Binding of transcription factor activator protein 1(AP-1) is not affected by interleukin-4 (IL-4). Nuclear extracts were isolated from human synovial fibroblast cultures treated for 1hour with 100 ng of IL-1β/ml, 10 ng IL-4/m1, or both IL-1 and IL-4, as well as from control cultures. Binding of 5 μg of nuclear extract to a 32P-labeled oligo(dT) probe corresponding to the AP-1 site in the stromelysin promoter was determined by electrophoretic mobility shift assay. P = probe alone, without nuclear extract, C = control, without interleukin.