THE CHINESE HERBAL REMEDY, T2, INHIBITS MITOGEN-INDUCED CYTOKINE GENE-TRANSCRIPTION BY T-CELLS, BUT NOT INITIAL SIGNAL-TRANSDUCTION

T2, an extract of Tripterygium wilfordii Hook F, has been reported to be effective in the treatment of a variety of autoimmune diseases, inc luding rheumatoid arthritis. Previous studies have shown that T2 inhib ited mitogen- or antigen-induced proliferation of human peripheral blo od T cells and B cells, 11-2 production by T cells and Ig production b y B cells. In contrast, T2 did not affect monocyte functions, such as IL-1 produciton and antigen presentation. The current studies sought t o localize the immunosuppressive action of T2 more precisely. Results show that T2 prevented [H-3]-uridine uptake by mitogen-stimulated T ce lls and arrested them in the early G1 phase of the cell cycle. The inh ibitory effects of T2 could be partially overcome by costimulating PHA activated T cells with PFAA and completely nullified by costimulation with PMA plus a monoclonal antibody to CD28. Moreover, T2 had no effe ct on expression of IL-2R or the transferrin receptor (CD71), but inhi bited production of a number of cytokines, including 1L-2 and IfN-gamm a by activated T cells. T2 suppressed IL-2 mRNA levels, but not IL-2R mRNA levels, in activated T cells. T2-mediated inhibition reflected su ppression of IL-2 gene transcription as indicated by suppression of th e expression of a reporter gene driven by the IL-2 promoter. T2 had li ttle inhibitory effect on either IL-2 gene expression or cell cycle pr ogression when added after initial mitogenic stimulation, indicating t hat an early step in the cascade of activation events was inhibited. H owever, initial activation events including protein tyrosine phosphory lation, the generation of diacylglycerol, IP3, and the translocation o f protein kinase C were not inhibited by T2. Moreover, T2 did not inhi bit the phosphatase activity of calcineurin. These results have locali zed the effect of T2 to a step in the T cell activation cascade after initial second messenger generation, tyrosine phosphorylation and prot ein kinase activation, but before IL-2 gene transcription.