MARCO expression and actin cytoskeleton organization on untreated, M-CSF–, and GM-CSF–treated microglial cells. (A-F) Nonactivated and (G-L) LPS-activated microglial cells were double stained for filamentous actin (green) and MARCO (red). MARCO-positive, nonactivated, and activated GM-CSF–treated microglial cells are mostly round and slightly adherent; some do not show any phalloidin staining (arrows). Original magnifications: nonactivated microglial cells (A, B, G, H), × 600; all other panels, × 400.