Differential identification of mouse granulocyte (CFU-g) and macrophage (CFU-m) precursors in plasma clots

Because benzidine and its derivatives have possible carcinogenic activity, a safe method is needed to demonstrate endogenous peroxidase activity. Colonies derived from mouse bone marrow cells in plasma clot culture were classified as granulocyte (CFU-g) or macrophage (CFU-m) precursors by peroxidase and naphthol AS acetate (NASA) esterase staining, respectively. Endogenous peroxidase activity was measured using benzidine or p-phenylenediazine-pyrocatechol (PPD-PC). The effectiveness of peroxidase staining with both reagents was evaluated under several conditions, and the enzyme property was confirmed by inactivation with a variety of inhibitors. The level of peroxidase activity did not differ significantly between PPD-PC and benzidine. Colony number and number of cultured cells were strongly correlated (P greater than 0.983). We conclude that PPD-PC safely demonstrates peroxidase activity in cultured cells and is as accurate, reliable, and efficient as benzidine.