Platelet-derived Angpt1 prevents neutrophil-induced plasma leakage. (A-C) Angpt1^lox/lox and Angpt1^PltKO mice were injected intraperitoneally with anti–Gr-1 or control IgG antibodies to deplete neutrophils and were stimulated intrascrotally 24 hours later with IL-1β. Four hours later, fluorescent microspheres were injected IV, and cremaster whole mounts were prepared and stained for PECAM-1 and MRP14 5 minutes later. Arrowheads indicate microsphere leakage. Scale bars, 40 µm (left panels), 15 µm (right panels). Microsphere leakage (B) and transmigrated neutrophils (C) per vessel were quantified. (D) Lysates of platelets isolated from Angpt1^lox/lox or Angpt1^PltKO mice were submitted to an Angpt1 enzyme-linked immunosorbent assay (Bosterbio), according to the manufacturer’s instructions, to measure Angpt1 content. Results are representative of 5 (A) or are pooled from 3 (D) or 5 (B-C) independent experiments, with 50 vessels analyzed. Data are mean ± SEM. ***P < .001, 1-way ANOVA. n.s., not significant.