Macrophages form podosomes. (a) A human monocyte-derived macrophage, grown on a fibronectin coated coverslip in RPMI, 10% FCS, and 120 ng/ml of recombinant CSF-1, was fixed and stained for F-actin (red) and pY118 paxillin (green). Inset in the merge panel demonstrates the central F-actin-rich stud and the surrounding pY118 paxillin collar. (b) Cytoskeletal TEM preparation of a human monocyte-derived macrophage, grown on a glass coverslip, demonstrating many podosomes at the presumed leading edge. The arrow highlights a good example of a podosome containing a central dense actin column surrounded by radially orientated actin filament spokes. (c) Mouse bone marrow-derived macrophages were plated on Alexa-488 labeled fibronectin overlaying gelatin for 24 hours prior to fixation, staining for F-actin (red) and examination by confocal microscopy to demonstrate a podosomal rosette digesting the underlying matrix.
