CD1a expression remained down-regulated during DC activation. Cells were incubated with IL-4 plus GM-CSF (50 ng/mL) for 5 days at 37°C in a 5% CO₂ atmosphere. After this period, cells were incubated in the presence or absence of TNF-α for 48 hours at 37°C in a 5% CO₂ atmosphere. Next, CD14 and CD1a expression was analyzed by flow cytometry. Data in bars are expressed as percentage of CD14⁺ cells (A) or CD1a⁺ cells (B). Open bars represent cells obtained from noninfected donors (CTR; n = 8), and shaded bars represent cells obtained from HTLV-1–infected donors (n = 12). Data are mean ± SD of 8 independent experiments. *Significantly different from control (P < .05).