Treatment with granulocyte colony-stimulating factor aggravates thrombocytopenia in irradiated mice

Ionizing radiation can damage the hematopoietic system, and treatment with cytokines, including granulocytecolony-stimulating factor (G-CSF), is used to enhance hematopoietic recovery. In the present study, mice were whole-body irradiated with a sublethal dose of 5 Gy to produce severe myelosuppression and to evaluate the hematologic consequences of G-CSF treatment following irradiation. G-CSF (100 μg/kg of body weight) was injected immediately after irradiation, and then every three days for 3 weeks. G-CSF significantly ameliorated the decrease in peripheral neutrophils typically observed after exposure to radiation, but it also aggravated the decrease in the number of peripheral platelets during days 3–14 following irradiation. In the histological analysis, while the number of megakaryocytes was significantly decreased in the bone marrow, a number of trapped megakaryocytes were observed in the spleen of G-CSF-treated and irradiated mice. These data suggest that radiation-induced thrombocytopenia is worsened by G-CSF administration, possibly due to a decrease in the number of megakaryocytes in the bone marrow and an increase in the trapping of megakaryocytes in the spleen.