Fas clusters in KG1a and U937 cell lines.

KG1a cells (A, C) and U937 (B, D) were treated (C, D) or not (A, B) with 0.5 μg/mL Fas-L for 4 hours. After washing, cells were incubated for 2 hours with ZB4 monoclonal antibody and then with FITC-conjugated goat–anti-mouse monoclonal antibody. Confocal analysis was performed as described in “Materials and methods.” Fas aggregation was shown as dense patchy staining (see arrows).