['(5R)-5-hydroxytriptolide (LLDT-8) displayed immunosuppressive activities both in vitro and in autoimmune disease models. Here, we aim to further clarify the effect of LLDT-8 on the immune responses of human peripheral blood mononuclear cells (PBMC).', 'Cell proliferation of human PBMC from healthy donors was evaluated by [3H]-thymidine uptake. NK cell cytotoxicity was assayed using K562 cells in a [3H] lysis assay. Cytokine production was determined by enzyme-linked immunosorbent assay. The expression of cell surface molecules was detected with flow cytometry. The mRNA expression and the protein phosphorylation levels were detected by RT-PCR and Western immunoblot assay.', 'LLDT-8 at 25 and 50 nM significantly inhibited the PHA- and recall antigens-induced T cell proliferation, and suppressed mixed lymphocyte reaction. LLDT-8 reduced cytokines production (IFN-gamma, IL-2, TNF-alpha) in PHA- and Sac-activated PBMC. LLDT-8 did not alter the increased expression of MHC class I/II and B7.1, but reduced B7.2 by approximately 30%. No effect of LLDT-8 was observed for the expression of T cell activation markers (CD69, CD154). However, LLDT-8 significantly reduced IFN-gamma-expressing T cell percentages and IFN-gamma mRNA transcription in PHA-activated T cells. It also inhibited the phosphorylation levels of JNK and p38. LLDT-8 did not affect NK cytotoxic activity against K562 cells.'] Does ( 5R ) -5-hydroxytriptolide inhibit the immune response of human peripheral blood mononuclear cells?