Induction of 4-1BB in T cells by HTLV-1 Tax. (A) Tax expression in JPX-9 (wt Tax) and JPX-9M (inactive Tax mutant) cells was induced by 20 μM CdCl₂. RNA was harvested after 0, 6, 12, 24, and 48 hours, and transcripts of Tax, 4-1BB, and ACTB were detected by RT-PCR. (B) Jurkat cells were transfected with increasing amounts (5, 10, 15, 20, or 30 μg) of Tax expression plasmid or 30 μg of pcDNA3 as control. After 48 hours, Tax, 4-1BB and ACTB transcripts were detected by RT-PCR. (C) The Tax, 4-1BB, and ACTB mRNAs in the samples from panel B were quantified by real-time RT-PCR. Correlation of Tax and 4-1BB mRNA expression was tested using Pearson test.