Meilin A, Shoham J, Schreiber L, Sharabi Y
Department of Life Sciences, Bar-Ilan University, Ramat Gan, Israel.
Scand J Immunol. 1995 Aug;42(2):185-90. doi: 10.1111/j.1365-3083.1995.tb03644.x.
The basic tenet underlying the present work and supported by recent studies is that there is a dialogue between developing thymocytes and thymic stromal cells. One direction in this dialogue, i.e. thymic stromal cell role in shaping thymocyte maturation, has been extensively studied. The other direction, thymocyte effect on stromal cell development and function, started to emerge only recently on the basis of in vivo observations in SCID and knockout mice. An in vitro approach to the analysis of this interaction may add substantial insight into the process, as demonstrated by the present work. We made use of a culture system of either murine thymic epithelial cells (TEC line) cultured alone or cocultured with thymocytes. Unstimulated thymocytes or their supernatant caused 40-80% inhibition of TEC cell proliferation, as measured by 3H-thymidine incorporation. Cell cycle analysis by flow cytometry indicated that this inhibition can be attributed to reduction in G2/M phase cell number pari passu with an increase in Go/G1 cell number. This inhibitory effect was found to be partially mediated by TGF-beta produced by thymocytes. On the other hand, thymocytes augmented IL-6 production by TEC cells in coculture, an effect which could not be reproduced by thymocyte culture supernatant and was not inhibited by thymocyte pretreatment with formaldehyde or emetine. Furthermore, antibodies against thymocyte adhesion molecules (CD2, LFA-1) blocked the thymocyte-induced IL-6 secretion. IL-6 was found to be an autocrine growth factor of TEC in culture, since a combination of anti IL-6 and anti IL-6 receptor antibodies caused 70% inhibition of TEC proliferation and addition of exogenous recombinant IL-6 doubled the rate of proliferation. These results suggest that thymocytes regulate thymic epithelial cell growth by a complex set of inhibitory and enhancing signals mediated through either soluble factors or direct contact. The ultimate effect is dependent on the balance between different signals and may be different in different microenvironmental settings in vivo. In coculture in vitro the dominant effect was growth inhibition of the epithelial cells by thymocytes.
本研究的基本宗旨以及近期研究所支持的观点是，发育中的胸腺细胞与胸腺基质细胞之间存在对话。在这种对话中，一个方向，即胸腺基质细胞在塑造胸腺细胞成熟过程中的作用，已得到广泛研究。另一个方向，即胸腺细胞对基质细胞发育和功能的影响，只是最近才基于对重症联合免疫缺陷（SCID）小鼠和基因敲除小鼠的体内观察而开始显现。正如本研究所表明的，体外分析这种相互作用的方法可能会为这一过程带来实质性的深入了解。我们利用了单独培养或与胸腺细胞共培养的小鼠胸腺上皮细胞（TEC系）培养系统。通过³H-胸腺嘧啶核苷掺入法测定，未受刺激的胸腺细胞或其上清液导致TEC细胞增殖受到40 - 80%的抑制。流式细胞术进行的细胞周期分析表明，这种抑制可归因于G2/M期细胞数量的减少以及Go/G1期细胞数量的相应增加。发现这种抑制作用部分由胸腺细胞产生的转化生长因子β（TGF-β）介导。另一方面，胸腺细胞在共培养中增强了TEC细胞的白细胞介素-6（IL-6）产生，这种作用不能由胸腺细胞培养上清液重现，并且不受甲醛或依米丁预处理胸腺细胞的抑制。此外，针对胸腺细胞黏附分子（CD2、淋巴细胞功能相关抗原-1（LFA-1））的抗体阻断了胸腺细胞诱导的IL-6分泌。发现IL-6是培养中TEC的自分泌生长因子，因为抗IL-6和抗IL-6受体抗体的组合导致TEC增殖受到70%的抑制，而添加外源性重组IL-6使增殖速率加倍。这些结果表明，胸腺细胞通过一组由可溶性因子或直接接触介导的复杂抑制和增强信号来调节胸腺上皮细胞的生长。最终效果取决于不同信号之间的平衡，并且在体内不同的微环境中可能有所不同。在体外共培养中，主要作用是胸腺细胞对上皮细胞的生长抑制。
