Figure 5. Promoter deletion assay for interleukin-6 (IL-6). Three recombinant plasmids, in which different fragments of the activator protein-1 (AP-1)-binding site on the human IL-6 promoter were deleted, were used. After transfection with each plasmid, fibroblasts were incubated with 10 ng/ml transforming growth factor (TGF)-β1 for 72 h. The luciferase activity was then determined and expressed as the percent of the no-TGF-β1 treatment control. Data represent the mean±SD of results from three independent experiments. The asterisks refer to a significant difference (p<0.001) compared to the wild type.