Prominent HLA-G expression in liver disease but not after liver transplantation

Abstract

Background.HLA-G is a nonclassical MHC class I molecule and its physiological expression restricted to placental extravillous trophoblasts contributes to maternal tolerance to the semiallogeneic fetus. Aberrant expression of HLA-G in human organ grafts has been proposed to contribute to graft acceptance.Methods. We studied HLA-G expression in liver tissue and serum of adult liver transplant recipients before, early, and late after transplantation in relation to liver function and operational tolerance. Results. Cirrhotic explant livers showed robust HLA-G expression on hepatocytes, whereas the majority of noncirrhotic livers and graft biopsies taken before or after liver transplantation (LTX) showed no, or weak, HLA-G expression. The HLA-G expression was induced on hepatocytes in vitro by TGF-β, but not by other relevant cytokines. Serum levels of the HLA-G isoforms 1 + 5 gradually declined after LTX. Early after LTX, serum HLA-G levels were higher in patients with acute rejection episodes than nonrejectors. Late after LTX, serumHLA-G levels did not differ between operationally tolerant patients and patients on regular immunosuppressive therapy. Conclusions. Our data do not support a graft-protective role for HLA-G after LTX, but show that end-stage liver diseases are associated with HLA-G expression on hepatocytes, which may determine a negative feedback to protect the liver against immunological damage.