Nuclear Receptors in B Cell Tolerance and Humoral Immune Responses

项目总结/摘要 这项提案的长期目标是利用孤儿核激素Nr 4a家族的生物学特性， 受体来选择性地操纵抗原特异性B细胞应答。如果成功，这将改变我们的 疫苗接种和治疗免疫介导疾病的方法。 Nr 4a家族成员（Nur 77、Nurr 1和Nor 1）由三个基因（分别为Nr 4a 1 -3）编码， 在淋巴细胞中通过抗原（Ag）刺激快速诱导。尽管它们被认为是配体- 独立的、组成型活性转录因子、小分子激动剂和拮抗剂配体已经被 使它们变得可药用。我们已经表明，Nr 4a 1表达的荧光报告基因（Nur 77- eGFP BAC Tg）与Ag刺激的强度成比例，并且还与天然细胞中的自身反应性相关。 在健康小鼠和三种不同的BCR Tg模型中存在B细胞。我们最近发现Nur 77 抑制应答慢性和急性Ag刺激的B细胞的存活和扩增， B细胞耐受层。重要的是，Nr 4a家族在其DNA中具有相当大的结构同源性， 因此，它们在T细胞中表现出深刻的功能冗余，在T细胞中它们也发挥着重要的作用。 重要的监管作用。这种冗余可能与它们在B细胞中的功能高度相关（其 主要表达Nr 4a 1和Nr 4a 3），但从未在实验上得到解决。这表示 我们的知识存在重大差距，限制了对这些因素的充分治疗利用。 在这里，我们报告说，新产生的小鼠与B细胞特异性缺失的Nr 4a 1和Nr 4a 3显示了重大突破 在B细胞耐受中，包括自发性生发中心和自身抗体的发展。这些 缺陷与响应Ag刺激的新靶基因的深刻超诱导相关-包括 募集T细胞所需的几个基因的帮助-这在很大程度上是掩盖时，即使一个功能Nr 4a 等位基因仍然存在。因此，我们假设Nr 4a家族介导Ag下游的负反馈， 通过关键靶基因的转录抑制进行刺激。我们建议，这有两个功能：（a） 在信号2（共刺激）不存在的情况下抑制接受信号1（抗原）的自身反应性克隆，和（B） 抑制免疫优势克隆独占正常的体液免疫应答， 克隆多样性在这一补助金中，我们建议： (1)明确Nr 4a家族在调节中枢和外周B细胞耐受中的作用，并鉴定 在BCR Tg和天然存在的自身反应性B细胞中介导这些功能的转录机制。 (2)为了明确Nr 4a家族在调节B细胞克隆间竞争和克隆多样性中的作用， 主要的T依赖性体液免疫应答及其对限制免疫优势的贡献。 (3)确定新鉴定的Nr 4a靶基因Batf在介导这些过程中的作用。

Project Summary/Abstract This proposal's long-term goal is to take advantage of the biology of the Nr4a family of orphan nuclear hormone receptors to selectively manipulate antigen-specific B cell responses. If successful, this could transform our approach to vaccination and treatment of immune-mediated diseases. Nr4a family members (Nur77, Nurr1, and Nor1) are encoded by three genes (Nr4a1-3, respectively) that are rapidly induced by antigen (Ag) stimulation in lymphocytes. Although they are thought to function as ligand- independent, constitutively active transcription factors, small molecule agonist and antagonist ligands have been developed, rendering them druggable. We have shown that a fluorescent reporter of Nr4a1 expression (Nur77- eGFP BAC Tg) scales with the intensity of Ag stimulation, and also correlates with self-reactivity in naturally occurring B cells in healthy mice and in three different BCR Tg models. We have recently shown that Nur77 curbs the survival and expansion of B cells in response to chronic and acute Ag stimulation, imposing a novel layer of B cell tolerance. Importantly, the Nr4a family harbor considerable structural homology in their DNA- binding domain and, as a result, exhibit profound functional redundancy in T cells, where they also play an important regulatory role. Such redundancy is likely highly relevant to their function in B cells (which predominantly express Nr4a1 and Nr4a3) yet has never been experimentally addressed. This represents a major gap in our knowledge that limits full therapeutic exploitation of these factors. Here we report that newly generated mice with B cell-specific deletion of Nr4a1 and Nr4a3 show a major break in B cell tolerance, including the development of spontaneous germinal centers and autoantibodies. These defects correlate with profound super-induction of novel target genes in response to Ag stimulation – including several genes required for recruitment of T cell help – that is largely masked when even one functional Nr4a allele remains. We therefore hypothesize that the Nr4a family mediates negative feedback downstream of Ag stimulation via transcriptional repression of key target genes. We propose that this serves two functions: (a) to restrain self-reactive clones that receive signal 1 (antigen) in the absence of signal 2 (co-stimulation), and (b) restrain immunodominant clones from monopolizing normal humoral immune responses, in order to preserve clonal diversity. In this grant, we propose: (1) To define the role of the Nr4a family in regulating central and peripheral B cell tolerance, and identify transcriptional mechanisms that mediate these functions in BCR Tg and naturally occurring self-reactive B cells. (2) To define the role of the Nr4a family in regulating B cell inter-clonal competition and clonal diversity during the primary T-dependent humoral immune response and its contribution to limiting immunodominance. (3) To define the role of the newly identified Nr4a target gene Batf in mediating these processes.