Figure 10. Fibrin is deposited at the interface between avascular soft-tissue callus and vascularized hard-tissue callus.

Histological evaluation of the fracture callus of Plg^–/– mice at 14 DPF discloses angiogram contrast–perfused blood vessels (safranin O, yellow arrow) at the interface of the soft-tissue callus (asterisks) and hard-tissue callus (pound symbols). Immunohistochemical staining for CD31 (brown staining) highlights thin-walled blood vessels filled with angiogram contrast material (CD31, yellow arrows) at the interface of soft- and hard-tissue callus. Immunohistochemistry also identifies fibrin (brown staining) at this interface surrounding angiogram contrast–perfused blood vessels (fibrin, yellow arrows). Immunohistochemistry slides were counterstained with hematoxylin. Scale bars: 50 μm (left column); 20 μm (right column). Representative of n = 5.