Cytokine-induced tyrosine phosphorylation of Stat proteins. (A) Western blot analysis with an antiphosphotyrosine Stat4-specific antibody and control on extracts from cultured NK cells. (B) Western blot analysis with an antiphosphotyrosine Stat5-specific antibody and control on extracts from cultured NK cells. (C) Densitometric analysis of panel A. (D) Densitometiric analysis of panel B. The data are representative of 2 separate experiments.