IFNγ inhibits colony formation and produces apoptosis of erythroid cells. Day-5 cells at 200 cells/well were plated in 0.2-mL plasma clots with or without rhIFNγ. The clots were fixed at day 15 and stained with benzidine-hematoxylin. The size of the colonies was estimated as follows: large colonies, greater than 500 cells/colony; medium colonies, 50 to 500 cells/colony; and small colonies, 2 to 49 cells/colony. The colonies that contained 10% or more cells with the morphologic changes of apoptosis were counted as apoptotic colonies, and the percentage of apoptotic colonies is shown in the top panel.