FIG. 3.

Down-modulation of CD81. Human B cells were preincubated for 4, 8, or 12 h at 37°C in the presence of purified anti-CD81 MAb (closed circles) or purified anti-HLA class I MAb as a control (open circles), washed, and incubated for 30 min at 4°C with the same anti-CD81 MAb. Cells were then washed, incubated with a PE-labeled goat anti-mouse serum, and washed again; then MFI determined by flow cytometry. MFI values in the presence of preincubation with anti-HLA MAb (positive control), in the presence of preincubation with anti-CD81 MAb (experimental values), and in the absence of MAb (negative control) were measured, and specific down-modulation of CD81 was determined as [(positive control MFI − experimental MFI)/(positive control MFI − negative control MFI)] × 100.