Electron micrograph of a peripheral blood neutrophil from a C/EBPɛ−/−mouse (A and B) and a wild-type mouse (C). (A) The C/EBPɛ−/− peripheral blood neutrophil shows signs of immaturity; the absolute number of granules is reduced and tertiary, bacilliform-shaped granules are missing. (B) Higher magnification of middle section of C/EBPɛ−/− neutrophil: The ratio of the larger, primary (electron-dense) granules (arrows) to the smaller less electron-dense, secondary granules is increased. In the less mature C/EBPɛ−/− neutrophils, most secondary granules appear electron-lucent, most likely due to extraction by glutaraldehyde fixation (arrowheads) as previously described.46 (C) For comparison, mature wild-type granulocyte has multiple, small secondary granules (arrows) and bacilliform tertiary granules (arrowhead).