Effects of irradiation on macrophagic response and transport of particles across the alveolar epithelium.

Macrophagic production and particulate penetration into the lung were studied in mice depleted of monocytes by whole body irradiation. Subsequent intratracheal instillation of 4 mg carbon resulted in a much smaller adaptive increase in the number of alveolar macrophages, as compared with nonirradiated animals. The decreased macrophagic output was associated with increased passage of free carbon across the Type 1 alveolar epithelium in increased accumulation of carbon in interstitial macrophages and hilar lymph nodes of irradiated mice. The results suggest that interference with the adaptive outpouring of alveolar macrophages following a particulate load facilitates the interaction of particles with macrophages within the pulmonary interstitium, where fibrogenic factors released in response to toxic agents would have a maximum effect.