Effect of TGF-β₁ on the Fas-responsiveness of Lin⁻ BM progenitor cells. Two thousand Lin⁻ murine BM cells were plated in IMDM containing 20% FCS, 1.2% methylcellulose, and cytokines at predetermined optimal concentrations as indicated. Cultures were incubated in the absence (▤) or presence of 0.5 μg/mL Jo2 added at initiation of culture (▪) or after 48 hours (▤). Colonies (<50 cells) were scored after 7 to 9 days of incubation at 37°C and 5% CO₂ in air. An irrelevant hamster IgG control antibody had no effect on colony formation (data not shown). Results represent the mean values of three independent experiments with duplicate determinations; error bars show the SEM.