Effects of granulocyte colony-stimulating factor (G-CSF) on bleomycin-induced lung injury of varying severity

We evaluated the effects of granulocyte colony-stimulating factor (G-CSF) on bleomycin (BLM)-induced lung injury that developed diffuse alveolar damage and subsequent pulmonary fibrosis (PF) of varying severity. G-CSF (100 microg/kg/day) was administered subcutaneously to BLM (0.2, 20, 2,000 microg)-treated or -untreated rats for 3 or 14 days. In the BLM 0.2 microg group, slight alveolar mononuclear cell infiltration was observed, although PF was not noted. In the BLM 20-microg and 2,000-microg groups, diffuse alveolar damage along with neutrophil infiltration and subsequent PF were observed. In the saline + G-CSF group and BLM 0.2 microg + G-CSF group, a marked increase in the number of alkaline phosphatase (ALP)-positive neutrophils was noted in the alveolar capillaries, although there was neither neutrophil infiltration in alveoli nor exacerbation of lung injury. In the BLM 20 microg + G-CSF and BLM 2,000 microg + G-CSF groups, an exacerbation of lung injury along with an increase in the number of ALP-positive neutrophils in the alveoli was observed. These results indicate that the administration of G-CSF to rats with slight lung injury bearing no PF does not exacerbate the lung injury. The exacerbating effects of G-CSF seem to be associated not only with the marked infiltration of activated neutrophils but also with the severity of underlying lung injury.