Role of STAT3 in hematopoietic progenitor responses to G-CSF. Wild-type (WT) and STAT3-deficient (KO) mice were injected with G-CSF (250 μg/kg; +) or BSA carrier alone (−), and bone marrow cells were collected 24 hours after treatment. (A) The proportion of LSKs and GMPs was determined by flow cytometry, as indicated. Data are representative of 3 independent experiments. (B) The frequency of LSKs (BSA, ●; G-CSF, ■) and GMPs (BSA, ▲; G-CSF, ▼) within individual mice is indicated for wild-type or STAT3-deficient animals. (C) Absolute numbers of bone marrow LSKs and GMPs in 2 femurs and 2 tibiae were determined by enumeration. (B-C) Average values from 3 independent experiments are shown. Error bars represent SEM (n = 8, WT BSA; n = 4, WT G-CSF; n = 5, KO BSA; n = 3, KO G-CSF). *P < .05 compared with BSA-treated controls. (D) GMPs from WT and STAT3-deficient mice were stained with CFSE, cultured in G-CSF for 3 days, and analyzed by flow cytometry. Data are representative of 3 independent experiments.