Role of fascin1 in dendritic cell-mediated immunity against listeria infection

描述（由申请人提供）：本R03申请的目的是确定fascin1在树突状细胞（DC）免疫抵抗单核增生李斯特菌（Lm）感染中的体内作用。dc是最有效的抗原提呈细胞，在先天免疫和获得性免疫中发挥核心作用。当树突状细胞遇到病原体时，它们经历被称为成熟的终末分化：它们聚集大量的面纱状膜突起，从外周组织移动到引流淋巴结，并将抗原呈递给幼稚的t细胞。Fascin1是DC中独特的肌动蛋白结合蛋白，因为它在DC成熟过程中被特异性诱导。在未成熟的DC或其他血细胞（包括巨噬细胞、中性粒细胞和自然杀伤细胞）中不存在Fascin1，这表明在成熟后的DC生物学中，Fascin1具有特定的作用。事实上，我们和其他人已经证明，fascin1对成熟相关功能至关重要，包括肌动蛋白细胞骨架的大规模重组、dc向引流淋巴结的趋化迁移、t细胞激活和免疫突触的组装。我们发现，通过表征fascin1 KO dc， fascin1在dc介导的宿主防御系统中起着新的作用。据报道，树突状细胞比巨噬细胞对Lm具有更强的胞内杀伤活性。这种对Lm的抵抗被认为对树突状细胞抗原呈递的主要功能至关重要：树突状细胞必须在外周感染后存活，然后移动到引流淋巴结，将抗原信息传递给t细胞。我们发现fascin1 KO dc对lm介导的杀伤表现出更高的易感性。重要的是，具有高fascin1表达的树突状细胞对Lm感染具有极强的抵抗力。我们进一步发现，fascin1使lm包被的吞噬体酸性增强，并增加自噬通量。这些结果表明，fascin1增加了吞噬体和自噬体的溶酶体融合，以清除细菌，这解释了为什么DCs （fascin1阳性）比巨噬细胞（fascin1阴性）更具抗性。然而，一个关键问题仍有待回答：在体内，fascin1是否对基于dc的抗Lm感染的适应性和先天免疫至关重要？我们将通过使用Lm小鼠模型来检验，是否fascin1 KO小鼠对Lm感染表现出适应性和先天免疫反应的降低。该提案可能提供重要的信息，将帮助我们开发新的基于dc的免疫疗法对抗细菌感染。

DESCRIPTION (provided by applicant): The goal of this R03 application is to determine in vivo roles of fascin1 in dendritic cell (DC)-based immunity against infection of Listeria monocytogenes (Lm). DCs, the most potent antigen presenting cells, play central roles in both innate and acquired immunity. When DCs encounter pathogens, they undergo terminal differentiation called maturation: they assemble numerous veil-like membrane protrusions, travel from the peripheral tissues to draining lymph nodes, and present antigens to naive T-cells. Fascin1 is a unique actin-bundling protein in DCs because it is greatly and specifically induced upon DC maturation. Fascin1 is absent in immature DCs or in other blood cells including macrophages, neutrophils and natural killer cells, suggesting a specific role for fascin1 in DC biology upon maturation. Indeed, we and others have demonstrated that fascin1 is critical for the maturation-associated functions including massive reorganization of the actin cytoskeleton, chemotactic migration of DCs into draining lymph nodes, T-cell activation and assembly of the immunological synapse. We have found, by characterizing fascin1 KO DCs, that fascin1 plays a novel role in a DC-mediated host defense system. It has been reported that DCs show a stronger intracellular killing activity toward Lm than do macrophages. This resistance to Lm is thought to be crucial for the DCs primary function of antigen presentation: DCs must survive infection at the periphery and then move to draining lymph nodes for transferring antigen information to T-cells. We found that fascin1 KO DCs displayed higher susceptibility to Lm-mediated killing. Importantly, DCs with high fascin1 expression was extremely resistant to Lm infection. We further found that fascin1 made Lm-encapsulated phagosomes more acidic, and increases autophagy flux. These results indicate that fascin1 increases lysosomal fusion of both phagosomes and autophagosomes for bacterial clearance, explaining why DCs (fascin1-positive) are more resistant than macrophages (fascin1-negative). However, a key question remains to be answered: Is fascin1 crucial for DC-based adaptive and innate immunity against Lm infection in vivo? We will examine, by using the Lm mouse model, whether fascin1 KO mice show reduced adaptive and innate immune responses to Lm infection. The proposal is likely to provide vital information that will help us develop new DC-based immunotherapy against bacterial infection.