Using microbially-experienced mice to study the innate immune response in sepsis

脓毒症是由宿主对感染的反应失调引起的危及生命的器官功能障碍。早期 脓毒症的阶段以由促炎细胞因子驱动的过度炎症为标志（即，IL-1 β、IL-6、IFN γ， 和TNF）。在人类中进行假设驱动的研究的困难证明了临床- 相关的实验性脓毒症模型。许多模型通常用于研究多因素 脓毒症的病理生理学，并且用于脓毒症研究的主要哺乳动物生物体是小鼠（Mus 肌肉）。虽然关于发生的复杂变化的知识已经有了巨大的扩展， 在脓毒症事件后的免疫系统中，迄今为止发表的几乎所有临床前脓毒症研究 依赖于使用在无特定病原体（SPF）条件下饲养的小鼠。环境病原体 暴露是基本人类和实验室小鼠生物学之间的一个重要区别， 在使用小鼠评估免疫系统适应性时考虑。人类自然会接触到这两种物质 从出生开始，每天都有大量的细菌和病原微生物，成年人的免疫系统已经被破坏了。 通过每一次感染和疫苗接种经历训练和塑造。虽然SPF级实验室小鼠的住房 有助于提高实验的可重复性，同时也使小鼠 作为人类的模型，很大程度上是因为SPF小鼠在有限的微生物暴露下生活。 这项提议利用了一种新的小鼠模型，该模型模拟了人类生物学的一个关键方面-暴露于 多重进行中的和已解决的感染训练免疫系统对新病原体作出强有力的反应。 我们的中心假设认为，脓毒症患者急性反应和死亡率的增加， (CoH)小鼠源于腹膜驻留Mf引起的活动过度和器官功能障碍/损伤增加 源于升高的中性粒细胞反应-很大程度上是因为这些细胞的能力增强， 吞噬细胞通过增加模式识别受体表达识别感染。我们也 通过共居的微生物暴露增加了肠道微生物组的“致病性”，这也有助于 增强免疫系统的反应。在目标1中，我们将定义TLR4信号传导的重要性。 腹膜内Mf在脓毒症期间调节急性免疫应答的幅度。 目标2中的实验将定义中性粒细胞在导致器官功能障碍/损伤中所起的作用， 脓毒症CoH小鼠的死亡率。最后，目标3中的研究将确定肠道微生物组的变化， 重症监护中脓毒症患者的部分常规治疗，包括广谱抗生素， 肠内营养中断，导致微生物群功能障碍，增加晚期脓毒症死亡率。当 本建议书中的概念、初步数据和拟议的研究被概括考虑，本项目将 展示了使用CoH小鼠更好地询问脓毒症的免疫学分支的能力。

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Early stages of sepsis are marked by hyperinflammation driven by proinflammatory cytokines (i.e., IL-1β, IL-6, IFNγ, and TNF). The difficulty in performing hypothesis-driven research in humans justifies the need for a clinically- relevant, experimental sepsis model. A number of models are commonly used to study the multifactorial pathophysiology of sepsis, and the dominant mammalian organism used in sepsis research is the mouse (Mus musculus). While there has been a vast expansion in knowledge regarding the intricate changes that occur within the immune system following a septic event, virtually all preclinical sepsis research published to date has relied on the use of mice housed under specific pathogen-free (SPF) conditions. Environmental pathogen exposure is one important difference between basic human and laboratory mouse biology that must be considered when using mice to evaluate immune system fitness. Humans are naturally exposed to both commensal and pathogenic microbes daily from birth, and the immune system of adult humans has been trained and shaped by each infection and vaccination experienced. While SPF housing of laboratory mice has been instrumental in increasing experimental reproducibility, it has simultaneously further distanced the mouse as a model from humans largely because SPF mice live their lives with limited microbial exposure. This proposal leverages a novel mouse model that mimics a critical aspect of human biology – exposure to multiple ongoing and resolved infections trains the immune system for robust responses to new pathogens. Our central hypothesis holds that the exacerbated acute response and mortality seen in septic cohoused (CoH) mice stems from hyperactivity by peritoneal resident Mf and increased organ dysfunction/damage stemming from elevated neutrophil responses – largely because of an augmented capacity of these phagocytes to recognize infection via increased pattern recognition receptor expression. We also posit microbial exposure via cohousing increases the ‘pathogenicity’ of the gut microbiome, which also contributes to the increased response by the immune system. In Aim 1, we will define the importance of TLR4 signaling within peritoneal resident Mf in regulating the magnitude of the acute immune response during sepsis. Experiments in Aim 2 will define the role played by neutrophils leading to the organ dysfunction/damage and mortality in septic CoH mice. Finally, studies in Aim 3 will determine how changes in the gut microbiome as part of the routine treatments for sepsis patients in critical care, including broad-spectrum antibiotics and interruption of enteral nutrition, lead to the dysfunction of microbiota that increases late sepsis mortality. When the concepts, preliminary data, and proposed studies in this proposal are considered in sum, this project will showcase the power of using CoH mice to better interrogate the immunological ramifications of sepsis.