TGF-β₁ abrogates Fas-induced growth suppression of Lin⁻ BM progenitors responsive to CSF-1 as well as a combination of multiple cytokines. (A) 3,000 or (B) 1,000 Lin⁻ BM cells were preincubated for 48 hours in IMDM containing 20% FCS, 1.2% methylcellulose and CSF-1 (A), or a “cocktail” of cytokines (CSF-1 + GM-CSF + IL-3 + IL-6 + SCF; B) in the presence or absence of TNF-α and/or TGF-β₁ , as indicated. 0.5 μg/mL Jo2 was added after 48 hours of incubation, as indicated. Colonies were scored after 7 to 9 days of incubation at 37°C and 5% CO₂ in air. An irrelevant hamster IgG had no effect on colony formation. Results represent the mean values of three separate experiments with duplicate determinations; error bars show the SEM.