Regulation of Id1 expression by cytokines. (A) LSK progenitors from Id1/GFP knockin mice were treated with SCF plus indicated cytokines for 48 hours. (B) Mac-1⁺ or CD19⁺ whole bone marrow cells of Id1/GFP knockin mice were treated with the same cytokines for 24 hours. Histograms of GFP fluorescence in cells treated with indicated cytokines are indicated by solid lines, whereas those in cells treated with SCF alone are indicated by dotted lines. Data are representative of at least 3 independent experiments.