(A) Endocytosis of 1-μm carriers coated with anti-M6PR after incubation for 30 min at 37°C with activated HUVECs, compared to anti-ICAM carriers or control IgG carriers. Phase contrast (top panels) shows total carriers bound and internalized. Fluorescence images (bottom panels) show surface-bound, non-internalized carriers. Arrowheads mark non-internalized carriers and arrows mark endocytosed ones. Scale bar = 10 μm. (B) Low, although specific, internalization of anti-M6PR carriers compared to anti-ICAM carriers and control IgG carriers, quantified as in (A). Mean ± standard error of the mean. *Compared to anti-ICAM carriers; #compared to IgG carriers (p< 0.05).