Stat6 inhibits transcription driven by the intact IL-4 promoter. pCAT 265, which contains all of the known NFAT P elements including the P2 Stat6 site (solid box), was transfected into unstimulated Jurkat cells together with a control (Empty) or a Stat6 expression vector, and the cells were incubated without (□) or with (▪) IL-4 (50 ng/mL) for 18 hours before assays for reporter gene expression by ELISA. Results are expressed relative to the constitutive activity of pCAT 265 without IL-4 and are the mean ± SEM of four independent experiments. IL-4 significantly downregulated promoter activity only in Stat6-cotransfected cells.