Fig. 7. Internalized anti-ICAM-1 immunobeads associate with the actin cytoskeleton. (A,b) HUVEC incubated in either the absence (A) or presence (B) of anti-ICAM-1 immunobeads for 15 minutes were fixed and then treated with rhodamine phalloidin to label filamentous actin. Note the stimulation of actin stress fibers by anti-ICAM-1 immunobeads. Bar, 10 µm. (C,D) HUVEC were incubated with anti-ICAM-1 immunobeads for 15 (C) or 30 (D) minutes, fixed, then immunostained to double-label surface-bound material (blue, arrowheads). Arrows denote internalized immunobeads in vesicles associated with stress fibers. Bar, 10 µm.