Protein S blocks basal PMP uptake only in HAECs. Fluorescent PMPs pre-treated with or without 10 μg/ml protein S were incubated for 1 h with HUVECs (A) or HAECs (B). PMP uptake was measured by flow cytometry. The combinatory effect of protein S and Gas6 on PMP uptake was measured by incubating fluorescent PMPs with 10 μg/ml protein S in the presence of increasing amounts of Gas6 before incubating the PMPs with HUVECs (C) or HAECs (D). Fluorescent PMPs were incubated with 250 ng/ml Gas6 and 0 or 1 μg/ml annexin V before feeding them to HUVECs (E). PMPs were incubated with 250 ng/ml Gas6 and increasing amounts of sAxl before uptake was evaluated in HAECs (F) and HUVECs (G). Data show the mean and S.D. of at least three separate experiments except for A and B, which show representative histograms from three individual experiments. ns, not significant; *, p < 0.05; **, p < 0.001; ****, p < 0.0001. MFI, mean fluorescent intensity.