Chronic rejection of rat renal allograft. III. Ultrastructure of vascular and glomerular changes.

The main histological features for 'chronic' rejection of rat renal allograft are ongoing perivascular and interstitial inflammation, vascular intimal hyperplasia and glomerular sclerosis. In this communication we have investigated the ultrastructural features of renal parenchyma by comparing chronically rejecting rat renal allografts immunosuppressed initially with cyclosporine to similarly immunosuppressed syngeneic transplants. Electron microscopy confirmed that the primary arterial change was smooth muscle cell proliferation in media, thickening and focal destruction of the internal elastic lamina, and influx of smooth muscle cells and their proliferation in the intima, leading to a nearly complete occlusion of the lumen. In the glomeruli, the most prominent features were mesangial matrix increase, narrowing of capillary lumen, and basement membrane thickening with a double contour appearance in capillary walls. A thin membrane, similar to lamina densa, appeared beneath the endothelium in some segments. Mesangial interposition, formation of new basement membrane and mesangial widening due to increase of basement membrane-like material was nearly always present. As none of these vascular and glomerular changes were observed in similarly immunosuppressed syngeneic transplants, we consider these ultrastructural alterations characteristic for chronic rejection in a rat renal allograft.