Expression of major histocompatibility complex antigens and replacement of donor cells by recipient ones in human liver grafts.

The disappearance of certain cell populations of donor origin and their replacement by recipient-specific cells constitutes a possible explanation for the relatively mild course of acute rejection despite lack of MHC compatibility in human orthotopic liver transplantation (OLT). In the present report, graft biopsies of 12 OLT patients from a total of 42 patients were studied for expression of MHC antigens after transplantation using monoclonal antibodies to HLA-ABC and HLA-DR. The patients were selected based upon donor-recipient mismatching for HLA-A2, B7, Drw52, or DQw1. Monoclonal antibodies to these 4 polymorphic HLA antigens and monoclonal antibodies to HLA-ABC and -DR were applied to frozen tissue sections and visualized using an immunoperoxidase technique. Expression of HLA-ABC and -DR on, respectively, hepatocytes and bile duct epithelium were observed in posttransplant graft conditions such as viral infections, cholangitis, and acute rejection. However, no specific pattern of MHC antigen distribution was observed for these various pathological graft conditions. Disappearance of DR-positive Kupffer cells of donor origin and immigration of recipient ones was encountered in the early posttransplant biopsies. This Kupffer cell replacement coincided with a reversible episode of acute rejection. The disappearance of highly immunogenic cellular components as HLA-DR positive Kupffer cells of graft origin may be one of the mechanisms contributing to the mild rejection response observed in human liver transplantation.