PF4 increases E-selectin surface expression on HUVECs. (A) Contour plots of flow cytometric analysis of HUVECs before (0 hours) and after (2 and 6 hours) PF4 exposure. Data are gated on CD31⁺ cells as described in “Materials and methods.” Data shown are representative of 3 or more independent experiments. (B) Quantitation of E-selectin expression. GMFI indicates the geometric mean of the fluorescence intensity. Data are presented as the mean ± SEM of 3 to 4 independent experiments.