Subpopulations of Human Lung Alveolar Macrophages: Ultrastructural Features

Lung alveolar macrophages (LAM), obtained by bronchoalveolar lavage of healthy donors, were separated into four subfractions on discontinuous gradients of Percoll and subjected to light micro-scopic, transmission (TEM) and scanning electron microscopic (SEM) studies. Alveolar macrophage morphometric analysis was performed on cytocen-trifuged preparations. TEM of subpopulations revealed considerable morphologic heterogeneity. By SEM, cells of the most dense (D) subtraction were small, round, and, typically, the surface was highly ruffled with small membrane pseudopods. Cells of the least dense subtraction (A) showed a low degree of membrane folding or filopodia and were often totally disorganized.

In smokers, macrophages of fraction A had a greater area and perimeter compared with non-smokers, whereas the inverse relationship was observed for C and D cells. Also, the number of electron-dense inclusions and the level of acid phosphatase were higher in smokers than in non-smokers. Coupled with functional heterogeneity the morphologic differences described in this paper suggest that density-separated subpopulations of LAM may represent different stages of differentiation or maturation.