DCs derived from HTLV-1–infected individuals have a reduced capacity for activation in vitro. 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. After 7 days, CD83, CD86, and HLA-DR expression was analyzed by flow cytometry. Data in bars are expressed as percentage of CD14⁻CD83⁺ cells (A), CD14⁻CD86⁺ cells (B), or CD14⁻HLA-DR⁺ cells (C). Open bars represent cells obtained from noninfected donors (CTR; n = 10), and shaded bars represent cells obtained from HTLV-1–infected donors (n = 12). Data are mean ± SD of 9 independent experiments. * and ** Indicate significantly different from DCs unstimulated with TNF-α (P < .05). (D) Representative experiment showing CD83, CD86, and HLA-DR expression patterns in cells from noninfected and HTLV-1–infected donors (region M2 comprises positive cells).