In vivo responses induced by G-CSF in (A) W/W^V mice and littermate controls and (B) Mpl-null mice and littermate controls. Progenitor cell cultures were stimulated with IL-3 alone in (A) and SCM in (B). Mean results at baseline and after G-CSF at 200 μg/kg/d for 5 days; three mice per group in (A) and four mice per group in (B). Error bars represent SD.