['Currently, 5-fluorouracil (5-FU) is still one of the widely applied chemotherapeutic agents for tumors. Interleukin-12 (IL-12) can promote the differentiation of Th1 cells and induce the production of interferon-gamma (IFN-gamma) by CD8+ T cells. This study was to investigate the suppression mechanism of 5-FU on the immune response mediated by T cells from normal human peripheral blood, and to determine the effect of IL-12 on the immune suppression induced by 5-FU.', 'The effects of 5-FU on the proliferation of peripheral blood mononuclear cells (PBMCs) and liver cancer cell line HepG2 were examined. PBMCs were stimulated with either anti-CD3 alone or anti-CD3 plus anti-CD28 in the presence or absence of 5-FU at different concentrations (0.20-50.00 microg/ml). The level of IFN-gamma in the culture supernatant was determined by ELISA. PBMCs were pretreated with 5-FU and stimulated with anti-CD3 and anti-CD28 for 2 days. The proportions of CD4+IFN-gamma+, CD8+IFN-gamma+, CD4+IL-2+ and CD8+IL-2+ T cells, and the expression of CD25 on CD4+ and CD8+ T cells were examined by flow cytometry (FCM). PBMCs were cultured in different combinations with anti-CD3 plus anti-CD28, IL-12 and/or 5-FU for 48 h. IFN-gamma level in the supernatant was detected by ELISA. The expression of IFN-gamma on CD4+ and CD8+ T cells were examined by FCM.', '5-FU inhibited the proliferation of HepG2 cells and PBMCs, and suppressed INF-gamma production in PBMCs in a dose-dependent manner. The proportions of immune T cells were lower in 5-FU-pretreated PBMCs than in control PBMCs (0.7% vs. 2.1% for CD4+IFN-gamma+ T cells, 2.2% vs. 3.9% for CD8+IFN-gamma+ T cells, 0.7% vs. 2.5% for CD4+IL-2+ T cells, 0.2% vs. 0.4% for CD8+IL-2+ T cells). Both the positive rate and mean fluorescence intensity (MFI) of CD25 on CD4+ and CD8+ T cells were decreased after pretreatment of 5-FU. When stimulated by anti-CD3 and anti-CD28, the proportions of CD4+IFN-gamma+ and CD8+IFN-gamma+ T cells were 1.1% and 3.2% before adding IL-12, and 1.6% and 4.1% after treatment of IL-12. When stimulated by anti-CD3, anti-CD28, and 5-FU, the proportions of CD4+IFN-gamma+ and CD8+IFN-gamma+ T cells were 0.5% and 1.1% before adding IL-12, and 1.0% and 2.5% after treatment of IL-12.'] Does [ Interleukin-12 restore and promotes the T-cell immune function inhibited by 5-fluorouracil ]?