Neutrophil Dynamics in Nasal Mucosa

鼻粘膜（NM）具有几种关键的生理功能，包括作为化学感受器官、作为下呼吸道吸入空气的过滤器和调节表面以及作为对抗空气传播感染的第一道防线。在哺乳动物中，鼻通道在解剖学上是复杂的，具有不同的亚隔室，具有不同的形态和细胞特征，可能发挥专门的功能，但迄今知之甚少。由于其不断暴露于不断变化的环境中，NM可以说是哺乳动物中最常见的感染组织。除了作为许多真菌、病毒和细菌病原体的优选初始靶标之外，其中一些病原体随后可能扩散到下呼吸道、血液、大脑或其他颅骨区域，鼻腔还被专门的微生物组定殖，其可以作为机会性病原体的储存库。尽管NM对人类健康的重要性，很少有人知道的机制，局部免疫反应的启动和/或调节。可以说，NM必须具有专门的功能，以使适当的先天性和适应性免疫反应，对各种各样的挑战。NM是已知的窝藏一个人口的上皮下血管外免疫细胞，但他们的起源，组成，并在稳态和病理条件下的作用知之甚少。为了解决这个问题，设计了一种新的活体显微镜（IVM）模型来跟踪活小鼠NM中白细胞的动态行为。初步结果表明，小鼠稳态NM窝藏一个突出的人口血管外中性粒细胞（EVN），是丰富的常规和无菌小鼠，这表明它们的存在是不是由微生物刺激。此外，鼻EVN可以细分为三个表型不同的亚群：一个群体（称为N1）是CD 11bint Ly 6 Gint，而其他两个亚群都是CD 11bhi Ly 6 Ghi，并可通过CD 11 c和SiglecF的缺失（N2）或存在（N3）来区分。该项目的主要目标是确定这些不寻常的EVN亚群是如何产生的，它们如何应对感染性挑战以及它们在健康和疾病中发挥什么作用。据推测，每个鼻EVN子集有一个独特的起源，通过离散的机制访问NM，并发挥专门的功能，在组织内稳态和宿主防御微生物感染。为了验证这一假设，目标1将探索稳态鼻EVN子集的起源和迁移特性，而目标2将定义每个EVN子集在稳态和鼻内病原体激发后的功能。拟议工作的结果不仅可以提高我们对NM作为关键屏障组织的理解，而且还可以揭示可能影响鼻疫苗功效的免疫机制以及影响鼻腔的病理条件，如过敏和呼吸道感染。

The nasal mucosa (NM) has several critical physiologic functions, including as a chemosensory organ, as a filter and conditioning surface of inhaled air for the lower airways, and as a first line of defense against airborne infections. In mammals, the nasal passage is anatomically complex, with different sub-compartments with distinct morphological and cellular features that may exert specialized, but as yet poorly understood, functions. Owing to its constant exposure to ever-changing environments, the NM is arguably the most frequently infected tissue in mammals. Aside from being a preferred initial target for many fungal, viral and bacterial pathogens, some of which may subsequently spread to the lower airways, blood, brain or other cranial regions, the nasal cavity is also colonized by a specialized microbiome that can serve as a reservoir for opportunistic pathogens. Despite the NM's importance for human health, little is known about the mechanisms by which local immune responses are initiated and/or regulated. Arguably, the NM must possess specialized features to enable appropriate innate and adaptive immune responses against a broad variety of challenges. The NM is known to harbor a population of subepithelial extravascular immune cells, but their origin, composition, and role at steady-state and in pathologic conditions are poorly understood. To address this issue, a novel intravital microscopy (IVM) model was devised to track the dynamic behavior of leukocytes in the NM of living mice. Preliminary results indicate that murine steady-state NM harbors a prominent population of extravascular neutrophils (EVN) that are abundant in both conventional and germ-free mice, suggesting that their presence is not driven by microbial stimuli. Furthermore, nasal EVN can be subdivided into three phenotypically distinct subsets: one population (termed N1) is CD11bint Ly6Gint, while the other two subsets are both CD11bhi Ly6Ghi and distinguishable by the absence (N2) or presence (N3) of CD11c and SiglecF. The primary objective of this project is to define how these unusual EVN subsets arise, how they respond to infectious challenges and what role they play in health and disease. It is hypothesized that each nasal EVN subset has a distinct origin, accesses the NM by discrete mechanisms, and exerts specialized functions in tissue homeostasis and in host defense against microbial infections. To test this hypothesis, Aim 1 will explore the origin and migratory properties of steady-state nasal EVN subsets, whereas Aim 2 will define the function of each EVN subset in homeostasis and after intranasal pathogen challenge. Results from the proposed work may not only improve our understanding of the NM as a critical barrier tissue, but also shed new light on immunological mechanisms that may impact the efficacy of nasal vaccines and on pathologic conditions affecting the nasal cavity such as allergies and a host of respiratory infections.