Formation of podosomes by normal immature DCs.

Normal immature DCs plated for 2 hours on fibronectin form podosomes. DCs were stained with TRITC-phalloidin (panels A, D, G) or antivinculin (panel B), antiphosphotyrosine (panel E), or anti–Arp2/3 (panel H) antibodies. Merged images are shown in panels C, F, and I. Under these conditions, the majority of normal DCs adopt a polarized morphology. An abundant f-actin pool is concentrated in punctate condensations at the cell-substratum interface situated just behind the leading edge (arrowheads in panels A, D, G). Rings of vinculin around the actin core confirm that these are podosomes (panel B and insert arrows in panel B). Both tyrosine-phosphorylated proteins (panel E) and the Arp2/3 complex (panel H) colocalize with f-actin in podosomes (panels F, I). Scale bars represent 10 μm.