Investigating murine follicular T cells as well as the contribution of the antagonistic CD155 ligands TIGIT and CD226 to their differentiation and function

滤泡T细胞代表多种高度特化的CD 4 T细胞，其能够迁移到B细胞滤泡中并控制适应性免疫应答。对于这些过程最重要的是滤泡辅助T（TFH）和滤泡调节T（TFR）细胞，其抵消TFH驱动的活动。TFR细胞来源于胸腺起源的经典调节性T细胞。相比之下，TFH细胞从幼稚的CD 4 T细胞分化成几个步骤，最终导致它们位于生发中心（GC）。在GC反应期间，TFH细胞协助快速分裂的B母细胞发育成浆细胞或记忆细胞。它们还帮助GC B细胞进行类别转换重组和它们表达的抗体的超突变。我们可以证明，细胞表面受体CD 155及其配体CD 226是至关重要的参与建立一个规则的池滤泡T细胞在派尔集合淋巴结（PP）。此外，缺乏CD 155的小鼠在口服抗原时仅产生低于标准的次级体液免疫应答。值得注意的是，由IgM介导的主要反应不受影响。我们建立了协议，使我们能够更精确地定义TFH和TFR细胞。如该提案中所概述的，这使得能够改进由缺乏CD 155或CD 226引起的表型TFH细胞缺陷的定义。最近，发现了另一种CD 155的反受体，称为TIGIT。与代表T细胞共活化剂的⑶ 226相反，TIGIT显示抑制T细胞应答。我们观察到发育成TFH细胞的T细胞通过下调CD 226和上调TIGIT来进行CD 155配体转换。这表明TIGIT可有助于控制TFH细胞维持和功能，并且⑶ 226和TIGIT的适当平衡表达协调TFH细胞进程。有了这个建议，我们打算完善我们的TFH和TFR细胞的分析。为此，我们将进行基因芯片分析。通过体内迁移试验，我们将TFH亚群与其在淋巴结内的定位相关，TFH亚群由其流式细胞术表型定义。新的标准将用于研究体内和体外TFH和TFR细胞的发育和功能，包括缺乏TIGIT或CD 226的那些。此外，将测试经遗传操作以防止⑶ 226下调和/或TIGIT上调的T细胞在体内发育成TFH细胞的能力。拟议的研究将集中于PP起源的细胞和那些在免疫后在外周存在的细胞;数据的比较将有助于揭示这两种不同免疫区室中TFH和TFR细胞生成的潜在差异。由于现有证据表明，CD 155在粘膜免疫学中特别重要，我们还将研究TIGIT缺失对哮喘模型中T细胞的影响。

Follicular T cells represent a variety of highly specialized CD4 T cells capable to immigrate into B cell follicles and to govern adaptive immune responses. Of utmost importance for these processes are follicular helper T (TFH) and follicular regulatory T (TFR) cells that counteract TFH driven activities. TFR cells are derived from classical regulatory T cells of thymic origin. In contrast, TFH cells differentiate from naïve CD4 T cells in several steps that finally results in their location in the germinal centre (GC). During a GC reaction, TFH cells assist rapidly dividing B blasts to develop into either plasma or memory cells. They also help GC B cells to perform class switch recombination and hypermutation of the antibodies they express. We could show that the cell surface receptor CD155 and its ligand CD226 are critically involved in the establishment of a regular pool of follicular T cell in Peyers Patches (PP). Moreover, mice lacking CD155 developed only a substandard secondary humoral immune response when antigen was administered orally. Notably, the primary response mediated by IgM was not affected. We established protocols allowing us to more precisely define TFH and TFR cells. As outlined in this proposal, this enabled an improved definition of the phenotypic TFH cell deficiencies caused by lack of CD155 or CD226. Recently, another counter-receptor for CD155 was discovered, named TIGIT. In contrast to CD226 that represents a T cell co-activator, TIGIT was shown to suppress T cell responses. We observed that T cells developing into TFH cells perform a CD155 ligand switch by down-regulating CD226 and up-regulating TIGIT. This suggests that TIGIT may contribute to control TFH cell maintenance and function and that a properly balanced expression of CD226 and TIGIT orchestrates a TFH cells curriculum. With this proposal, we intend to refine our analyses of TFH and TFR cells. To this end, we will perform gene chip analyses. By in vivo migration assays, we will correlate TFH subpopulations defined by their flow cytometric phenotype with their localization inside a lymph node. The new standards will be exploited to investigate development and function of TFH and TFR cells in vivo and in vitro including those lacking TIGIT or CD226. Moreover, T cells genetically manipulated to prevent CD226 down-regulation and/or TIGIT up-regulation will be tested for their capacity to develop into TFH cells in vivo. The proposed studies will focus on cells of PP origin and those coming into existence in periphery following immunization; a comparison of the data will help reveal potential differences in the generation of TFH and TFR cells in these two different immunological compartments. Since available evidence suggests that CD155 is of particular importance in mucosal immunology, we will also study the influence of TIGIT absence on T cells in an asthma model.