Decay accelerating factor dependent inhibition of T cell immunity

摘要 衰变加速因子(DAF，CD55)是一种糖磷脂酰肌醇(GPI)连接的细胞表面表达因子 具有已知主要功能的蛋白质，作为一种固有的(在其表达的细胞表面上)调节 补体级联激活。我们发现DAF在调节T细胞免疫方面起着至关重要的作用 局部调节补体激活的反应。我们还表明，在同源T细胞/APC期间 相互作用后，表面DAF的表达迅速(在数小时内)，但瞬时(24-48小时)下调。我们 假设这种短暂的下调至关重要地允许局部补体激活来驱动诱导 同时抑制调节性T细胞的诱导、功能和稳定性 (Treg)。虽然已经产生了DAF缺陷的动物，并表现出增强的T细胞免疫反应， 这一假说的正式检验需要有能力在免疫上强制稳定的DAF表达 活体内的细胞表面。我们的假设预测，这种强制的DAF表达将抑制APC的激活和 限制Treg免疫的诱导，同时将允许和促进Treg诱导/稳定 抑制保护性抗病毒T细胞免疫，支持针对异基因或异基因的免疫耐受 自身抗原。如果我们的工作模型是正确的，那么这些发现在概念上将是创新的，并具有重大意义 他们将支持一种在体内对T细胞免疫施加控制的新机制。拟议的工作将 导致产生具有可诱导的、稳定的DAF表面表达形式的小鼠，从而增加了 生物试剂工具箱中必要的缺失工具可用于研究适应性之间的联系 免疫和补体激活。我们建议在这个R21应用程序中通过2 目的：1)通过加强DAF在造血细胞中的表达来调节T细胞免疫；2)产生 并分析可诱导的、有条件的DAF转基因小鼠的T细胞免疫反应。得出的结论是 从这种高风险、高回报的R21应用可能会为DAF的影响提供新的见解 体内T细胞免疫反应上的表达(而不是缺失)，这是一个尚未解决的问题 代表着我们现有知识的一个缺口。如果我们的工作模型是正确的，研究结果将提供 在诱导耐受性反应方面增加DAF表达的新治疗策略的基础 预防和/或治疗自身免疫性疾病、移植排斥反应和移植物抗宿主疾病。此外，在 完成这笔R21赠款后，我们将生产出新的生物工具，包括可诱导的DAF 转基因小鼠将允许我们在自身免疫和移植中测试依赖DAF的耐受策略 模型，确定DAF是否以及如何影响幼稚和/或记忆性T细胞的激活和 在每种情况下的功能，并提供对生理DAF下调的潜在机制的洞察。

Abstract Decay accelerating factor (DAF, CD55) is a glycophosphatidylinositol (GPI)-linked, cell surface-expressed protein with a known primary function as an intrinsic (on the cell surface on which it is expressed) regulator of complement cascade activation. We among others discovered that DAF crucially modulates T cell immune responses by locally regulating complement activation. We also showed that during cognate T cell/APC interactions surface DAF expression is rapidly (within hours) yet transiently (24-48h) downregulated. We hypothesize that this transient downregulation crucially permits local complement activation to drive induction of effector T cells (Teff) while simultaneously inhibiting induction, function and stability of regulatory T cells (Treg). While DAF deficient animals have been produced and exhibit enhanced T cell immune responses, formal testing of this hypothesis requires the ability to constitutively enforce stable DAF expression on immune cell surfaces in vivo. Our hypothesis predicts that this enforced DAF expression will inhibit APC activation and limit induction of Teff immunity and simultaneously will permit and facilitate Treg induction/stability, together dampening protective anti-viral T cell immunity while favoring immunological tolerance directed toward allo- or autoantigens. If our working model is correct, the findings will be conceptually innovative and significant in that they would support a novel mechanism that exerts control over T cell immunity in vivo. The proposed work will result in production of a mouse with an inducible, stable surface expressed form of DAF, thereby adding an essential missing tool to the toolbox of biological reagents available for studying links between adaptive immunity and complement activation. We propose to test this hypothesis in this R21 application through 2 aims: 1) To modulate T cell immunity by enforced DAF expression in hematopoietic cells and 2) To produce and analyze T cell immune responses in an inducible, conditional, DAF transgenic mouse. The findings derived from this “high-risk high-reward” R21 application are likely to provide new insight into the impact of DAF expression (rather than its absence) on in vivo T cell immune responses, an issue that has not been addressed and represents a gap in our current knowledge. If our working model is correct, the findings would provide the basis for novel therapeutic strategies to increase DAF expression in efforts to induce tolerogenic responses that prevent and/or treat autoimmune disease, transplant rejection and graft vs. host disease. In addition, at the completion of this R21 grant we will have produced novel biological tools including inducible DAF transgenic mice that will permit us to test DAF-dependent tolerogenic strategies in autoimmune and transplant models, determine whether and how DAF impacts induction of naïve and/or memory T cell activation and function in each situation, and provide insight into mechanisms underlying physiological DAF downregulation.