IFN-γ inhibits MKP-1 expression and elongates ERK activity through a Stat-1–dependent mechanism. (A) Quiescent macrophages from wild-type (WT) and Stat-1 knockout mice were treated with M-CSF for the indicated periods of times in the presence or absence of IFN-γ. Activation of ERK-1 and -2 was analyzed by in-gel kinase assay. (B). MKP-1 expression was determined by Northern blotting after 30 minutes of treatment with M-CSF in the presence or absence of IFN-γ. These experiments were done 3 times with equivalent results.