BACKGROUND: A simultaneously transplanted liver shields a bowel graft from immunologic attack in small animals, while the possible immuno-tolerance induced by the liver in liver and small bowel transplantation (LSBT) is uncertain in large animal models. To investigate the clinically suspected beneficial effect of the liver on small bowel allograft, we developed a new model of composite LSBT in the pig. METHODS: Seventy outbred long-white pigs were randomized into four groups. LSBT without immunosuppressive treatment (n=10, group A); LSBT with routine immunosuppressive treatment (n=10, group B); LSBT with a lower dose of immunosuppressive treatment (n=10, group C); and small bowel segment allotransplantation without immunosuppressive treatment (n=10, group D). RESULTS: There was no remarkable difference in survival time between groups A and D (10.33 vs. 12.89 days, P>0.05), but the initial time of acute rejection of the intestinal graft in group A was clearly delayed when compared to group D (8.22 vs. 4.33 days, P<0.05), and the rejection scores in group A were remarkably lower than those in group D at each postoperative time point (0 vs. 0.44 on day 3, P<0.05; 0.22 vs. 1.78 on day 5, P<0.05; 1.11 vs. 2.56 on day 7, P<0.05). There were evident differences in postoperative survival time, initial time of acute rejection and postoperative rejection scores between groups A, B and C. Postoperative survival time (30.00 vs. 28.13 days, P>0.05), initial acute rejection time (25.40 vs. 22.13 days, P>0.05) or rejection score did not differ between groups B and C within one postoperative month. CONCLUSIONS: Compared to isolated segment small bowel allotransplantation, the intestinal graft in LSBT (group A) had a delayed initial time of acute rejection and a lower postoperative acute rejection score, and a lower dose of immunosuppressive treatment led to persistent graft immuno-tolerance in LSBT. Thus the simultaneously transplanted liver graft may reduce the risk of intestinal rejection and protect the bowel graft from sever
