Fibronectin more than vitronectin inhibits PF4/heparin complex binding to platelets. GFPs were incubated with 25 µg/mL PF4 in the presence of increasing concentrations of UFH and 50 µg/mL fibronectin or buffer (A) or UFH and 10 µg/mL vitronectin or buffer (B). PF4 binding was detected with an FITC-labeled anti-human PF4 antibody using flow cytometry, and antibody binding was quantified by GMFI. PF4 binding in the presence of buffer was defined as 100%. Data are mean ± standard deviation of 3 independent experiments.