Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
J Immunol. 2012 Apr 1;188(7):3332-41. doi: 10.4049/jimmunol.1102322. Epub 2012 Feb 29.
The acquisition of long-lived memory B cells (MBCs) is critical for the defense against many infectious diseases. Despite their importance, little is known about how Ags trigger human MBCs, even though our understanding of the molecular basis of Ag activation of B cells in model systems has advanced considerably. In this study, we use quantitative, high-resolution, live-cell imaging at the single-cell and single-molecule levels to describe the earliest Ag-driven events in human isotype-switched, IgG-expressing MBCs and compare them with those in IgM-expressing naive B cells. We show that human MBCs are more robust than naive B cells at each step in the initiation of BCR signaling, including interrogation of Ag-containing membranes, formation of submicroscopic BCR oligomers, and recruitment and activation of signaling-associated kinases. Despite their robust response to Ag, MBCs remain highly sensitive to FcγRIIB-mediated inhibition. We also demonstrate that in the absence of Ag, a portion of MBC receptors spontaneously oligomerized, and phosphorylated kinases accumulated at the membrane and speculate that heightened constitutive signaling may play a role in maintaining MBC longevity. Using high-resolution imaging, we have provided a description of the earliest events in the Ag activation of MBCs and evidence for acquired cell-intrinsic differences in the initiation of BCR signaling in human naive and MBCs.
长期记忆 B 细胞（MBC）的获得对于抵抗许多传染病至关重要。尽管它们很重要，但人们对 Ag 如何触发人类 MBC 知之甚少，尽管我们对模型系统中 Ag 激活 B 细胞的分子基础的理解已经有了很大的进展。在这项研究中，我们使用定量、高分辨率、单细胞和单分子水平的实时成像来描述人同种型转换 IgG 表达 MBC 中最早的 Ag 驱动事件，并将其与 IgM 表达幼稚 B 细胞进行比较。我们表明，在 BCR 信号起始的每个步骤中，人 MBC 比幼稚 B 细胞更健壮，包括对含 Ag 的膜的询问、亚微观 BCR 寡聚体的形成，以及信号相关激酶的募集和激活。尽管对 Ag 有强烈的反应，但 MBC 仍然对 FcγRIIB 介导的抑制高度敏感。我们还证明，在没有 Ag 的情况下，一部分 MBC 受体自发寡聚化，并且磷酸化激酶在膜上积累，并推测增强的组成性信号可能在维持 MBC 寿命方面发挥作用。通过高分辨率成像，我们提供了 Ag 激活 MBC 中最早事件的描述，并提供了证据证明在人类幼稚和 MBC 中 BCR 信号起始的获得性细胞内在差异。
