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In dogs, the rejection of the allotransplanted pancreas was studied using the electron microscope. Eighteen pancreatic grafts were examined 48 hr to 10 days after transplantation without immunosuppresive therapy.


Within 3 days, interstitial edema and large mononuclear cell infiltration were observed, but the pancreatic parenchyma and small vessels showed no clear changes. From the 4th to 5th day, large mononuclear cell and lymphocyte infiltration increased around the vessels and often large mononuclear cells were observed adherent to the acinar cells. At the same time, zymogen granules decreased in number and lipid droplets and autophagosomes appeared in the acinar cells. The islet cells and the endothelial cells of small vessels appeared to be normal. From the 6th to 10th day, a large quantity of electron-dense fiber-like material was found in the interstitial spaces, and plasma cell infiltration had increased. In the small vessels, mitochondrial swelling of the endothelial cells and destruction of cristae, as well as deposits of platelets and thrombus formation in the capillary lumen were observed. In the acinar cells, a decreased number of zymogen granules, fragmentation of the rough endoplasmic reticulum, and enlargement of cisternae with an increment of large autophagosomes were seen. Islet cells showed little change, with some swelling of mitochondria, destruction of cristae, and reduced Golgi complex activity. However, ganglion cells and their fibers were normal.


From these results, it is suggested that in pancreatic grafts, infiltrating immunologically competent cells may have a more important role in rejection than in ischemic changes attributable to vascular damage.

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