Steady-state receptor levels and STAT activation in the presence of ligand. (A) Flow cytometric analysis of G-CSF-R levels on 32D.cl8.6 cells expressing wild-type or mutant G-CSF-R either growing on IL-3 (line indicates median FACS signal) or switched to G-CSF for 1 day (dots). Percentages indicate the proportion of G-CSF–stimulated cells with G-CSF-R expression either above or below the median level on IL-3. Similar results were obtained with three independent clones. (B) STAT activation in 32D.cl8.6 cells expressing wild-type or mutant G-CSF-R, either growing on IL-3, washed, or switched to G-CSF for the times indicated, using m67 and β-cas probes. This is a representative of three independent clones.