Suppression of 5-FU and GM-CSF–induced granulopoiesis in STAT5f/f:Mx1-Cre mice. Persistent reduction of peripheral neutrophils in Stat5a/b-mutant mice in homeostasis without compensatory influences over time. (A) Similar peripheral white blood cell and (B) peripheral neutrophil counts of the same Stat5f/f:Mx1-Cre mice (n = 7) 3 weeks and 15 weeks after the last PolyIC injection. (C) Granulopoiesis after 5-FU injection. On injection of 5-FU, peripheral neutrophils from Stat5f/f and Stat5f/f:Mx1-Cre mice were counted every 3 days. Data are mean ± SD; n = 5 mice per group. (D) In vivo administration of G-CSF and GM-CSF. Stat5f/f and Stat5f/f:Mx1-Cre mice were injected subcutaneously with G-CSF or GM-CSF, and peripheral blood was collected daily 6 hours after injection. The ratio of neutrophils in Stat5f/f mice (n = 7) to the neutrophils in Stat5f/f:Mx1-Cre mice (n = 7) is shown. The ratio at day 0 was normalized to 1. *P < .05, **P < .01, fold increase of neutrophils in Stat5f/f versus Stat5f/f:Mx1-Cre mice on cytokine injection.
