Monocyte morphology. Monocytes were cultured with medium and 10% fetal calf serum over slide glass for 5 days at 37°C with 5% CO₂. After that, cells were stained with a PanOptic kit. (A) Monocytes obtained from noninfected donors; (B) monocytes obtained from HTLV-1–infected donors. Original magnification ×40 objective, visualized under inverted phase-contrast microscopy.