INTERFERON-GAMMA ENHANCES THE LPS-INDUCED G-CSF GENE-EXPRESSION IN HUMAN ADHERENT MONOCYTES, WHICH IS REGULATED AT TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL LEVELS

Human adherent monocytes were studied with regard to the expression of granulocyte colony-stimulating factor (G-CSF) at mRNA and protein levels in response to lipopolysaccharide (LPS) and gamma-interferon (IFN-gamma) stimulation. Monocytes did not express G-CSF transcripts in response to IFN-gamma treatment. In contrast, monocytes exposed to IFN-gamma plus LPS showed a dose-dependent increase in G-CSF mRNA accumulation and protein secretion compared to LPS-stimulated monocytes. The augmented G-CSF mRNA expression in response to IFN-gamma plus LPS was the result of a slight increase in the G-CSF transcription rate (2.2-fold) and a more than 6-fold increase in the G-CSF mRNA half-life (20 minutes vs. > 120 minutes). In addition, it was shown that the effects of IFN-gamma on LPS-induced G-CSF protein secretion could be mimicked by the calcium ionophore A23187, suggesting that the Ca2+-dependent pathway might be triggered after binding of the ligand to the receptor. Finally, it was observed that the potentiating effects of IFN-gamma on LPS-induced G-CSE: secretion could be blocked by interleukin-4 (IL4). These data indicate that two cytokines produced by activated T cells have opposite effects on G-CSF production by human activated monocytes.