Adhesion to PF4 causes cytoskeletal rearrangement in CD34⁺ hematopoietic cells. CD34⁺ cells were let to adhere on immobilized poly-L-lysine (A), the 51-kDa COOH-terminal fragment of fibronectin (B), and PF4 (C). To visualize focal points of adhesion, cells were stained with phalloidin-FITC. Pictures were taken with confocal microscope 1 μm above the surface of the slide. F-actin did not form during adhesion to poly-L-lysine (uniform circumferential staining). In contrast, focal points of adhesion (indicated by coarse punctate staining) were seen in cells adherent to both fibronectin fragment and PF4. Original magnification for all panels, × 400.