Objective : This study was carried out for the purpose of knowing the effect from thymus T cell differentiation of the C57BL/6 mice by the extraction from a ESC. Methods : The second costimulatory signal determines the activation threshold and the functional out come of the antigen-. specific activation. The activation threshold is mtdulated by costimulatory signals, and their dysregulation may play a critical role in the activation of autorextive T cells. CD80/CI)%-CrK 8/CTL.k4 is the most important costimulatory molecules. Th1 cells prduce IIW v and II-2 and play a n impxtant rolt, in allograft rejection, whereas Th2 cells stcrete LL-4, Jl-5, lL6. 11, 10, and IL- 13 and are associated with the prolongation of graft survival and tolcrrince induction. IIowever. this Thl,/Th2 p:uxiigm is more complex. CD4CD25+ T cells were shown to control autoreactive T cells, and CDU mediates leukocyte activation ii nd CD69 acts as a costimulatory moltcule for T cell activation and proliferation. So we investigated the effects of ESC on these cytokines and cell surface antigens(CD25, CD28, CD44. CD69. CD80) expressed by T cells following activation. Results : 1. In order to know the effect of the cytotoxicitp from extraction of EC, we had to examine the safe density of that on lung fibroblast cells of the mouse(m1,I;C;s). ESC did not show cytotoxicity against rnLFCs. 2. In the proliferous effect of thymus T cells, water extracts of ESC playtd an important. role on the proliferating thymus T cells compared with control group at high density. 3. ESC promoted the CD80(B7-1) and T h l cytokines especially IFN V, IL-2, IL-4 gene exprtbssion, but not CTLA-4, T h F a , CrY28 gene expression. 4. ESC up- regulates CD44`CD69`CD`L5`, CD4`CD25`, CD8`CD25`, CLB`CDXO` expression but not CD3`CD2 8` by anti--CD3-stimulated T cells. 5. Binding activity of transcription factors(NF-KB NFAT, AP-1) was increased by ESC. We thought that ESC also could regulate the expression of a variety of inducible genes by increasing the binding activity of transcription factors(NF-KB, NFAT, A1`- 1 ). Conclusions : Above results indicates that ESC play an important role in the activation of autoreactive T cells by promoting The cytohne(I?T-~, II-2) and cftlcreasiny C T A-4 , CD28 and Th2 cytokines IL-4 gene expression, by up-regulating cell surface molecule(CD80, CD35, 1144). Binding activity of transcription factor ~(NF-KB. NFAT, AP-1) was increased by ESC. We thought that ESC also could regulate the expression of a variety of inducible genes by inc?-easing the binding activity of transcription factordNF-KB, NFAT, AP-1). Therefore further deep studies shoud be accomplished about its mechanisms.