Liver allograft rejection in pigs: histology of the graft and role of swine leukocyte antigen-D.

The porcine liver is often considered an immunologically privileged organ as liver allografts in unrelated pigs can survive without any form of immunosuppression. When donor and receptor animals were mismatched for swine leukocyte antigen-D (SLA-D) antigens as tested in mixed-lymphocyte culture (MLC), liver allografts were rejected in all but one of the 14 cases studied. In contrast, from the 10 animals receiving a liver from an MLC-matched donor 8 survived without any significant sign of rejection. The diagnosis of rejection was made by histologic examination of serial needle biopsies of the liver. Based on survival time and histological type of cellular infiltrate an early and a late form of rejection could be distinguished. The early form, with a survival time from 6 to 10 days, was characterized by lymphocytic infiltration of the portal tracts and the liver parenchyma. The late form, with a survival time ranging from 15 to 80 days, showed a lymphocytic and plasma cellular infiltration of the portal tracts. These results show that the outcome of liver allotransplantation in pigs is strongly dependent on SLA-D histocompatibility. It is concluded that porcine liver allografts are under immunological control.