IMMUNOMODULATION OF VASCULAR ENDOTHELIUM - INDUCTION OF LA ANTIGEN EXPRESSION IN REJECTING VENOUS ALLOGRAFTS

MHC class II antigens (Ia) are important to the primary transplantation response. The present study investigates the kinetics of expression of Ia antigens on endothelial cells of rat vein autografts and allografts. The superficial epigastric veins of 15 ACI rats were anastomosed to the femoral artery of Lewis recipients using standard microsurgical technique. Eighteen Lewis-to-Lewis or ACI-to-ACI autografts served as controls. Veins were studied for Ia expression at 1, 4, and 7 days after grafting using the immunogold electron microscopic technique. All grafts remained patent for the duration of the experiment. Endothelial cells from control grafts did not demonstrate labeling of Ia antigens on their cell surfaces. Similarly, few mononuclear-adventitial cells in control grafts were Ia positive. When endothelial cells from vein allografts were studies for Ia antigen expression, 40% of the endothelial cells showed labeling for Ia at 4 days after transplantation. At 1 week following grafting, endothelial survival was inadequate for study because of cell loss secondary to rejection. In comparison to autografts, rejecting vein allografts showed numerous Ia-positive mononuclear cells permeating the vessel adventitia. Expression of Ia antigens by vascular endothelium may enable these cells to perform tasks traditionally ascribed to monocytes or dendritic cells. Effort to alter Ia expression may suggest an approach to long-term vein allograft survival.