Presence of C7 on the endothelial cells surface. (A) The amount of C7 and C3 secreted by HUVECs grown to confluence was measured by ELISA in the culture supernatant. The presence of C7 and C3 on the cell membrane was evaluated by ELISA on whole cells using biotin-labeled goat antibodies to C7 or C3 (5 μg/mL), followed by AP-labeled streptavidin. (B) FACS analysis of nonpermeabilized HUVECs for surface expression of mC7 using mAbs anti-C7 (black line), anti-C3 (gray line; 10 μg/mL), and irrelevant IgG (dotted line) followed by FITC-labeled goat anti–mouse IgG. (C) TEM analysis of HUVECs incubated with mAb anti-C3 or anti-C7 (both used at 1:50) followed by biotinylated secondary antibodies and gold-labeled streptavidin. Magnification bar represents 200 nm. One of 3 experiments with similar results is shown.