Deciphering the role of NIK in T cell central tolerance and autoimmunity

中枢T细胞耐受发生在胸腺中，其中发育中的胸腺细胞必须成功地掌握各种检查点，然后才能进入成熟的外周T细胞库。在胸腺中，特化的胸腺髓质上皮细胞（mTEC）将组织特异性（自身）抗原（TSA）呈递给发育中的T细胞，在阴性选择期间消除那些对自身具有高亲和力TCR的细胞。此外，以随机的方式，一些自身反应性T细胞被指示成为调节性T细胞（Tcells），其离开胸腺以在很大程度上控制外周耐受性。mTEC的成熟以及它们呈递TSA的能力都依赖于NF-kB诱导激酶（NIK）。缺乏功能性NIK的小鼠会产生轻度迟发性多器官自身免疫，血清中可检测到自身抗体水平。然而，NIK究竟如何影响mTEC的发展和负选择仍然难以捉摸。因此，我们产生了条件性NIKfl/fl小鼠，并将其与胸腺基质特异性Foxn 1-Cre+小鼠杂交，导致NIK的TEC特异性缺失。与NIK的种系缺失相反，TEC特异性NIK基因缺失导致出生后不久出现致命的自身免疫表型。这种表型可能是迄今为止在小鼠中观察到的最严重的自身免疫病理学。通过该提议，我们旨在了解NIK在i）TEC成熟中的作用，并因此在ii）中枢耐受中的作用。我们将表征TEC特异性NIK缺失对发育中的T细胞池的影响，包括TcB的形成和稳定性。此外，我们将解决的问题，为什么TEC特异性消融的NIK的结果在一个更严重的自身免疫表型相比，种系删除的NIK，可能解开尚未未知的耐受机制。

Central T cell tolerance occurs in the thymus, where developing thymocytes have to successfully master various checkpoints before they can enter the pool of mature peripheral T cells. In the thymus specialized medullary thymic epithelial cells (mTECs) present tissue specific (self)-antigens (TSAs) to developing T cells, eliminating those with a high-affinity TCR for self during negative selection. Additionally, in a stochastic manner, some of the autoreactive T cells are instructed to become regulatory T cells (Tregs), which leave the thymus to largely control peripheral tolerance. Both the maturation of mTECs as well as their ability to present TSAs depends on NF-kB-inducing kinase (NIK). Mice lacking functional NIK develop mild late-onset multi-organ autoimmunity and detectable levels of autoantibodies in the serum. However, it remained elusive how exactly NIK influences mTEC development and negative selection. Therefore, we generated a conditional NIKfl/fl mouse and crossed it to the thymic stroma specific Foxn1-Cre+ mouse, resulting in the TEC specific deletion of NIK. In contrast to germline deletion of NIK, TEC-specific deletion oft the NIK gene resulted in a fatal autoimmune phenotype manifesting shortly after birth. This phenotype is perhaps the most severe autoimmune pathology observed in mice to date. With this proposal we aim to understand the role of NIK in i) TEC maturation and consequently in ii) central tolerance. We will characterize the impact of the TEC specific NIK deletion on the developing T cell pool, including the formation and stability of Tregs. Further, we will address the question as to why TEC specific ablation of NIK results in a more severe autoimmune phenotype compared to germline deleted NIK, possibly unraveling yet unknown mechanisms of tolerance.