TGF-β inhibits IL-12–induced DNA binding of STAT4-containing complexes. Six-day alloactivated T cells were incubated in medium alone (lanes 1 and 2), IL-12 (5 U/10⁶cells, lanes 3 and 4), TGF-β (1 ng/10⁶ cells, lanes 7 and 8), or IL-12 + TGF-β (lanes 5 and 6) at 37°C for 20 minutes. Nuclear cell extracts were prepared and an EMSA was done using the GRR oligonucleotide probe. Where indicated, antiserum against STAT4 (lanes 2, 4, 6, and 8) was incubated with the cell extracts for 60 minutes before addition of the probe. Similar results were obtained in three separate experiments.