Decay accelerating factor dependent inhibition of T cell immunity

摘要 衰变加速因子（decay accelerating factor，CD55）是一种糖磷脂酰肌醇（glycophosphatidylinositol，GPI）连接的细胞表面表达的 已知主要功能为内源性（在其表达的细胞表面）调节剂的蛋白质 补体级联激活。我们和其他人一起发现， 通过局部调节补体激活的反应。我们还表明，在同源T细胞/APC过程中， 相互作用表面的表达迅速（在数小时内）但短暂（24 - 48小时）下调。我们 假设这种瞬时下调关键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T细胞缺陷动物并表现出增强的T细胞免疫应答， 对这一假设的正式检验需要能够组成性地在免疫细胞上强制稳定的表达， 细胞表面。我们的假设预测，这种增强的APC表达将抑制APC激活， 限制Teff免疫的诱导，同时将允许和促进Treg诱导/稳定性， 抑制保护性抗病毒T细胞免疫，同时有利于针对同种异体或同种异体的免疫耐受性， 自身抗原如果我们的工作模式是正确的，研究结果将在概念上具有创新性和重要意义， 它们将支持一种在体内控制T细胞免疫的新机制。拟议的工作将 导致产生具有可诱导的、稳定的表面表达形式的BMPs的小鼠，从而增加了 生物试剂工具箱的基本缺失工具，可用于研究适应性 免疫和补体激活。我们建议在R21应用程序中通过2 目的：1）通过在造血细胞中增强的T细胞表达来调节T细胞免疫，以及2）产生 并分析可诱导的、条件性的转基因小鼠中的T细胞免疫应答。研究结果表明， 从这种"高风险高回报"的R21应用可能会提供新的见解的影响， 在体内T细胞免疫应答中的表达（而不是其缺失），这是一个尚未解决的问题， 代表了我们现有知识中的一个空白。如果我们的工作模型是正确的，研究结果将提供 新的治疗策略的基础，以增加在努力诱导耐受原性反应的表达 其预防和/或治疗自身免疫性疾病、移植排斥和移植物抗宿主病。此外在 完成这项R21资助后，我们将生产出新的生物工具，包括可诱导的基因工程。 转基因小鼠，这将使我们能够测试DAF依赖的耐受性策略，在自身免疫和移植 模型，确定是否以及如何影响幼稚和/或记忆T细胞活化的诱导， 在每种情况下的功能，并提供深入了解生理学下调的机制。

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.