Farrerol, a new type of 2,3-dihydro-flavonoid, has been isolated from the leaves of Rhododendron dauricum L. In the present study, we found that farrerol exerted potent immunosuppressive effects on murine T cells both in vitro and in vivo. In vitro, farrerol markedly suppressed concanavalin A (ConA)-induced lymphocyte proliferation, Th1 and Th2 cytokine production, cluster of differentiation 4-positive (CD4(+)) T cell populations, and the ratio of CD4(+)/cluster of differentiation 8-positive (CD8(+)) T cells. Moreover, farrerol significantly inhibited the T cell-mediated delayed-type hypersensitivity (DTH) reaction in vivo. In addition, we investigated signal transduction mechanisms to determine the effects of farrerol by Western blotting. The data revealed that farrerol could downregulate the activation of the nuclear factor κB (NF-қB) and nuclear factor of activated T cells 2 (NFAT2) signal transduction pathways. These findings suggested that farrerol has potential effects on the regulation of the immune system and could be developed as a practicable immunosuppressive compound.
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