Radiosensitivity of macrophage colony-forming cells-implications for their heterogeneity

We compared the radiosensitivity of macrophage (M) colony-forming cell (CFC) in and outside the hemopoietic bone marrow. Murine bone marrow cells (BMC) are stimulated by either macrophage colony-stimulating factor (CSF-1) or murine recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) to form M- and granulocyte- macrophage (GM) colonies on soft agarose medium, whereas both peritoneal exudate cells (PEC) and pulmonary alveolar macrophages (PAM) also have a capacity to make only M- colonies either by rGM-CSF or CSF-1. The clonal growth of peritoneal exudate CFC (PE-CFC) and alveolar macrophage CFC (AL-CFC) was more effectively achieved with rGM-CSF, and their cloning efficiencies were much higher than bone marrow CFC (BM-CFC). Following in vitro exposures to gamma-irradiation (1Gy/min), the dose-survival response of each M-CFC grown by cultures with either rGM-CSF or CSF-1 indicates that the radiosensitivity was the highest in BM-CFC, whereas Al-CFC was more radioresistant than PE-CFC. Surface antigen expression, such as macrophage-specific F4/80, on these CFCs, was invariable before or after irradiation except that it was diminished on irradiated PE-CFC. These results indicate the heterogeneity of tissue M-CFCs in their radiosensitivities as well as in responsiveness to CSFs.