Innate Immunity in Hepatitis C Virus Infection.

Activation and viral control of the innate immune response are hallmarks of hepatitis C virus (HCV) infection and are major determinants of spontaneous clearance or progression to chronic infection and liver disease. In this review, we provide a contemporary overview of how HCV is sensed by the host cell to trigger innate immune activation and the mechanisms deployed by the virus to evade this response. Type I and III interferons (IFNs) are crucial mediators of antiviral innate immunity against HCV, and we specifically highlight the importance of IFN-λ host genetics for the outcome of HCV infection. Last, we focus on the proinflammatory responses elicited by HCV infection and describe our current understanding of how interleukin (IL)-1ß signaling and cross talk between the IL-1ß and IFN signaling pathways lead to sustained inflammation and increased risk of liver pathology.

Modulation of calcium signaling pathway by hepatitis C virus core protein stimulates NLRP3 inflammasome activation.

Hepatitis C virus (HCV) infection remains a major cause of hepatic inflammation and liver disease. HCV triggers NLRP3 inflammasome activation and interleukin-1ß (IL-1ß) production from hepatic macrophages, or Kupffer cells, to drive the hepatic inflammatory response. Here we examined HCV activation of the NLRP3 inflammasome signaling cascade in primary human monocyte derived macrophages and THP-1 cell models of hepatic macrophages to define the HCV-specific agonist and cellular processes of inflammasome activation. We identified the HCV core protein as a virion-specific factor of inflammasome activation. The core protein was both necessary and sufficient for IL-1ß production from macrophages exposed to HCV or soluble core protein alone. NLRP3 inflammasome activation by the HCV core protein required calcium mobilization linked with phospholipase-C activation. Our findings reveal a molecular basis of hepatic inflammasome activation and IL-1ß release triggered by HCV core protein.

Hepatitis regulation by the inflammasome signaling pathway.

Hepatitis is damage and inflammation of the liver. It is triggered by both environmental and endogenous insults and is a platform for developing liver cirrhosis and cancer. Both innate and adaptive immune activation contribute to hepatic inflammation and disease. Viral hepatitis is the most common form of hepatitis and is typically associated with chronic viral infection. Alcohol-induced and non-alcoholic steatohepatitis are two rising hepatic problems. The innate immune inflammasome signaling cascade mediates the production of essential proinflammatory cytokines interleukin-1ß (IL-1ß) and IL-18. These cytokines regulate hepatic cell interaction and crosstalk of the various inflammatory pathways and influence disease outcome.

IL-1ß production through the NLRP3 inflammasome by hepatic macrophages links hepatitis C virus infection with liver inflammation and disease.

Chronic hepatitis C virus (HCV) infection is a leading cause of liver disease. Liver inflammation underlies infection-induced fibrosis, cirrhosis and liver cancer but the processes that promote hepatic inflammation by HCV are not defined. We provide a systems biology analysis with multiple lines of evidence to indicate that interleukin-1ß (IL-1ß) production by intrahepatic macrophages confers liver inflammation through HCV-induced inflammasome signaling. Chronic hepatitis C patients exhibited elevated levels of serum IL-1ß compared to healthy controls. Immunohistochemical analysis of healthy control and chronic hepatitis C liver sections revealed that Kupffer cells, resident hepatic macrophages, are the primary cellular source of hepatic IL-1ß during HCV infection. Accordingly, we found that both blood monocyte-derived primary human macrophages, and Kupffer cells recovered from normal donor liver, produce IL-1ß after HCV exposure. Using the THP-1 macrophage cell-culture model, we found that HCV drives a rapid but transient caspase-1 activation to stimulate IL-1ß secretion. HCV can enter macrophages through non-CD81 mediated phagocytic uptake that is independent of productive infection. Viral RNA triggers MyD88-mediated TLR7 signaling to induce IL-1ß mRNA expression. HCV uptake concomitantly induces a potassium efflux that activates the NLRP3 inflammasome for IL-1ß processing and secretion. RNA sequencing analysis comparing THP1 cells and chronic hepatitis C patient liver demonstrates that viral engagement of the NLRP3 inflammasome stimulates IL-1ß production to drive proinflammatory cytokine, chemokine, and immune-regulatory gene expression networks linked with HCV disease severity. These studies identify intrahepatic IL-1ß production as a central feature of liver inflammation during HCV infection. Thus, strategies to suppress NLRP3 or IL-1ß activity could offer therapeutic actions to reduce hepatic inflammation and mitigate disease.

Innate immune tolerance and the role of kupffer cells in differential responses to interferon therapy among patients with HCV genotype 1 infection.

BACKGROUND & AIMS: In patients with hepatitis C virus (HCV) infection, interferon alfa (IFN-α) alters expression of IFN-stimulated genes (ISGs), but little is understood about factors that determine outcomes of therapy. We used a systems biology approach to evaluate the acute response of patients with chronic hepatitis C to IFN-α therapy. METHODS: We collected liver biopsy samples from 8 treatment-naïve patients with chronic HCV genotype 1 infection at baseline and 24 hours after treatment with IFN-α-2a (10 MU subcutaneously). Blood samples were collected before and up to 48 hours after administration of IFN-α-2a to measure HCV RNA levels and for gene expression analysis. Patients then received pegylated IFN-α-2a and ribavirin on day 5 of the study; therapy continued for up to 48 weeks. RESULTS: Based on the kinetics of HCV RNA during the first 12 weeks of therapy, 2 patients were rapid virologic responders, 4 were early virologic responders, and 2 did not respond to therapy (nonresponders). Nonresponders had high pretreatment levels of ISG expression in the liver but not in peripheral blood mononuclear cells. In responders, after administration of IFN-α, intrahepatic ISG expression increased significantly from baseline and was associated with a rapid phase 1 decrease in HCV. We identified distinct hepatic expression and tissue distribution patterns of ISGs that segregated with treatment outcome. Importantly, Kupffer cells were a local source of IFN that promoted basal expression of ISG in hepatocytes of nonresponders. This finding was validated in cultured THP1 human macrophages that expressed IFN-ß after exposure to viable HCV 2a. When Huh7 K2040 and Huh7 L2198S hepatoma cells were incubated with IFN-α-2a, expression of ISGs peaked by 4 hours and decreased by 72 hours, associated with an increase in level of HCV RNA. This indicates that constitutive exposure to IFN causes hepatoma cells to become tolerant of ISG function. CONCLUSIONS: In patients with chronic HCV infection, IFN production by Kupffer cells might promote innate immune tolerance, characterized by a lack of response to IFN therapy. Strategies to disrupt the virus-host interactions that induce innate immune tolerance should improve therapy.

IL-1ß signaling promotes CNS-intrinsic immune control of West Nile virus infection.

West Nile virus (WNV) is an emerging flavivirus capable of infecting the central nervous system (CNS) and mediating neuronal cell death and tissue destruction. The processes that promote inflammation and encephalitis within the CNS are important for control of WNV disease but, how inflammatory signaling pathways operate to control CNS infection is not defined. Here, we identify IL-1ß signaling and the NLRP3 inflammasome as key host restriction factors involved in viral control and CNS disease associated with WNV infection. Individuals presenting with acute WNV infection displayed elevated levels of IL-1ß in their plasma over the course of infection, suggesting a role for IL-1ß in WNV immunity. Indeed, we found that in a mouse model of infection, WNV induced the acute production of IL-1ß in vivo, and that animals lacking the IL-1 receptor or components involved in inflammasome signaling complex exhibited increased susceptibility to WNV pathogenesis. This outcome associated with increased accumulation of virus within the CNS but not peripheral tissues and was further associated with altered kinetics and magnitude of inflammation, reduced quality of the effector CD8(+) T cell response and reduced anti-viral activity within the CNS. Importantly, we found that WNV infection triggers production of IL-1ß from cortical neurons. Furthermore, we found that IL-1ß signaling synergizes with type I IFN to suppress WNV replication in neurons, thus implicating antiviral activity of IL-1ß within neurons and control of virus replication within the CNS. Our studies thus define the NLRP3 inflammasome pathway and IL-1ß signaling as key features controlling WNV infection and immunity in the CNS, and reveal a novel role for IL-1ß in antiviral action that restricts virus replication in neurons.

Fidelity of pathogen-specific CD4+ T cells to the Th1 lineage is controlled by exogenous cytokines, interferon-gamma expression, and pathogen lifestyle.

The degree of lineage stability achieved by pathogen-specific CD4(+) T cells in vivo, and how this impacts host defense against infection, remains unclear. We demonstrate that in response to Th1-polarizing intracellular bacterial or viral pathogens, only 80%-90% of responding polyclonal T cells become indelibly committed to this lineage. Th1 commitment was nearly invariant in cells that proliferated extensively, but perturbations to the extrinsic cytokine milieu or the pathogen's ability to enter the cytosol impeded commitment and promoted plasticity for future IL-17 expression. Conversely, cell-intrinsic interferon-gamma expression and acquisition of permissive chromatin at the Ifng gene during priming predicted heritable Th1 commitment. Importantly, CD4(+) T cells that retained plasticity conferred protection against Mycobacterium tuberculosis, while these protective effects were abolished with Th17 polarization. These findings illustrate the immune signals that induce memory CD4(+) T cell responses required for maintaining host defense against infection yet are adaptable in novel environmental contexts.

Multiple effects of silymarin on the hepatitis C virus lifecycle.

UNLABELLED: Silymarin, an extract from milk thistle (Silybum marianum), and its purified flavonolignans have been recently shown to inhibit hepatitis C virus (HCV) infection, both in vitro and in vivo. In the current study, we further characterized silymarin's antiviral actions. Silymarin had antiviral effects against hepatitis C virus cell culture (HCVcc) infection that included inhibition of virus entry, RNA and protein expression, and infectious virus production. Silymarin did not block HCVcc binding to cells but inhibited the entry of several viral pseudoparticles (pp), and fusion of HCVpp with liposomes. Silymarin but not silibinin inhibited genotype 2a NS5B RNA-dependent RNA polymerase (RdRp) activity at concentrations 5 to 10 times higher than required for anti-HCVcc effects. Furthermore, silymarin had inefficient activity on the genotype 1b BK and four 1b RDRPs derived from HCV-infected patients. Moreover, silymarin did not inhibit HCV replication in five independent genotype 1a, 1b, and 2a replicon cell lines that did not produce infectious virus. Silymarin inhibited microsomal triglyceride transfer protein activity, apolipoprotein B secretion, and infectious virion production into culture supernatants. Silymarin also blocked cell-to-cell spread of virus. CONCLUSION: Although inhibition of in vitro NS5B polymerase activity is demonstrable, the mechanisms of silymarin's antiviral action appear to include blocking of virus entry and transmission, possibly by targeting the host cell.

Functional characterization of core genes from patients with acute hepatitis C virus infection.

BACKGROUND: The hepatitis C virus (HCV) core protein is implicated in diverse aspects of HCV-induced pathogenesis. There is a paucity of information on core in acute hepatitis C infection. METHODS: We analyzed core gene sequences and protein functions from 13 patients acutely infected with HCV genotype 1. RESULTS: Although core isolates differed slightly between patients, core quasispecies were relatively homogeneous within each patient. In 2 of 4 patients studied temporally, core quasispecies did not change over time. Comparison with more than 2700 published core isolates indicated that amino acid changes from a prototype reference strain found in acute core isolates were present in chronically infected persons at low frequency (6.4%; range, 0%-32%). Core isolates associated with lipid droplets to similar degrees in Huh7 cells. Core diffusion in cells was not affected by nonconservative changes F130L and G161S in the lipid targeting domain of core. Core isolates inhibited interferon-stimulated response element- and nuclear factor kappaB-dependent transcription and tumor necrosis factor alpha-induced nuclear translocation of nuclear factor kappaB and were also secreted from Huh7 cells. CONCLUSIONS: The data suggest that upon transmission, core quasispecies undergo genetic homogenization associated with amino acid changes that are rarely found in chronic infection and that, despite genetic variation, acute core isolates retain similar functions in vitro.