Histological and immunohistochemical evaluations of lobular dissecting hepatitis in American cocker spaniel dogs.

Histological and immunohistochemical evaluations of lobular dissecting hepatitis (LDH) were performed in nine American cocker spaniel dogs. Histological examination showed diffuse fibrosis with weak inflammatory reaction of extensive neutrophils, macrophages, lymphocytes and plasma cells. Immunohistochemical examination revealed that the myofibroblastic cells positive for anti-α-smooth muscle actin and anti-vimentin antibodies produced reticular and collagen fibers and brought about the dissection of hepatic cords and diffuse disappearance of hepatocytes. Reticular fibers invading between hepatocytes and the surrounding small group of hepatocytes were strongly positive for anti-collagen type III and anti-collagen type IV antibodies. The positivity to anti-fibronectin and anti-laminin antibodies was frequently continuous on the basement membrane of the sinusoids of the remaining hepatic cords and between the hepatocytes. Positive findings for anti-E-cadherin antibody were not observed between the hepatocytes showing positive findings for anti-collagen type III and anti-collagen type IV antibodies. These results may explain the expression of fibronectin and laminin that occurs prior to the invasion of reticular fibers between hepatocytes. The present study further suggests that expression of an extracellular matrix mainly containing fibronectin and laminin between the hepatocytes and proliferation of collagen fibers and reticular fibers have a major role in the rupture of the hepatic cords and disappearance of hepatocytes.