Patient PBMC-derived DCs have morphologic abnormalities and severely reduced F-actin content. DCs were left to adhere to fibronectin-coated glass coverslips for 4 hours and were then fixed in 4% paraformaldehyde. (A) Phase contrast imaging shows poor spreading of patient DCs compared with controls. Scale bar = 20 μm. (B) Quantification of the percent of cells that had spread. (C-D) Cells were stained for DNA (4,6 diamidino-2-phenylindole, blue), F-actin (Alexa Fluor 488 phalloidin, green), and vinculin (red), and images were acquired by confocal microscopy. Podosome structures were clearly present in control cells (F-actin cores surrounded by vinculin in 22 of 29 cells; white arrows) but completely absent in patient cells (0 of 121 cells). Data were acquired in a single experiment. Scale bar = 10 μm. (E) Western blot of MKL1 in THP1 cells expressing SCR (THP1 SCR) and against MKL1 (THP1 MKL1). (F) F-actin content in THP1 SCR and THP1 MKL1 DCs analyzed by flow cytometry. (G) Quantification of the spreading of THP1 SCR and THP1 MKL1 DCs. (H-I) Confocal images of F-actin- and vinculin-stained cells demonstrate the lack of podosomes in THP1 MKL1 DCs. Scale bar = 10 μm. THP1 MKL1 DC data were acquired in 3 independent experiments. **P < 0.01; ***P < .001.