The distribution of cell-surface nucleolin in different tissues. (A) Purified antinucleolin Ab was injected intravenously into mice bearing S180 xenograft tumors or Matrigel plugs. Heart, kidney, liver, lung, spleen with tumors, and Matrigel plugs were removed 6 hours after injection for immunohistochemical assay. Cell-surface nucleolin was visualized by TRITC-secondary antibody against primary injected antibodies (red). The endothelial cells of blood vessels were stained with FITC–anti-CD31 (green), and nuclei were counterstained with DAPI (blue). Antinucleolin Ab specifically accumulated at angiogenic vessels of tumors or Matrigel plugs but did not appear in normal organs. (B) Nonspecific isotype Ab was injected as a control. Bar, 50 μm.