The effect of two different types of colony-stimulating factor on the expression of aminopeptidase on marrow-derived murine macrophages.

The expression of aminopeptidase, a surface-membrane-bound enzyme, on macrophages formed in liquid cultures of hemopoietic progenitor cells was studied over a period of 20 days. The cultures were stimulated by two biochemically distinct types of colony-stimulating factor (CSF) derived from mouse-lung-conditioned medium (MLCM) and L-cell-conditioned medium (LCCM), respectively. The enzyme content of single cells was determined microphotometrically after staining with Fast Blue B salt and leucine 4-methoxy-2-naphthylamide. In LCCM-stimulated cultures the number of cells expressing aminopeptidase, the enzyme content per cell and the enzyme concentration increased markedly from day 10 onward, while macrophages from MLCM-stimulated cultures only showed borderline yet significantly positive aminopeptidase levels. Maximum enzyme concentrations were found earlier than maximum enzyme content indicating an early local increase in the aminopeptidase concentration on the membrane and subsequently a more uniform distribution over the cell surface. The two types of CSF differ not only in their effect on macrophage production but also in their influence on the expression of the surface enzyme aminopeptidase on these cells.