Flow cytometric analysis of ERK1/2 and p38 MAPK phosphorylation on monocyte subsets. Purified monocytes were precultured with macrophage colony-stimulating factor (M-CSF) for 3 days, and treated with 40 ng/ml receptor activator of NF-κB ligand (RANKL) for 5 min (pink), 10 min (blue) or 20 min (orange), or were left untreated (light green). The cells were then stained either with phospho-ERK1/2 (T202/Y204) or phospho-p38 MAPK (T180/Y182) after fixation and permeabilization. Isotype controls were shown in dotted line. The data shown are representative of three independent experiments.