Human Hepatic Stellate Cells Inhibit T-Cell Response Through B7-H1 Pathway

Background. The liver is an immunologic privileged organ; liver allografts are accepted across major histocompatibility complex barriers in many species. However, hepatocyte transplants are acutely rejected, suggesting a role for liver nonparenchymal cells in regulating the immunoresponse. We have shown potent immunoregulatory activity of hepatic stellate cells (HSCs) in mice. The aim of this study was to examine the immunoregulatory activity of human HSCs. Methods. HSCs were isolated from normal human livers for analyses of their impact on T-cell response. Results. HSCs expressed low HLA-DR and costimulatory molecules CD40 and CD80 but constitutively expressed high levels of CD54. Interferon-gamma stimulated HSCs to express B7-H1 in a dose-dependent manner and produce the suppressive cytokines interleukin-6, interleukin-10, and transforming growth factor-beta but did not affect expression of HLA-DR, CD40, and CD80. Human HSCs did not stimulate allogeneic T-cell proliferative response, indicating that they are not professional antigen-presenting cells. HSCs markedly inhibited T-cell response elicited by either allogeneic antigen-presenting cells or CD3/CD28 beads, which was associated with increases in activated CD4 and CD8 T-cell apoptosis. Addition of anti-B7-H1 blocking antibody significantly reversed the inhibitory effect. Conclusions. Human HSCs demonstrate potent immunoregulatory activity via B7-H1-mediated induction of apoptosis in activated T cells. Understanding of the involved mechanisms may lead to development of novel therapeutic approaches for treatment of liver diseases.