Intrinsic and Extrinsic Controls of B Cell Tolerance

未成熟B细胞阶段是B细胞可以识别多态性抗原并对其作出反应的第一发育阶段，因此可以最初识别内源性抗原或自身抗原。因此，未成熟B细胞的出现提供了第一次机会来清除具有引发自身免疫性疾病的潜力的自身反应性B细胞的库。我们最近发现，未成熟B细胞上的B细胞受体（BCR）在聚集后不能区室化成脂筏，这与失败的信号传导有关。基于我们的累积数据，我们认为BCR刺激的未成熟B细胞的内在或“硬连线”反应是凋亡，这表明缺失是默认机制 在这个阶段的宽容。然而，很清楚的是，缺失不是消除自身反应性未成熟B细胞的唯一机制。我们已经确定了骨髓（BM）中的一种细胞成分，可以保护BCR刺激的未成熟B细胞免于凋亡，并将反应重新定向为持续的免疫球蛋白（IG）轻链重组和受体编辑。最后，我们的数据表明，抗原特异性T细胞可以中止BCR诱导的外周过渡性未成熟B细胞凋亡，并将其重新定向到激活程序。这些研究的拟议继续将集中于定义这些过程的体外机制，以及建立其在体内的免疫学相关性。提出了三个具体目标：（1）确定BCR在未成熟B细胞中不能区室化成脂筏的内在能力是否阻止了持续的BCR信号传导，以及质膜胆固醇和脂质组成的发育调节差异是否影响BCR诱导的信号传导;（2）确定BM保护细胞（BMPC）的细胞特性，其机制 参与调节抗原刺激的未成熟B细胞的凋亡应答，以及其在调节受体编辑中的特定作用;以及，（3）定义过渡性未成熟B细胞从抗原特异性T细胞引发抗凋亡信号的能力，并评估这种相互作用对T细胞对第二次抗原相遇的应答的影响。与该计划的其他成员一起，这些研究将解决与诱导和维持免疫细胞对自身抗原耐受性相关的问题。重要的是，这些研究将考虑这些过程发生的复杂微环境，同时在机制层面解决这些问题。

The immature B cell stage is the first developmental stage where a B cell can recognize and respond to polymorphic antigen, and therefore where endogenous or self-antigens can initially be recognized. As such, the emergence of immature B cells provides the first opportunity to purge the repertoire of self-reactive B cells with the potential to initiate autoimmune disease. We have recently found that the B cell receptor (BCR) on immature B cells fails to compartmentalize into lipid rafts following aggregation and that this is associated with abortive signaling. Based on our cumulative data, we have argued that the intrinsic or "hardwired" response of BCR stimulated immature B cells is apoptotic, suggesting that deletion is the default mechanism for tolerance at this stage. However, it is quite clear that deletion is not the sole mechanism for the elimination of self-reactive immature B cells. We have identified a cellular constituent in the bone marrow (BM) that can protect the BCR-stimulated immature B cell from apoptosis and redirect the response to continued immunoglobulin (Ig) light chain recombination and receptor editing. Finally, our data indicate that antigen-specific T cells can abort BCR-induced apoptosis by peripheral transitional immature B cells and redirect them towards an activation program. The proposed continuation of these studies will focus on defining the mechanisms underlying these processes in vitro as well as to establish their immunological relevance in vivo. Three specific aims are proposed: (1) determine if the intrinsic inability of the BCR to compartmentalize into lipid rafts in immature B cells prevents sustained BCR signaling and if developmentally regulated differences in plasma membrane cholesterol and lipid composition influence BCR-induced signaling; (2) define the cellular identity of the BM protective cell (BMPC), the mechanisms involved in modulating the apoptotic response of antigen-stimulated immature B cells, and its specific role in regulating receptor editing; and, (3) define the ability of transitional immature B cells to elicit anti-apoptotic signals from antigen-specific T cells and assess the impact of this interaction on T cell responses to secondary antigen encounter. Together with other members of this program, these studies will address issues relevant to the induction and maintenance of immune cell tolerance to self-antigens. Importantly, these studies will consider the complex microenvironments in which these processes occur while at the same time addressing these issues at the mechanistic level.