Monocytes activate natural killer cells via inflammasome-induced interleukin 18 in response to hepatitis C virus replication

Interaction and Mutual Activation of Different Innate Immune Cells Is Necessary to Kill and Clear Hepatitis C Virus-Infected Cells

Innate immune cells can sense hepatitis C virus (HCV)-infected cells and respond with anti-viral actions including secretion of interferons (IFNs). In previous studies, the response of individual innate immune cells against HCV was analyzed in detail. We hypothesized that interaction of multiple innate immune cells increases the magnitude of the immune response and eventually leads to clearance of HCV-infected cells. To investigate this, we co-cultured Huh-7 HCV subgenomic replicon (SGR) cells with peripheral blood mononuclear cells (PBMCs). We confirm secretion of IFNα by plasmacytoid dendritic cells (pDCs) and IFNγ by natural killer (NK) cells in the co-culture setup. Moreover, we observed that also monocytes contribute to the anti-viral response. Flow cytometry and ImageStream analysis demonstrated that monocytes take up material from HCV SGR cells in co-culture with PBMCs. Preceding the uptake, PBMCs caused apoptosis of HCV SGR cells by tumor necrosis factor-related apoptosis inducing ligand (TRAIL) expression on NK cells. We observed that only the interplay of monocytes, pDCs, and NK cells resulted in efficient clearance of HCV SGR cells, while these cell populations alone did not kill HCV SGR cells. Despite similar TRAIL receptor expression on Huh-7 control cells and HCV SGR cells, HCV activated PBMCs specifically killed HCV SGR cells and did not target Huh-7 control cells. Finally, we showed that HCV replicating cells per se are sensitive toward TRAIL-induced apoptosis. Our results highlight the importance of the interplay of different innate immune cells to initiate an efficient, rapid, and specific response against HCV-infected cells.

Role of the inflammasome-related cytokines Il-1 and Il-18 during infection with murine coronavirus

The inflammasome, a cytosolic protein complex that mediates the processing and secretion of pro-inflammatory cytokines, is one of the first responders during viral infection. The cytokines secreted following inflammasome activation, which include IL-1 and IL-18, regulate cells of both the innate and adaptive immune system, guiding the subsequent immune responses. In this study, we used murine coronavirus, mouse hepatitis virus (MHV), infection of the central nervous system and liver to assess of the role of the inflammasome and its related cytokines on pathogenesis and host defense during viral infection. Mice lacking all inflammasome signaling due to the absence of caspase-1 and -11 were more vulnerable to infection, with poor survival and elevated viral replication compared to wild-type mice. Mice lacking IL-1 signaling experienced elevated viral replication but similar survival compared to wild-type controls. In the absence of IL-18, mice had elevated viral replication and poor survival, and this protective effect of IL-18 was found to be due to promotion of interferon gamma production in αβ T cells. These data suggest that inflammasome signaling is largely protective during murine coronavirus infection, in large part due to the pro-inflammatory effects of IL-18.

Immune Reconstitution After HCV Clearance With Direct Antiviral Agents: Potential Consequences for Patients With HCC?

Recent introduction of all-oral direct-acting antiviral (DAA) treatment has revolutionized care of patients with chronic hepatitis C virus infection. Because patients with different liver disease stages have been treated with great success including those awaiting liver transplantation, therapy has been extended to patients with hepatocellular carcinoma as well. From observational studies among compensated cirrhotic hepatitis C patients treated with interferon-containing regimens, it would have been expected that the rate of hepatocellular carcinoma occurrence is markedly decreased after a sustained virological response. However, recently 2 studies have been published reporting markedly increased rates of tumor recurrence and occurrence after viral clearance with DAA agents. Over the last decades, it has been established that chronic antigen stimulation during persistent infection with hepatitis C virus is associated with continuous activation and impaired function of several immune cell populations, such as natural killer cells and virus-specific T cells. This review therefore focuses on recent studies evaluating the restoration of adaptive and innate immune cell populations after DAA therapy in patients with chronic hepatitis C virus infection in the context of the immune responses in hepatocarcinogenesis.

Rapid decrease in hepatitis C viremia by direct acting antivirals improves the natural killer cell response to IFNα

OBJECTIVE

Chronic HCV infection is characterised by innate immune activation with increased interferon-stimulated genes (ISG) expression and by an altered phenotype of interferon-responsive natural killer (NK) cells. Here, we asked whether a rapid reduction in viremia by daclatasvir (DCV) and asunaprevir (ASV) improves the response to pegylated interferon (PegIFN) in patients who had previously failed a standard course of PegIFN/ribavirin (RBV) therapy.

DESIGN

Twenty-two HCV-infected non-responders to previous PegIFN/RBV therapy were studied for IFN-responsiveness of NK cells during quadruple (QUAD) therapy with DCV, ASV, PegIFN and RBV. A direct comparison of early NK cell responses in PegIFN/RBV therapy and QUAD therapy was performed for seven patients using paired cryopreserved peripheral blood mononuclear cells (PBMC) from both treatment courses. As a validation cohort, nine DCV/ASV-treated patients were studied for their NK cell response to in vitro stimulation with IFNα.

RESULTS

The 24 h virological response to QUAD therapy correlated with an increase in signal transducer and activator of transcription 1 (STAT1), phosphorylated STAT1 (pSTAT1) and tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) expression in NK cells, and the STAT1/pSTAT1/TRAIL induction was greater during QUAD therapy than during previous PegIFN/RBV therapy. Successful QUAD therapy as well as successful IFN-free DCV/ASV regimen resulted in an improved functional NK cell response (degranulation and TRAIL expression) to in vitro stimulation with IFNα.

CONCLUSIONS

IFN-responsiveness can be improved by inhibiting HCV replication and reducing the HCV-induced activation of the innate immune response. This may provide a rationale for clinical trials of a brief period of direct acting antiviral therapy followed by PegIFN/RBV therapy to reduce the overall treatment costs in low-income and middle-income countries.

TRIAL REGISTRATION NUMBERS

NCT01888900 and NCT00718172.

Inflammatory monocytes require type I interferon receptor signaling to activate NK cells via IL-18 during a mucosal viral infection

Although type I interferon is critical for NK cell activation, the underlying mechanism is under debate and is unknown during a mucosal infection. Lee et al. have determined that type I interferon induces inflammatory monocytes to produce IL-18 to directly activate NK cells to combat viral infections.

The requirement of type I interferon (IFN) for natural killer (NK) cell activation in response to viral infection is known, but the underlying mechanism remains unclear. Here, we demonstrate that type I IFN signaling in inflammatory monocytes, but not in dendritic cells (DCs) or NK cells, is essential for NK cell function in response to a mucosal herpes simplex virus type 2 (HSV-2) infection. Mice deficient in type I IFN signaling, Ifnar^−/− and Irf9^−/− mice, had significantly lower levels of inflammatory monocytes, were deficient in IL-18 production, and lacked NK cell–derived IFN-γ. Depletion of inflammatory monocytes, but not DCs or other myeloid cells, resulted in lower levels of IL-18 and a complete abrogation of NK cell function in HSV-2 infection. Moreover, this resulted in higher susceptibility to HSV-2 infection. Although Il18^−/− mice had normal levels of inflammatory monocytes, their NK cells were unresponsive to HSV-2 challenge. This study highlights the importance of type I IFN signaling in inflammatory monocytes and the induction of the early innate antiviral response.

CD14+ monocyte-derived galectin-9 induces natural killer cell cytotoxicity in chronic hepatitis C

Natural killer (NK) cell activation is associated with both liver injury and persistent infection in chronic hepatitis C (CHC); however, the detailed mechanism of this activation has not yet been fully elucidated. Because galectin-9 (Gal-9) has been reported to be increased in the serum and liver tissue of CHC patients, we investigated the function of Gal-9 in NK cell activation in CHC. First, we evaluated the function of Gal-9 on NK cytotoxicity in vitro. Gal-9 treatment resulted in increased cytotoxicity of naïve NK cells, and the Gal-9-activated NK cells demonstrated cytotoxicity toward hepatoma cells and T cells. Additionally, coculturing peripheral blood mononuclear cells (PBMCs) with JFH-1/Huh7.5.1 cells increased both Gal-9 production and NK cell cytotoxicity. Next, we investigated the source of Gal-9 and the mechanism of Gal-9 production. Deletion of CD14⁺ monocytes from PBMCs resulted in reduced Gal-9 production in the coculture with JFH-1/Huh7.5.1 cells. Gal-9 production was driven by coculturing of PBMCs with apoptotic hepatocytes. Blocking integrin α_v β₃ , a receptor for phosphatidylserine expressed on apoptotic cells, also resulted in decreased Gal-9 production. Finally, we found that serum Gal-9 levels were significantly higher in CHC patients than in healthy donors and patients who achieved sustained virologic response. Among CHC patients, serum Gal-9 levels were significantly higher in patients with elevated alanine aminotransferase (ALT) than in those with normal ALT.

CONCLUSION

These results demonstrate that CD14⁺ monocyte-derived Gal-9 increases NK cell cytotoxicity in HCV infection, which might be associated with liver injury and persistent infection. (Hepatology 2017;65:18-31).

T-bet-mediated Tim-3 expression dampens monocyte function during chronic hepatitis C virus infection

Hepatitis C virus (HCV) induces a high rate of chronic infection via dysregulation of host immunity. We have previously shown that T-cell immunoglobulin and mucin domain protein-3 (Tim-3) is up-regulated on monocyte/macrophages (M/Mφ) during chronic HCV infection; little is known, however, about the transcription factor that controls its expression in these cells. In this study, we investigated the role of transcription factor, T-box expressed in T cells (T-bet), in Tim-3 expression in M/Mφ in the setting of HCV infection. We demonstrate that T-bet is constitutively expressed in resting CD14⁺ M/Mφ in the peripheral blood. M/Mφ from chronically HCV-infected individuals exhibit a significant increase in T-bet expression that positively correlates with an increased level of Tim-3 expression. Up-regulation of T-bet is also observed in CD14⁺ M/Mφ incubated with HCV⁺ Huh7.5 cells, as well as in primary M/Mφ or monocytic THP-1 cells exposed to HCV core protein in vitro, which is reversible by blocking HCV core/gC1qR interactions. Moreover, the HCV core-induced up-regulation of T-bet and Tim-3 expression in M/Mφ can be abrogated by incubating the cells with SP600125 - an inhibitor for the c-Jun N-terminal kinase (JNK) signalling pathway. Importantly, silencing T-bet gene expression decreases Tim-3 expression and enhances interleukin-12 secretion as well as signal transducer and activator of transcription 1 phosphorylation. These data suggest that T-bet, induced by the HCV core/gC1qR interaction, enhances Tim-3 expression via the JNK pathway, leading to dampened M/Mφ function during HCV infection. These findings reveal a novel mechanism for Tim-3 regulation via T-bet during HCV infection, providing new targets to combat this global epidemic viral disease.

IL-28B Genetic Variants Determine the Extent of Monocyte-Induced Activation of NK Cells in Hepatitis C

BACKGROUND

Immuno-genetic studies suggest a functional link between NK cells and λ-IFNs. We recently showed that NK cells are negative for the IFN-λ receptor IFN-λR1 and do not respond to IFN-λ, suggesting a rather indirect association between IL-28B genotype and NK cell activity.

METHODS

A total of 75 HCV(+) patients and 67 healthy controls were enrolled into this study. IL-28B (rs12979860) and IFNL-4 (rs368234815) genotypes were determined by rtPCR. Total PBMC, monocytes, and NK cells were stimulated with IL-29, the TLR-7/8 agonist R848, or a combination of both. NK cell IFN-γ response was analysed by FACS. IL-12 and IL-18 secretion of monocytes was studied by ELISA. In blocking experiments anti-IL-12/anti-IL-18 were used.

RESULTS

Following stimulation of total PBMCs with R848 we found NK cell IFN- γ responses to vary with the IL-28B genotype, with carriers of a T/T genotype displaying the lowest frequency of IFN-γ(+)NK cells. When isolated NK cells were studied no such associations were observed, indicating an indirect association between IL-28B genotype and NK cell activity. Accordingly, we found R848-stimulated monocytes of patients with a T/T genotype to be significantly less effective in triggering NK cell IFN- γ production than monocytes from carriers of a non-T/T genotype. In line with these findings we observed monocytes from T/T patients to secrete significantly lower concentrations of IL-12 than monocytes from non-T/T individuals.

CONCLUSIONS

Our data indicate that monocytes from carriers of an IL-28B T/T genotype display a reduced ability to stimulate NK cell activity and, thus, provide a link between IL-28B genotype and NK functions.

TNFα Augments Cytokine-Induced NK Cell IFNγ Production through TNFR2

NK cells play a central role in innate immunity, acting directly through cell-mediated cytotoxicity and by secreting cytokines. TNFα activation of TNFR2 enhances NK cell cytotoxicity, but its effects on the other essential function of NK cells - cytokine production, for which IFNγ is paramount - are poorly defined. We identify the expression of both TNFα receptors on human peripheral blood NK cells (TNFR2 > TNFR1) and show that TNFα significantly augments IFNγ production from IL-2-/IL-12-treated NK cells in vitro, an effect mimicked by a TNFR2 agonistic antibody. TNFα also enhanced murine NK cell IFNγ production via TNFR2 in vitro. In a mouse model characterized by the hepatic recruitment and activation of NK cells, TNFR2 also regulated NK cell IFNγ production in vivo. Specifically, in this model, after activation of an innate immune response, hepatic numbers of TNFR2-expressing and IFNγ-producing NK cells were both significantly increased; however, the frequency of IFNγ-producing hepatic NK cells was significantly reduced in TNFR2-deficient mice. We delineate an important role for TNFα, acting through TNFR2, in augmenting cytokine-induced NK cell IFNγ production in vivo and in vitro, an effect with significant potential implications for the regulation of innate and adaptive immune responses.

Monocyte Heterogeneity: Consequences for Monocyte-Derived Immune Cells

Blood monocytes are precursors of dendritic cells, macrophages, and osteoclasts. They are a heterogeneous cell population with differences in size, phenotype, and function. Although monocytes maintain several tissue-specific populations of immune cells in homeostasis, their contribution to populations of dendritic cells, macrophages, and osteoclasts is significantly increased in inflammation. Identification of a growing number of functionally different subsets of cells within populations of monocyte-derived immune cells has recently put monocyte heterogeneity into sharp focus. Here, we summarize recent findings in monocyte heterogeneity and their differentiation into dendritic cells, macrophages, and osteoclasts. We also discuss these advances in the context of the formation of functionally different monocyte-derived subsets of dendritic cells, macrophages, and osteoclasts.

Organ system view of the hepatic innate immunity in HCV infection

An orchestration of innate and adaptive immunity determines the infection outcome and whether the host achieves clearance or allows the pathogen to establish persistent infection. The robust activation of the innate immune response plays the most critical role in both limiting viral replication and halting the spread of the pathogen immediately after infection. The magnitude of innate immune activation is coupled with the efficient mounting of the adaptive immunity. Although immunity against HCV infection is known to be inadequate as most cases transitions to chronicity, approximately 25% of acute infection cases result in spontaneous clearance. The exact immune mechanisms that govern the infection outcome remain largely unknown; recent discoveries suggest that the innate immune system facilitates this event. Both infected hepatocytes and local innate immune cells trigger the front line defense program of the liver as well as the recruitment of diverse adaptive immune cells to the site of infection. Although hepatocyte is the target of HCV infection, nearly all cell types that exist in the liver are involved in the innate defense and contribute to the pathophysiology of hepatic inflammation. The main focus of this comprehensive review is to discuss the current knowledge on how each hepatic cell type contributes to the organ system level innate immunity against HCV infection as well as interplays with the viral evasion program. Furthermore, this review article also aims to synchronize the observations from both molecular biological studies and clinical studies with the ultimate goal of improving our understanding of HCV mediated hepatitis. J. Med. Virol. 88:2025-2037, 2016. © 2016 Wiley Periodicals, Inc.

Impact of natural killer cells on chronic hepatitis C and hepatocellular carcinoma

Natural killer (NK) cells are involved in the pathogenesis of hepatitis C viral (HCV) infection and hepatocellular carcinoma (HCC). Recent immunological progresses have revealed the molecular mechanisms of activation or inhibition of NK cells. In patients infected with HCV, the percentages of NK cells are decreased and the NK receptor expression and function of NK cells including cytotoxicity and cytokine production are altered. These alterations in NK cells are associated with persistent infection with HCV, liver injury, liver fibrosis and liver carcinogenesis. In HCV treatment, NK cells play a role in the eradication of HCV in both interferon (IFN)-based therapy and IFN-free therapy using direct-acting antivirals (DAA). In HCC patients, the exhaustion of NK cells that represents lower cytotoxicity and impaired cytokine production may contribute to the progression of HCC. Several immunotherapies targeting NK cells have been reported. NK cell transfer and NK-activating gene therapy have been demonstrated to be effective in mouse liver cancer models and several clinical trials are ongoing. Recently, the role of major histocompatibility complex class I-related chain A (MICA), a human ligand of NKG2D, has attracted attention in the development of HCC. The expression of MICA could be controlled by anti-HCC drugs including sorafenib. A new chemo-immunotherapy may be expected in the treatment of HCC. In this review, we summarize the impact of NK cells on chronic hepatitis C and HCC.

Natural killer cells in hepatitis C: Current progress

Patients infected with the hepatitis C virus (HCV) are characterized by a high incidence of chronic infection, which results in chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. The functional impairment of HCV-specific T cells is associated with the evolution of an acute infection to chronic hepatitis. While T cells are the important effector cells in adaptive immunity, natural killer (NK) cells are the critical effector cells in innate immunity to virus infections. The findings of recent studies on NK cells in hepatitis C suggest that NK cell responses are indeed important in each phase of HCV infection. In the early phase, NK cells are involved in protective immunity to HCV. The immune evasion strategies used by HCV may target NK cells and might contribute to the progression to chronic hepatitis C. NK cells may control HCV replication and modulate hepatic fibrosis in the chronic phase. Further investigations are, however, needed, because a considerable number of studies observed functional impairment of NK cells in chronic HCV infection. Interestingly, the enhanced NK cell responses during interferon-α-based therapy of chronic hepatitis C indicate successful treatment. In spite of the advances in research on NK cells in hepatitis C, establishment of more physiological HCV infection model systems is needed to settle unsolved controversies over the role and functional status of NK cells in HCV infection.

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-1β (IL-1β) and IL-18. These cytokines regulate hepatic cell interaction and crosstalk of the various inflammatory pathways and influence disease outcome.

Hepatitis C Virus-Induced Monocyte Differentiation Into Polarized M2 Macrophages Promotes Stellate Cell Activation via TGF-β

BACKGROUND & AIMS

Monocyte and macrophage (MΦ) activation contributes to the pathogenesis of chronic hepatitis C virus (HCV) infection. Disease pathogenesis is regulated by both liver-resident MΦs and monocytes recruited as precursors of MΦs into the damaged liver. Monocytes differentiate into M1 (classic/proinflammatory) or M2 (alternative/anti-inflammatory) polarized MΦs in response to tissue microenvironment. We hypothesized that HCV-infected hepatoma cells (infected with Japanese fulminant hepatitis-1 [Huh7.5/JFH-1]) induce monocyte differentiation into polarized MΦs.

METHODS

Healthy human monocytes were co-cultured with Huh7.5/JFH-1 cells or cell-free virus for 7 days and analyzed for MΦ markers and cytokine levels. A similar analysis was performed on circulating monocytes and liver MΦs from HCV-infected patients and controls.

RESULTS

Huh7.5/JFH-1 cells induced monocytes to differentiate into MΦs with increased expression of CD14 and CD68. HCV-MΦs showed M2 surface markers (CD206, CD163, and Dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN)) and produced both proinflammatory and anti-inflammatory cytokines. HCV-induced early interleukin 1β production promoted transforming growth factor (TGF)β production and MΦ polarization to an M2 phenotype. TGF-β secreted by M2-MΦ led to hepatic stellate cell activation indicated by increased expression of collagen, tissue inhibitor of metalloproteinase 1, and α-smooth muscle actin. In vivo, we observed a significant increase in M2 marker (CD206) expression on circulating monocytes and in the liver of chronic HCV-infected patients. Furthermore, we observed the presence of a unique collagen-expressing CD14⁺CD206⁺ monocyte population in HCV patients that correlated with liver fibrosis.

CONCLUSIONS

We show an important role for HCV in induction of monocyte differentiation into MΦs with a mixed M1/M2 cytokine profile and M2 surface phenotype that promote stellate cell activation via TGF-β. We also identified circulating monocytes expressing M2 marker and collagen in chronic HCV infection that can be explored as a biomarker.

Global gene expression analysis of peripheral blood mononuclear cells in rhesus monkey infants with CA16 infection-induced HFMD

Coxsackievirus A16 (CA16) is a dominant pathogen that results in hand, foot, and mouth disease and causes outbreaks worldwide, particularly in the Asia-Pacific region. However, the underlying molecular mechanisms remain unclear. Our previous study has demonstrated that the basic CA16 pathogenic process was successfully mimicked in rhesus monkey infant. The present study focused on the global gene expression changes in peripheral blood mononuclear cells of rhesus monkey infants with hand, foot, and mouth disease induced by CA16 infection at different time points. Genome-wide expression analysis was performed with Agilent whole-genome microarrays and established bioinformatics tools. Nine hundred and forty-eight significant differentially expressed genes that were associated with 5 gene ontology categories, including cell communication, cell cycle, immune system process, regulation of transcription and metabolic process were identified. Subsequently, the mapping of genes related to the immune system process by PANTHER pathway analysis revealed the predominance of inflammation mediated by chemokine and cytokine signaling pathways and the interleukin signaling pathway. Ultimately, co-expressed genes and their networks were analyzed. The results revealed the gene expression profile of the immune system in response to CA16 in rhesus monkey infants and suggested that such an immune response was generated as a result of the positive mobilization of the immune system. This initial microarray study will provide insights into the molecular mechanism of CA16 infection and will facilitate the identification of biomarkers for the evaluation of vaccines against this virus.

Natural Killer Cells in Viral Hepatitis

Natural killer (NK) cells are traditionally regarded as first-line effectors of the innate immune response, but they also have a distinct role in chronic infection. Here, we review the role of NK cells against hepatitis C virus (HCV) and hepatitis B virus (HBV), two agents that cause acute and chronic hepatitis in humans. Interest in NK cells was initially sparked by genetic studies that demonstrated an association between NK cell-related genes and the outcome of HCV infection. Viral hepatitis also provides a model to study the NK cell response to both endogenous and exogenous type I interferon (IFN). Levels of IFN-stimulated genes increase in both acute and chronic HCV infection and pegylated IFNα has been the mainstay of HCV and HBV treatment for decades. In chronic viral hepatitis, NK cells display decreased production of antiviral cytokines. This phenotype is found in both HCV and HBV infection but is induced by different mechanisms. Potent antivirals now provide the opportunity to study the reversibility of the suppressed cytokine production of NK cells in comparison with the antigen-induced defect in IFNγ and tumor necrosis factor-α production of virus-specific T cells. This has implications for immune reconstitution in other conditions of chronic inflammation and immune exhaustion, such as human immunodeficiency virus infection and cancer.

Inflammasome activation and function in liver disease

Inflammation contributes to the pathogenesis of most acute and chronic liver diseases. Inflammasomes are multiprotein complexes that can sense danger signals from damaged cells and pathogens and assemble to mediate caspase-1 activation, which proteolytically activates the cytokines IL-1β and IL-18. In contrast to other inflammatory responses, inflammasome activation uniquely requires two signals to induce inflammation, therefore setting an increased threshold. IL-1β, generated upon caspase-1 activation, provides positive feed-forward stimulation for inflammatory cytokines, thereby amplifying inflammation. Inflammasome activation has been studied in different human and experimental liver diseases and has been identified as a major contributor to hepatocyte damage, immune cell activation and amplification of liver inflammation. In this Review, we discuss the different types of inflammasomes, their activation and biological functions in the context of liver injury and disease progression. Specifically, we focus on the triggers of inflammasome activation in alcoholic steatohepatitis and NASH, chronic HCV infection, ischaemia-reperfusion injury and paracetamol-induced liver injury. The application and translation of these discoveries into therapies promises novel approaches in the treatment of inflammation in liver disease.

Inflammasome control of viral infection

The inflammasome is a caspase-1 containing complex that activates the proinflammatory cytokines IL-1β and IL-18 and results in the proinflammatory cell death known as pyroptosis. Numerous recent publications have highlighted the importance of inflammasome activation in the control of virus infection. Inflammasome activation during viral infection is dependent on a variety of upstream receptors including the NOD-like receptor, RIG-I-like receptor and AIM2-like receptor families. Various receptors also function in inflammasome activation in different cellular compartments, including the cytoplasm and the nucleus. The effectiveness of inflammasomes at suppressing virus replication is highlighted by the prevalence and diversity of virus encoded inflammasome inhibitors. Also, the host has a myriad of regulatory mechanisms in place to prevent unwanted inflammasome activation and overt inflammation. Finally, recent reports begin to suggest that inflammasome activation and inflammasome modulation may have important clinical applications. Herein, we highlight recent advances and discuss potential future directions toward understanding the role of inflammasomes during virus infection.

Differential expression of immune-related cytokine genes in response to J group avian leukosis virus infection in vivo

Infection with J group avian leukosis virus (ALV-J) can result in immunosuppression and subsequently increased susceptibility to secondary infection. The innate immune system is the first line defense system in prevention of further bacterial and viral infections. Cytokines play key roles in the innate immune system. In this study, we used RT-qPCR technology to test the cytokine mRNA expression levels in various immune tissues, including the spleen, bursa of fabricius and cecal tonsil, in the days following ALV-J infection. The results indicated that in the infected group, the expression levels of interleukin-6 (IL-6), IL-18, interferon-α (IFN-α) and IFN-γ significantly increased in the spleen and reached peak levels that were thousandfolds higher than baselines at 9-12 days post-infection (d.p.i.). The levels in the bursa of fabricius slightly increased, and the levels in the cecal tonsil were not significantly altered. Moreover, the pattern of the expression of these three cytokines in the spleens of the infected group was similar to the pattern of viremia of this group. These results suggest that the spleen plays an important role in the interaction between ALV-J infection and the innate immune system. This study contributes to the understanding of innate immune responses to ALV-J infection and also elucidates the mechanisms of the pathogenicity of ALV-J in chickens.

Innate immune cell networking in hepatitis C virus infection

Persistent viral infection, such as HCV infection, is the result of the inability of the host immune system to mount a successful antiviral response, as well as the escape strategies devised by the virus. Although each individual component of the host immune system plays important roles in antiviral immunity, the interactive network of immune cells as a whole acts against the virus. The innate immune system forms the first line of host defense against viral infection, and thus, virus elimination or chronic HCV infection is linked to the direct outcome of the interactions between the various innate immune cells and HCV. By understanding how the distinct components of the innate immune system function both individually and collectively during HCV infection, potential therapeutic targets can be identified to overcome immune dysfunction and control chronic viral infection.