两种小鼠胸腺基质细胞对胸腺细胞凋亡的不同作用

The different effects of two thymic stromal cells on programmed cell death of thymocytes cultured in vitro

采用两种体外建系的小鼠胸腺基质细胞（ＴＳＣ）系，即上皮样ＴＳＣ（ＭＴＥＣ１）和树突状ＴＳＣ（ＭＴＳＣ４），观察其对胸腺细胞凋亡的影响。小鼠胸腺细胞在体外培养过程中，可自发地出现细胞凋亡的特征，表现为ＤＮＡ呈梯度断裂片段，细胞经ＦＡＣＳ分析出现亚二倍体ＤＮＡ波峰，以及Ｆｅｕｌｇｅｎ′ｓ染色镜检所见的ＤＮＡ凝聚和断裂。胸腺细胞在与ＴＳＣ共育后，在ＭＴＥＣ１组可见其凋亡过程受到抑制和存活率的增加；在ＭＴＳＣ４组，仅在共育１２至１８小时时，见到胸腺细胞凋亡加强，而其存活率不受影响。结果提示在胸腺细胞发育过程中，其阴性选择作用的主要机制之一的ＰＣＤ过程受不同来源的胸腺基质细胞的调节。

We investigated the regulation of thymic stromal cells on the process of programmed cell death of thymocytes. By using DNA electrophoreses and propidium iodide-DNA staining flow cytometry assay ,we investigated the effects of mouse thymic stromal cells (MTSC) on the process of programmed cell death of cultured thymocytes. The progressive DNA fragmentation and higher percentage of apoptotic cells hypodiploid DNA were observed in thymocytes at subsequent time point. When the thymocytes were cocultured with mouse thymic epithelial cell line (MTECI) , a sharp decrease of DN A fragmentation was observed in thymocytes at different culture time , while the mouse thymic dendritic cell line (MTSC4 ) en- hanced the DNA fragmentation of thymocytes at 12 to 18 h-coculture time. FACS assay quantitatively con- firmed these observation. MTEC1 , but not MTSC4 enhanced the survival rate of thymocytes in vitro. By histochentistry DNA in situ staining method , we observed the presence of apoptotic cells around the two thymic stromal cells. These results suggest that thymic stromal cells may regulate the process of thymocytes during the negative selection in thymus through different mechanisms in which providing survival signals and engulfing apoptotic cells. may be included.