Immune Activation in the Liver by Nucleic Acids

Benign course of residual inflammation at end of treatment of liver transplant recipients after sofosbuvir based therapy

BACKGROUND

Persistent inflammation on histology after successful hepatitis C (HCV) treatment has been reported. However, data regarding the long-term impact in liver transplant recipients is limited, particularly after using direct-acting antiviral (DAA) therapies.

AIM

To evaluate the impact of successful treatment with DAAs on histological changes and occult HCV and to describe the clinical course of residual inflammation in liver transplant recipients.

METHODS

We conducted a case series of 13 chronic HCV infected liver transplant recipients successfully treated with DAAs between December 2013 and May 2014. All patients were treated for 24 wk and had non-detectable serum HCV RNA by the time of biopsy. Only patients with at least one liver biopsy at or after treatment were included. We examined liver biopsies for evidence of residual inflammation and the presence of intrahepatic HCV RNA.

RESULTS

Persistent inflammation was seen in 12/13 patients on end of treatment biopsy. Inflammation was still seen in the available five follow-up biopsies (range 38-48 wk after the end of treatment). Intrahepatic HCV RNA was undetectable in all biopsies. All patients had preserved graft function for a mean follow-up of 2.5 years, except one that developed chronic rejection.

CONCLUSION

After successful HCV treatment with DAAs, liver transplant recipients may have persistent inflammation on biopsy without evidence of intracellular RNA. The clinical outcome remained favorable in most patients. Further studies with a larger number and longer follow-up are needed to establish the implication of this finding on long-term graft function.

Hepatitis B Virus-Hepatocyte Interactions and Innate Immune Responses: Experimental Models and Molecular Mechanisms

Chronic hepatitis B virus (HBV) infection is a major cause of liver disease and cancer worldwide. While current therapeutic approaches can efficiently control viral infection, efficient curative antivirals are absent. The understanding of virus-hepatocyte interactions and sensing of viral infection is an important prerequisite for the development of novel antiviral therapies for cure. Hepatocyte intrinsic innate immunity provides a rapid first line of defense to combat viral infection through the upregulation of antiviral and inflammatory genes. However, the functional relevance of many of these antiviral signaling pathways in the liver and their role in HBV pathogenesis is still only partially understood. The recent identification of intracellular RNA and DNA sensing pathways and their involvement in disease biology, including viral pathogenesis and carcinogenesis, is currently transforming our understanding of virus-host interactions. Here the authors review the current knowledge on intrinsic antiviral innate immune responses including the role of viral nucleic acid sensing pathways in the liver. Since HBV has been designated as a "stealth virus," the study of the impact of HBV on signaling pathways in the hepatocyte is of significant interest to understand viral pathogenesis. Characterizing the mechanism underlying these HBV-host interactions and targeting related pathways to enhance antiviral innate responses may open new strategies to trigger noncytopathic clearance of covalently closed circular DNA to ultimately cure patients with chronic HBV infection.

Innate immunity in stem cell-derived hepatocytes

Stem cell-derived hepatocyte-like cells (HLCs) offer great opportunities for studies of host-pathogen interactions and tissue regeneration, as well as hepatotoxicity. To reliably predict the outcome of infection or to enhance graft survival, a finely tuned innate immune system is essential. Hepatocytes have long been considered solely metabolic and their critical innate immune potential is only recently gaining attention. Viral infection studies show that pathogen detection by cytosolic receptors leads to interferon (IFN) induction in primary hepatocytes and HLCs. IFN expression in HLCs is characterized by strong expression of type III IFN and low expression of type I IFN which is also a characteristic of primary hepatocytes. The response to IFN differs in HLCs with lower interferon-stimulated gene (ISG)-expression levels than in primary hepatocytes. Tumour necrosis factor-alpha (TNF-α) signalling is less studied in HLCs, but appears to be functional. Expression of toll-like receptors (TLR) 2-5, 7 and 9 has been reported in primary hepatocytes but has been poorly studied in HLCs. In summary, although they retain some immature features, HLCs are in many ways superior to hepatoma cell lines for cell-based modelling. In this review, we will provide an overview of innate immune signalling in HLCs and how this compares with primary hepatocytes.This article is part of the themed issue 'Designer human tissue: coming to a lab near you'.