TNF Receptor Superfamily Signaling in Immune Tolerance

描述（由申请方提供）：胸腺中的阴性选择和调节性T细胞发育是中枢和外周耐受性的关键组成部分。这两个过程都与TCR对自身肽：MHC复合物的亲和力有关;阳性选择需要与此类自身抗原的弱相互作用，而天然Treg发育和阴性选择通常需要与此类抗原的中等至更高亲和力的相互作用。我们现在有一个实质性的，但不完整的知识基础的亲和力和亲和力的肽配体参与这些过程。相比之下，负选择和Treg发育的基础信号通路仍然不完善。虽然已经确定了调节负选择和Treg发育的单个信号分子，但我们缺乏对这些过程中涉及的更大途径的基本理解，以及类似的信号途径如何产生完全相反的结果-即通过负选择的胸腺细胞死亡与通过分化为Treg的存活。这项研究的核心假设是这些过程受肿瘤坏死受体超家族（TNFRSF）的三个成员- GITR，OX 40和TNFR 2的调节。我们的初步数据证明，这三种TNFRSF受体的表达与TCR信号强度直接相关，并且是Treg发育所需的。我们提出TCR信号强度表现为特异性TNFRSF成员表达的增加，并且更高的TNFRSF信号传导导致优先发展TCR，从而使Treg TCR库偏向于更高的自身反应性。另外的初步数据表明，GITR、0X 40和TNFR 2也影响TCR依赖性阴性选择。我们提出，通过GITR，OX 40和TNFR 2的信号转导引发发育中的胸腺细胞通过不同的下游信号转导途径进行阴性选择和Treg发育。在我们的模型中，TNFRSF信号引发了CD 4+胸腺细胞的细胞死亡以及细胞对IL 2的反应;那些随后接受IL 2信号的细胞优先分化为T细胞，而那些未能接受IL 2信号的细胞优先分化为T细胞。 起始IL 2依赖性信号经历克隆缺失。这项研究将直接验证这些假设，并确定共刺激受体CD 28如何影响这些过程。最后，我们将确定是否改变TNFRSF依赖的信号，特别是在TGFRP改变其功能的移植物抗宿主病模型。因此，在这项资助申请中提出的研究将阐明特异性TNFRSF成员如何将TCR和CD 28信号与功能性Treg库的建立联系起来，并有助于扩大经历负选择的胸腺细胞的库。这些研究还将阐明TNFRSF激动剂和拮抗剂如何在未来用于增强TdR的治疗潜力。

DESCRIPTION (provided by applicant): Negative selection and regulatory T cell development in the thymus are critical components of central and peripheral tolerance. Both of these processes have been linked to the affinity of the TCR for self-peptide:MHC complexes; positive selection requires weak interactions with such self-antigens while natural Treg development and negative selection typically require moderate to higher affinity interactions with such antigens. We now have a substantial albeit incomplete knowledge base about the affinity and avidity of peptide ligands involved in these processes. In contrast, the basic signaling pathways that underlie negative selection and Treg development still remain poorly established. While individual signaling molecules that regulate negative selection and Treg development have been identified, we lack a basic understanding of the larger pathways involved in these processes and how similar signaling pathways can give rise to diametrically opposed outcomes - namely death of a thymocyte via negative selection versus survival via differentiation into a Treg. The central hypothesis underlying this grant is that these processes are regulated by three members of the tumor necrosis receptor superfamily (TNFRSF) - GITR, OX40 and TNFR2. Our preliminary data document that expression of these three TNFRSF receptors correlates directly with TCR signal strength and is required for Treg development. We propose that TCR signal strength is manifested as increasing expression of specific TNFRSF members and that higher TNFRSF signaling leads to preferential development of Tregs, thereby skewing the Treg TCR repertoire in favor of higher self-reactivity. Additional preliminary data suggest that GITR, OX40 and TNFR2 also influence TCR-dependent negative selection. We propose that signaling via GITR, OX40 and TNFR2 primes developing thymocytes for both negative selection and Treg development via distinct downstream signaling pathways. In our model TNFRSF signaling primes CD4+ thymocytes for cell death as well as cell responsiveness to IL2; those cells that subsequently receive an IL2 signal preferentially differentiate into Tregs while those that fail to initiate IL2-dependent signals undergo clonal deletion. The studies proposed in this grant will directly test these hypotheses as well define how the costimulatory receptor CD28 impinges on these processes. Finally, we will determine whether altering TNFRSF-dependent signals specifically in Tregs alters their function in a model of graft-versus-host disease. Thus, the studies proposed in this grant application will elucidate how specific TNFRSF members link TCR and CD28 signals to the establishment of a functional Treg pool and help broaden the repertoire of thymocytes undergoing negative selection. These studies will also illuminate how TNFRSF agonists and antagonists could be used to augment the therapeutic potential of Tregs in the future.