Fig. 3. Angiogenic endothelial cells do not express the 6ß4 integrin in explant cultures. Segments of human saphenous vein were grown as explant cultures in fibrin gels for 14 days. The plus sign indicates the explant tissue, with the outer surface of the original explant tissue outlined with a dotted blue line in A,C,E. (A,B) Cross sections of explant and outgrowth stained with antibodies to vWF, which stained outgrowing endothelial cells as well as endothelial cells remaining in the vasa vasorum and lining the saphenous vein lumen. A higher magnification of a region of outgrowth is shown in B. (C,E) Cross sections stained with 3E1 to ß4 (C) showing no ß4 expression on either the explant saphenous vein or the outgrowing endothelial cells, and 1A4 to smooth muscle actin (E) which stained the original explant, but not outgrowing cells. (D,F) Phase contrast images of C and E, respectively. Arrows indicate the direction of outgrowth. Controls with secondary antibody alone showed insignificant staining similar to the controls for the immunostainings in Fig. 2 (data not shown). Scale bars: (A,C-F) 200 µm; (B) 20 µm.