Reduced response of hematopoietic progenitor cells from ICSBP^−/− mice to M-CSF. (A) Dose-response curves of bone marrow cells from 6-week-old ICSBP^+/+ (-▪-) and ICSBP^−/− (-○-) mice cultured in the presence of rmM-CSF. Data shown represent mean ± SEM of 1 of 6 independent experiments performed in triplicate with 2 mice per group. (B) Fetal liver cells isolated at day 12.5 postcoitum were cultured in the presence of M-CSF at 10 ng/mL. (C) Reduced number of M-CSFR–expressing cells in ICSBP^−/− bone marrow. Freshly prepared cells from wild-type (left) or ICSBP^−/− (right) bone marrow were stained with antibodies recognizing the murine M-CSF receptor (c-fms) and the macrophage marker F 4/80 and analyzed by flow cytometry as described in Materials and Methods.