Abstract

A variety of preparations of Tripterygium wilfordii Hook.F (TWHF) have been reported to be effective in the treatment of autoimmune diseases, including a chloroform methanol extract termed T2 and an ethyl acetate (EA) extract. The immunosuppressive activity of the EA extract was analyzed and the components accounting for this effect determined and compared to those of T2. More than 0.25 microgram/ml of the EA extract inhibited antigen- and mitogen-stimulated human T cell proliferation. The inhibitory effect of the EA extract on T cell proliferation resulted largely from suppression of interleukin-2 production. At concentrations that inhibited T cell function, the EA extract also profoundly suppressed [3H]-thymidine incorporation by mitogen-stimulated B cells, but it did not inhibit antigen presentation by monocytes and only modestly affected interleukin-6 production by lipopolysaccharide-stimulated monocytes. The profile of inhibition was comparable to that previously reported for the chloroform-methanol extract of Tripterygium wilfordii Hook.F, T2. To delineate the components of these extracts that might account for their immunosuppressive effect, we analyzed the composition of diterpenoid compounds. Both extracts contained triptolide and tripdiolide as the major immunosuppressive diterpenoids, but at different concentrations. Comparison of the composition of these extracts and the inhibitory capacity of the purified components indicated that the triptolide concentration of the EA extract can account for its immunosuppressive activity, although the combination of both triptolide and tripdiolide or other unknown components may be necessary to explain the inhibitory effects of T2.