IL-9 and IL-4 repress TNF-induced NF-κB–dependent transcription. (A) BW5147 cells were transfected with the pGL3-TK-κBPD plasmid and pRL-TK as an internal control and were stimulated with IL-9 (100 U/mL) or TNF (10 ng/mL) or were left unstimulated. In the upper panel, cells were cultured with or without cytokines for 48 hours before luciferase assay. In the middle panel, cells were stimulated only for 8 hours. In the bottom panel, cells were incubated or not incubated with IL-9 for 48 hours, and TNF was added for the last 8 hours before luciferase assay. The results are expressed as arbitrary units of luciferase activity, with 1 U being defined as the luciferase activity in unstimulated cells. (B) BW5147 cells were transfected with pGL3-TK-κBPD plasmid and pRL-TK as an internal control and stimulated with IL-4 (500 U/mL) with or without TNF (10 ng/mL) or were left unstimulated. Luciferase was monitored after 48 hours.