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CD4T细胞，能够迁移到B细胞滤泡并控制适应性免疫反应。对这些过程最重要的是卵泡辅助性T细胞(TFH)和卵泡调节性T细胞(TFR)，它们可以抵消TFH驱动的活动。TFR细胞来源于胸腺来源的经典调节性T细胞。相反，TFH细胞通过几个步骤从幼稚的CD4T细胞分化，最终导致它们位于生发中心(GC)。在GC反应中，TFH细胞帮助B母细胞快速分裂为浆细胞或记忆细胞。它们还帮助GC B细胞进行类别转换、重组和它们所表达的抗体的超突变。我们可以证明，细胞表面受体CD155及其配体CD226在Peyers斑块(PP)滤泡T细胞库的建立中起着至关重要的作用。此外，当口服抗原时，缺乏CD155的小鼠只产生不符合标准的次级体液免疫反应。值得注意的是，由IgM介导的初级反应没有受到影响。我们制定了协议，使我们能够更准确地定义TFH和TFR细胞。如本提案所述，这使得对缺乏CD155或CD226引起的表型TFH细胞缺陷有了更好的定义。最近，又发现了CD155的另一个反向受体，命名为TIGIT。与代表T细胞共激活剂的CD226相反，TIGIT被证明抑制T细胞反应。我们观察到，发育成TFH细胞的T细胞通过下调CD226和上调TIGIT来执行CD155配体切换。这表明TIGIT可能有助于控制TFH细胞的维持和功能，CD226和TIGIT的适当平衡表达可以协调TFH细胞的课程。有了这个建议，我们打算改进我们对TFH和TFR细胞的分析。为此，我们将进行基因芯片分析。通过体内迁移分析，我们将把由其流式细胞术表型定义的TFH亚群与其在淋巴结内的定位相关联。新的标准将被用来研究体内和体外TFH和TFR细胞的发育和功能，包括那些缺乏TIGIT或CD226的细胞。此外，通过基因操作防止CD226下调和/或TIGIT上调的T细胞将在体内测试其发育为TFH细胞的能力。拟议的研究将集中在PP起源的细胞和免疫后出现在外周的细胞；数据的比较将有助于揭示这两个不同免疫间隔中TFH和TFR细胞生成的潜在差异。由于现有证据表明CD155在粘膜免疫学中具有特别重要的作用，我们还将研究TIGIT缺失对哮喘模型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.