In vitro differentiation of rat peritoneal macrophages into mast cells: an enzymecytochemical study.

Under special culture conditions, rat peritoneal mononuclear phagocytes have previously been shown to transform into typical mast cells, based on their histamine contents, the increase of their membrane IgE-receptors, and the development of metachromatic, electron-dense cytoplasmic granules. In the present investigation, the enzyme-cytochemical characteristics of these cells were examined prior to and during culture. The peritoneal macrophages were found to have strong paranuclear activity of nonspecific esterases and acid hydrolases, while they were negative for peroxidase and chloroacetate esterase. During culture, two main changes in enzyme activity were observed within all the cells: (1) Paranuclear activity was lost in favour of granular enzyme activity throughout the cytoplasm, and (2) chloroacetate esterase appeared in cultured cells and developed a strong granular activity. These findings are consistent with the macrophage nature of the seeded cells and their development into mast cells during culture. They give support to the theory that mast cells originate from the monocyte-macrophage lineage.