P-selectin and VWF colocalize in rod-shaped WPBs of ECs and cluster to cell membrane on stimulation. HUVECs were stimulated with solution buffer (DPBS), histamine, or VEGF-A₁₆₅ for 7.5 minutes, fixed, labeled with antisera, and visualized with a Zeiss LSM 510 confocal fluorescent microscope. Shown is the subcellular localization of P-selectin (A,D,G; TRITC staining, colored red), VWF (B,E,H; FITC staining, colored green), and their colocalization in WPBs (C,F,I; colocalized pixels are colored yellow). In DPBS-treated cells, WPBs were distributed homogeneously (A-C), whereas in cells treated with VEGF-A₁₆₅ (D-F) and histamine (G-I), WPBs clustered along the cell membrane (arrows). For control experiments, HUVECs were prepared according to the labeling procedure except that primary antibodies were omitted (not shown). Original magnification: ×630.