BCR-intrinsic regulation of memory B cell responses

B淋巴细胞的抗体产生受B细胞抗原受体（BCR）信号的控制。naïve B细胞激活后，原发性免疫反应的特征是产生免疫球蛋白M （IgM）抗体。次生反应主要是IgG抗体在激活Ig类转换记忆B细胞时分泌。我们最近发现，表达mIgG或含有mige的bcr的类转换B细胞的抗原受体具有保守的基于酪氨酸的信号基序，这在naïve细胞上的含有mIgM或migd的bcr中不存在。这个基序被称为免疫球蛋白尾酪氨酸（ITT），它通过募集由适配蛋白Grb2组织的信号复合体来放大来自mIgG-和mIgE-BCR的信号。我们项目的中心目标之一是研究ITT信号在小鼠二抗反应中的作用。为此，我们产生了两种新的敲入小鼠菌株，它们在mIgG1或mIgE的ITTs中具有酪氨酸到苯丙氨酸（Y到F）的替换。我们将详细分析这些小鼠的免疫能力。此外，我们将确定单个信号组件以及整个信号网络对维持和/或激活Ig类转换记忆B细胞的贡献。这部分将由两个技术进步来推动。首先，我们将通过定量质谱法对全球B细胞磷蛋白组进行全面测定。其次，我们将建立新型荧光生物传感器来研究原代记忆B细胞稀缺群体中的信号事件。总之，基因工程小鼠突变体与信号转导研究的新工具相结合，将为阐明记忆B细胞的分子信号特征提供基础。

The production of antibodies by B lymphocytes is controlled by signals from the B cell antigen recep-tor (BCR). Following the activation of naïve B cells, primary immune responses are characterised by the production of immunoglobulin M (IgM) antibodies. Secondary responses are dominated by IgG antibodies secreted upon activation of Ig class-switched memory B cells. We recently showed that the antigen receptors of class-switched B cells expressing mIgG- or mIgE-containing BCRs possess a conserved tyrosine-based signalling motif that is not present in mIgM- or mIgD-containing BCRs on naïve cells. This motif, termed immunoglobulin tail tyrosine (ITT), amplifies signals from the mIgG- and mIgE-BCR by recruiting a signalling complex that is organised by the adaptor protein Grb2. One of the central aims of our project is to investigate the role of ITT signalling for secondary antibody responses in the mouse. To this end we have generated two novel knock-in mouse strains possessing tyrosine-to-phenylalanine (Y to F) substitutions in the ITTs of mIgG1 or mIgE. The immunological competence of these mice will be analysed in detail. Furthermore, we will determine the contribution of individual signalling components as well as entire signalling networks for the maintenance and/or activation of Ig class-switched memory B cells. This part will be promoted by two technical advances. First, we will perform a comprehensive determination of the global B cell phosphoproteome by quantitative mass spectrometry. Second, we will establish novel fluorescent biosensors to study signalling events in scarce populations of primary memory B cells. Collectively, genetically engineered mouse mutants in combination with novel tools for signal transduction research will provide a basis towards the elucidation of a molecular signal signature of memory B cells.