Laboratory of Molecular and Cellular Biology, Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan.
Int Immunol. 2012 May;24(5):283-92. doi: 10.1093/intimm/dxr127. Epub 2012 Feb 1.
B-cell receptor (BCR)-mediated apoptosis is critical for B-cell development and homeostasis. CD40 signaling has been shown to protect immature or mature B cells from BCR-mediated apoptosis. In this study, to understand the fate of CD40-pre-activated splenic B cells stimulated by BCR engagement in the presence of CD40 signaling, murine splenic B cells were cultured with anti-Igκ and anti-CD40 antibodies after pre-activation with anti-CD40 antibody. We found that apoptosis was induced in the cultured B cells even in the presence of CD40 signaling during the 3-4 days cultivation. We detected up-regulation of Bim expression followed by Bax activation in this apoptotic process and cessation of the apoptosis in Bim-deficient B cells, indicating that Bim is a key regulator of the BCR-mediated apoptosis in the presence of CD40 signaling in CD40-pre-activated B cells. Importantly, this BCR-mediated apoptosis in CD40-pre-activated B cells was shown to be induced at the initiation of plasma cell differentiation at around the preplasmablast stage, and Bim-deficient B cells cultured under these conditions differentiated into plasma cells. Additionally, transforming growth factor-β was found to protect CD40-pre-activated B cells from BCR-mediated apoptosis in the presence of CD40 signaling. Our identified BCR-mediated apoptosis, which is unpreventable by CD40 signaling, suggests a potential mechanism that regulates the elimination of peripheral B cells, which should be derived from nonspecific T-dependent activation of bystander B cells and continuous stimulation with antigens including self-antigens in the presence of T cell help through CD40.
B 细胞受体 (BCR) 介导的凋亡对于 B 细胞的发育和稳态至关重要。已经表明 CD40 信号可以保护未成熟或成熟的 B 细胞免受 BCR 介导的凋亡。在这项研究中，为了了解在 CD40 信号存在下，BCR 交联刺激预激活的 CD40 预处理的脾 B 细胞的命运，我们在抗 CD40 抗体预处理后，用抗 Igκ 和抗 CD40 抗体培养鼠脾 B 细胞。我们发现，即使在存在 CD40 信号的情况下，在培养的 B 细胞中也会在 3-4 天的培养过程中诱导凋亡。在这个凋亡过程中，我们检测到 Bim 表达的上调，随后 Bax 激活，并且在 Bim 缺陷的 B 细胞中停止凋亡，表明 Bim 是 CD40 预处理的 B 细胞中存在 CD40 信号时 BCR 介导的凋亡的关键调节剂。重要的是，这种在 CD40 预处理的 B 细胞中 BCR 介导的凋亡被证明是在浆细胞分化的起始时诱导的，大约在前浆母细胞阶段，并且在这些条件下培养的 Bim 缺陷的 B 细胞分化为浆细胞。此外，转化生长因子-β被发现可以保护 CD40 预处理的 B 细胞免受 CD40 信号存在下的 BCR 介导的凋亡。我们鉴定的 BCR 介导的凋亡不能被 CD40 信号预防，这表明了一种潜在的机制，该机制可以调节外周 B 细胞的消除，这些 B 细胞应该是通过 T 细胞辅助通过 CD40 对旁观者 B 细胞的非特异性 T 依赖性激活和对包括自身抗原在内的抗原的持续刺激而衍生的。
