IL-13 protein secretion and Tax mRNA levels in HTLV-1-infected and uninfected T-cell lines. (A) T cells were suspended in fresh media at 1 × 10⁶ cells per milliliter and incubated for 24 hours. Culture medium was then collected and IL-13 protein was quantified by ELISA. (B) HTLV-1 Tax mRNA was quantified by TaQman RT-PCR analysis. Tax cDNA copy numbers are expressed as the log₁₀ of the Tax cDNA copy number relative to 1 × 10⁵ copies of GAPDH cDNA. IL-13 protein and Tax mRNA levels are the mean of at least 3 determinations with standard deviations of less than 10% of the mean value.