Stemucronatoside L, a Pregnane Glycoside from the Roots of Stephanotis mucronata , Inhibits Th1/Th2 Immune Responses in vitro

temucronatoside L (SML), isolated from Stephanotis mucronata , could suppress the activation of T cells in vitro. However, the mechanisms responsible for its immunosuppressive activity remain poorly understood. The purpose of this study was to investigate whether SML could suppress Th1/Th2 immune responses and to characterize the cellular mechanisms involved. Effects of SML on T‐lymphocyte subsets and the production of Th1 cytokines IL‐2 and IFN‐ γ , and Th2 cytokines IL‐4 and IL‐10 from ConA‐stimulated mice splenocytes were detected by flow‐cytometric analysis and ELISA method, respectively. Furthermore, effects of SML on mRNA expression level of Th1/Th2 cytokines and transcription factors T‐bet and GATA‐3 were evaluated by RT‐PCR analysis. SML not only significantly decreased the percentage of CD4 + T cells and the CD4 + /CD8 + ratio, but reduced the production of Th1/Th2 cytokines in a concentration‐dependent manner. The mRNA expression levels of Th1/Th2 cytokines and transcription factors (T‐bet and GATA‐3) were also suppressed by SML. These results suggested that SML could simultaneously inhibit Th1/Th2 immune responses by suppressing gene expression of Th1/Th2 cytokines and transcription factors.