Tie2-Expressing Monocytes and Tumor Angiogenesis: Regulation by Hypoxia and Angiopoietin-2

TEM recruitment to tumors. A, a human glioblastoma orthotopically injected in the mouse brain shows several TEMs (labeled by green fluorescent protein, green) associated with the tumor blood vessels (red, stained by an anti-CD31 monoclonal antibody). B, a human gastric adenocarcinoma stained with an anti-Tie2 monoclonal antibody. Note the Tie2⁺ blood vessels and the presence of scattered Tie2⁺ mononuclear cells (TEMs, arrows) in the stroma. Section was counterstained by H&E. C, a human colon carcinoma stained with a fluorescent anti-Tie2 monoclonal antibody (red) shows Tie2⁺ blood vessels and scattered Tie2⁺CD14⁺ TEMs (arrows). Green, CD14⁺ monocytes were stained with a FITC-conjugated anti-CD14 monoclonal antibody. Double-positive cells (i.e., TEMs) appear yellow. Bar, 50 μm.