Pancreatic Inflammation and Fibrosis

In early pancreatitis, interlobular thin fibrosis and mild intralobular fibrosis are simultaneously observed. Inflammatory cells appear to various degrees in and around the pancreatic lobules. In the intermediate stage, intralobular fibrosis is observed to a much greater extent. It appears particularly as periduc-tular fibrosis and dilatation of the ductules in the centers of the lobules together with inflammatory cells such as neutrophils or lymphocytes, but fewer macrophages. In end-stage pancreatitis, pancreatic parenchymal tissue decreases and fibrosis increases in and around the lobules, or replaces the original tissue, resulting in loss of function.

In the early stage of obstructive pancreatitis, fibrosis is located in the periductal and intralobular areas. In the intermediate to late stages, fibrosis extends into the interlobules and the intralobules resulting in diffuse fibrosis, i.e. severe pancreatitis. In this stage, many myofibroblasts between collagen fibers can be identified by immunohistochemistry, especially underneath the pancreatic ductal epithelial cells, with erosion.

Are myofibroblasts to be found in these stages of pancreatic inflammation? In general, a few myofibroblasts can be found in the periductal areas of pancreatic tissue without inflammation. Normally, pancreatic stellate cells are located in the periacinar areas. Pancreatic acini are connected to the central pancreatic duct system via centroacinar cells and also ductules. Immuno-histochemistry for a-SMA indicates that myofibroblasts are located not only in the periductal areas, but also in the periacinar or perilobular areas where normal myofibroblasts are not usually present. In intermediate obstructive pancreatitis, a few myofibroblasts proliferate between the lobules, showing as thin fibrosis. Myofibroblasts surround the peripheral acini, but are not present in the central acini of the lobules. This suggests that the influence of inflammation is different between the peripheral areas and the central areas in obstructive pancreatitis.

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