Department of Immunology, National Jewish Health and University of Colorado School of Medicine, Denver, CO 80206.
Department of Immunology, National Jewish Health and University of Colorado School of Medicine, Denver, CO 80206
Proc Natl Acad Sci U S A. 2014 Jul 8;111(27):E2797-806. doi: 10.1073/pnas.1402159111. Epub 2014 Jun 23.
Newly generated immature B cells are selected to enter the peripheral mature B-cell pool only if they do not bind (or bind limited amount of) self-antigen. We previously suggested that this selection relies on basal extracellular signal-regulated kinase (Erk) activation mediated by tonic B-cell antigen receptor (BCR) signaling and that this signal can be replaced by an active rat sarcoma (Ras), which are small GTPase proteins. In this study we compared the activity of Ras and Erk in nonautoreactive and autoreactive immature B cells and investigated whether activation of Ras can break tolerance. Our results demonstrate lower levels of active Erk and Ras in autoreactive immature B cells, although this is evident only when these cells display medium/high avidity for self-antigen. Basal activation of Erk in immature B cells is proportional to surface IgM and dependent on sarcoma family kinases, whereas it is independent of B-cell activating factor, IFN, and Toll-like receptor signaling. Ectopic expression of the constitutively active mutant Ras form N-RasD12 in autoreactive cells raises active Erk, halts receptor editing via PI3 kinase, and promotes differentiation via Erk, breaking central tolerance. Moreover, when B cells coexpress autoreactive and nonautoreactive BCRs, N-RasD12 leads also to a break in peripheral tolerance with the production of autoantibodies. Our findings indicate that in immature B cells, basal activation of Ras and Erk are controlled by tonic BCR signaling, and that positive changes in Ras activity can lead to a break in both central and peripheral B-cell tolerance.
新生成的未成熟 B 细胞只有在不结合（或结合有限量的）自身抗原的情况下，才能被选择进入外周成熟 B 细胞池。我们之前曾提出，这种选择依赖于由持续的 B 细胞抗原受体（BCR）信号介导的基础细胞外信号调节激酶（Erk）激活，并且这种信号可以被活性大鼠肉瘤（Ras）取代，Ras 是一种小 GTP 酶蛋白。在这项研究中，我们比较了非自身反应性和自身反应性未成熟 B 细胞中 Ras 和 Erk 的活性，并研究了 Ras 的激活是否可以打破耐受。我们的结果表明，尽管自身反应性未成熟 B 细胞中只有当这些细胞对自身抗原显示中/高亲和力时，才会出现 Erk 和 Ras 的活性较低，但自身反应性未成熟 B 细胞中 Erk 和 Ras 的活性较低。未成熟 B 细胞中 Erk 的基础激活与表面 IgM 成正比，并且依赖于肉瘤家族激酶，而与 B 细胞激活因子、IFN 和 Toll 样受体信号无关。在自身反应性细胞中异位表达组成性激活的 Ras 突变体 N-RasD12 会提高活性 Erk，通过 PI3 激酶阻止受体编辑，并通过 Erk 促进分化，从而打破中枢耐受。此外，当 B 细胞共表达自身反应性和非自身反应性 BCR 时，N-RasD12 也会导致外周耐受的破坏，产生自身抗体。我们的发现表明，在未成熟 B 细胞中，Ras 和 Erk 的基础激活受持续 BCR 信号的控制，并且 Ras 活性的正向变化可导致中枢和外周 B 细胞耐受的破坏。
