Immunoblotting of nonphosphorylated (A; upper portion) and phosphorylated p42 MAP kinase (A; lower portion) and nonphosphosporylated (B; upper portion) and phosphorylated Stat3 (B; lower portion) protein in retrovirus-transfected KG1a cells with or without IFN-γ stimulation. Similar results were also obtained when MAP kinase activity in immunoprecipitates (by anti-MAP kinase MoAb) was also measured using MBP as a substrate (not shown).