Cooke M P, Heath A W, Shokat K M, Zeng Y, Finkelman F D, Linsley P S, Howard M, Goodnow C C
Howard Hughes Medical Institute, Stanford University, California 94305.
J Exp Med. 1994 Feb 1;179(2):425-38. doi: 10.1084/jem.179.2.425.
The specificity of antibody (Ab) responses depends on focusing helper T (Th) lymphocyte signals to suitable B lymphocytes capable of binding foreign antigens (Ags), and away from nonspecific or self-reactive B cells. To investigate the molecular mechanisms that prevent the activation of self-reactive B lymphocytes, the activation requirements of B cells specific for the Ag hen egg lysozyme (HEL) obtained from immunoglobulin (Ig)-transgenic mice were compared with those of functionally tolerant B cells isolated from Ig-transgenic mice which also express soluble HEL. To eliminate the need for surface (s)Ig-mediated Ag uptake and presentation and allow the effects of sIg signaling to be studied in isolation, we assessed the ability of allogeneic T cells from bm12 strain mice to provide in vivo help to C57BL/6 strain-transgenic B cells. Interestingly, non-tolerant Ig-transgenic B cells required both allogeneic Th cells and binding of soluble HEL for efficient activation and Ab production. By contrast, tolerant self-reactive B cells from Ig/HEL double transgenic mice responded poorly to the same combination of allogeneic T cells and soluble HEL. The tolerant B cells were nevertheless normally responsive to stimulation with interleukin 4 and anti-CD40 Abs in vitro, suggesting that they retained the capacity to respond to mediators of T cell help. However, the tolerant B cells exhibited a proximal block in the sIg signaling pathway which prevented activation of receptor-associated tyrosine kinases in response to the binding of soluble HEL. The functional significance of this sIg signaling defect was confirmed by using a more potent membrane-bound form of HEL capable of triggering sIg signaling in tolerant B cells, which markedly restored their ability to collaborate with allogeneic Th cells and produce Ab. These findings indicate that Ag-specific B cells require two signals for mounting a T cell-dependent Ab response and identify regulation of sIg signaling as a mechanism for controlling self-reactive B cells.
抗体（Ab）反应的特异性取决于将辅助性T（Th）淋巴细胞信号聚焦到能够结合外来抗原（Ag）的合适B淋巴细胞上，同时远离非特异性或自身反应性B细胞。为了研究防止自身反应性B淋巴细胞激活所涉及的分子机制，将从免疫球蛋白（Ig）转基因小鼠中获得的针对抗原卵清溶菌酶（HEL）的B细胞的激活需求，与从同样表达可溶性HEL的Ig转基因小鼠中分离出的功能耐受B细胞的激活需求进行了比较。为了消除对表面（s）Ig介导的抗原摄取和呈递的需求，并能够单独研究sIg信号传导的作用，我们评估了来自bm12品系小鼠的同种异体T细胞在体内为C57BL/6品系转基因B细胞提供帮助的能力。有趣的是，不耐受的Ig转基因B细胞需要同种异体Th细胞和可溶性HEL的结合才能有效激活并产生抗体。相比之下，来自Ig/HEL双转基因小鼠的耐受自身反应性B细胞对同种异体T细胞和可溶性HEL的相同组合反应较弱。然而，这些耐受的B细胞在体外对白介素4和抗CD40抗体的刺激仍能正常反应，这表明它们保留了对T细胞辅助介质作出反应的能力。但是，耐受的B细胞在sIg信号通路中存在近端阻断，这使得它们在可溶性HEL结合时无法激活受体相关的酪氨酸激酶。通过使用一种更有效的能够在耐受B细胞中触发sIg信号的膜结合形式的HEL，证实了这种sIg信号缺陷的功能意义，这显著恢复了它们与同种异体Th细胞协作并产生抗体的能力。这些发现表明，抗原特异性B细胞需要两个信号来引发依赖T细胞的抗体反应，并确定sIg信号传导的调节是控制自身反应性B细胞的一种机制。
