(a) A PMN in patient no. 2 after 10 days of ATRA treatment. The nuclei are irregularly lobulated, with some of them being connected by nuclear filamentous structures, and heterochromatin is condensed along the nuclear membrane. (Original magnification × 13,100.) (b) Higher magnification of a portion of the cell in (a). The cytoplasmic granules are large and spherical, and some of them contain flocculent material and central cores with higher electron density. (Original magnification × 20,200.)