Immunohistochemistry of the hepatic extracellular matrix in acute viral hepatitis

The distribution of several extracellular matrix components in the liver of patients with acute viral hepatitis was studied by light and electron microscopy using indirect immunoperoxidase methods. Light microscopy revealed type III and type V collagen and fibronectin in the portal tracts and the area of focal necrosis, showing cell infiltration. Type III and type V collagen were more strongly stained in the periphery of focal necrosis. Type IV collagen was seen around the vessels and hepatocytes near the focal necrosis. Electron microscopy showed many transitional Ito cells in the area of focal necrosis and fibroblasts were observed in the portal tracts, showing collagen fiber deposition. Numerous collagen fibrils were observed around fibroblasts, Ito cells and hepatocytes. Using immunoelectron microscopy, type III and type IV collagen and fibronectin were observed in the rough endoplasmic reticulum of Ito cells and hepatocytes localized near the area of focal necrosis or fiber deposition. In addition, type IV collagen was seen in the rough endoplasmic reticulum of endothelial cells forming capillary vessels. These results suggest that several extracellular matrix components such as types III, IV and V collagen and fibronectin, produced by Ito cells, hepatocytes or endothelial cells, play important roles in the healing of liver damage in acute viral hepatitis.