Hepatitis B core antigen is a potent inductor of interleukin-18 in peripheral blood mononuclear cells of healthy controls and patients with hepatitis B infection

The Role of Interleukins in HBV Infection: A Narrative Review

Hepatitis B virus (HBV) infection is a worldwide medical issue with significant morbidity and mortality, as it is the main cause of chronic liver disease and hepatocellular carcinoma (HCC). Both innate and adaptive immune responses play a key role in HBV replication and suppression. Recently, the pathophysiological function of interleukins (IL) in the natural course of HBV has gained much attention as a result of the broad use of anti-interleukin agents for a variety of autoimmune diseases and the accompanying risk of HBV reactivation. We present a narrative review regarding the role of IL in HBV infection. Collectively, the pro-inflammatory ILs, namely IL-1, IL-5, IL-6, IL-12 and IL-21, seem to play a critical role in the suppression of HBV replication. In contrast, the anti-inflammatory cytokines IL-10, IL-23 and IL-35 probably act as HBV replication enhancers, while IL-17 has been correlated with HBV-related liver injury. Interestingly enough, IL-2, IL-4 and IL-12 have been tried as therapeutic options against HBV infection with contradictory results. Lastly, the role of IL-22 remains largely ill defined, although preliminary data suggest that it may play a significant role in HBV replication, proliferation and subsequent liver damage.

Distinct Types of Cell Death and Implications in Liver Diseases: An Overview of Mechanisms and Application

Cell death is associated with a variety of liver diseases, and hepatocyte death is a core factor in the occurrence and progression of liver diseases. In recent years, new cell death modes have been identified, and certain biomarkers have been detected in the circulation during various cell death modes that mediate liver injury. In this review, cell death modes associated with liver diseases are summarized, including some cell death modes that have emerged in recent years. We described the mechanisms associated with liver diseases and summarized recent applications of targeting cell death in liver diseases. It provides new ideas for the diagnosis and treatment of liver diseases. In addition, multiple cell death modes can contribute to the same liver disease. Different cell death modes are not isolated, and they interact with each other in liver diseases. Future studies may focus on exploring the regulation between various cell death response pathways in liver diseases.

Activation of AIM2 by hepatitis B virus results in antiviral immunity that suppresses hepatitis C virus during coinfection

IMPORTANCE

Clinical data suggest that Hepatitis C virus (HCV) levels are generally lower in Hepatitis B virus (HBV) co-infected patients, but the mechanism is unknown. Here, we show that HBV, but not HCV, activated absent in melanoma-2. This in turn results in inflammasome-mediated cleavage of pro-IL-18, leading to an innate immune activation cascade that results in increased interferon-γ, suppressing both viruses.

Race between virus and inflammasomes: inhibition or escape, intervention and therapy

The inflammasome is a multiprotein complex that further regulates cell pyroptosis and inflammation by activating caspase-1. The assembly and activation of inflammasome are associated with a variety of diseases. Accumulative studies have shown that inflammasome is a key modulator of the host's defense response to viral infection. Indeed, it has been established that activation of inflammasome occurs during viral infection. At the same time, the host has evolved a variety of corresponding mechanisms to inhibit unnecessary inflammasome activation. Therefore, here, we review and summarize the latest research progress on the interaction between inflammosomes and viruses, highlight the assembly and activation of inflammosome in related cells after viral infection, as well as the corresponding molecular regulatory mechanisms, and elucidate the effects of this activation on virus immune escape and host innate and adaptive immune defenses. Finally, we also discuss the potential therapeutic strategies to prevent and/or ameliorate viral infection-related diseases via targeting inflammasomes and its products.

The HBV web: An insight into molecular interactomes between the hepatitis B virus and its host en route to hepatocellular carcinoma

Hepatitis B virus (HBV) is a major aetiology associated with the development and progression of hepatocellular carcinoma (HCC), the most common primary liver malignancy. Over the past few decades, direct and indirect mechanisms have been identified in the pathogenesis of HBV-associated HCC which include altered signaling pathways, genome integration, mutation-induced genomic instability, chromosomal deletions and rearrangements. Intertwining of the HBV counterparts with the host cellular factors, though well established, needs to be systemized to understand the dynamics of host-HBV crosstalk and its consequences on HCC progression. Existence of a vast array of protein-protein and protein-nucleic acid interaction databases has led to the uncoiling of the compendia of genes/gene products associated with these interactions. This review covers the existing knowledge about the HBV-host interplay and brings it down under one canopy emphasizing on the HBV-host interactomics; and thereby highlights new strategies for therapeutic advancements against HBV-induced HCC.

HBeAg mediates inflammatory functions of macrophages by TLR2 contributing to hepatic fibrosis

BACKGROUND

We and others have confirmed activation of macrophages plays a critical role in liver injury and fibrogenesis during HBV infection. And we have also proved HBeAg can obviously induce the production of macrophage inflammatory cytokines compared with HBsAg and HBcAg. However, the receptor and functional domain of HBeAg in macrophage activation and its effects and mechanisms on hepatic fibrosis remain elusive.

METHODS

The potentially direct binding receptors of HBeAg were screened and verified by Co-IP assay. Meanwhile, the function domain and accessible peptides of HBeAg for macrophage activation were analyzed by prediction of surface accessible peptide, construction, and synthesis of truncated fragments. Furthermore, effects and mechanisms of the activation of hepatic stellate cells induced by HBeAg-treated macrophages were investigated by Transwell, CCK-8, Gel contraction assay, Phospho Explorer antibody microarray, and Luminex assay. Finally, the effect of HBeAg in hepatic inflammation and fibrosis was evaluated in both human and murine tissues by immunohistochemistry, immunofluorescence, ELISA, and detection of liver enzymes.

RESULTS

Herein, we verified TLR-2 was the direct binding receptor of HBeAg. Meanwhile, C-terminal peptide (122-143 aa.) of core domain in HBeAg was critical for macrophage activation. But arginine-rich domain of HBcAg hided this function, although HBcAg and HBeAg shared the same core domain. Furthermore, HBeAg promoted the proliferation, motility, and contraction of hepatic stellate cells (HSCs) in a macrophage-dependent manner, but not alone. PI3K-AKT-mTOR and p38 MAPK signaling pathway were responsible for motility phenotype of HSCs, while the Smad-dependent TGF-β signaling pathway for proliferation and contraction of them. Additionally, multiple chemokines and cytokines, such as CCL2, CCL5, CXCL10, and TNF-α, might be key mediators of HSC activation. Consistently, HBeAg induced transient inflammation response and promoted early fibrogenesis via TLR-2 in mice. Finally, clinical investigations suggested that the level of HBeAg is associated with inflammation and fibrosis degrees in patients infected with HBV.

CONCLUSIONS

HBeAg activated macrophages via the TLR-2/NF-κB signal pathway and further exacerbated hepatic fibrosis by facilitating motility, proliferation, and contraction of HSCs with the help of macrophages.

Pyroptosis in Steatohepatitis and Liver Diseases

Pyroptosis is an inflammatory form of regulated cell death, which functions in the clearance of intracellularly replicating pathogens by cell lysis in order to induce further immune response. Since the discovery of the gasdermin (GSDM) family, pyroptosis has attracted attention in a wide range of inflammatory diseases such as nonalcoholic steatohepatitis and other liver diseases. Due to the cleavage of GSDMs by different caspases, the amino-terminal GSDM fragments form membrane pores essential for pyroptosis that facilitate the release of inflammatory cytokines by loss of ionic gradient and membrane rupture. In this review, we address the key molecular and cellular processes that induce pyroptosis in the liver and its significance in the pathogenesis of common liver diseases in different human and experimental mice studies.

Macrophage Phenotypes and Hepatitis B Virus Infection

Globally, hepatitis B virus (HBV) infection and its related liver diseases account for 780,000 deaths every year. Outcomes of HBV infection depend on the interaction between the virus and host immune system. It is becoming increasingly apparent that Kupffer cells (KCs), the largest population of resident and monocyte-derived macrophages in the liver, contribute to HBV infection in various aspects. These cells play an important role not only in the anti-HBV immunity including virus recognition, cytokine production to directly inhibit viral replication and recruitment and activation of other immune cells involved in virus clearance but also in HBV outcome and progression, such as persistent infection and development of end-stage liver diseases. Since liver macrophages play multiple roles in HBV infection, they are directly targeted by HBV to benefit its life cycle. In the present review, we briefly outline the current advances of research of macrophages, especially the studies of their phenotypes, in chronic HBV infection.

Cell Death in Liver Diseases: A Review

Regulated cell death (RCD) is pivotal in directing the severity and outcome of liver injury. Hepatocyte cell death is a critical event in the progression of liver disease due to resultant inflammation leading to fibrosis. Apoptosis, necrosis, necroptosis, autophagy, and recently, pyroptosis and ferroptosis, have all been investigated in the pathogenesis of various liver diseases. These cell death subroutines display distinct features, while sharing many similar characteristics with considerable overlap and crosstalk. Multiple types of cell death modes can likely coexist, and the death of different liver cell populations may contribute to liver injury in each type of disease. This review addresses the known signaling cascades in each cell death pathway and its implications in liver disease. In this review, we describe the common findings in each disease model, as well as the controversies and the limitations of current data with a particular focus on cell death-related research in humans and in rodent models of alcoholic liver disease, non-alcoholic fatty liver disease and steatohepatitis (NASH/NAFLD), acetaminophen (APAP)-induced hepatotoxicity, autoimmune hepatitis, cholestatic liver disease, and viral hepatitis.

HBV-Pol is crucial for HBV-mediated inhibition of inflammasome activation and IL-1β production

BACKGROUND & AIMS

Hepatitis B virus (HBV) infection is the most critical factor underlying liver cirrhosis and hepatocellular carcinoma worldwide. IL-1β and IL-18, generated by activation of the inflammasome/caspase-1 signaling pathway, play important roles in the control and clearance of HBV. However, the specific relationship between the inflammasome response and IFN-α resistance or viral persistence is yet to be established.

METHODS

Blood samples of patients and supernatant fractions of HBV cell lines were collected for analysis and the effects on inflammasome activation and IL-1β production evaluated via enzyme-linked immunosorbent assay (ELISA), western blot, quantitative RT-PCR and immunofluorescence.

RESULTS

IL-1β and IL-18 levels produced in sera of IFN-α non-responders were significantly lower than those of responders and normal donors. Additionally, expression of IL-1β and inflammasome components was decreased in peripheral blood mononuclear cells (PBMC) of non-responders, compared with those of responders. In vitro experiments on HepG2, HepG2.2.15 and HepAD38 cell lines showed that HBV induces a significant decrease in IL-1β production through inhibiting activation of the NF-κB signaling and inflammasome/caspase-1 pathways. And hepatitis B virus polymerase (HBV-Pol) appeared crucial for these inhibitory effects of HBV.

CONCLUSION

IL-1β production is suppressed in HBV carriers and IFN-α non-responders. HBV induces a significant decrease in IL-1β production through inhibiting the NF-κB signaling and inflammasome pathways, for which HBV-Pol is a crucial requirement. Trial approval number: 20 173 402.

Pyroptosis in Liver Disease: New Insights into Disease Mechanisms

There has been increasing interest in pyroptosis as a novel form of pro-inflammatory programmed cell death. The mechanism of pyroptosis is significantly different from other forms of cell death in its morphological and biochemical features. Pyroptosis is characterized by the activation of two different types of caspase enzymes—caspase-1 and caspase-4/5/11, and by the occurrence of a proinflammatory cytokine cascade and an immune response. Pyroptosis participates in the immune defense mechanisms against intracellular bacterial infections. On the other hand, excessive inflammasome activation can induce sterile inflammation and eventually cause some diseases, such as acute or chronic hepatitis and liver fibrosis. The mechanism and biological significance of this novel form of cell death in different liver diseases will be evaluated in this review. Specifically, we will focus on the role of pyroptosis in alcoholic and non-alcoholic fatty liver disease, as well as in liver failure. Finally, the therapeutic implications of pyroptosis in liver diseases will be discussed.

Hepatitis B core antigen can regulate NLRP3 inflammasome pathway in HepG2 cells

Hepatitis B virus (HBV) has four open reading frames (ORFs) of which ORF C is consists of the pre Core and Core genes encodes the Hepatitis B core antigen (HBcAg) and Hepatitis B e antigen (HBeAg). Studies have shown that HBeAg significantly inhibits the NLRP3 inflammasome activation and interleukin-1β (IL-1β) production. However, the role of HBcAg and ORF C proteins (in this paper, ORF C proteins = HBcAg + HBeAg) were remain unclear. Our study aims to assess whether HBcAg and ORF C proteins can affect the NLRP3 inflammasome pathway. Vectors expressing ORF C proteins and HBcAg were designed and transfected into HepG2 cells. And then, cells were stimulated with lipopolysaccharide (LPS). Activation of the NLRP3 inflammasome and the levels of IL-1β and IL-18 were evaluated by Western blot analysis, quantitative reverse-transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and immunofluorescence. The expression of NLRP3 and IL-1β peaked when HepG2 cells were stimulated with 1000 ng/mL LPS for 18 to 24 hours. HBcAg, but not ORF C proteins, promoted LPS-induced NLRP3 inflammasome activation and IL-1β production. These findings provide a novel mechanism on how the HBV causes liver inflammation and may provide insights into the search for new therapeutic strategies.

The role of the NLRP3 inflammasome and the activation of IL-1β in the pathogenesis of chronic viral hepatic inflammation

BACKGROUND AND AIMS

Chronic viral hepatitis is a prevalent disease with major health implications. Its underlying pathophysiological mechanisms are not fully understood. IL-1β and the NLRP3 inflammasome involvement has been suggested in recent years, from in vitro data and data from peripheral blood samples. Therefore, we investigated IL-1β and the NLRP3 inflammasome in liver tissues in an effort to clarify their role in the pathophysiology of chronic viral hepatitis.

METHODS

We studied liver biopsies from patients with a new diagnosis of either chronic hepatitis B (CHB) and chronic hepatitis C (CHC) or patients with chronic hepatitis B in remission (CHB-rem). The biopsies were separated in two parts. The first part was sent to histology to determine the grade of inflammation and fibrosis. From the second part, RNA was extracted and converted to cDNA used in semi-quantitative Real-Time PCR to measure the levels of IL1B, CASP1, NLRP3, ASC and IL1RA. The cell lines used in the in vitro experiments were Huh7.5, LX2 and THP-1 in variety of combinations of monocultures, co-cultures and triple cultures with one of the cell lines infected with the JFH-1 HCV clone. From the cell cultures RNA was extracted and converted to cDNA. For cell lines, we focused in the expression of IL1B and NLRP3.

RESULTS

The expression of IL1B, CASP1 and NLRP3 were found significantly different between our groups (p = 0.001, p = 0.001 and p = 0.038, respectively). CHB patients displayed significantly higher IL1B and CASP1 mRNA levels compared to both CHB-rem and CHC patients. IL1B expression significantly correlates with liver biochemical data in CHB patients (AST: p = 0.006, r = 0.457; ALT p = 0.002, r = 0.497). Finally, mRNA levels of IL1B in CHB patients significantly correlate with the degree of inflammation (p = 0.016) but not the stage of fibrosis (p = 0.362). Interestingly, the relative expression of IL1B in triple culture experiments in vitro was below of 1.5-fold, suggesting no activation of IL1B. Moreover, no activation of NLRP3 was demonstrated in all investigated in vitro conditions.

CONCLUSION

IL-1β might play an important role in the pathogenesis of chronic hepatic inflammation from HBV, but not from HCV.

Role of Inflammasomes in the Development of Gastrointestinal Diseases

Many diseases of the gastrointestinal tract have been attributed to chronic inflammation, and a few have identified the role of inflammasomes in their pathogenesis. Inflammasomes are a group of protein complexes comprising of several intracellular proteins that link the sensing of microbial products and metabolic stress to the proteolytic activation of the proinflammatory cytokines. Recent studies have implicated activation of several families of NOD-like receptors (NLRs) which are major components of inflammasomes in the development and exacerbation of many diseases of human systems. In this chapter, we discuss the role of inflammasomes in some of the most prevalent diseases of the gastrointestinal tract and highlight potential targets for treatment.

Hepatitis B vaccine non response: A predictor of latent autoimmunity?

Unresponsiveness to Hepatitis B virus (HBV) vaccine has been associated with interleukins involved with Th1 functioning including Interleukin-8 (IL-18) and Interferon-γ (IFN-γ). IL-18 and IFN-γ have also been implicated in the onset of different types of immune-mediate inflammatory conditions such as Type 1 Diabetes (T1D), Celiac disease (CD), rheumatoid arthritis (RA), obesity and systemic lupus erythematosus (SLE). Taking into account that HBV vaccination is provided in the 1st year of life worldwide, I propose that all babies should be tested for anti-HBs response after completion of the vaccine series. And I suggest that children with undetectable anti-HBs titers after recommended immunization schedule as well as the additional booster doses should be followed up over time because they may be at risk of developing a number of autoimmune disorders. In this light, the non-responsiveness to HBV vaccine might be a predictor of latent autoimmunity. For that reason, research studies are needed in order to verify the existence of potential IL-18 and IFN-γ gene polymorphisms to utilize as biomarkers of latent autoimmunity. As a final point, administration of neutralizing antibodies against IFN-γ and/or IL-18 might represent a future target for immune-modulatory therapeutic approach to halt or even reverse autoimmune phenomena.

The evaluation of fibrotic effects of the hepatitis B virus pre-core in hepatic stellate cells

The role of the hepatitis B virus (HBV) endogenous pre-core protein in liver fibrosis is controversial. Whether the expression of the pre-core induces the activation of human stellate cells (HSCs) has not yet been reported. Plasmids expressing HBx, or pre-core protein were transfected into LX-2 cells. Subsequently, total RNA extracted and reverse transcription-quantitative polymerase chain reaction was performed to measure the fold change of collagen type I, α1 chain, α-smooth muscle actin and TIMP metalloproteinase inhibitor-1. Moreover, transforming growth factor (TGF)-β in the supernatant of HSCs was evaluated by ELISA assay. In addition, a MTT assay was performed to test the cytotoxicity of the endogenous expression in LX-2 cells. None of the plasmids exhibited cytotoxic nor significant proliferative effects on LX-2 cells by MTT assessment. The gene expression analysis of fibrotic genes in LX-2 cells demonstrated that the pre-core protein presented no significant (P>0.05) fibrotic impact when compared to the empty control plasmid and HBx. The data from the TGF-β ELISA was consistent with the mRNA expression as detected with the control plasmid (P>0.05). The endogenous expression of the HBV pre-core exhibited no fibrotic impression in HSCs when compared to HBx.

Inflammasomes in Inflammation-Induced Cancer

The inflammasome is an important multiprotein complex that functions during inflammatory immune responses. The activation of inflammasome will lead to the autoactivation of caspase-1 and subsequent cleavage of proIL-1β and proIL-18, which are key sources of inflammatory manifestations. Recently, the roles of inflammasomes in cancers have been extensively explored, especially in inflammation-induced cancers. In different and specific contexts, inflammasomes exhibit distinct and even contrasting effects in cancer development. In some cases, inflammasomes initiate carcinogenesis through the extrinsic pathway and maintain the malignant cancer microenvironment through the intrinsic pathway. On the contrary, inflammasomes also exert anticancer effects by specialized programmed cell death called pyroptosis and immune regulatory functions. The phases and compartments in which inflammasomes are activated strongly influence the final immune effects. We systemically summarize the functions of inflammasomes in inflammation-induced cancers, especially in gastrointestinal and skin cancers. Besides, information about the current therapeutic use of inflammasome-related products and potential future developing directions are also introduced.

Evaluation of NLRC4, NLRP1, and NLRP3, as Components of Inflammasomes, in Chronic Hepatitis B Virus-Infected Patients

Nucleotide-binding domain leucine repeats (NLRs) are required for the recognition of various molecules that are expressed within microbes and are able to actuate appropriate immune responses via activation of cytokines. The current study evaluates the expression levels of NLRP1 and NLRC4, which are components of inflammasomes, in chronic hepatitis B (CHB) virus-infected patients. This study recruited two series of CHB patients (each contained 60 patients) and 60 healthy controls. Real-time polymerase chain reaction (PCR) was employed to evaluate mRNA expression levels of NLRP1, NLRP3, and NLRC4 as well as hepatitis B virus (HBV)-DNA copy number. Serum levels of liver markers were also used to evaluate the patients. Hepatitis B envelope antigen (HBeAg) and hepatitis B surface antigen (HBsAg) were also examined in all patients to evaluate infection. The data showed that expression levels of NLRC4 and NLRP1 were not significantly different in circulating monocytes of CHB patients when compared with those of healthy controls. Furthermore, the data indicate that mRNA levels of NLRP1, NLRP3, and NLRC4 were also not altered in CHB patients regardless of HBV-DNA copy numbers/mL and HBeAg status. The data revealed that mRNA expression levels of NLRP1 and NLRC4 were not altered in CHB patients, suggesting that these genes are not responsible for the impaired immune responses against HBV observed in these patients.

Molecular dissection of HBV evasion from restriction factor tetherin: A new perspective for antiviral cell therapy

Viruses have evolved various strategies to escape from the innate cellular mechanisms inhibiting viral replication and spread. Extensive evidence has highlighted the ineffectiveness of interferon (IFN) therapy against chronic hepatitis B virus (HBV) infection, implying the existence of mechanisms by which HBV evades IFN-induced antiviral responses. In our current study, we demonstrate that HBV surface protein (HBs) plays a crucial role in counteracting the IFN-induced antiviral response mediated by tetherin (also known as BST-2). The type I IFN treatment of HBV-producing cells marginally but significantly inhibited the release of HBsAg and viral DNA, but this release was recovered by the knockdown of tetherin. HBs can interact with tetherin via its fourth transmembrane domain thereby inhibiting its dimerization and antiviral activity. The expression of a tetherin mutant devoid of the HBs-binding domain promoted a prominent restriction of HBV particle production that eventually resulted in the alleviation of caspase-1-mediated cytotoxicity and interleukin-1β secretion in induced pluripotent stem cell (iPSC)-derived hepatocytes. Our current results thus reveal a previously undescribed molecular link between HBV and tetherin during the course of an IFN-induced antiviral response. In addition, strategies to augment the antiviral activity of tetherin by impeding tetherin-HBs interactions may be viable as a therapeutic intervention against HBV.

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.

Expression of AIM2 is correlated with increased inflammation in chronic hepatitis B patients

Background

The absent in melanoma 2 (AIM2), a cytosolic dsDNA inflammasome, can be activated by viral DNA to trigger caspase-1. Its role in immunopathology of chronic hepatitis B and C virus (HBV, HCV) infection is still largely unclear. In this study, the expression AIM2, and its downstream cytokines, caspase-1, IL-18 and IL-1β, in liver tissue of patients with chronic hepatitis B and C (CHB, CHC) were investigated.

Methods

A total of 70 patients diagnosed with chronic hepatitis were enrolled, including 47 patients with CHB and 23 patients with CHC. A liver biopsy was taken from each patient, and immunohistochemistry was used to detect the expression of AIM2 and inflammatory factors caspase-1, IL-18, and IL-1β in the biopsy specimens. The relationship between AIM2 expression and these inflammatory factors was analyzed.

Results

The expression of AIM2 in CHB patients (89.4 %) was significantly higher than in CHC patients (8.7 %), and among the CHB patients, the expression of AIM2 was significantly higher in the high HBV replication group (HBV DNA ≥ 1 × 10⁵copies/mL) than in the low HBV replication group (HBV DNA < 1 × 10⁵copies/mL). The expression of AIM2 was also correlated with HBV-associated inflammatory activity in CHB patients statistically. Additionally, AIM2 levels were positively correlated with the expression of caspase-1, IL-1β and IL-18 in CHB patients, which implied that the AIM2 expression is directly correlated with the inflammatory activity associated with CHB.

Conclusions

AIM2 upregulation may be a component of HBV immunopathology. The underlying mechanism and possible signal pathway warrant further study.

The sterile inflammation in the exacerbation of HBV-associated liver injury

Exacerbation of hepatitis B virus-associated liver injury is characterized by abnormal immune response which not only mobilizes specific antiviral effects but also poses a potentially lethal nonspecific sterile inflammation to the host. How nonspecific sterile inflammation is triggered after the preexisting injury caused by specific immune injury remains elusive. In the setting of sterile inflammation, endogenous damage-associated molecular patterns are released by stressed and dying hepatocytes, which alarm the immune system through their potential pattern recognition receptors and related signaling pathways, orchestrate the influx of diverse cytokines, and ultimately amplify liver destruction. This review highlights current knowledge about the sterile hepatic inflammation in the exacerbation of chronic hepatitis B.

Anti-inflammatory cytokines, pro-fibrogenic chemokines and persistence of acute HCV infection

Chemokines and cytokines play a vital role in directing and regulating immune responses to viral infections. Persistent hepatitis C virus (HCV) infection is characterized by the loss of anti-HCV cellular immune responses, while control of HCV infection is associated with maintenance of anti-HCV cellular immune responses. To determine whether plasma concentrations of 19 chemokines and cytokines controlling T-cell trafficking and function differed based on infection outcome, we compared them in at-risk subjects followed prospectively for HCV infection. Levels were compared over time in subjects who controlled HCV infection (Clearance) and subjects who developed persistent HCV infection (Persistence) at two time points during acute infection: (i) first viraemic sample (initial viraemia) and (ii) last viraemic sample in Clearance subjects and time-matched samples in Persistence subjects. At initial viraemia, increased pro-inflammatory tumour necrosis factor α (TNFα) plasma concentrations were observed in the Clearance group, while the plasma levels of anti-inflammatory interleukin (IL)-2, IL-10 and IL-13 were higher in the Persistence group. IL-13 was positively correlated with IL-2 and IL-10 at initial viraemia in the Persistence group. At the time of last viraemia, plasma levels of eotaxin, macrophage chemoattractant protein-4 (MCP-4), IL-5 and IL-10 were higher in the Persistence group and IL-10 and IL-5 levels were positively correlated. Collectively, these results suggest that the development of persistent infection is associated with an anti-inflammatory and pro-fibrogenic chemokine and cytokine profile that is evident at the onset of infection and maintained throughout acute infection.

Changes in CD4+ T lymphocyte subsets and clinical outcomes of hepatitis B virus infection

Various clinical manifestations may develop in people infected with hepatitis B virus (HBV), ranging from asymptomatic infection to acute severe hepatitis B. Some infections become self-limiting when the virus is cleared, while approximately 90% of children and 10% of adults become HBV carriers or patients with chronic hepatitis B, who can further develop cirrhosis and hepatocellular carcinoma. CD4⁺ T lymphocytes play a central role in anti-infection immunity and can be divided into different subsets, including Th1, Th2, Treg, Th17, Th22, Th9 and Tfh. These T lymphocyte subsets all come from the same progenitor cells (Th0), although they have particular differentiation pathway and secrete different kinds of cytokines. Furthermore, they are able to interact with each other and change into each other. Particularly, the balances of Th1/Th2 and Th17/Treg play a vital role in determining the clinical outcomes of HBV infection.

Correlation of AIM2 expression in peripheral blood mononuclear cells from humans with acute and chronic hepatitis B

The AIM2 (absent in melanoma 2) protein promotes host defenses against invading viruses and pathogenic bacteria through corresponding adapter molecules leading to the initiation of innate immune responses. We investigated the expression of AIM2 in peripheral blood mononuclear cells (PBMCs) from patients with acute hepatitis B (AHB) and chronic hepatitis B (CHB) during different clinical phases, and analyzed the correlation between AIM2 and clinical profiles in these groups. This study indicated that there is higher expression of AIM2, IL-1β, and IL-18 in AHB compared with expression in CHB. The expression of AIM2 mRNA was significantly negatively correlated with serum hepatitis B virus (HBV) load, HBeAg, and significantly positively correlated with IL-1β and IL-18 in AHB patients and CHB patients with immune clearance, which suggests that AIM2 expression is correlated with the immune clearance of HBV in the host. We summarized that there is a higher immune status in AHB, and a lower immune response in CHB. This suggests that the down-regulation of AIM2 may be associated with the chronic development of HB.

New insights into how HBV manipulates the innate immune response to establish acute and persistent infection

The mechanisms by which HBV establishes and maintains chronic infection are poorly understood. Although adult acquired HBV is generally cleared by a robust immune response, most individuals infected at childbirth or in very early childhood develop lifelong chronic infection. In addition, acute infections are unresolved in approximately 5% of individuals infected in adulthood. The host cell mechanisms that ensure establishment and resolution of acute infection and persistent infection remain unclear. Currently, two schools of thought suggest that either HBV is a 'stealth' virus, which initially establishes infection by avoiding host innate immune responses, or that HBV facilitates initial infection and progression to persistence by actively manipulating the host innate immune response to its advantage. There is increasing evidence that activation of innate host cell signalling pathways plays a major role in limiting adult acquired HBV infection and that, in turn, HBV has evolved numerous strategies to counteract these defence mechanisms. In this review, we summarize current knowledge regarding innate immune responses to HBV infection and discuss how HBV regulates cell signalling pathways to its advantage, particularly in the setting of chronic HBV infection. In turn, we show how an intimate knowledge of innate immune responses is driving development of novel therapeutic agents to treat chronic HBV infection.

Inflammasomes in liver diseases

Inflammation is a common element in the pathogenesis of most chronic liver diseases that lead to fibrosis and cirrhosis. Inflammation is characterized by activation of innate immune cells and production of pro-inflammatory cytokines IL-1α, IL-1β, and TNFα. Inflammasomes are intracellular multiprotein complexes expressed in both parenchymal and non-parenchymal cells of the liver that in response to cellular danger signals activate caspase-1, and release IL-1β and IL-18. The importance of inflammasome activation in various forms of liver diseases in relation to liver damage, steatosis, inflammation and fibrosis is discussed in this review.

The role of innate immunity in HBV infection

Hepatitis B virus (HBV) infection is one of the main causes of chronic liver diseases. Whether HBV infection is cleared or persists is determined by both viral factors and host immune responses. It becomes clear that innate immunity is of importance in protecting the host from HBV infection and persistence. However, HBV develops strategies to suppress the antiviral immune responses. A combined therapeutic strategy with both viral suppression and enhancement of antiviral immune responses is needed for effective long-term clearance and cure for chronic HBV infection. We and others confirmed that bifunctional siRNAs with both gene silencing and innate immune activation properties are beneficial for inhibition of HBV and represent a potential approach for treatment of viral infection. Understanding the nature of liver innate immunity and their roles in chronic HBV progression and HBV clearance may aid in the design of novel therapeutic strategies for chronic HBV infection.

Modulation of serum interleukin-18 concentrations and hepatitis B virus DNA levels during interferon therapy in patients with hepatitis B e-antigen-positive chronic hepatitis B

The aim of this study was (1) to determine plasma values of interleukin-18 (IL-18) in patients with different clinical manifestations of hepatitis B (HB) and (2) to analyze the correlation between presence of circulatory levels of IL-18 and levels of HB virus (HBV) DNA during interferon-alpha (IFN-α)-induced HBe seroconversion in patients with chronic HB (CHB). The IL-18 levels in serum did not significantly differ between healthy control subjects (99 ± 25 pg/mL), HB-immune patients (85 ± 33), and asymptomatic carriers of HB surface antigen (144 ± 44 pg/mL). In contrast, anti-HBe (HBV DNA <10⁴ copies/mL, 555 ± 248, P < 0.05), anti-HBe (HBV DNA >10⁴ copies/mL, 280 ± 85, P < 0.05), and HBe-antigen-reactive (373 ± 108, P < 0.0001) patients with symptomatic CHB had significantly elevated levels in circulation compared with healthy control subjects (99 ± 25 pg/mL). An inverse correlation was found between serum HBV DNA copies and IL-18 levels during therapy (r = -0.54, P < 0.001). We consistently observed an IFN-α-induced suppression of viral replication, which was followed by the alanine aminotransferase (ALT) flare. There was a significant increase in IL-18 production after the ALT flare, where the peak of IL-18 preceded or coincided with the time of HBe seroconversion in patients who cleared the virus. These results suggest that IL-18 is involved in the pathogenesis of CHB and that IFN-α therapy can augment the production of IL-18 in patients with CHB.

Central roles of NLRs and inflammasomes in viral infection

The immune response to viral infections is determined by a complex interplay between the pathogen and the host. Innate immune cells express a set of cytosolic sensors to detect viral infection. Recognition by these sensors induces the production of type I interferons and the assembly of inflammasome complexes that activate caspase-1, leading to production of interleukin-1β (IL-1β) and IL-18. Here, I discuss recent progress in our understanding of the central roles of NOD-like receptors (NLRs) and inflammasomes in the immune response during viral infections. This information will improve our understanding of host defence mechanisms against viruses and provide new avenues for interfering in the pathogenesis of infectious diseases.

Inhibition of protein kinase C phosphorylation of hepatitis B virus capsids inhibits virion formation and causes intracellular capsid accumulation

Capsids of hepatitis B virus and other hepadnaviruses contain a cellular protein kinase, which phosphorylates the capsid protein. Some phosphorylation sites are shown to be essential for distinct steps of viral replication as pregenome packaging or plus strand DNA synthesis. Although different protein kinases have been reported to phosphorylate the capsid protein, varying experimental approaches do not allow direct comparison. Furthermore, the activity of a specific protein kinase has not yet been correlated to steps in the hepadnaviral life cycle. In this study we show that capsids from various sources encapsidate active protein kinase Calpha, irrespective of hepatitis B virus genotype and host cell. Treatment of a virion expressing cell line with a pseudosubstrate inhibitor showed that inhibition of protein kinase C phosphorylation did not affect genome maturation but resulted in capsid accumulation and inhibited virion release to the medium. Our results imply that different protein kinases have distinct functions within the hepadnaviral life cycle.

Hepatitis B virus-induced hFGL2 transcription is dependent on c-Ets-2 and MAPK signal pathway

Fibrinogen-like protein 2 (FGL2)/fibroleukin plays a pivotal role in the pathogenesis of experimental and human fulminant and chronic viral hepatitis. To define the transcription factor(s) and upstream signal transduction pathways involved in the transcription of human FGL2 (hFGL2) in response to hepatitis B (HB) virus, hepatitis B core (HBc), hepatitis B virus S protein (HBs), or hepatitis B virus X protein (HBx) protein, expression plasmids were cotransfected with an hFGL2 promoter luciferase reporter construct into Chinese hamster ovary and HepG2 cells, respectively. HBc and HBx proteins, but not HBs protein, enhanced hFGL2 transcription in both cell lines. A strong regulatory region from -712 to -568 (relative to the transcriptional starting site) was shown to be responsible for hFGL2 gene transcription in response to both HBc and HBx proteins. c-Ets-2 was shown to be translocated to the nucleus in association with hFGL2 expression in response to both HBc and HBx proteins. Short hairpin RNA (shRNA) interference of c-Ets-2 expression inhibited hFGL2 gene transcription by 64.8 and 60.0% in response to HBc and HBx, respectively. c-Ets-2 protein was highly expressed in peripheral blood mononuclear cells from patients with severe chronic hepatitis B (CHB) in contrast to patients with mild CHB. Increased phosphorylation of ERK and JNK was detected in peripheral blood mononuclear cells from patients with severe CHB. ERK inhibitor PD098059 or ERK shRNA abolished the nuclear c-Ets-2 DNA binding activity and hFGL2 induction in response to HBc, whereas JNK inhibitor SP600125 or JNK shRNA abolished the nuclear c-Ets-2 DNA binding activity and hFGL2 induction in response to HBx. In conclusion, HBc and HBx proteins enhance transcription of hFGL2 through c-Ets-2 dependent on MAPK signal pathways.

Mechanism of T cell hyporesponsiveness to HBcAg is associated with regulatory T cells in chronic hepatitis B

AIM

To study the mechanisms of hyporesponsiveness of HBV-specific CD4+ T cells by testing TH1 and TH2 commitment and regulatory T cells.

METHODS

Nine patients with chronic hepatitis B were enrolled. Peripheral blood mononuclear cells were stimulated with HBcAg or HBsAg to evaluate their potential to commit to TH1 and TH2 differentiation. HBcAg-specific activity of regulatory T cells was evaluated by staining with antibodies to CD4, CD25, CTLA-4 and interleukin-10. The role of regulatory T cells was further assessed by treatment with anti-interleukin-10 antibody and depletion of CD4+CD25+ cells.

RESULTS

Level of mRNAs for T-bet, IL-12R beta2 and IL-4 was significantly lower in the patients than in healthy subjects with HBcAg stimulation. Although populations of CD4+CD25highCTLA-4+ T cells were not different between the patients and healthy subjects, IL-10 secreting cells were found in CD4+ cells and CD4+CD25+ cells in the patients in response to HBcAg, and they were not found in cells which were stimulated with HBsAg. Addition of anti-IL-10 antibody recovered the amount of HBcAg-specific TH1 antibody compared with control antibody (P < 0.01, 0.34% +/- 0.12% vs 0.15% +/- 0.04%). Deletion of CD4+CD25+ T cells increased the amount of HBcAg-specific TH1 antibody when compared with lymphocytes reconstituted using regulatory T cells (P < 0.01, 0.03% +/- 0.02% vs 0.18% +/- 0.05%).

CONCLUSION

The results indicate that the mechanism of T cell hyporesponsiveness to HBcAg includes activation of HBcAg-induced regulatory T cells in contrast to an increase in TH2-committed cells in response to HBsAg.

Cytokine Induction by the Hepatitis B Virus Capsid in Macrophages Is Facilitated by Membrane Heparan Sulfate and Involves TLR2

The hepatitis B virus (HBV) core Ag (HBcAg) serves as the structural subunit of the highly immunogenic capsid shell. HBcAg harbors a unique arginine-rich C terminus that was implicated in immune responses induced by the capsid. In this study, we examined the capacity of the HBV capsid to induce proinflammatory and regulatory cytokines in human THP-1 macrophages and the possible underlying mechanism. Full-length HBc capsids, but not HBc-144 capsids lacking the arginine-rich domain of HBcAg, efficiently bound differentiated THP-1 macrophages and strongly induced TNF-alpha, IL-6, and IL-12p40. Capsid binding to macrophages and cytokine induction were independent of the RNA associated with the arginine-rich domain. Soluble heparin and heparan sulfate but not chondroitin sulfates greatly diminished cytokine induction through inhibition of capsid binding to THP-1 macrophages. Furthermore, serine phosphorylation in the arginine-rich domain modulates capsid binding to macrophages and the cytokine response. Induction of cytokines by the capsid involved activation of NF-kappaB, ERK-1/2, and p38 MAPK and did not require endosomal acidification. Finally, NF-kappaB activation by the capsid in HEK 293 cells specifically required expression of TLR2 and was compromised by soluble heparin. Thus, cytokine induction by the HBV capsid in macrophages is facilitated by interaction of its arginine-rich domain with membrane heparan sulfate and involves signaling through TLR2.

Immunostimulatory potential of hepatitis B nucleocapsid preparations: lipopolysaccharide contamination should not be overlooked

The nucleocapsid of hepatitis B virus (HBV) allows insertions of heterologous peptides and even complete proteins. Because of its outstanding capacity to induce B-cell, T-helper and cytotoxic T-cell responses, this structure is considered to be an important instrument for future vaccine development. Most of the evidence for the unique immunogenic qualities of nucleocapsids has been generated in mice, which are not natural hosts of HBV. Moreover, most nucleocapsid preparations used in these studies were produced in a recombinant manner in Escherichia coli. Such preparations have been shown to contain lipopolysaccharide (LPS). Not unexpectedly, it is shown here that contaminating LPS, rather than the nucleocapsid structure itself, is responsible for the activation of human antigen-presenting cells. Careful examination of the literature dealing with the immunogenicity of HBV nucleocapsids suggests that the possible presence of LPS has been largely ignored or underestimated in several studies. This raises doubts on some of the underlying mechanisms that have been proposed to explain the unique immunogenicity of the HBV nucleocapsid.

Down-regulatory effects of HBsAg promoter ⅠDNA binding protein 1 on IL-18 gene expression

AIM: To investigate the relationship between HBsAg promoterⅠDNA binding protein 1 (SBP1) and IL-18 promoter gene expression.

METHODS: Recombinant plasmid, named pcDNA3.1(-)-SBP1, were constructed by inserting a gene fragment of hepatitis B virus surface antigen promoterⅠDNA binding protein1 (SBP1) into pcDNA3.1(-). Then it was transfected into HepG2 cells transfected with pCAT3-IL-18P by FuGENE 6 transfection reagents. The activity of chloramphenicol acetyltransferase (CAT) in HepG2 cells was detected by enzyme-linked immunoassay (ELISA) after 48 h.

RESULTS: pcDNA3.1(-)-SBP1 was confirmed by restriction enzyme digestion and sequencing. The expression of CAT in HepG2 cells co-transfected with pCAT3-IL-18P and pcDNA3.1(-)-SBP1 was 0.37 times of that transfected with pCAT3-basic, and 0.17 times of that transfected with pCAT3-IL-18P. The inhibitory rate was about 86.32%.

CONCLUSION: SBP1 can down-regulate the expression of IL-18P promoter, which provides new evidence to explain the molecular biological mechanisms of SBP1 in the interactions between IL-18P and hepatocytes.

Circulating concentrations of interleukin-18, interleukin-18 binding protein, and gamma interferon in patients with alcoholic hepatitis

BACKGROUND

Alcoholic hepatitis (AH) is associated with dysregulated inflammatory and immune responses. interleukin-18 (IL-18), described as gamma interferon (gammaIFN)-inducible factor, and its natural antagonist, IL-18 binding protein (IL-18 BP), has not been fully studied in patients with AH. Thus, our aim was: (i) to determine plasma values of IL-18, IL-18 BP, gammaIFN, and tumor necrosis factor alpha (TNF)-alpha in patients hospitalized for biopsy-proven AH; (ii) to correlate these cytokines with the severity of AH, as assessed by Maddrey's discriminant function (DF), the degree of liver failure using the Child-Pugh score and blood neutrophils; (iii) to compare cytokines values in survivors and non-survivors.

METHODS

Cytokines were measured using specific immunoassays within 7 days of admission. The diagnosis of AH was based on histology in all cases. We studied 43 cirrhotic patients with a Maddrey's DF>/=32 (severe AH), 29 patients with a score <32 (non-severe AH), 12 patients with abstinent alcoholic cirrhosis, and 10 healthy subjects.

RESULTS

IL-18 and TNFalpha were increased in severe AH as compared with healthy subjects. Plasma IL-18 BP was elevated in patients with severe and non-severe AH as compared with healthy subjects. gammaIFN did not differ between groups. In patients with severe and non-severe AH, IL-18, IL-18 BP, TNFalpha, but not gammaIFN, were positively correlated to DF and Child-Pugh score. Neither IL-18 nor IL-18 BP correlated to TNFalpha. Patients who died (n=10) during the hospitalization had higher IL-18 BP and TNFalpha at admission as compared with survivors (322 [172-504] vs 222 [109-441] ng/ml; 7.5 [2.2-17.3] vs 3 [0.6-20] pg/ml, P<0.01, respectively).

CONCLUSION

In cirrhotic patients with AH, IL-18, IL-18 BP, and TNFalpha correlate to the hepatitis severity and to the degree of liver failure. High IL-18 BP and TNFalpha at hospital admission in non-survivors suggest it may be of prognostic value.

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