Figure 7. Model for changes in airway epithelial progenitor cell behavior post-IR.

Following exposure to ionizing radiation, a dose-dependent decrease in the pool of available progenitor cells occurs (indicated by grey club cells). Therefore, as the lung epithelium undergoes normal turnover, fewer progenitors have the capacity to divide, so that the progenitors that retain proliferate capacity must divide more frequently to maintain the airway epithelium, giving rise to patches. This proliferative response following exposure to radiation could contribute to carcinogenesis.