Effect of p38 MAPK inhibitor on production of IFN-γ in response to IL-12 and IL-18. (A) PBMCs (50 000 cells per well) obtained from a healthy control subject were incubated in medium containing IL-12 100 U/mL and IL-18 10 ng/mL; a specific inhibitor of p38 MAPK (SB203580) or control reagent (SB202474) were added at the concentrations indicated. Values are mean ± SD of IFN-γ levels in supernatants of duplicate wells as measured by ELISA. The experiment was repeated once with similar results. (B) PBMCs (50 000 cells per well) obtained 3 months after transplantation from 3 patients with lymphoma were incubated with cytokines and 10 μM p38 MAPK inhibitor (▨) or 10 μM control reagent (▪) as indicated. Values are mean ± SE of supernatant IFN-γ levels. The P value for comparison of p38 MAPK inhibitor versus control reagent results is ≤ .025 (*).