Radiosensitivity of pulmonary alveolar macrophage colony-forming cells

The proliferative state and the radiosensitivity of pulmonary alveolar macrophage colony-forming cells were investigated. The fraction of colony-forming cells in S phase was determined by exposing these cells in vitro to [³H]thymidine with a high specific activity. No appreciable reduction in the number of colony-forming cells was found. It is concluded from these data that only a very small fraction of them are in active cell cycle or they proliferate very slowly, if at all, in vivo. These colony-forming cells were more resistant to γ irradiation than peritoneal exudate macrophage colony-forming cells. The values of D(o) obtained from the in vitro and in vivo irradiation were 200 and 198 rad, respectively. The dose-response curve had a wide shoulder, and the values of D(q) for both mouse and hamster colony-forming cells were 97 and 141 rad, respectively.