Isokinetic separation and characterization of mouse pulmonary alveolar colony forming cells

The authors attempted to isolate alveolar macrophage colony-forming cells (AM-CFC) and compare their properties to those of blood mononuclear colony-forming cells (BM-CFC) to determine if the AM-CFC were newly arrived monocytes. Free alveolar cells obtained by airway lavage were separated by velocity sedimentation on a continuous Ficoll gradient. The gradient was collected in 10 8-ml fractions. The AM-CFC were enriched to an average of 42% in the 6 fractions furthest from the center of rotation. These cells were 98% esterase positive, 80 to 90% phagocytic and 60 to 80% positive for Fc receptors. By electron microscopy they were typical large AM with many lysosomal granules. The AM-CFC were markedly depleted to an average 4% in the 4 fractions closest to the center of rotation. By electron microscopy more than 80% of these cells were lymphocyte-like. The BM-CFC peak was in fractions 5 and 6 which consisted of cells smaller than the majority of AM-CFC and difficult to differentiate from lymphocytes by electron microscopy. These results indicate that AM-CFC are a subclass of AM rather than monocytes.