Effect of TGF-β on IL-12–induced IFN-γ production of alloactivated T cells. Alloactivated T cells were incubated at 1.10⁶/mL for 48 hours in medium alone, IL-12 (2 U/10⁶ cells), TGF-β (2.5 ng/10⁶ cells), or IL-12 plus TGF-β. Culture supernatants were then collected and tested for IFN-γ production. Results are presented as mean ± SD of duplicate determinations. IFN-γ maximal production represents the IFN-γ production obtained with IL-12. Similar results were obtained with TGF-β ranging from 1 to 5 ng/10⁶ cells. Equivalent results were obtained in three separate experiments.