Different function of VAP-1 in endothelial and smooth muscle cells. A: Tissue explants used for the smooth muscle cell adhesion assays. After the endothelial layer was denuded from the luminal aspect (L) of the vein, the tissue was incubated with the primary mAbs 1B2 against VAP-1 and 3G6 as a negative control (1° ex vivo), washed, snap-frozen, sectioned, and subjected to immunoperoxidase reactions with the indicated mAbs (1° on section), and with the second-stage HRP-conjugated rabbit anti-mouse Ig (rαm, 2° on section). Note that the anti-VAP-1 MAb penetrates only about 10 μm from the surface of the specimen (second panel), even though the antigen is present throughout the tissue (fourth panel). B: Binding of PBLs to smooth muscle cells. PBLs were incubated with the de-endothelized vascular explant, the nonadherent cells were removed by 1× gravitation, and the adherent cells (some pointed out by arrows) were fixed to the sections and counterstained. Magnification, ×100. C: VAP-1 mediates PBL binding to HEV but not to smooth muscle cells. The results of the in vitro HEV and smooth muscle (SM) cell binding assays and of the ex vivo vascular explant (vein) assays after mAb blocking of the indicated molecules are presented as mean ± SEM of four or more independent experiments. Analyses were made under rotatory (rot) or static (stat) conditions at +7°C or at room temperature (RT).