The current view on the origin of pulmonary macrophages.

In the present contribution the current view on the origin of macrophages is briefly summarized. Recent studies on the kinetics of pulmonary macrophages in the normal steady state and during an inflammatory reaction induced by heat-killed BCG applied intravenously or by aerosol are reported in more detail, and the effect of glucocorticosteroids on the kinetics of these cells is described. The results support the general conclusion that pulmonary macrophages derive mainly from circulating monocytes, exclude the existence of an interstitial pool of dividing precursors cells, and provide evidence that the limited local production of pulmonary macrophages is the result of division of mononuclear phagocytes recently derived from the circulation.