Changes in membrane-bound aminopeptidase on bone marrow-derived macrophages during their maturation in vitro

Myeloid colonies obtained by culturing mouse bone marrow cells with mouse lung conditioned medium were kept for up to 21 days in culture and the aminopeptidase content in single cells measured after staining with leucine 4-methoxy-2-naphthylamide. The enzyme was detectable only in mononuclear and not in granulocytic cells. The number of cells carrying the enzyme and the concentration of the enzyme in the mononuclear cells taken from whole dishes or single colonies increased remarkably but not uniformly from 7 days to maximal values at 13 days of culture, and then decreased again. The timing varied for individual colonies. Maximal enzyme concentrations were found in cells intermediate between the center and the fringe of a colony. However, most cells in a given colony showed concentration increases up to 13 days of culturing. During its life span in culture the mononuclear cell appears to gain aminopeptidase at the cell membrane and lose it again prior to death.