Portal versus systemic venous drainage for small-bowel allografts

The effect of portal venous drainage (PV-D) on the survival of accessory small-bowel allografts was studied in a rat model. In the LBN-F1----LEW combination (rejection reaction only), grafts with caval venous drainage (CV-D) were rejected acutely (mean 11.8 days) and those with PV-D were rejected chronically (mean, 22.8 days). In the LEW----LBN-F1 combination, the survival of recipients subject perforce to a fatal graft-versus-host reaction was not influenced by the type of venous drainage used (CV-D: 14.1 days; PV-D: 14.8 days). These findings suggest that the delaying influence of the liver on the rejection process is not due to unspecific filtration of antigens but must involve their specific recognition or alteration. In the BN----LEW combination, in which rejection and the graft-versus-host reaction occur simultaneously, the type of venous drainage used did not influence graft survival (CV-D: 16.2 days; PV-D: 15.5 days), nor did it modify the rejection process. This indicates that the liver has a minor effect on the rejection process, sufficient to inhibit the rejection of semiallogeneic LBN-F1 grafts but insufficient to alter the rejection of allogeneic BN grafts by LEW recipients. With CV-D, LBN-F1 grafts were rejected as rapidly as were BN grafts. This unexpected finding may be explained by the fact that in the LBN-F1----LEW combination only rejection occurs, unimpeded by a graft-versus-host reaction, which is known to impair the immune system of the recipient; in the BN----LEW combination, however, the graft-versus-host reaction temporarily opposes the rejection reaction, thereby allowing prolonged graft survival.