A cell kinetic study of the alveolar wall following dust deposition.

The stathmokinetic technique was used to study quantitatively the proliferative response of cells comprising the alveolar wall of inbred mice which had inhaled coal or quartz. The exposures occupied 4 weeks and the observations continued over an extended period thereafter. Control observations suggested that mitotic inhibition was induced solely by residence in the exposure chamber, since cessation of exposure was quickly followed by a temporary rise of proliferative activity. This feature was not apparent when dust was inhaled, though with comparable exposure to both coal and quartz there was an elevation in mitotoic incidence of alveolar wall cells in dust-free areas of lung at a later interval. In dust-laden areas the rise was less in evidence, a situation that persisted throughout the post-exposure survival. The difference in mitotic incidence between dust-free and dust-containing areas was more evident after coal than after quartz inhalation, whilst in higher concentration a quartz aerosol induced a continued depression of mitotic activity. The proliferative response seen in the alveolar walls of control and dusted mice is most likely to be contributed by the interstitial precursors of alveolar macrophages, cells which are recognized to be marrow derived. The changes observed in mitotic incidence are interpreted in terms of demand for alveolar macrophages according to the nature of the dust and the inintensity of the exposure.