Alveolar Macrophage Number: An Index of the Effect of Radiation on the Lungs

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Abstract
A technique for the absolute quantitation of pulmonary alveolar macrophages in mice was described. The total number of alveolar macrophages fell between 3 and 7 days following X-irradiation of the thorax, reached a minimum at 2 wk and returned to control levels over the following 6-10 wk. This effect was due to damage to the population of dividing macrophage precursors in the pulmonary interstitium. In mice given single exposures of X-radiation to the thorax, the number of alveolar macrophages recoverable 2 wk later decreased exponentially as a function of the dose of X-rays. The Do was 1582 rad. In fractionation experiments the D2-D1 decreased to a negative value when separation between fractions was 72 h. The clinical implications of a reduction in alveolar macrophages following thoracic irradiation, and possible research applications, were discussed.