Background The transcription factor,repressor of GATA-3 (ROG),can simultaneously suppress the expression of T helper cells (Th1 and Th2) cytokines.Since the suppression of Th2 cytokines by GATA-3 is well understood,it is postulated that there are other molecular targets of ROG that can suppress the expression of the Th1 cytokines.We hypothesized that ROG might suppress the stimulators of T lymphocyte cytokines such as CD3,CD28,and inducible costimulator (ICOS),or indirectly enhance the expression of cytokine suppressors such as T lymphocyte-associated antigen-4 (CTLA-4) and CD45.The objective of this study was to clarify the molecular targets of ROG involved in suppressing Th1 or Th2 cytokines.Methods Real-time quantitative PCR (RT-PCR) and Westem blotting were performed to evaluate the mRNA and protein levels of CD3,CD28,ICOS,CTLA-4,and CD45 in Th1 and Th2 cells during vadous levels of ROG expression.Enzyme-linked immunosorbent assay (ELISA) was used to measure the levels of interferon-y (IFN-y) and intedeukin (IL)-4 in culture media of Th1 and Th2 cells.Results The results showed that the mRNA and protein levels of ROG were relatively low in Th1 and Th2 cells (P＜0.01).After ROG-pcDNA3.1 transfection,the mRNA and protein level of ROG was significantly elevated,while the expression of ICOS,IFN-y,and IL-4 was markedly down-regulated (P ＜0.01 ).Conversely,transfection of ROG-siRNA led to inhibition of ROG expression and up-regulation of ICOS,IFN-y and IL-4 (P ＜0.01).However,the expression levels of CD3,CD28,CTLA-4 and CD45 did not change in either ROG-pcDNA3.1 or ROG-siRNA-transfected Th1 and Th2 cells (P＞0.05).Conclusion It is concluded that ROG can inhibit the expression of Th1 and Th2 cytokines by down-regulating the expression of ICOS,which might be a potential molecular target for asthma treatment.