Presence of HMGB1 in the developing venous thrombus. (A) Immunofluorescence staining of cross sections of the IVC for HMGB1 (green) and DAPI (blue) 1, 6, 12, and 48 hours after flow reduction. Arrowheads show HMGB1 deposition, dotted line indicates endothelium; bar, 200 µm. (B) Left, Scanning electron microscopy of the IVC 6 hours after flow reduction, showing the intact endothelium covered by cell aggregates and fibrin; bar, 5 µm. Right, Three-dimensional reconstruction of images from intravital 2-photon microscopy showing the vessel wall (second harmonic generation, red), with adherent platelets (yellow) and neutrophils (green); bar, 50 µm. Box, Platelet-myeloid leukocyte aggregates indicated by arrowheads at higher magnification. (A-B) Images representative of n = 3 experiments.