Electron micrographs of bone marrow cells from a myelokathexis patient 2 during granulocyte colony-stimulating factor treatment.

(A) Low-magnification image of bone marrow shows numerous differentiated neutrophils. Magnification ×3750. (B) Mature neutrophils in bone marrow observed at higher magnification appear normal and show negligible evidence of apoptosis. Magnification ×5000. (C) Mature neutrophil shows typical microvillar structures (arrowheads) on the cell surface. Nuclear lobes (N) appear normal and show regular chromatin distribution. Magnification ×7000. (D) Mature neutrophil (bottom) and promyelocyte (top) in the bone marrow. The promyelocyte contains extensive rough endoplasmic reticulum (arrowheads) and electron-dense granules (arrows). N, nucleus. Magnification ×7000.