Attenuation of IL-12–induced tyrosine phosphorylation of STAT4. Western blot analysis of 6-day alloactivated T cells incubated in medium alone, IL-12 (5 U/10⁶ cells), TGF-β (1 ng/10⁶ cells), or IL-12 + TGF-β at 37°C for 20 minutes. The STAT4 immunoprecipitates were resolved on 10% SDS-PAGE, transferred to nitrocellulose membrane, and blotted sequentially with anti-phosphotyrosine (upper panel) and anti-STAT4 (C-20) Abs (lower panel). Similar results were obtained in six separate experiments.