BCR signaling during B cell development and maintenance

描述(由申请人提供)：B淋巴细胞发育、选择和分化的主要决定因素是B细胞抗原受体(BCR)，它的抗体可变区识别抗原，其信号单位(免疫球蛋白α/β异二聚体)将信号传递到细胞内部。由Igα/β胞浆尾巴激活的信号通路控制细胞对抗原选择的反应，包括抗原诱导的耐受以避免自身免疫和抗体反应。BCR信号似乎也是成熟B细胞生存所必需的。通过Igα/Beta的细胞质尾巴进行信号传递需要被称为ITAM的基于酪氨酸的激活基序的磷酸化。然而，有证据表明，主要来自细胞系的研究表明，这些尾巴中其他保守的磷酸化靶点，包括丝氨酸和苏氨酸残基也参与了信号转导。本提案旨在通过在小鼠中进行定向突变，确定这些残基在体内B细胞发育和激活中的作用。类似地，我们将使用可诱导基因打靶系统，分析细胞质尾巴在维持成熟B细胞中的作用以及它们与B细胞激活因子介导的生存的相互作用。关于B细胞存活控制的知识对于理解B细胞稳态以及对B细胞介导的自身免疫和B细胞淋巴瘤生长的治疗干预至关重要。在提案的最后部分，我们将阐述B细胞到B-1和B-2亚集的分化在多大程度上是由在这两个亚集之间不均匀分布的BCR特异性所驱动的。B-1细胞被认为在自然免疫防御中发挥主要作用，并容易产生自身抗体，而B-2细胞是适应性抗体反应的主要参与者。我们将使用一个基因开关，允许细胞在体内从典型的B-I表达切换到B-2典型的BCR表达，反之亦然，以确定B-1和B-2表型在多大程度上代表不同的激活状态，而不是由不同的发育程序决定。此外，还将尝试通过诱导SHP-1磷酸酶失活来将成熟的B-2细胞转换为B-1表型。SHP-1磷酸酶在B细胞前体细胞中的失活会导致B-1细胞的近乎排他性产生

DESCRIPTION (provided by the applicant): A major determinant in the development, selection and differentiation of B lymphocytes is the B cell antigen receptor (BCR) whose antibody variable regions recognize antigen and whose signaling unit (the Igalpha/Beta heterodimer transmits signals into the interior of the cell. Signaling pathways activated by Igalpha/Beta cytoplasmic tails control the response of the cells to antigenic selection including tolerance induction by antigen to avoid autoimmunity and antibody responses to pathogens. BCR signaling also seems to be required for mature B cell survival. Signaling through the cytoplasmic tails of Igalpha/Beta requires phosphorylation of tyrosine-based activation motifs termed ITAMs. However, there is evidence mainly from work on cell lines that other conserved targets of phosphorylation in these tails including serine and threonine residues also contribute to signal transduction. The present proposal aims at defining the role of these residues in B cell development and activation in the in vivo context, using targeted mutagenesis in the mouse. We will similarly analyze the roles of the cytoplasmic tails in the maintenance of mature B cells and their interplay with B-cell activation factor mediated survival, using systems of inducible gene targeting. Knowledge about the control of B cell survival is critical for an understanding of B cell homeostasis and therapeutic intervention in B cell-mediated autoimmunity and B cell lymphoma growth. In a final part of the proposal, we will address to which extent the differentiation of B cells into the B-1 and B-2 subsets is driven by BCR specificities which are unequally distributed between the two subsets. B-1 cells are thought to play a major role in natural immune defense and to be prone to autoantibody production, whereas B-2 cells are the major players in adaptive antibody responses. We will use a genetic switch allowing the cells to switch in vivo from the expression of a B-I typical to a B-2-typical BCR and vice versa, to determine to which extent the B-1 and B-2 phenotypes represent distinct states of activation as opposed to being determined by distinct developmental programs. This will be complemented by an attempt to switch mature B-2 ceils to a B-1 phenotype by induced inactivation of SHP- 1 phosphatase whose inactivation in B cell progenitors leads to near-exclusive production of B- 1 cells