The role of lymph node structural organization in naïve T cell decline with age

项目摘要/摘要 该项目的目标是了解与年龄相关的淋巴结变化是如何导致淋巴结减少的 幼稚T细胞的存活，这是免疫老化的标志。幼稚T细胞是解决感染所必需的 由新发现的病原体引起，但它们在T细胞群体中的数量和频率减少 随着年龄的增长戏剧性地增加。这有助于降低衰老免疫反应的大小和延迟时间。 对抗传染病。原始T细胞的生存需要来自组织环境的持续信号，而它 已经得到了很好的支持，即老化的环境在维持幼稚T细胞稳态方面存在缺陷。 原始T细胞主要与淋巴结的组织相互作用，战略性地组织组织间隔 分布于全身，作为免疫反应的协调中心。的广泛变化。 无论是小鼠还是人类，淋巴结的大小和结构都是随着年龄的变化而描述的；然而， 推动这些变化的机制，以及它们如何影响幼稚的T细胞，目前尚不清楚。我们的数据显示 随年龄变化为称为成纤维细胞网状细胞(FRC)的淋巴结基质细胞类型。幼稚T细胞 附着于FRC并沿着FRC网络爬行以导航淋巴结。FRCS在A中的原位区分 这一过程需要持续的淋巴毒素-β(LTβ)信号。成熟FRC表达动态平衡细胞因子 它们对幼稚T细胞的存活和促进淋巴内相互作用和运动的趋化因子是必不可少的 节点。CCL21等稳态趋化因子在促进幼稚T细胞方面的作用得到了广泛的评价 但是它们的表达和分布是如何受到 年龄尚不清楚。在我们的初步工作中，我们确定了LTbR(淋巴毒素-1)在淋巴结间质中的表达。 β受体)和CCL21随增龄而显著降低。我们还发现了FRC分化的证据 随着年龄的增长而受损，因为早期的FRC前体在频率上减少，并且存在 堆积中间的FRC前驱体。对FRC前驱体的扰动与降低相关 LTbR的表达，表明老化的FRC前体细胞无法接收到必要的LTβ信号 完全成熟。我们假设，随着FRC分化受损，FRC变得纤维化和空间化。 在淋巴结内重新分布，这抑制了幼稚T细胞生存所必需的相互作用。在这 我们将确定与年龄相关的炎症通过LTβR和 促进淋巴结纤维化(目标1)，以及是否增加了淋巴结微环境的纤维化 损害幼稚T细胞存活(目标2)。我们的实验方法使用活细胞双光子显微镜，它 使我们能够在完整的组织中实时可视化幼稚T细胞与FRC的相互作用。完成度 该项目将支持一种机制，通过这种机制，衰老的组织微环境推动幼稚的磨损 T细胞。建立这种联系可以导致修复老化的淋巴间质的治疗方法的发展 并促进老年人幼稚T细胞的存活和功能。

PROJECT SUMMARY/ABSTRACT The project goal is to understand how age-associated changes to the lymph nodes contribute to decreased survival of naïve T cells, a hallmark of immune aging. Naïve T cells are essential for resolving infections caused by newly encountered pathogens, but their number and frequency within the T cell population decrease dramatically with age. This contributes to reduced magnitude and delayed timing of the aged immune response against infectious disease. Naïve T cell survival requires constant signaling from the tissue environment, and it has been well-supported that the aged environment is defective in its ability to maintain naïve T cell homeostasis. Naïve T cells primarily interact with the tissues of the lymph nodes, organized tissue compartments strategically located throughout the body that serve as coordination centers for the immune response. Broad changes to the size and structure of the lymph nodes have been described with age, for both mice and humans; however, the mechanisms driving these changes, and how they impact naïve T cells, are unknown. Our data have revealed changes with age to the lymph node stromal cell type known as the fibroblastic reticular cell (FRC). Naïve T cells adhere to FRCs and crawl along the FRC network to navigate the lymph nodes. FRCs differentiate in situ in a process that requires continuous lymphotoxin-beta (LTβ) signaling. Mature FRCs express homeostatic cytokines that are essential for naive T cell survival and chemokines that promote interactions and motility within the lymph nodes. Homeostatic chemokines such as CCL21 have well-appreciated roles in promoting naïve T cell recruitment to and migration within the lymph nodes, but how their expression and distribution are impacted by age is not clear. In our preliminary work, we determined that lymph node stromal expression of Ltbr (lymphotoxin- beta receptor) and Ccl21 were significantly decreased with age. We also found evidence that FRC differentiation is impaired with age, in that early FRC precursors were decreased in frequency, and that there was an accumulation intermediate FRC precursors. The perturbation to FRC precursors was correlated to decreased expression of LTBR, suggesting that aged FRC precursors were unable to receive the LTβ signals necessary to complete maturation. We hypothesize that with impaired FRC differentiation, FRCs become fibrotic and spatially redistributed within the lymph node, which inhibits the interactions necessary for naïve T cell survival. In this project we will determine the role of age-associated inflammation in impairing signals through LTβR and promoting lymph node fibrosis (Aim 1), and whether increased fibrosis of the lymph node microenvironment impairs naïve T cell survival (Aim 2). Our experimental approach uses live-cell 2-photon microscopy, which enables us to visualize the interaction of naïve T cells with FRCs in real time within intact tissues. The completion of the project will support a mechanism by which the aged tissue microenvironment drives the attrition of naïve T cells. Establishing this link can lead to development of therapeutics to restore the aged lymph node stroma and promote the survival and function of naïve T cells in older individuals.