Ultrastructure of microcirculation in renal grafts in patients with acute or chronic rejections

Using electron microscopy, we studied the renal microcirculation in 31 biopsied specimens from 24 transplants in patients with acute or chronic rejection. Endothelial damage was followed by extensive denudation and platelet attachment, fibrin deposition, focal or whole cytoplasmolysis, rarefaction necrosis of the medial smooth muscle cells, with or without the attachment of inflammatory cells. Medial smooth muscle cells modified by hyperplasia of ergastoplasm, appeared to migrate into the intima and to proliferate there. The endothelium was regenerated with time. Chronic rejection was characterized by "moth-eaten-like" atrophic changes of the medial smooth muscle cells in interlobular arteries with an increase in intercellular spaces with necrotic debris and basement membrane densities. Larger interlobular arteries showed additional mucoid lamellar thickening of the intima, with stenosis. Acute changes in glomerular capillaries included endothelial injury and denudation, thrombotic occlusion and enlargement of subendothelial spaces, apparently due to an increase in permeability. Extensive circumferential mesangial interposition was present in one case of a repeated rejection. Thus, chronicity with various rejections leads to severe luminal narrowing and obstruction in both interlobular arteries and the glomerulus of the grafts.