Acute rejection of porcine small bowel allograft. An extended histological scoring system.

Using nonimmunosuppressed piglet small bowel grafts, we performed a detailed histological study on acute rejection and analyzed altogether 45 different histological parameters throughout the bowel wall, in 10 allografts and 6 autografts. Heterotopic grafts were followed by full-thickness biopsies every other day beginning on the 3rd day after transplantation. The parameters were scored from 0 to 3 according to the severity of the change and the values of every variable were compared statistically between the 2 groups. The earliest significant changes, beginning on days 3-5, were infiltration of inflammatory cells and pyroninophilia among these cells in lamina propria; edema, fibrosis, and inflammation in submucosa and muscularis; vacuolar degeneration of myocytes; and endothelial and intimal changes in vessels. Villous blunting and cuboidal epithelium were the other early markers. On day 7, the epithelial and vascular changes became most significant. We want to emphasize especially the vascular parameters: endothelial swelling and proliferation, intimal thickening, intramural inflammation, and obliteration of the lumen. The dilatation of lymph vessels and changes of Peyer's patches had no value in the estimation of rejection. All allografts became necrotic by day 11 after transplantation.