Morphologic features of rejection in long-surviving canine small bowel transplants.

We studied morphologic features of small bowel transplants in 25 dogs immunosuppressed by cyclosporine, and preoperative graft irradiation. Graft and host bowel were compared with respect to multiple histologic parameters in a blinded analysis. A lymphoplasmacytic infiltrate in nerves and vessels in submucosa and muscle was present in 18 graft bowels and only 3 host bowels, suggesting that these findings represent a cellular rejection reaction. The other histologic parameters were the same in graft and host bowel. Although the dogs did not exhibit clinical signs of rejection, end-stage scarring of the bowel and death occurred in 6 dogs. The animals did not develop systemic graft-verus-host reaction. These findings indicate that under cyclosporine therapy, a subclinical rejection reaction persists deep in the wall and may remain undetectable in mucosal biopsies, but may progress to destroy the graft.