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The maturation of dendritic cells (DC) is influenced by various factors, in particular cytokine-mediated signaling events. These include modulation of the activation of nuclear factor kappa B (NF-κB), which controls the transcription of genes encoding major histocompatibility complex (MHC) antigens, and costimulatory/accessory molecules for T-cell activation. Here, we investigated the influence of cyclosporine A (CsA) on the in vitro maturation of DC, and on the nuclear translocation and DNA binding of NF-κB.DC progenitors were propagated from mouse bone marrow in granulocyte-macrophage colony-stimulating factor (GM-CSF) or in GM-CSF plus either transforming growth factor (TGF)-β or interleukin (IL)-4, in the presence or absence of CsA (1 μg/ml). After 5 days of culture, cell surface expression of MHC class I/II, CD40, CD80, and CD86 was analyzed by flow cytometry, and nuclear NF-κB proteins by electrophoretic mobility shift, antibody supershift, and Western blot assays. The antigen-presenting function of DC was determined in one-way mixed leukocyte reactions.Exposure of replicating DC progenitors propagated in GM-CSF or GM-CSF+TGF-β to CsA reduced costimulatory molecule expression, without affecting MHC antigen expression. Nuclear extracts from the CsA-treated DC revealed a decrease in nuclear translocation of NF-κB (p50). Mixed leukocyte reaction data were consistent with the flow cytometry and gel shift assay results, and showed reduced allostimulatory ability of the CsA-treated cells compared with untreated controls. Addition of IL-4 from the start of DC cultures conferred resistance to CsA-induced inhibition of NF-κB nuclear translocation and DC maturation.CsA differentially inhibits the expression of key cell surface costimulatory molecules by in vitro-generated DC. This effect can be overcome, at least in part, by IL-4 and augmented by TGF-β. The inhibition is linked to a decrease in nuclear translocation/DNA binding of NF-κB. Thus, CsA can alter the antigen-presenting function of DC for T-cell activation.