PD-L1 is induced in hepatocytes by viral infection and by interferon-α and -γ and mediates T cell apoptosis

doi:10.1016/j.jhep.2006.05.007

Journal of Hepatology

Volume 45, Issue 4, October 2006, Pages 520-528

https://doi.org/10.1016/j.jhep.2006.05.007 Get rights and content

Background/Aims

B7-H1 (PD-L1) is a B7-family member that binds to programmed death-1 (PD-1). Recently, deficiency of PD-L1 has been demonstrated to result in accelerated hepatocyte damage in experimental autoimmune hepatitis, and PD-L1 was suggested to play a critical role in regulating T cell homeostasis. Absence of PD-1 enhanced proliferation of T cells in adenovirus-infected livers and resulted in a rapid clearance of the virus. Here, we aimed to get more insight into hepatic PD-L1 expression, regulation and function.

Methods

PD-L1 expression was analyzed by quantitative PCR and FACS-analysis in primary human liver cells and hepatoma cells. Furthermore, coculture experiments with primary human T cells or Jurkat T cells were established.

Results

In addition to nonparenchymal liver cells, also hepatocytes constitutively expressed low levels of PD-L1. PD-L1 expression in hepatocytes was strongly enhanced by activated T cells and viral infection, and markedly augmented by further stimulation with type I or type II interferons. Moreover, PD-L1 expression on hepatocytes induced apoptosis in T cells.

Conclusions

Our results suggest a novel bidirectional interaction between hepatocytes and lymphocytes modulated by PD-L1 expression in hepatocytes, which may contribute to the unique immunological properties of the liver.

Introduction

The liver is constantly exposed to bacterial products and food-derived antigens. These antigens and microbiologically derived molecules provide a unique hepatic microenvironment and require unique immunological properties of the liver which often induces peripheral tolerance rather than immunity [1], [2]. Hepatic tolerance may also contribute to the common ineffectiveness of immune responses against hepatitis viruses such as HBV and HCV which often results in chronic persistence of viral infection [3]. The molecular mechanisms underlying these observations have not yet been elucidated. However, it has been hypothesized that there are unusual interactions within the hepatic milieu and immune cells [1].

B7-like molecules and their cognate receptors constitute important costimulatory pathways that control and fine-tune immune responses. In recent years, an array of new members of the B7 family have been identified, including B7-H1 (PD-L1) and B7-DC (PD-L2) [3]. Both are ligands for programmed death-1 (PD-1), which is expressed on activated T and B cells [4], [5], [6]. PD-L1 has been described to be inducibly expressed in a variety of organs [3], [7], [8], [9], [10], [11], [12], [13]. An overwhelming number of studies supported the role of PD-L1 as a negative regulator of T cell responses and suggest that PD-L1 promotes peripheral tolerance [14].

Recently, hepatic accumulation and impaired apoptosis in CD8+ T cells have been observed in experimental autoimmune hepatitis in PD-L1-deficient mice leading to accelerated hepatocyte damage [15]. Similarly, adenoviral infection of PD-1-deficient mice resulted in increased proliferation of effector T cells in the liver and more rapid clearance of the virus compared to wild-type mice, leading to a more severe but more transient hepatitis [16].

Hepatic PD-L1 expression was reported recently in murine non-parenchymal liver cells [16], [17]. Here, we analyzed PD-L1 expression in human liver cells. We report that – in addition to non-parenchymal liver cells – also hepatocytes constitutively express PD-L1 and provide data suggesting a novel bidirectional interaction between hepatocytes and lymphocytes modulated by PD-L1 expression in hepatocytes.

Section snippets

Cell isolation and cell culture

Isolation and culture of hepatocytes and non-parenchymal liver cells were performed as described [18], [19].

HepG2 and PLC cells were purchased from the American Type Culture Collection (Rockville, MD). HepG2.2.15 cells with integrated full-length HBV genome were kindly provided by Dr. Jilg (Institute of Medical Microbiology and Hygiene, University of Regensburg). For some experiments, cells were stimulated with recombinant IFN-α2a (R&D Systems, Wiesbaden, Germany) or IFN-γ (Sigma, Deisenhofen,

PD-L1 expression in primary liver cells

Initially, we analyzed PD-L1 mRNA expression in fractionally isolated human liver cells. In accordance with previous studies analyzing murine liver cells [16], [17] we detected PD-L1 mRNA expression in Kupffer cells and endothelial cells. Further, a faint band was also visible in freshly isolated hepatic stellate cells (HSC) while a strong band was found in HSC activated in vitro. In addition, PD-L1 mRNA expression was clearly detectable in primary human hepatocytes (PHH) (Fig. 1A).

Accordingly,

Discussion

We demonstrated for the first time that hepatocytes constitutively express low levels of PD-L1, while its expression is strongly enhanced by activated T cells and viral infection, and markedly augmented by further stimulation with type I or type II interferons. Moreover, PD-L1 expression on hepatocytes induces apoptosis in T cells.

The detection of constitutive PD-L1 expression in human hepatocytes in addition to non-parenchymal liver cells is novel and surprising, since a recent study analyzing

Acknowledgements

We are indebted to Dr. Wolfgang Jilg (Institute of Medical Microbiology and Hygiene, University of Regensburg, Germany) for providing HepG2.2.15 and to Gertrud Lallinger and Dagmar Halbritter for excellent technical assistance. This work was supported by grants from the Else-Kröner Fresenius Stiftung to C.H., Deutsche Krebshilfe to C.B., and Wilhelm Sander-Stiftung to M.F.

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^♯: Both authors contributed equally to this work.

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PD-L1 is induced in hepatocytes by viral infection and by interferon-α and -γ and mediates T cell apoptosis

Background/Aims

Methods

Results

Conclusions

Introduction

Section snippets

Cell isolation and cell culture

PD-L1 expression in primary liver cells

Discussion

Acknowledgements

Local control of the immune response in the liver

Immunol Rev

Neighborhood politics: the immunoregulatory function of organ-resident liver endothelial cells

Trends Immunol

Fas ligand-induced apoptosis as a mechanism of immune privilege

Science

B7-H1, a third member of the B7 family, co-stimulates T-cell proliferation and interleukin-10 secretion

Nat Med

Engagement of the PD-1 immunoinhibitory receptor by a novel B7 family member leads to negative regulation of lymphocyte activation

J Exp Med

PD-L2 is a second ligand for PD-1 and inhibits T cell activation

Nat Immunol

Induction of tolerance to autoimmune diabetes with islet antigens

J Exp Med

The expression of B7-H1 on keratinocytes in chronic inflammatory mucocutaneous disease and its regulatory role

Immunol Lett

Probing the mechanism of TNF-alpha(cachectin)- and TNF-beta(lymphotoxin)-induced pancreatic inflammation with transgenic mice

Res Immunol

Costimulator B7-1 confers antigen-presenting-cell function to parenchymal tissue and in conjunction with tumor necrosis factor alpha leads to autoimmunity in transgenic mice

Proc Natl Acad Sci USA

Differential induction of adhesion molecule and chemokine expression by LTalpha3 and LTalphabeta in inflammation elucidates potential mechanisms of mesenteric and peripheral lymph node development

J Immunol

BLC expression in pancreatic islets causes B cell recruitment and lymphotoxin-dependent lymphoid neogenesis

Immunity

Accessory cell function of airway epithelial cells

Am J Physiol Lung Cell Mol Physiol

The balance of immune responses: costimulation verse coinhibition

J Mol Med

B7-H1 determines accumulation and deletion of intrahepatic CD8(+) T lymphocytes

Immunity

PD-1 inhibits antiviral immunity at the effector phase in the liver

J Exp Med

Inhibition of T-cell responses by hepatic stellate cells via B7-H1-mediated T-cell apoptosis in mice

Hepatology

Expression of intracellular adhesion molecule 1 by activated hepatic stellate cells

Hepatology

Activated hepatic stellate cells express keratinocyte growth factor in chronic liver disease

Am J Pathol

Mature but not immature Fas ligand (CD95L)-transduced human monocyte-derived dendritic cells are protected from Fas-mediated apoptosis and can be used as killer APC

J Immunol

Blockade of programmed death-1 ligands on dendritic cells enhances T cell activation and cytokine production

J Immunol

Program death-1 engagement upon TCR activation has distinct effects on costimulation and cytokine-driven proliferation: attenuation of ICOS, IL-4, and IL-21, but not CD28, IL-7, and IL-15 responses

J Immunol

B7-H1 is expressed by human endothelial cells and suppresses T cell cytokine synthesis

J Immunol