Increased number of myeloid progenitor cells generated in ICSBP^−/− mice in response to IL-3 and GM-CSF in vitro. Single-cell suspensions from hematopoietic organs and peripheral blood from either ICSBP^−/− or from wild-type mice were plated in soft agar in the presence of the rmIL-3 (10 ng/mL) and GM-CSF (10 ng/mL). Colonies of more than 50 cells were scored on day 7 postplating. Data shown represent the mean ± standard error of mean (SEM) of colonies counted in 2 independent experiments performed in triplicate with 4 mice per group in each experiment. (A) Bone marrow, spleen, and liver cells at 17 days and 6 weeks of age. (B) Peripheral blood leukocytes of 17-day-old and 6-week-old mice (G-CSF, 100 ng/mL). (C) Fetal liver cells (12.5 dpc).