Up-regulation of 4-1BB mRNA in HTLV-1/Tax–positive cells. (A) Transcripts of 4-1BB and β-actin (ACTB) were detected by RT-PCR. Vertical lines have been inserted to indicate a repositioned gel lane. (B) Transcripts of 4-1BB were quantified by real-time RT-PCR. Relative copy number was determined by normalizing the 4-1BB transcripts to those of β-actin. The means of 3 independent experiments plus or minus standard error are shown. (C) Relative copy numbers of 4-1BB mRNA in HTLV-1/Tax–positive cell lines (Tesi, MT-2, C91-PL, HuT-102, StEd, ATL-3, PaBe, JuanaW, Abgho, Eva, Nilu, Xpos) were compared with those of HTLV-1/Tax–negative controls (CCRF-CEM, HuT-78, Tesi + tet, PBMCs) using a 2-tailed Mann-Whitney test. Horizontal bars indicate the median; •, HTLV-1/Tax–positive cell lines; and ▴, the HTLV-1/Tax–negative controls.