In vitro effects of mycophenolic acid on cell cycle and activation of human lymphocytes

The immunosuppressant mycophenolic acid (MPA) selectively inhibits prolifer ation of T- and B-lymphocytes by blocking inosine 5'-monophosphate-dehydrog enase (IMPDH), the key enzyme for de-novo-synthesis of guanine nucleotides. In an in vitro study the effects of MPA on human peripheral blood lymphocy te activation markers and on cell cycle characteristics were investigated. Mononuclear cells from healthy volunteers were incubated with phytohaemaggl utinin (PHA) and increasing doses of MPA. After 72 h incubation an aliquot of the cells was stained with propidium iodide and measured by FAGS analyse s to assess the DNA shape, in addition, the expression of the activation ma rkers HLA-DR and CD25 on T- and B-lymphocytes was determined by flow cytome try analysis. PHA stimulation led to a significant increase of the S-phase of cell cycle. PHA stimulation clearly increased mean fluorescence intensity (MFI) of HLA -DR expression on B-lymphocytes. PHA stimulation also elevated the number o f CD25 positive B-lymphocytes. Expression of HLA-DR on T-lymphocytes was no t influenced by PHA, whereas CD25 expression and MFI significantly increase d. All the observed PHA induced effects were reduced by co-incubation with increasing doses of MPA, The data presented show that in vitro the immunosu ppressive effect of MPA can be demonstrated using FAGS technology on a cell ular level. MPA leads to an inhibition of cell cycle proliferation in perip heral blood lymphocytes. (C) 2000 Elsevier Science B.V. All rights reserved .