Controls in the Study of Lung Cellular Immune Defenses

To the Editor.—The article by Shennib et al¹ contains many points for criticism. The authors concluded that atelectasis caused a dysfunction in alveolar macrophages (AMs) as measured by in vitro phagocytosis. They argued that the reduced phagocytic activity was the result of a decreased percentage of AMs and argued that the recovery of the AM—polymorphonuclear leukocyte (PML) ratio correlated with an improved phagocytic index. It is interesting that in reviewing their data there was a recovery of the AM-PML ratio 24 hours after collapse and repeated lavage, despite a severe fall in the phagocytic index. Shennib et al ignored two plausible explanations for this. First, the rise in the AM-PML ratio at 24 hours in group 1 could merely represent a recovery of AMs during the interval without lavage. Shennib et al argued that in their experience with this species, contrary to data from other species of animals,