Gibson L F, Piktel D, Landreth K S
Department of Pediatrics, West Virginia University Health Sciences Center, Morgantown 26506.
Blood. 1993 Nov 15;82(10):3005-11.
Commitment to B-lymphocyte differentiation is characterized by expression of the B220 form of the common leukocyte antigen (Ly-5) and D-JH rearrangement of the Ig heavy chain gene complex. B-lineage progenitor cells, or pro-B cells, that have initiated Ig gene rearrangement, but do not express detectable Ig heavy or light chain protein, have recently been shown to retain substantial capacity for expansion in vitro in the presence of bone marrow (BM) stromal cells and interleukin-7 (IL-7). Although the potentiating effect of stromal cells on pro-B-cell proliferation can be partially attributed to the ligand for the proto-oncogene receptor c-kit (c-kit ligand [KL] or stem cell factor), several lines of evidence suggest that c-kit-mediated cell signalling is not required for pro-B-cell expansion. Previous studies from this laboratory demonstrated that insulin-like growth factor-1 (IGF-1) potentiated the proliferative effect of IL-7 on nonadherent cells from lymphoid long-term BM cultures in a manner similar to that shown for KL. To further delineate specific cell stages that respond to lymphopoietic cytokines, we derived continuously proliferating pro-B-cell lines from day-14 murine fetal liver in the presence of IL-7 and BM stromal cell clone S10. Initial expansion and continued proliferation of these pro-B-cell lines was absolutely dependent on the presence of both IL-7 and stromal cells. In the absence of KL, IL-7-stimulated proliferation of these cells in short-term cultures and addition of either recombinant IGF-1 or KL significantly potentiated this proliferative response. Although IGF-2 and insulin also potentiated the effect of IL-7, our data suggest that neither IGF-2 nor insulin represent normal regulators of intramyeloid lymphocyte development. IGF-1 and KL activate unique cascades of intracellular signalling events and inclusion of both cytokines in cultures of IL-7-stimulated pro-B cells resulted in additive potentiation of the proliferative response. Taken together, these results suggest that expansion of pro-B cells in vivo is maintained by at least three stromal cell-derived cytokines. IL-7 appears to be unique in delivering the primary proliferative signal for pro-B-cell expansion; however, both KL and IGF-1 potentiate the proliferative effect of IL-7 on these cells. The functional redundancy and additive effects of IGF-1 and KL as amplification signals for developing B-lineage cells underscore the essential nature of clonal expansion and diversification in development of immunocompetent lymphoid cells.
B淋巴细胞分化的特征是共同白细胞抗原（Ly-5）的B220形式的表达以及Ig重链基因复合体的D-JH重排。已经启动Ig基因重排但不表达可检测到的Ig重链或轻链蛋白的B系祖细胞，即前B细胞，最近被证明在存在骨髓（BM）基质细胞和白细胞介素-7（IL-7）的情况下在体外具有相当大的扩增能力。尽管基质细胞对前B细胞增殖的增强作用可部分归因于原癌基因受体c-kit的配体（c-kit配体[KL]或干细胞因子），但几条证据表明c-kit介导的细胞信号传导对于前B细胞扩增并非必需。本实验室先前的研究表明，胰岛素样生长因子-1（IGF-1）以与KL相似的方式增强了IL-7对来自长期BM淋巴细胞培养物的非贴壁细胞的增殖作用。为了进一步描绘对淋巴细胞生成细胞因子作出反应的特定细胞阶段，我们在IL-7和BM基质细胞克隆S10存在的情况下从第14天的小鼠胎儿肝脏中获得了持续增殖的前B细胞系。这些前B细胞系的初始扩增和持续增殖绝对依赖于IL-7和基质细胞的存在。在没有KL的情况下，IL-7刺激这些细胞在短期培养中的增殖，添加重组IGF-1或KL可显著增强这种增殖反应。尽管IGF-2和胰岛素也增强了IL-7的作用，但我们的数据表明IGF-2和胰岛素都不是骨髓内淋巴细胞发育的正常调节因子。IGF-1和KL激活独特的细胞内信号传导事件级联，并且在IL-7刺激的前B细胞培养物中同时加入这两种细胞因子会导致增殖反应的累加增强。综上所述，这些结果表明体内前B细胞的扩增由至少三种基质细胞衍生的细胞因子维持。IL-7似乎在传递前B细胞扩增的主要增殖信号方面是独特的；然而，KL和IGF-1都增强了IL-7对这些细胞的增殖作用。IGF-1和KL作为发育中的B系细胞的扩增信号的功能冗余和累加效应强调了免疫活性淋巴细胞发育中克隆扩增和多样化的本质。
