Effects of anti-Fas MoAbs, CH-11 and ZB4, on IFNγ inhibition of cell growth and erythroid colony formation by day-5 cells. Replicate aliquots of day-5 cells were cultured in liquid medium in the presence of CH-11 (100 ng/mL) and/or ZB4 (500 ng/mL) with or without 50 U/mL rhIFNγ (A). After incubation for 96 hours, the cells were harvested and trypan blue stains were performed. Aliquots of day-5 cells from the same experiment were plated in 0.2-mL plasma clots at 200 cells/well with same concentrations of rhIFNγ and antibodies (B). At day 15, the clots were fixed and stained. (▪) Large colonies, containing more than 500 cells per colony; (▨) medium colonies, containing 50 to 500 cells per colony; (□) small colonies, containing 2 to 49 cells per colony.