Separation of bronchoalveolar cells from the guinea pig on continuous density gradients of Percoll: morphology and cytochemical properties of fractionated lung macrophages.

Cells recovered by lavage from lungs of normal guinea pigs were centrifuged on continuous density gradients of colloidal silica (Percoll). The gradient was divided into six fractions based on the banding pattern of cells. This pattern was highly reproducible from animal to animal. Cell types in the fractions were identified by morphological and cytochemical criteria and the volume of the cells was determined by measuring their diameter and tritiated water space. More than 70% of the cells put on the gradient were recovered in the six fractions and there was no selective loss of cell types. Macrophages comprised more than 95% of the cells in fractions 3, 4, and 5. These fractions were of intermediate density (1.037-1.078 gm/ml) and together contained more than 85% of the recovered macrophages. Fraction 6 (density 1.078-1.130 gm/ml) was enriched for lymphocytes and granulocytes. Macrophages in fraction 5 were smaller, had more densely staining cytoplasm, and exhibited more nonspecific cytoplasmic esterase activity than macrophages in other fractions (5 greater than 4 greater than 3 greater than 2). These results indicate that density-gradient centrifugation on Percoll is an efficient method for purifying guinea pig alveolar macrophages and demonstrate that macrophages that differ in bouyant density also differ in morphologic and cytochemical properties. In a companion paper we report that macrophages in fractions 3, 4, and 5 differ functionally as well [9].