Lymphatic endothelial cells as inducers of systemic peripheral tolerance

描述（由申请方提供）：本申请的目的是确定控制淋巴结驻留淋巴内皮细胞诱导外周免疫耐受能力的分子和细胞机制。我们和另外两个小组已经描述了一种机制，即淋巴结中的基质细胞直接表达通常与其他组织相关的蛋白质。将衍生自这些蛋白质的表位直接呈递给CD8 T细胞导致增殖失败和缺失。已显示介导该过程的淋巴结基质细胞群体包括：胸腺外表达Aire的细胞（eTAC）、成纤维细胞网状细胞和淋巴管内皮细胞。特别是，我们已经证明， CD 8 T细胞对源自酪氨酸酶的表位的耐受性是由淋巴结驻留淋巴内皮细胞介导的，该细胞外源性表达该蛋白质，该蛋白质的表达通常仅限于黑素细胞和视网膜色素上皮细胞。上文定义的3个淋巴结基质群体表达至少部分不同的外周组织抗原子集。在自身免疫调节元件Aire的影响下，外周组织抗原也在胸腺中表达。Aire还控制eTAC淋巴结基质亚群中外周组织抗原的表达。然而，无论是成纤维网状细胞，淋巴管内皮细胞表达Aire，和控制外周组织抗原mRNA在这些淋巴结间质人群的转录机制是未知的。本申请的一个目标是鉴定导致淋巴管内皮细胞中外周组织抗原表达的转录因子。这将阐明新的机制，控制外周组织抗原的表达，除了Aire，系统性外周耐受的发展的基础。我们的初步工作已经确定，淋巴结驻留的淋巴管内皮细胞不同于其对应物，通过外周组织抗原的表达升高和酪氨酸酶特异性T细胞呈递酪氨酸酶表位的能力形成组织淋巴管。淋巴结驻留淋巴管内皮细胞也表达许多免疫相关分子，这些分子不被它们的组织淋巴对应物表达。其中，最重要的是PD-L1，我们已经证明它在耐受诱导期间负责T细胞缺失。我们还建立了淋巴结本身的淋巴管内皮细胞亚群的存在，并表明，酪氨酸酶的耐受性主要是由那些形成髓窦。因此，淋巴管内皮细胞诱导外周耐受的能力是由LN微环境调节的。本申请的第二个主要目标是鉴定调节这种致耐受性表型的LN微环境的细胞和分子方面。这项工作将为进一步了解淋巴管内皮细胞在人类自身耐受性和自身免疫性疾病发展中的作用奠定基础。

DESCRIPTION (provided by applicant): The goal of this application is to identify the molecular and cellular mechanisms that control the ability of lymph node resident lymphatic endothelial cells to induce peripheral immunological tolerance. We and two other groups have described a mechanism in which stromal cells in lymph nodes directly express proteins that are normally associated with other tissues. Direct presentation of epitopes derived from these proteins to CD8 T cells leads to abortive proliferation and deletion. Populations of lymph node stromal cells that have been shown to mediate this process include: extra thymic Aire-expressing cells (eTAC), fibroblastic reticular cells, and lymphatic endothelial cells. In particular, 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 mediated by lymph node resident lymphatic endothelial cells that adventitiously express it. The 3 lymph node stromal populations defined above express at least partially distinct subsets of peripheral tissue antigens. Peripheral tissue antigens are also expressed in the thymus under the influence of the autoimmune regulatory element Aire. Aire also controls the expression of peripheral tissue antigens in the eTAC lymph node stromal subset. However, neither fibroblastic reticular cells nor lymphatic endothelial cells express Aire, and the mechanisms that control transcription of peripheral tissue antigen mRNAs in these lymph node stromal populations are unknown. One goal of this application is to identify transcription factors that lead to peripheral tissue antige expression in lymphatic endothelial cells. This will illuminate new mechanisms for control of peripheral tissue antigen expression, apart from Aire, that underlie the development of systemic peripheral tolerance. Our preliminary work has established that the lymph node resident lymphatic endothelial cells differ from their counterparts that form tissue lymphatic vessels by elevated expression of peripheral tissue antigens and the ability to present tyrosinase epitopes to tyrosinase-specific T cells. Lymph node resident lymphatic endothelial cells also express a number of immunologically relevant molecules that are not expressed by their tissue lymphatic counterparts. Of these, the most important is PD-L1, which we have shown to be responsible for T cell deletion during tolerance induction. We have also established the existence of subpopulations of lymphatic endothelial cells in the lymph node itself, and shown that tolerance to tyrosinase is primarily induced by those that form the medullary sinus. Thus, the ability of lymphatic endothelial cells to induce peripheral tolerance is regulated by the LN microenvironment. A second major goal of this application is to identify the cellular and molecular aspects of the LN microenvironment that regulate this tolerogenic phenotype. This work will set the stage for further understanding of the role lymphatic endothelial cells may play in self-tolerance and the development of autoimmune disease in humans.