Neutrophil Dynamics in Nasal Mucosa

鼻黏膜(NM)具有多种重要的生理功能，包括作为化学感受器、作为吸入空气的过滤和调节下呼吸道的表面以及作为抵御空气传播感染的第一道防线。在哺乳动物中，鼻道在解剖学上是复杂的，有不同的亚室，具有不同的形态和细胞特征，可能发挥特殊的功能，但目前尚不清楚。由于不断暴露在不断变化的环境中，NM可以说是哺乳动物中感染最频繁的组织。除了是许多真菌、病毒和细菌病原体的首选目标外，其中一些病原体随后可能传播到下呼吸道、血液、大脑或其他颅骨区域，鼻腔还被一种特殊的微生物群定植，可以作为机会性病原体的储存库。尽管NM对人类健康很重要，但人们对局部免疫反应的启动和/或调节机制知之甚少。可以说，NM必须拥有专门的功能，才能针对广泛的挑战做出适当的先天和适应性免疫反应。已知NM含有血管外上皮下免疫细胞，但其来源、组成及其在稳态和病理条件下的作用尚不清楚。为了解决这个问题，设计了一种新的活体显微镜(IVM)模型来跟踪活着的小鼠NM中白细胞的动态行为。初步结果表明，小鼠稳态NM中存在大量的血管外中性粒细胞(EVN)，在常规小鼠和无菌小鼠中都很丰富，这表明它们的存在不是由微生物刺激驱动的。此外，鼻腔EVN还可以细分为三个不同的表型亚群：一个群体(称为N1)是CD11bint Ly6Gint，而另外两个亚群都是CD11bhi Ly6Ghi，并通过CD11c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亚型是如何产生的，它们如何应对传染性挑战，以及它们在健康和疾病中发挥什么作用。假设每个鼻腔EVN亚群都有不同的起源，通过不同的机制进入NM，并在组织内稳态和宿主防御微生物感染方面发挥特殊功能。为了验证这一假设，目标1将探索稳态鼻腔EVN亚组的起源和迁移特性，而目标2将定义每个EVN亚组在稳态和鼻内病原体攻击后的功能。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，还可以为可能影响鼻用疫苗效力的免疫学机制以及影响鼻腔的病理条件(如过敏和一系列呼吸道感染)提供新的线索。

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.