Comparison of the response of SOCS3^ΔSB/ΔSB and SOCS3^ΔVAV/− bone marrow cells to administration of G-CSF in vivo using radiation chimeras. C57BL/6.SJL (Ly5.1) mice reconstituted with SOCS3^+/+, SOCS3^ΔSB/ΔSB, and SOCS3^ΔVAV/− bone marrow cells (4 of each genotype per group) were injected intraperitoneally twice daily with either 2.5 μg/kg G-CSF or saline/BSA vehicle for 4 or 8 days. Mice were killed on days 0, 4, or 8. (A) Peripheral blood neutrophil count. (B) Spleen weight. (C) Peripheral blood colony-forming cells. Peripheral blood (10 μL for G-CSF–treated, 30 μL for vehicle-treated) from all mice was cultured in triplicate in the presence of SCF/IL-3 for 7 days, fixed, and stained, and the number of colonies was counted at × 40 magnification. Results are means (± SD).