Fulminant second-set allograft rejection and endoscopic findings following small bowel transplantation in the rat.

In the presensitized recipient who has been exposed to donor antigens, second-set rejection takes the form of severe hyperacute graft rejection. Second-set allograft rejection was studied following small bowel transplantation in the rat. Heterotopic intestinal grafting was performed from DA (RT1a) donors to PVG (RT1c) recipients 4 weeks after DA skin sensitization. The endoscopic images and histological specimens were compared with those of syngeneic and first-set rejected grafts. Endoscopically, diffuse erosions of the graft were detected from day 1. Mucosal necrosis progressed rapidly, and was accompanied by massive bleeding on days 3-5. These findings were similar to the course of severe necrotizing hemorrhagic enteritis. Histologically, interstitial edema and hemorrhage with massive infiltrations of neutrophils were manifested from day 1. Mesenteric vessels were completely occluded by thrombi on days 3-5. The grafted intestine had became totally necrotic by day 5. Microscopic findings strongly suggested that destructive graft necrosis was due to vascular damage caused by humoral factors. All the presensitized rats (n = 11) died showing systemic septic signs by day 11 after small bowel transplantation. We conclude that lethal hyperacute rejection occurred in presensitized recipients, even when the graft was transplanted heterotopically. Endoscopic evaluation is beneficial for the early diagnosis of graft rejection. Immediate graft removal should be mandatory as a rescue treatment in second-set rejection of the small intestine.