Trivalent antimonials trigger the reorganization of PML NBs in APL Cells. NB4 cells were subjected to double-immunofluorescence staining with a polyclonal anti-PML antibody and a monoclonal anti–SUMO-1 antibody. Labeling was performed on untreated cells (A through C), cells treated for 36 hours with 1 μmol/L RA (D through F), or cells treated for 10 hours with either 1 μmol/L As₂O₃ (G through I), 1 μmol/L Sb₂O₃ (J through L), or 1 μmol/L Bi₂O₃ (M through O). The staining pattern was analyzed by confocal laser microscopy. The red signal (PML) is obtained with an anti-rabbit Ig Texas red–conjugated secondary antibody, the green signal (SUMO-1) with an anti-mouse Ig fluorescein–conjugated secondary antibody. Superimposing of the two colors (merge) results in a yellow signal, where both proteins colocalize.