LRP is required for PF4 induction of E-selectin in HUVECs. (A) MEF-1 (□) or MEF-2 (▦) cells were incubated in the presence of either PF4 (20 μg/mL) or LPS (100 ng/mL) for 4 hours prior to measurement of luciferase activity as described in Figure 4. Similar experiments were also performed in HUVECs (B). Buffer indicates no PF4 control; α-LRP, anti-LRP antibody; IgG, isotype control. The asterisk indicates statistical significance compared to PF4 alone (P < 0.001). Data are the mean ± SEM of 3 independent experiments performed in triplicate.