细菌性肺炎是成人和儿童的一种重要的肺部疾病，仅在美国就影响了100多万成年人，每年有30,000人死亡。尽管最近在认识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细胞，它募集到肺部是抵抗呼吸道细菌的重要保护机制之一；矛盾的是，中性粒细胞过度聚集对细菌的反应可显著促进肺损伤。更好地了解中性粒细胞流入的机制对于设计新的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部的机制，我们建议使用一种由嗜肺军团菌引起的肺部疾病(肺炎)的模型。嗜肺性乳杆菌引起被称为“军团病”的严重肺炎，其特征是广泛的中性粒细胞堆积。我们最近已经证明了中性粒细胞吸引分子CXCL5在肺部疾病(肺炎)进展中的重要性。在这项提案中，我们将确定CXCL5在嗜肺乳杆菌引起的细菌性肺炎中的作用。这项研究的结果将有助于我们理解CXCL5在细菌性疾病(肺炎)中诱导中性粒细胞在肺部聚集中所起的作用。预计这些研究将导致开发新的和创新的治疗策略，通过控制肺部中性粒细胞的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.