Human B cell Differentiation in a Model system

描述(申请人提供)：IgM B细胞的分化 进入抗体分泌细胞是对由 活化的CD4T细胞。在这方面的一个关键分子是CD40配体 (CD154)由活化的T细胞通过其同源相互作用表达 CD40刺激B细胞增殖分化的实验研究 抗原激活的IgM B细胞。CD40近端表达与细胞因子表达的关系 然而，信号事件和下游功能还没有完全阐明，它 众所周知，该多步骤过程需要激活多个 信号转导通路。我们的实验室一直对 确定课堂所需的早期细胞因子和CD40介导的信号 人B细胞开关重组(CSR)。尽管网络的关键作用 这些信号在CSR中被很好地识别，分子机制被 整合这些不同类别信号的B细胞很差 特色化的。我们已经确认了一种B细胞免疫缺陷 以对CD40和IL-4信号的缺陷反应为特征。来自a的B细胞 被诊断为高IgM综合征的年轻女性患者(PT#1)正常 CD40的表达，但在CD40的一个子集中明显缺乏-和 IL-4反应功能，包括CD23表达和早期信号 用于开关重组。B细胞的一个耐人寻味的特征 在特定的体外条件下，它们重新获得了“功能” 响应性“，并在表达下游亚型中进行转换。 提出PT#1缺陷存在于对两者都重要的重叠途径中 CD40和IL-4诱导的B细胞分化。为了检验这一假设，我们 建议1)确定直接受 PT#1缺陷，2)使用CD23和I-Gamma启动子构建来研究 转录因子的功能，以及3)利用基因识别缺陷 互补技术。这些研究的完成将显著地 增加我们对B细胞如何利用CD40和IL-4信号级联的知识 激活CSR和B细胞分化。此外，这些研究的结果 拟议的实验应该通过以下方式增加我们对高IgM综合征的理解 确定与这种疾病的发病机制有关的一个新基因。

DESCRIPTION (provided by the applicant): The differentiation of IgM+ B cells into Ab secreting cells occurs in response to an array of signals provided by activated CD4+ T cells. A critical molecule in this regard is the CD40 ligand (CD154) expressed by activated T cells which through its cognate interaction with CD40 on B cells drives the proliferation and differentiation of antigen-activated IgM+ B cells. The relationship between proximal CD40 signaling events and downstream functions are not fully elucidated however, it is known that this multi-step process requires that activation of numerous signal transduction pathways. Our laboratory has had an ongoing interest in defining the early cytokine- and CD40-mediated signals required for class switch recombination (CSR) in human B cells. Although the critical roles of these signals in CSR are well recognized, the molecular mechanisms utilized by B cells to integrate these distinct classes of signals are poorly characterized. We have identified a B cell immunodeficiency that is distinguished by defective responses to CD40 and IL-4 signaling. B cells from a young female patient (pt#1) diagnosed with hyper-IgM syndrome have normal expression of CD40 but are clearly deficient in a subset of CD40- and IL-4-responsive functions including CD23 expression and early signals required for switch recombination. One intriguing characteristic of the patient B cells is that under specific in vitro conditions they regain "functional responsiveness" and undergo switching in express downstream isotypes. We propose that the pt#1 defect is in an overlapping pathway important for both CD40- and IL-4-medicated B cell differentiation. To test this hypothesis, we propose to 1) identify signaling pathways that are directly affected by the pt#1 defect, 2) use CD23 and I-gamma promoter constructs to investigate transcription factor function, and 3) identify the defect using genetic complementation techniques. Completion of these studies should significantly increase our knowledge of how B cells utilize CD40 and IL-4 signaling cascades to activate CSR and B cell differentiation. Furthermore, results from these proposed experiments should increase our understanding of hyper-IgM syndrome by identifying a novel gene involved in the pathogenesis of this disease.