Department of Immunopathology, Sanquin Research and Landsteiner Laboratory, Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands.
Synthetic Systems Biology and Nuclear Organization, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, Netherlands.
Front Immunol. 2019 Mar 13;10:415. doi: 10.3389/fimmu.2019.00415. eCollection 2019.
Growing evidence indicate that large antigen-containing particles induce potent T cell-dependent high-affinity antibody responses. These responses require large particle internalization after recognition by the B cell receptor (BCR) on B cells. However, the molecular mechanisms governing BCR-mediated internalization remain unclear. Here we use a high-throughput quantitative image analysis approach to discriminate between B cell particle binding and internalization. We systematically show, using small molecule inhibitors, that human B cells require a SYK-dependent IgM-BCR signaling transduction via PI3K to efficiently internalize large anti-IgM-coated particles. IgM-BCR-mediated activation of PI3K involves both the adaptor protein NCK and the co-receptor CD19. Interestingly, we here reveal a strong NCK-dependence without profound requirement of the co-receptor CD19 in B cell responses to large particles. Furthermore, we demonstrate that the IgM-BCR/NCK signaling event facilitates RAC1 activation to promote actin cytoskeleton remodeling necessary for particle engulfment. Thus, we establish NCK/PI3K/RAC1 as an attractive IgM-BCR signaling axis for biological intervention to prevent undesired antibody responses to large particles.
越来越多的证据表明，含有大量抗原的颗粒会诱导强烈的 T 细胞依赖性高亲和力抗体反应。这些反应需要 B 细胞受体 (BCR) 在 B 细胞上识别后，大量颗粒内吞。然而，BCR 介导的内吞作用的分子机制仍不清楚。在这里，我们使用高通量定量图像分析方法来区分 B 细胞颗粒结合和内吞作用。我们系统地使用小分子抑制剂表明，人类 B 细胞需要 SYK 依赖性 IgM-BCR 信号转导通过 PI3K 来有效地内吞大的抗 IgM 包被颗粒。IgM-BCR 介导的 PI3K 激活涉及衔接蛋白 NCK 和共受体 CD19。有趣的是，我们在这里揭示了一种强烈的 NCK 依赖性，而在 B 细胞对大颗粒的反应中，共受体 CD19 的要求并不深刻。此外，我们证明 IgM-BCR/NCK 信号事件促进 RAC1 的激活，从而促进吞噬颗粒所需的肌动蛋白细胞骨架重塑。因此，我们确立了 NCK/PI3K/RAC1 作为一种有吸引力的 IgM-BCR 信号轴，可用于生物干预，以防止对大颗粒产生不期望的抗体反应。
