HTLV-I Tax did not transactivate IL-9Rα. (A) Schematic representation of IL-9Rα promoter constructs RP1, RP2, and RP3. (B) IL-9Rα promoter assay in HTLV-I–positive Hut102, MT-1, MT-2 cells and HTLV-I–negative Jurkat, CEM cells. The promoter activities were normalized by comparison to the Renilla value. The results are representative of 3 independent experiments. (C) FACS analysis of surface expression of IL-9Rα on HTLV-I-positive Hut102, MT-1, MT-2 cells and HTLV-I–negative Jurkat and CEM cells. PE-conjugated mouse IgG_2b was used as the control.