IL-10 inhibits the induction of IP-10 and ISG54 by IFN and IFNγ. Monocytes were treated with 10 ng/mL of IL-10 for 60 minutes before treatment with the indicated doses of (A) IFN or (B) IFNγ for 90 minutes. RNA was isolated from the cells, and RNAse protection assays were performed. The arrows indicate the protected fragment corresponding to IP-10 and the control gene, GAPDH. IL-10 inhibits IFN-induced expression of ISG54 by (C) IFN or (D) IFNγ. The arrows indicate the protected gene fragment for ISG54 and the control gene, GAPDH. For all RNAse protection assays, the ratio of the values for the IFN-induced gene divided by those for the control (GAPDH) gene was computed, and for cells that had been pretreated with IL-10 followed by IFN. The values were calculated from Phospho-Imager data analysis. The percentage of inhibition was calculated by subtracting the values for cells treated with IL-10 from values for IFN-treated cells and dividing this number by the values for the cells treated with IL-10 and IFN. The values under the gel represent the mean of 2 to 6 experiments ± standard deviation at the various doses.