Ballantyne J, Henry D L, Muller J R, Briere F, Snapper C M, Kehry M, Marcu K B
Department of Biochemistry and Cell Biology, Institute for Cell and Developmental Biology, State University of New York, Stony Brook 11794-5215, USA.
J Immunol. 1998 Aug 1;161(3):1336-47.
Maturing B lymphocytes possess a recombination activity that switches the class of heavy chain Ig. The nature of the recombination activity, its molecular requirements and regulation remain elusive questions about B lymphocyte biology and development. Class switch recombination is controlled by cytokine response elements that are required to differentially activate CH gene transcription before their subsequent recombination. Here, we show that cultures of purified murine and human B cells, stimulated only by CD40 receptor engagement, possess a potent switch recombination activity. CD40 ligand-stimulated murine and human B lymphocytes were infected with recombinant retroviruses containing Smu and S gamma 2b sequences. Chromosomally integrated switch substrate retrovectors (SSRs), harboring constitutively transcribed S sequences, underwent extensive recombinations restricted to their S sequences with structural features akin to endogenous switching. SSR recombination commenced 4 days postinfection (5 days poststimulation) with extensive switch sequence recombination over the next 2 to 3 days. In contrast, endogenous S gamma 2b and S gamma 1 sequences did not undergo appreciable switch recombination upon CD40 signaling alone. As expected, IL-4 induced endogenous Smu to S gamma 1 switching, while endogenous Smu to S gamma 2b fusions remained undetectable. Surprisingly, IL-4 enhanced the onset of SSR recombination in CD40-stimulated murine B cells, with S-S products appearing only 2 days postinfection and reaching a maximum within 2 to 3 days. The efficiency of switch recombination with SSRs resembles that seen for endogenous C(H) class switching.
成熟的B淋巴细胞具有一种重组活性，可转换重链Ig的类别。这种重组活性的本质、其分子要求和调控仍然是B淋巴细胞生物学和发育中难以捉摸的问题。类别转换重组由细胞因子反应元件控制，这些元件在随后的重组之前需要差异激活CH基因转录。在这里，我们表明，仅通过CD40受体结合刺激的纯化小鼠和人类B细胞培养物具有强大的转换重组活性。用含有Smu和Sγ2b序列的重组逆转录病毒感染CD40配体刺激的小鼠和人类B淋巴细胞。携带组成性转录S序列的染色体整合开关底物逆转录载体（SSR）发生了广泛的重组，仅限于其S序列，其结构特征类似于内源性转换。SSR重组在感染后4天（刺激后5天）开始，在接下来的2至3天内发生广泛的开关序列重组。相比之下，仅CD40信号传导时，内源性Sγ2b和Sγ1序列未发生明显的类别转换重组。正如预期的那样，IL-4诱导内源性Smu向Sγ1转换，而内源性Smu与Sγ2b融合仍然无法检测到。令人惊讶的是，IL-4增强了CD40刺激的小鼠B细胞中SSR重组的起始，S-S产物仅在感染后2天出现，并在2至3天内达到最大值。与SSR的转换重组效率类似于内源性C(H)类别转换所观察到的值。
