Increased angiogenic and spindle cell responses in random ischemic flaps in the absence of endogenous TSP1. Sections from necrotic areas of the excised skin flap in WT (A) and TSP1-null (B) mice are shown. In WT mice the epidermis (E) is necrotic and heavily infiltrated by polymorphonuclear leukocytes (P). A layer of loose granulation tissue (G) is present under the muscular layer (M). The layer of granulation tissue is significantly thicker and more heavily vascularized in the skin flap of the TSP1-null mouse. H + E; original magnification, × 4. Higher magnification of the granulation tissue in the WT (C) and TSP1-null (D) flaps shows more prominent spindle-cell proliferation and capillary formation in the TSP1-null flap. H + E; original magnification, × 20. Immunohistochemical staining with a TSP1 monoclonal antibody of wild-type flaps at 4 hours (E) and 72 hours (F) after surgery was performed. Tissue obtained 4 hours after surgery demonstrated diffuse TSP1 staining of the epidermis, subcutaneous arterioles (arrow), extracellular matrix, striated muscle, and inflammatory cells. At 72 hours after surgery staining was localized to muscle cell borders and extracellular matrix with less staining in other areas. Original magnification, × 20.