Control of the homeostatic regulatory T cell pool by RelB expression in steady state migratory dendritic cells

树突状细胞(DC)与调节性T细胞(Tregs)的相互作用通过控制Treg的诱导、维持和增殖在免疫耐受中发挥关键作用。利用在表皮角蛋白-5启动子作用下表达卵清蛋白(OVA)作为新自身抗原的转基因小鼠(K5-MoVA)和OVA特异性的CD4+T细胞受体转基因小鼠(OT-II)，我们发现OVA自身抗原在引流淋巴结中的提呈严格依赖于稳态迁移性DC(SsmDC)的运输，并导致初始的CD4+T细胞转化为CD4+Foxp3+Tregs。利用核因子-kB/Rel转录因子家族成员RelB、p52或p50的遗传缺陷小鼠，我们可以证明通过RelB/p52的替代核因子-kB信号通路控制ssmDC的迁移，从而控制Tregs。为了更深入地了解RelB转录因子对ssmDCs、Tregs和外周耐受的特定作用，我们现在开始研究CD11c+DCs中缺乏RelB的小鼠(RelBDCko)。这可以通过将在DC特异性启动子CD11c(CD11c-Cre)下表达Cre重组酶的小鼠与两个RelB等位基因都带有loxP位点(RelBfl/fl)的小鼠杂交来实现。我们的初步数据显示，RelBDCko小鼠看起来基本正常。然而，它们显示外周淋巴结中的ssmDC、CD4+Foxp3+Tregs和胸腺、淋巴结和脾中产生IL-2(可能依赖于IL-7)的CD4+CD44High T细胞亚群的频率增加。在这项建议中，我们想研究这三种细胞类型之间的功能关系。我们假设，在ssmDC中没有RelB的情况下，结合伙伴p52与我们将鉴定的其他NF-kB/REL家族成员形成替代的偶联。然后，我们想要测试RelBDCko小鼠的DC或T细胞中IL-2或IL-7的释放是否发生了变化，以及RelB缺乏如何影响ssmDC的周转。通过使用K5-Mova/OT-II系统，我们希望研究树突状细胞缺乏RelB对自然和诱导的Treg亚群的影响，以及它是否需要抗原特异性。我们将询问哪些表面受体或IL-2/IL-7细胞因子导致RelBDCko小鼠Treg和CD4+CD44High T细胞稳态频率增加。最后，我们希望确定在诱导过敏或自身免疫后，Treg水平升高的RelBDCko小鼠的耐受阈值是否会增加。该项目将有助于回答以下问题：Treg在体内的稳态水平是如何调节的，以及Treg群体的这些操作如何影响对过敏或自身免疫的易感性。

Interactions of dendritic cells (DCs) with regulatory T cells (Tregs) play a key role for immune tolerance by controlling Treg induction, maintenance and proliferation. Using a transgenic mouse expressing ovalbumin (OVA) as a neo-self-antigen under the keratin-5 promoter in the epidermis (K5-mOVA) and OVA-specific CD4+ T cell receptor transgenic mice (OT-II), we found previously that OVA-self-antigen presentation in the draining lymph nodes strictly depends on the transport by steady state migratory DCs (ssmDCs) and leads to conversion of naive CD4+ T cells into CD4+ Foxp3+ Tregs. Using mice with genetic deficiencies for the NF-kB/Rel transcription factor family members RelB, p52 or p50 we could show that the alternative NF-kB signaling pathway through RelB/p52 controls the migration of ssmDCs and thereby Tregs.To gain deeper insights into the specific role of the RelB transcription factor for ssmDCs, Tregs and peripheral tolerance, we started now to investigate mice that specifically lack RelB in CD11c+ DCs (RelBDCko). This could achieved by crossing Cre recombinase expressing mice under the DC-specific promoter CD11c (CD11c-Cre) with mice where both RelB alleles are flanked by loxP sites (RelBfl/fl). Our preliminary data indicate that RelBDCko mice appear largely normal. However, they show increased frequencies of ssmDCs in peripheral lymph nodes, of CD4+ Foxp3+ Tregs and of an IL-2-producing (presumably IL-7-dependent) CD4+ CD44high T cell subset in thymus, lymph nodes and spleen. In this proposal we would like to study the functional relations between these three cell types. We hypothesize that in the absence of RelB in ssmDCs the binding partner p52 forms alternative conjugates with other NF-kB/Rel family members that we will identify. Then we want to test whether the IL-2 or IL-7 release is altered in DC or T cells of RelBDCko mice and how RelB-deficiency influences the ssmDC turnover. By using the K5-mOVA/OT-II system we want to study the impact of RelB-deficiency by DCs on natural and inducible Treg subsets and whether it requires antigen-specificity. We will ask which surface receptors or the IL-2/IL-7 cytokines contribute to the increased steady state frequencies of Treg and CD4+ CD44high T cells in RelBDCko mice. Finally we want to determine if the tolerance threshold of RelBDCko mice with elevated levels of Tregs is increased after induction of allergy or autoimmunity.Together this project will contribute to answer the question how steady state levels of Tregs are adjusted in vivo and how these manipulations of Treg populations influence susceptibility against allergy or autoimmunity.