Synergy of IL-17 and TNF-α in the induction of GCP-2, RANKL and IL-6 and inhibition by IFN-γ. (a to d) Mouse embryo fibroblasts (MEF) cells of interferon-γ ligand knock-out (IFN-γ ligand KO) BALB/c mice were grown to confluence and stimulated for 48 hours with IL-17 (20 ng/ml) and/or TNF-α (20 ng/ml), or were left untreated in the absence or presence of IFN-γ (100 units/ml). (a, c, e and f) cDNA samples were prepared and subjected to quantitative PCR analysis. The relative quantity of granulocyte chemotactic protein-2 (GCP-2), receptor activator of nuclear factor-κB ligand (RANKL), IL-6, IP-10 and granulocyte macrophage colony-stimulating factor (GM-CSF) mRNA in each sample was normalized to the quantity of 18S RNA. (b, f) GCP-2, interferon-gamma-induced protein (IP-10) and GM-CSF protein present in the supernatants of stimulated MEF was measured by ELISA. (d) IL-6 protein present in the supernatants was quantified by the Bioplex system. Results represent the mean of two cultures ± standard error of the mean. Results are representative for (a, b) four and (c to f) two independent experiments.