Regulation of CD28 Signaling in T cells by Cytoplasmic Domain Membrane Binding

T细胞受体(TCR)是由单个细胞中的V、D和J片段在基因组水平上重排而产生的。因此，TCR谱系可以共同识别任何抗原。由于这种随机重排过程，T细胞缺乏区分自身抗原和病原体相关抗原的能力。相反，T细胞必须被先天免疫抗原提呈细胞(APC)激活，并被指示分化为效应细胞。这种激活信号需要抗原依赖的TCR刺激和通过CD28的共刺激，CD28是一种膜受体，在所有NAOVE T细胞和记忆T细胞亚群上都有表达。与其配体B7.1(CD80)或B7.2(CD86)结合在APC上，通过识别病原体相关分子而激活，提供与TCR信号协同的共刺激信号，促进细胞存活、增殖和效应功能。 TCR或CD28的配体结合导致受体触发和信号转导的机制尚不清楚；任何以磷酸酪氨酸为基础的免疫受体的受体触发的一般机制仍有待阐明。相反，阻止CD28和其他以磷酸酪氨酸为基础的受体自发和异常信号的机制也鲜为人知。使用荧光共振能量转移(FRET)显微镜、生化和细胞分析来评估T细胞的信号和功能，以及多发性硬化症(小鼠实验性自身免疫性脑脊髓炎)的体内模型，本研究将检验：a)CD28细胞质结构域(CD28CD)与质膜内叶的关联；b)这种关联对信号和T细胞功能的调节；以及c)生理条件下CD28CD从质膜中释放的机制。对CD28调控机制的理解将为我们提供一个更具普遍性的受体触发模型。

The T cell receptor (TCR) is generated by rearrangement of V, D and J segments in individual cells at the genomic level. Therefore, the TCR repertoire collectively can recognize any antigen. As a consequence of this random rearrangement process, T cells lack the ability to discriminate between self antigens and pathogen- associated antigens. Instead, T cells must be activated by innate immune antigen presenting cells (APCs) and instructed to differentiate into effector cells. This activating signal requires antigen-dependent stimulation of the TCR and costimulation through CD28, which is a membrane receptor constitutively expressed on all naove T cells and subsets of memory T cells. Binding to its ligands B7.1 (CD80) or B7.2 (CD86) expressed on APCs activated by recognition of pathogen-associated molecules delivers a costimulatory signal that synergizes with TCR signaling and promotes cell survival, proliferation and effector functions. The mechanism by which ligand engagement by TCR or CD28 leads to receptor triggering and signal transduction remains unknown; a general mechanism of receptor triggering remains to be elucidated for any phosphotyrosine-based immune receptor. Conversely, the mechanism preventing spontaneous and aberrant signaling of CD28 and other phosphotyrosine-based receptors is also poorly understood. Using a combination of fluorescence resonance energy transfer (FRET) microscopy, biochemical and cellular assays to assess T cell signaling and function, and an in vivo model of multiple sclerosis (murine experimental autoimmune encephalomyelitis), this research will examine: a) association of CD28 cytoplasmic domain (CD28CD) with the inner leaflet of the plasma membrane; b) the consequences of this association for regulation of signaling and T cell function; and c) the mechanism by which CD28CD is released from the plasma membrane under physiological conditions. Mechanistic understanding of CD28 regulation would provide insight into a more generalizable model of receptor triggering.