ADAMTS13 protein and mRNA expression in frozen sections of a liver specimen from a patient with hepatitis C–related chronic hepatitis. Immunostaining using ADAMTS13-specific monoclonal antibodies (A10) showed dense brown staining in perisinusoidal cells, but not in hepatocytes, inside the lobule (A). When the same liver section was stained with C7 antibodies, staining patterns were similar to those of A10 antibodies (B). The positive cells had a variety of morphologic forms. Examples shown here include a tripolar cell with long processes extending between hepatocytes (C), combined cells surrounding a hepatocyte (D), a dome-shaped cell (E), a bipolar cell with short processes (F), and a unipolar cell with long processes (G). Panels A-B: original magnification, × 200; panels C-G: original magnification, × 400. ADAMTS13 mRNA expression was examined using in situ hybridization. Strongly positive labeling was seen only in perisinusoidal cells, which were unipolar to dendritic in shape with irregularly elongated cytoplasmic processes extending between hepatocytes (H, arrows; original magnification, × 200). When sense probes were used, we observed no significant staining (I; original magnification, × 200). (Bar = 30 μM in A-I.)