Fractionation of rat alveolar macrophages by isopycnic centrifugation: morphological, cytochemical, biochemical, and functional properties.

Studies on alveolar macrophages have usually been performed on a single cell suspension obtained by lung lavage. However, recent evidence on the diversity of functions of the alveolar macrophage suggests that the macrophage is not a single population, but one composed of several subpopulations of macrophages. One approach toward determining if alveolar macrophages are heterogeneous would be to separate subpopulations based on density. To accomplish this, we developed a continuous gradient of iso-osmotic colloidal silica (Percoll) that separated alveolar macrophages from Fischer 344 rats into 18 density-defined subpopulations. The density-defined alveolar macrophage subpopulations were then characterized and were shown to be significantly different based on morphological, cytochemical, biochemical, and functional analysis. The results of this study suggest that alveolar macrophages are heterogeneous and that a continuous iso-osmotic gradient of colloidal silica is an efficient and reproducible method for separating subpopulations.