RANKL induces vascular hyperpermeability and leukocyte extravasation. (A) An in vitro [³H]sucrose permeability assay was performed as described in “Materials and methods.” Three independent experiments were performed in duplicate. Data are means ± SEs; * *P < .01 versus untreated control. (B) In vivo Miles vascular permeability assay. Various concentrations of RANKL (R) or PBS were injected intradermally into the skin of C57BL/6 mice (n = 7 per group) after intravenous injection of Evans blue. Representative picture (top) and quantity (bottom) of extravasated Evans blue in the mouse skin. Data are means ± SDs; *P < .05 versus PBS. (C) Leukocyte extravasation. Twenty-four hours after RANKL (3 μg) application as described in “Materials and methods,” mice (n = 5 per group) were perfused with the lectin L esculentum to visualize extravasated leukocytes (top). This experiment was performed twice. Leukocytes in the ear sections were immunostained with anti-CD11a antibody (bottom). Arrows indicate extravasated CD11a⁺ leukocytes. (D) Quantitative analysis of extravasated leukocytes. Data are means ± SDs; * *P < .01 versus PBS.