G-CSF treatment results in STAT3-dependent alterations in the chemokine profile of the bone marrow microenvironment. WT or STAT3-deficient (KO) mice were injected with G-CSF or left untreated. Total bone marrow cells were isolated after 24 hours, and purified RNA samples were analyzed by real-time PCR for (A) MIP-2 (Cxcl2), (B) KC (Cxcl1), or (C) CXCR2 (Il8rb) expression. Gene expression was determined relative to Rpl13a (n = at least 4). (D) SDF-1α binding assays were performed with purified bone marrow neutrophils from WT or STAT-deficient (KO) mice either by the use of freshly isolated neutrophils (0 hrs, open black histograms) or neutrophils cultured ex vivo in G-CSF for 6 hours (6 hours, open gray histograms). Staining with human-Fc (solid gray histograms) was used as a control. Results are representative of 3 independent experiments. (E) Neutrophils isolated from the bone marrow of WT (□) or KO (■) mice were tested for SDF-1–dependent chemotaxis (n = 4 for each genotype). Average values from 3 independent experiments are shown. (F) WT or STAT-deficient (KO) mice were treated with G-CSF or left untreated. SDF-1 (Cxcl12) mRNA expression was determined in total bone marrow 24 hours after treatment by the use of real-time PCR as in panels A to C (n = at least 4). Error bars represent SEM; *P < .05, **P < .01.