Inhibition of IL-12–induced tyrosine phosphorylation of JAK2 and Tyk2 kinases by TGF-β. 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 JAK2 (A) and Tyk2 (B) immunoprecipitates were resolved on 7% SDS-PAGE, transferred to nitrocellulose membrane, and probed with anti-phosphotyrosine Ab 4G10 (upper panels). The blots were stripped and reprobed with anti-JAK2 or anti-Tyk2 Abs (lower panels). Similar results were obtained in five separate experiments.