SOCS3 is not required for G-CSF–induced expansion or mobilization of immature granulocytes. Wild-type (WT) or myeloid SOCS3-deficient (SOCS3 KO) mice were treated daily with G-CSF (250 μg/kg/d) or BSA-containing buffer for 5 days. Bone marrow (A) or peripheral blood (B) cells were collected 3 hours following the last G-CSF dose. Cells were stained with anti–Gr-1 and anti-CD11b antibodies conjugated to FITC and PE, respectively. Samples were analyzed by flow cytometry, and the percentage of total Gr-1⁺/CD11b⁺ cells (top right quadrant), Gr-1^lo/CD11b⁺ cells (green), and Gr-1^hi/CD11b⁺ cells (blue) is indicated. Results of a representative experiment are shown.