ULTRASTRUCTURAL AND ULTRACYTOCHEMICAL ALTERATION OF RAT NEUTROPHILS INDUCED BY G-CSF

Recombinant human granulocyte colony-stimulating factor (G-CSF) was ad ministered intravenously to rats, and its effects on the neutrophils f rom bone marrow and peripheral blood were examined by electron microsc opy. Immature cells such as the promyelocytes in the bone marrow of th e rats 12 hours after G-CSF administration revealed more irregular nuc lei than those in untreated rats. Forty-eight hours after G-CSF admini stration, these changes became more marked. In the peripheral blood, t he number of cytoplasmic granules was increased 12 hours after adminis tration of G-CSF. The nuclei of mature neutrophils at 48 hours showed hypersegmentation with slight chromatin aggregation. The peroxidase re action observed by electron microscopy revealed an increase in the num ber of positive granules in the immature neutrophils 48 hours after G- CSF administration, and some of the granules tended to be large. Diffe rent from untreated mature granulocytes, a positive peroxidase reactio n was observed in the perinuclear space and rough endoplasmic reticulu m of mature cells in the peripheral blood 48 hours after G-CSF adminis tration. These granules also tended to be large. The present electron microscopic investigations demonstrated alterations of the neutrophils in G-CSF-administered rats, and these cells retained ultracytochemica l evidence of prematurity even at their mature stage.