TTP-like pathohistologic changes in rhVWF-challenged animals. (A) The presence of large aggregates of platelets (arrowheads) within the left ventricle 30 minutes after TTP induction (H&E, original magnification ×100). Bar represents 200 μm. (B) Myocardial necrosis and hemorrhage (arrowheads) as well as rolling and extravasation of neutrophilic granulocytes (arrows) within the first 3 hours of TTP induction (H&E, original magnification ×400). Bar represents 50 μm. (C) Vacuolation of myocytes (arrow) and perivascular infiltration of neutrophilic granulocytes (arrowheads) within 24 hours after TTP induction (H&E, original magnification ×200). Bar represents 100 μm. (D) Renal tubular necrosis (arrowheads) characterized by loss of cellular detail, increased eosinophilia of cytoplasm, and karyopyknosis within 24 hours after TTP induction (H&E, original magnification ×400). Bar represents 50 μm. (E) Myocardial artery (arrows) immunohistochemically strongly positive for VWF 60 minutes after TTP induction (VWF immunohistochemistry, original magnification ×600). Bar represents 33 μm. (F) Myocardial artery (arrows) of an untreated control animal with minor background staining for VWF resulting from cross-reactivity of the antibody with endogenous murine VWF (VWF immunohistochemistry, original magnification ×200). Bar represents 100 μm.