Novel pathways in T lymphocyte differentiation and function

产生针对不同病原体的高亲和力抗体的能力(即体液免疫)是脊椎动物免疫系统的基本属性，并确保宿主存活。体液免疫反应需要B淋巴细胞(具有产生抗体的能力)和辅助T细胞之间高度协调的相互作用。这些相互作用是由被称为T滤泡辅助细胞(TFH)的辅助性T细胞亚群介导的，它通过提供膜结合的共刺激分子和分泌极化细胞因子来直接帮助B细胞。我们以前已经证明，在免疫和寄生虫感染的背景下，TFH细胞提供产生体液免疫反应所需的IL-4和IL-21的关键来源(King等人，《自然免疫学》，2012)和寄生虫感染(King和Mohars，《实验医学杂志》，2009)。这项建议建立在这些发现的基础上，以确定以前未描述的分子和信号通路，这些分子和信号通路专门控制T细胞的分化和功能。 为了发现Tfh细胞独特表达的分子，我们使用微阵列技术进行了初步实验，将该亚群与从感染肠道蠕虫的小鼠炎症的肠系膜淋巴结中分离出的其他CD4+T细胞亚群进行比较。我们的结果表明，与其他CD4+T细胞相比，TFH细胞表达高水平的CD109。CD109是一种糖磷脂酰肌醇锚定蛋白，在免疫系统中的功能未知。利用角质形成细胞的功能研究表明，CD109是转化生长因子-β1信号的负调节因子，而转化生长因子-β1信号是一种显著影响T效应细胞分化的细胞因子。我的实验室的初步结果表明，关键的转化生长因子-β1靶基因，如Smad7，在TFH细胞中下调，这与CD109也在T细胞中负调控这一信号途径的想法一致。此外，CD109已被证明调节STAT3，一种促进TFH细胞分化的转录因子以及其他T效应亚群。因此，有必要深入分析CD109在T细胞生物学中的作用及其与淋巴细胞中转化生长因子-β1和信号转导通路的潜在关系。在这一应用中，我们提出了一个研究计划，旨在通过追求以下三个特定目标来阐明CD109在T细胞激活中的功能及其在控制T细胞分化和功能方面的特异性： 1.明确CD4+T细胞对CD109表达的要求。 2.确定CD109如何影响CD4+T细胞的激活和分化。 3.鉴定活化的CD4+T细胞中的CD109结合伙伴。 了解CD109在T细胞分化和/或功能中的功能将为控制这一重要免疫细胞群的分子机制提供新的见解。

The ability to generate high-affinity antibodies to diverse infectious agents (i.e. humoral immunity) is a fundamental property of the vertebrate immune system and ensures host survival. The humoral immune response requires highly coordinated interactions between B lymphocytes (which possess antibody-producing potential) and “helper” T cells. These interactions are mediated by a subset of helper T cells termed T follicular helper (Tfh) cells that provide direct help to B cells through provision of membrane-bound co-stimulatory molecules and secretion of polarizing cytokines. We have previously shown that Tfh cells provide critical sources of interleukin (IL)-4 and IL-21 required for the generation of humoral immune responses in the context of immunization (King et al, Nature Immunology, 2012) and parasitic helminth infection (King and Mohrs, Journal of Experimental Medicine, 2009). This proposal builds on these findings to identify previously undescribed molecules and signaling pathways that specifically control T cell differentiation and function. To discover molecules uniquely expressed by Tfh cells, we performed preliminary experiments using microarray technology comparing this subset to other CD4+ T cell subsets isolated from the inflamed mesenteric lymph nodes of mice infected with an intestinal helminth. Our results indicate that Tfh cells express high levels of CD109 compared to other CD4+ T cells. CD109 is a glycophosphatidylinositol-anchored protein with unknown function in the immune system. Functional studies using keratinocytes have demonstrated that CD109 acts as a negative regulator of transforming growth factor (TGF)-b1 signaling, a cytokine that dramatically influences T effector cell differentiation. Preliminary results from my laboratory indicate that key TGF-b1 target genes such as SMAD7 are downregulated in Tfh cells, findings consistent with the idea that CD109 is also negatively regulating this signaling pathway in T cells. In addition, CD109 has been been shown to regulate STAT3, a transcription factor that promotes Tfh cell differentiation as well as other T effector subsets. Thus, an in-depth analysis of CD109 in T cell biology and its potential relationship to TGF-b1 and STAT3-dependent signaling in lymphocytes is warranted. In this application, we propose a research program to elucidate the function of CD109 in T cell activation and its specificity in controlling T cell differentiation and function by pursuing 3 specific objectives: 1. Identify the requirements for CD109 expression by CD4+ T cells. 2. Determine how CD109 impacts CD4+ T cell activation and differentiation. 3. Identify CD109 binding partners in activated CD4+ T cells. Understanding the function of CD109 in T cell differentiation and/or function will provide new insight into the molecular mechanisms controlling this important immune cell population.