Alveolar macrophage number: an index of the effect of radiation on the lungs

A technique for the absolute quantitation of pulmonary alveolar macrophages in mice is described. The total number of alveolar macrophages falls between 3 and 7 days following x irradiation of the thorax, reaches a minimum at 2 weeks, and returns to control levels over the following 6 to 10 weeks. Evidence is provided that this effect is 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 weeks later decreases exponentially as a function of the dose of X rays. The D0 was 1582 rad. In fractionation experiments the D2 -- D1 decreased to a negative value when separation between fractions was 72 hr. The clinical implications of a reduction in alveolar macrophages following thoracic irradiation, and possible research applications, are discussed