Mechanism of sepsis development in pulmonary bacterial infection

描述（由申请人提供）：脓毒症和脓毒症相关的多器官衰竭仅在美国每年就造成250，000例死亡。在脓毒症期间，骨髓细胞的无节制刺激导致炎症反应过度，导致广泛的组织损伤和多个全身器官衰竭。虽然脓毒症可由于各种病理性损伤而发展，但呼吸道感染是脓毒症相关死亡率的主要原因。然而，所涉及的机制并不清楚。最近，我们的研究已经证明，在没有任何已知的细菌内毒素或外毒素的情况下，最终导致严重脓毒症的失调的宿主免疫应答与革兰氏阴性细菌病原体弗朗西斯氏菌的肺部感染的极端致死性相关。由于这种病原体具有极强的毒力且易于通过呼吸道传播，因此CDC将其归类为A类选择性病原体。拟进行的研究的目的是利用呼吸道弗朗西斯菌感染的小鼠吸入模型来了解导致脓毒症发展的分子事件。这些研究是创新的，因为我们正在研究以前未确定的宿主聚糖识别先天免疫分子（称为半乳糖凝集素）在脓毒症发展中的作用。新出现的证据表明，在炎症过程中，死亡或垂死的宿主细胞可以释放称为alarmins的内源性宿主因子，其在正常条件下包含在细胞内区室中时具有稳态功能，但在其细胞外释放时，可以引起高度炎症反应。这强调了alarmin的鉴定和表征可以指导针对炎症性疾病如脓毒症的有效疗法的开发。这包括拟议研究的目标。我们的初步分析，在小鼠感染致命的野生型弗朗西斯和那些接种了保护性突变体显示上调和细胞外释放的半乳糖凝集素-3和9，两个主机凝集素缺乏分泌信号，并表现出免疫调节特性（特征的报警），只有在致命的弗朗西斯感染。此外，与感染的野生型小鼠相比，弗朗西斯菌感染的半乳糖凝集素-3-/-和-9-/-小鼠表现出炎症反应的减弱、病理学的减轻和骨髓细胞表型的改变。因此，我们假设，这些半乳糖凝集素，一旦分泌在细胞外环境中，作为警报素引起炎症反应的募集和激活的先天性免疫细胞，导致败血症的恶化。因此，这些半乳糖凝集素在骨髓细胞活化中的作用，从而影响任何急性呼吸道感染中的脓毒症发展是未知的。拟议研究的基本原理是，将半乳糖凝集素鉴定为新型警报素将为开发脓毒症的有效治疗方法提供新的靶点。为了验证我们的假设，我们将：检查半乳糖凝集素作为警报素在肺部弗朗西斯菌感染期间的总体疾病严重程度中的作用（目的1）;为了理解所涉及的机制，阐明半乳糖凝集素在脓毒症中骨髓细胞浸润和活化中的作用（目的2）。

DESCRIPTION (provided by applicant): Sepsis and sepsis-associated multiple-organ failures account for 250,000 deaths annually in the United States alone. During sepsis, unbridled stimulation of myeloid cells resulting in a hyperinflammatory response leads to extensive tissue damage and failure of multiple systemic organs. Although sepsis can develop as a result of various pathological insults, respiratory infections are a leading cause of sepsis associated mortality. However, the mechanisms involved are not well understood. Recently, our studies have demonstrated that, in the absence any known bacterial endo- or exotoxins, a deregulated host immune response culminating in severe sepsis is associated with extreme lethality of pulmonary infection with a Gram negative bacterial pathogen Francisella. This pathogen has been categorized by CDC as a Category A select agent owing to its extreme virulence and the ease of its dissemination via respiratory route. The goal of proposed studies is to understand the molecular events that contribute to the development of sepsis using the murine inhalation model of respiratory Francisella infection. These studies are innovative as we are investigating a previously undetermined role of host glycan-recognizing innate immune molecules, called galectins, as alarmins in the development of sepsis. Emerging evidence suggests that during inflammation, dead or dying host cells can release endogenous host factors called alarmins, which have homeostatic functions when contained in intracellular compartments under normal conditions, but, upon their extracellular release, can cause hyper inflammatory response. This underscores that identification and characterization of alarmins can direct the development of effective therapies against inflammatory disorders such as sepsis. This encompasses the objective of the proposed studies. Our preliminary analyses in mice infected with lethal wild-type Francisella and those vaccinated with a protective mutant show an upregulation and extracellular release of galectin-3 and galectin-9, two host lectins lacking secretion signal and exhibiting immune modulatory properties (characteristic of alarmins), only during lethal Francisella infection. Additionally, the Francisella-infected galectin-3-/- and -9-/- mice exhibit attenuation of inflammatory response, reduced pathology, and altered myeloid cell phenotype in comparison with the infected wild-type mice. We thus hypothesize that these galectins, once secreted in extracellular milieu, act as alarmins to elicit inflammatory responses by recruitment and activation of innate immune cells resulting in exacerbation of sepsis. As such, the role of these galectins in myeloid cells activation thereby influencing sepsis development in any acute respiratory infection is unknown. The rationale for the proposed research is that, identifying galectins as novel alarmins will provide novel targets for developing effective therapeutics for sepsis. To test our hypothesis we will: examine the role of galectins as alarmins in overall disease severity during pulmonary Francisella infection (Aim 1) and; to understand the mechanisms involved, elucidate the role of galectins in infiltration and activation of myeloid cell in sepsis (Aim 2).