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

中枢T细胞耐受发生在胸腺，发育中的胸腺细胞必须成功地掌握各种检查点，才能进入成熟的外周T细胞池。在胸腺中，特化的胸腺髓质上皮细胞(MTECs)向发育中的T细胞递送组织特异性(自身)抗原(TSA)，在负选择过程中消除那些对自身具有高亲和力TCR的TSA。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(Treg)，这使得胸腺在很大程度上控制外周耐受。MTECs的成熟及其呈递TSA的能力都依赖于核因子-kB诱导激酶(NIK)。缺乏功能性NIK的小鼠会出现轻微的迟发性多器官自身免疫，并在血清中检测到自身抗体水平。然而，Nik究竟如何影响mTEC的发育和负选择仍然难以捉摸。因此，我们建立了一个有条件的NIKfl/fl小鼠，并将其与胸腺基质特异的Foxn1-Cre小鼠杂交，导致了TEC特异性的Nik缺失。与NIK基因的种系缺失相反，NIK基因的TEC特异性缺失会导致一种致命的自身免疫表型在出生后不久表现出来。这种表型可能是迄今为止在小鼠身上观察到的最严重的自身免疫病理。通过这一建议，我们的目的是了解NIK在i)TEC成熟中的作用，从而在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细胞库的影响，包括Tregs的形成和稳定性。此外，我们将解决为什么TEC特异性消融NIK会导致比生殖系缺失的NIK更严重的自身免疫表型的问题，这可能解开了尚不清楚的耐受机制。

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.