Induction of rejection after small-for-size liver transplantation: size matters.

Background: Reduced-size liver transplantation is associated with liver regeneration. This study was designed to analyze the influence of graft size on liver rejection and liver regeneration.
Methods: Reduced-size liver transplantations were performed in the rejecting ACI to Lewis and the graft acceptance BN to Lewis strain combination. The BN to Lewis control group was treated with the immunosuppressive drug FK506.
Results: An accelerated liver rejection in the ACI to Lewis strain combination was found in small-for-size partial liver grafts. Graft weight to recipient liver weight ratio (GW/RLW) showed a positive correlation with survival time. In the BN to Lewis strain combination, lethal rejection was seen in small-for-size partial liver grafts. A critical immunologic GW/RLW of 33% was calculated. In rats dying from lethal rejection, GW/RLW and survival time showed a positive correlation. However, GW/RLW showed a negative correlation with hepatocellular proliferation. In regenerating livers, MHC II upregulation was also observed in the control group. All control animals survived small-for-size liver transplantation.
Conclusions: The relative graft size seems to be a decisive factor influencing the kinetic of liver rejection and the induction of liver rejection. Relative critical immunologic liver mass was determined to be 33%.