Inhibition of effector functions of IL-17 by IFN-γ is STAT-1-dependent. Mouse embryo fibroblasts (MEF) of wild-type, signal transducer and activator of transcription (STAT)-1-/- and interferon regulatory factor (IRF)-1-/- C57BL/6 mice were grown to confluence and stimulated for 48 hours with IL-17 (20 ng/ml) and TNF-α (20 ng/ml), or were left untreated in the absence or presence of IFN-γ (100 units/ml). (a) 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) and IL-6 mRNA in each sample was normalized to the quantity of 18S RNA. (b) GCP-2 protein present in the supernatants of stimulated MEF was measured by ELISA.(a, b) All cultures were performed in duplicate/triplicate in two independent experiments and the percentage of inhibition was calculated as 100 × (expression in condition without IFN-γ – expression in condition with IFNγ)/expression in condition without IFN-γ). Results represent the mean of five cultures ± standard error of the mean. * P < 0.05 for comparison with corresponding wild-type and, except for IL-6, IRF-1-/- condition and ** P < 0.05 for comparison with corresponding wild-type and STAT-1-/- condition.