Expression of TEL/PDGFβR dose dependently inhibits IL-3–induced proliferation. XTT bioreduction metabolic assays using 1000 cells/well were set up as described in “Materials and methods.” (A-D) The closed squares represent cells incubated in the presence of 2 μg/mL Tet; the closed diamonds represent cells incubated in the absence of Tet. The mean values with SDs are plotted for each point. In all cases readings obtained in the absence of IL-3 were on average 0.19 to 0.37 absorbance units. The inserts in each panel show the levels of TEL/PDGFβR expression 48 hours after induction. (E) IL-3 dose-response characteristics of constitutive TEL/PDGFβR clone cTP14FI compared with BaF/3 tTA. Errors were plotted but are too small to be visible for cTP14FI. (F) Clone TP2 was cultured with different Tet concentrations or no Tet as indicated and XTT bioreduction assay performed with 2 ng/mL IL-3. The inserted immunoblot demonstrates levels of expression of TEL/PDGFβR in this experiment.