Myofibroblasts in the periacinar area of the pancreas have been thought to mediate fibrogenesis in pancreatic fibrosis. We elucidated, by immunohistochemical and ultrastructural studies on surgically resected pancreatic tissue, the presence of myofibroblasts in the pancreatic duct wall in normal and various chronically damaged states of the pancreas. a-Smooth muscle actin (a-SMA)-positive cells were detected in the duct wall, but not in the periacinar space, in normal tissue. In cases with focal pancreatitis, which showed focal stenosis of the main pancreatic duct and localized acinar atrophy with scanty inflammatory cell infiltration, proliferation of myofibroblasts was observed in the subepithelial space of the duct wall at the stenotic portion. At the same time, no proliferation of myofibroblasts was detected in the stenotic portion of the main pancreatic duct wall invaded by carcinoma cells. The myofibroblast distribution in pancreatic tissue of patients with ampullary carcinoma was classified into five patterns: (1) no proliferation, same as normal tissue; (2) proliferation only in the duct wall; (3) proliferation in the duct wall and periductal area; (4) proliferation in interlobular and periacinar area in addition to the duct wall, and (5) diffuse proliferation in the parenchyma. In all cases, the distribution of myofibroblasts coincided with the distribution of fibrosis. In bile pancreatitis, fibrosis was localized in both the periductal and interlobular areas, but myofibroblasts were detected only in the periductal area. In cases with chronic alcoholic pancreatitis and alcoholic liver cirrhosis, myofibroblasts proliferated in the area of characteristic interlobular and intralobular fibrosis. Our results suggest that proliferation of myofibroblasts in the duct wall might represent a wound-healing process of the duct wall or serve to prevent elevation of intraductal pressure, while myofibroblast proliferation in the parenchyma might be related to an inflammatory process in the parenchyma.

Copyright © 2007 S. Karger AG, Basel

Majno et al. introduced myofibroblasts as cells with features of both smooth muscle cells and fibroblasts in 1971 [1]. These cells have been shown to be present in normal and pathologic situations of various organs, such as the liver, the kidney, and the heart [2-17]. Several reports have shown that cells with features of myofibroblasts participate in the fibrogenic process of the pancreas parenchyma [18-22]. These cells are termed pancreatic stellate cells, because of their morphological and functional similarity to hepatic stellate cells. We previously showed the existence of myofibroblasts in the pancreatic duct wall in normal and pathologic conditions by immunohistochemical and ultrastructural methods [23, 24].

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