Mycophenolate mofetil (MMF) is a newly developed immunosuppressor, widely used in allogeneic bone marrow transplant. The purpose of this study was to evaluate the effects of mycophenolic acid (MPA), the active metabolite of MMF in vivo, on the maturation and immunologic function of murine bone marrow-derived dendritic cells (DC), and to explore the underlying mechanisms of MMF in graft versus host disease. Cultured DC were treated with MPA at doses of 0.01 and 0.1 micro mol/L. The immunophenotype of DC in control and treated groups was analyzed by flow cytometry. The capability of antigen presentation and the stimulatory activity of the DC on allogeneic T cells were tested by incorporation of (3)H-TdR and mixed lymphocyte reaction respectively. IL-12 production in culture supernatant and the levels of Th1/Th2 cytokines such as IL-2, IFN-gamma, IL-4 and IL-10 in mixed lymphocyte reaction (MLR) supernatant were examined by ELISA assay. The results showed that DCs cultured in the presence of MPA expressed low levels of CD40, CD80 and CD86, and exhibited weak activity in stimulating the proliferation of allogeneic T cells and antigen presenting function with a concurrent reduction of IL-12 production. Allogeneic T cells stimulated by MPA-treated DC expressed higher levels of Th2 cytokines such as IL-4 and IL-10 but lower levels of Th1 cytokines such as IL-2 and IFN-gamma than those stimulated by DC without MPA treatment. It is concluded that MPA, and hence MMF, exerts a negative effect on the maturation and immunologic functions of DC in culture, and drives a shift of Th1 to Th2 cytokines in MLR.