Recombinant human granulocyte-macrophage colony-stimulating factor triggers interleukin-10 expression in the monocytic cell line U937.

GM-CSF is a cytokine with pleiotropic biological activities and is increasingly used in clinical trials. The present study demonstrates the ability of recombinant human granulocyte-macrophage colony-stimulating factor (rGM-CSF) to induce elevation of interleukin-10 (IL-10) mRNA and protein production in the monocytic cell line U937. As shown by a semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), IL-10 mRNA increases up to 10 times when stimulated with rGM-CSF (100 U/ml) compared to nonstimulated control cells. Maximal IL-10 mRNA expression occurs at 6 h and remains high for 2 h. Thereafter IL-10 mRNA is downregulated and reaches basal level at approximately 24 h. IL-10 protein was measured by ELISA. The protein yield is dose-dependent on the rGM-CSF concentration. Combined stimulation of U937 cells with both GM-CSF and TNF-alpha results in an additive elevation of the IL-10 protein yield. Application of a neutralising antibody against TNF-alpha revealed that GM-CSF induces IL-10 expression independently from TNF-alpha. By using a luciferase reporter gene it was shown that rGM-CSF enhances IL-10 promoter activity 2-3-fold in a transient transfection assay.