Dissecting pathogen persistence- versus clearance-promoting functions of monocyte-derived cell populations during L. major infection

组织损伤和感染导致大量免疫细胞从血液中招募。在这些被招募的细胞中，单核细胞形成了一个多功能的吞噬细胞系统，可以吸收和中和病原体，激活适应性免疫系统，但也可以诱导组织修复。尽管在各种疾病模型中进行了密集的研究，但仍不清楚特定单核细胞亚群在被招募到组织后如何诱导不同的功能，以及这些功能如何有助于控制感染。这个问题对于像主要乳杆菌这样的细胞内病原体的感染尤其重要，对于这种病原体，单核细胞来源的细胞既可以作为病原体在细胞内生长的利基，也可以作为对抗感染的效应细胞。在我们之前的工作中，我们已经鉴定了不同的单核细胞来源的细胞亚群，它们含有不同的细胞内增殖率，表现出独特的基因表达模式，并被效应T细胞差异地参与。这些差异如何与单个单核细胞衍生的亚群的不同作用有关，即它们在多大程度上促进了病原体的细胞内存活和持久性，或者通过激活免疫系统来清除病原体。因此，拟议的研究的目的是调查以下问题：(1)单核细胞衍生的细胞亚群是如何被招募到皮肤感染部位并在那里被激活的？为了实现这一点，我们将使用荧光报告系统，使我们能够在体内跟踪单核细胞在感染部位的招募和激活。(2)不同的亚群如何与T细胞相互作用并调节T细胞效应器的功能？为此，我们将通过活体内双光子显微镜、活体细胞成像和体外RNA测序来研究不同的单核细胞衍生细胞亚群与效应T细胞相互作用并激活效应T细胞的能力。(3)在不同的单核细胞衍生细胞亚群中特异表达的候选基因如何影响这些亚群在促进病原体持久性与清除性方面的作用？为了研究这个问题，我们将应用混合骨髓嵌合模型结合部分细胞耗竭来研究候选基因缺陷在病理和感染过程中的细胞内在和细胞外在效应。所提出的研究将有助于我们理解不同的单核细胞来源的细胞亚群如何影响感染过程的机制和动力学。鉴于单核细胞广泛参与各种感染性、炎症性和恶性疾病，阐明控制这种免疫刺激和免疫调节功能的机制可以指导针对单核细胞这种平衡的新的治疗策略。

Tissue damage and infection results in the massive recruitment of immune cells from the bloodstream. Among these recruited cells, the monocytes give rise to a versatile system of phagocytes which can take up and neutralize pathogens, activate the adaptive immune system, but also induce tissue repair. Despite intense investigation in a variety of disease models, it has remained unclear how the different functions of specific monocyte subsets are induced after recruitment to the tissue, and how these functions contribute to the control of infections. This question is especially important for the infection with intracellular pathogens such as L. major, for which monocyte-derived cells can serve both as niches for intracellular growth of the pathogen, but also as effector cells fighting the infection.In our previous work, we have identified distinct subsets of monocyte-derived cells that harbour L. major with different intracellular proliferation rates, exhibit characteristic gene expression patterns, and are differentially engaged by effector T cells. How such differences relate to distinct effects of the individual monocyte-derived subsets, i.e. to what extent they promote intracellular survival and persistence of the pathogen, or pathogen clearance by activating the immune system, is unclear yet.The objective of the proposed research is therefore to investigate the following questions:(1) How are the monocyte-derived cell subsets are recruited to, and activated at, the site of L. major skin infection? To achieve this, we will employ fluorescent reporter systems that allow us to track in vivo the recruitment and activation of monocytes to the site of infection.(2) How do the different subsets interact with T cells and modulate T cell effector functions? For this, we will investigate by intravital 2-photon microscopy in vivo, and by live cell imaging and RNA sequencing ex vivo, the capacity of different monocyte-derived cell subsets to interact with and activate effector T cells.(3) How do candidate genes shown to be specifically expressed in distinct monocyte-derived cell subsets impact on the role of these subsets in promoting pathogen persistence versus clearance? To investigate this question, we will apply mixed bone marrow chimeric models combined with partial cell depletion to address cell-intrinsic versus cell extrinsic effects of candidate gene deficiencies on pathology and infection course.The proposed research should critically contribute to our understanding of the mechanisms and dynamics of how different monocyte-derived cell subsets impact on the course of infection. Given the widespread involvement of monocytes in a variety of infectious, inflammatory and malignant diseases, elucidating the mechanisms that control such immunostimulatory versus immunomodulatory functions could guide novel therapeutic strategies targeting this balance specifically in monocytes.