Lymphatic endothelial cells as inducers of systemic peripheral tolerance

描述（由申请人提供）：外周耐受阻止逃避胸腺阴性选择的自身反应性T细胞引起自身免疫。在固有外周耐受的主流模型中，静止的组织驻留树突状细胞（DC）迁移到淋巴结（LN），在那里它们交叉将自身ag呈递给T细胞，然后T细胞进行删除或激活。我们已经证明CD8 T细胞对酪氨酸酶衍生的表位的耐受性不是由胸腺阴性选择或交叉耐受性介导的，酪氨酸酶是一种蛋白，其表达通常局限于黑色素细胞和视网膜色素上皮细胞。相反，CD8 T细胞在LN驻留淋巴内皮细胞（LEC）的介导下增殖和缺失失败，而LEC不定地表达酪氨酸酶。我们和其他研究小组已经确定，至少有两种其他LN基质亚群也可以诱导CD8 T细胞耐受。这些亚群各自表达许多外周组织Ags的不同亚群，表明它们代表了一种主要的、以前未被认识的系统性内在外周耐受性机制。本应用程序的目的是提供证据来支持这一假设，特别关注LEC，并探讨影响LEC执行这一功能的能力的因素。在Aim 1中，我们将使用一个新开发的模型系统来确定表达MHC-II分子的LEC耐受CD4 T细胞的机制，并探索抗原表达水平在CD4和CD8 T细胞耐受结果中的作用。在Aim 2中，我们将探讨PD-L1在不同抗原提呈细胞诱导的耐受中的意义，LEC表达的PD-L1比任何其他LN细胞群表达的都要高。我们的初步研究表明，PD-L1信号可以在没有Ag同时参与的情况下发生，我们假设LEC作为看门人来加强免疫反应的质量。我们还将建立诱导T细胞增殖的机制，以及LEC在这一过程中的作用。增殖似乎是缺失过程的基本要素，但也可以使自身反应性T细胞积累。在Aim 3中，我们将定义存在于LN中的LEC（与组织淋巴管中的LEC相反）能够基于外周组织Ags和一组免疫调节分子（包括PD-L1）的表达诱导耐受的机制。我们将定义影响LN驻地LEC中这些分子表达的细胞和分子成分，并使用基因表达分析来确定控制LEC中这些分子和外周组织Ags表达的转录因子。总的来说，我们期望这项资助支持的研究能够为外周自身耐受性的建立和维持机制带来重要的新见解，这将有助于理解自身免疫性疾病的发展，以及自我耐受性如何限制对来自组织特异性蛋白的癌细胞Ags的免疫反应。

DESCRIPTION (provided by applicant): Peripheral tolerance prevents self-reactive T cells that escape thymic negative selection from causing autoimmunity. In the prevailing model of intrinsic peripheral tolerance, quiescent tissue-resident dendritic cells (DC) migrate to lymph nodes (LN) where they cross present self-Ag to T cells, which then undergo deletion or anergy. We have shown that CD8 T cell tolerance to an epitope derived from tyrosinase, a protein whose expression is normally confined to melanocytes and retinal pigment epithelial cells, is not mediated by either thymic negative selection or cross-tolerance. Rather, CD8 T cells undergo abortive proliferation and deletion mediated by LN resident lymphatic endothelial cells (LEC) that adventitiously express tyrosinase. We and other groups have established that at least two other LN stromal subsets can also induce CD8 T cell tolerance. These subpopulations each express distinct subsets of many peripheral tissue Ags, suggesting that they represent a major, previously unrecognized mechanism of systemic intrinsic peripheral tolerance. The goal of the present application is to provide evidence to support this hypothesis, with a specific focus on LEC, and to explore factors that influence the ability of LEC to carry out this function. In Aim 1 we will use a newly developed model system to determine the mechanisms by which LEC, which express MHC-II molecules, tolerize CD4 T cells, and explore the role of antigen expression levels on tolerogenic outcome in both CD4 and CD8 T cells. In Aim 2 we will explore the significance of PD-L1, which LEC express at a higher level than any other LN cell population, on tolerance inducedby different antigen presenting cells. Our preliminary studies suggest that PD-L1 signaling can occur without simultaneous Ag engagement, and we hypothesize that LEC act as gatekeepers to enforce the quality of immune responses. We will also establish the mechanisms by which proliferation of T cells destined to undergo deletion is induced, and the role of LEC in this process. Proliferation appears to be an essential element of the deletion process, but also can enable accumulation of autoreactive T cells. In Aim 3 we will define the mechanisms by which LEC that reside in LN, as opposed to those in tissue lymphatic vessels, are able to induce tolerance based on their expression of peripheral tissue Ags and a set of immunomodulatory molecules, including PD-L1. We will define the cellular and molecular components that influence expression of these molecules in LN resident LEC, and use gene expression analyses to identify the transcription factors that control expression of these molecules and peripheral tissue Ags in LEC. Collectively, we expect the studies supported by this grant to lead to significant new insights into the mechanisms by which peripheral self-tolerance is established and maintained, which will be relevant in understand the development of autoimmune disease and the ways in which self-tolerance limits immune responses to cancer cell Ags that are derived from tissue specific proteins.