Patients with chronic hepatitis B infection display deficiency of plasmacytoid dendritic cells with reduced expression of TLR9

Metabolic Deficiencies Underlie Plasmacytoid Dendritic Cell Exhaustion After Viral Infection

Type I Interferons (IFN-I) are central to host protection against viral infections 1 . While any cell can produce IFN-I, Plasmacytoid Dendritic Cells (pDCs) make greater quantities and more varieties of these cytokines than any other cell type 2 . However, following an initial burst of IFN- I, pDCs lose their exceptional IFN-I production capacity and become "exhausted", a phenotype that associates with enhanced susceptibility to secondary infections 3-5 . Despite this apparent cost for the host, pDC exhaustion is conserved across multiple species and viral infections, but the underlying mechanisms and the potential evolutionary advantages are not well understood. Here we characterize pDC exhaustion and demonstrate that it is associated with a reduced capacity of pDCs to engage both oxidative and glycolytic metabolism. Mechanistically, we identify lactate dehydrogenase B (LDHB) as a novel positive regulator of pDC IFN-I production in mice and humans, show that LDHB deficiency is associated with suppressed IFN-I production, pDC metabolic capacity, and viral control following a viral infection, and demonstrate that preservation of LDHB expression is sufficient to partially restore exhausted pDC function in vitro and in vivo . Furthermore, restoring LDHB in vivo in exhausted pDCs increased IFNAR dependent infection- associated pathology. Therefore, our work identifies a novel and conserved mechanism for balancing immunity and pathology during viral infections, while also providing insight into the highly preserved but previously unexplained phenomenon of pDC exhaustion.

H3K9 acetylation modification and TLR9 immune regulation mechanism in patients after anti-HBV treatment

To improve the curative effect of anti-hepatitis B virus (HBV) drugs, methods such as thymosin and entecavir combination have become a focus of clinical investigation. The aim of this retrospective experimental study was to explore the potential mechanism of action of thymosin a1 (Ta1) combined with entecavir in the treatment of HBV infection. A total of 28 patients with chronic hepatitis B, 29 patients treated with thymosin a1 and entecavir combination, and 15 healthy individuals were enrolled in this study. RT-qPCR was conducted to evaluate the mRNA levels of TLR9 in peripheral blood mononuclear cells (PBMCs). The serum level of TLR9 protein was analyzed by ELISA. The binding of TLR9 gene to the protein H3K9Ac in PBMCs was assessed by chromatin immunoprecipitation, and serum inflammatory factors were detected by Luminex technology. The expression levels of TLR9 mRNA and serum TLR9 protein in patients with HBV infection were significantly lower than those in subjects in the control group before treatment but increased after treatment with the Ta1 and entecavir combination. Moreover, the acetylation protein H3K9Ac was significantly bound to the promoter region of the TLR9 gene in patients with HBV infection treated with the Ta1 and entecavir combination compared to that in patients with HBV infection without treatment. Furthermore, the expression levels of interleukin 6 (IL-6), interleukin 12 (IL-12), interferon gamma, and necrosis factor alpha in patients with HBV infection after the combination treatment were slightly decreased compared to those in patients with HBV infection without treatment. In conclusion, the histone acetylation modification of TLR9 was significantly improved in patients with HBV infection after treatment with the Ta1 and entecavir combination, which elevated the expression of TLR9 at the mRNA and protein levels and further regulated the expression of IL-6, IL-12, and other cytokines.

Mesenchymal stem cells-based therapy in liver diseases

Multiple immune cells and their products in the liver together form a complex and unique immune microenvironment, and preclinical models have demonstrated the importance of imbalances in the hepatic immune microenvironment in liver inflammatory diseases and immunocompromised liver diseases. Various immunotherapies have been attempted to modulate the hepatic immune microenvironment for the purpose of treating liver diseases. Mesenchymal stem cells (MSCs) have a comprehensive and plastic immunomodulatory capacity. On the one hand, they have been tried for the treatment of inflammatory liver diseases because of their excellent immunosuppressive capacity; On the other hand, MSCs have immune-enhancing properties in immunocompromised settings and can be modified into cellular carriers for targeted transport of immune enhancers by genetic modification, physical and chemical loading, and thus they are also used in the treatment of immunocompromised liver diseases such as chronic viral infections and hepatocellular carcinoma. In this review, we discuss the immunological basis and recent strategies of MSCs for the treatment of the aforementioned liver diseases. Specifically, we update the immune microenvironment of the liver and summarize the distinct mechanisms of immune microenvironment imbalance in inflammatory diseases and immunocompromised liver diseases, and how MSCs can fully exploit their immunotherapeutic role in liver diseases with both immune imbalance patterns.

Toll-like receptor-mediated innate immunity orchestrates adaptive immune responses in HBV infection

Chronic hepatitis B virus (HBV) infection remains to be a substantial global burden, especially for end-stage liver diseases. It is well accepted that HBV-specific T and B cells are essential for controlling HBV infection. Toll-like receptors (TLRs) represent one of the major first-line antiviral defenses through intracellular signaling pathways that induce antiviral inflammatory cytokines and interferons, thereby shaping adaptive immunity. However, HBV has evolved strategies to counter TLR responses by suppressing the expression of TLRs and blocking the downstream signaling pathways, thus limiting HBV-specific adaptive immunity and facilitating viral persistence. Recent studies have stated that stimulation of the TLR signaling pathway by different TLR agonists strengthens host innate immune responses and results in suppression of HBV replication. In this review, we will discuss how TLR-mediated responses shape HBV-specific adaptive immunity as demonstrated in different experimental models. This information may provide important insight for HBV functional cure based on TLR agonists as immunomodulators.

Role of Innate Immune Regulatory Genes, FOXP3 and FOS in Chronic Hepatitis B Infection

Persistence of hepatitis B virus (HBV) infection leading to chronic infection and its sequalae is responsible for over half a million deaths worldwide. The reason for persistence of chronic hepatitis B (CHB) infection is still not clearly understood. An attempt was made to understand the role of immune regulatory genes in CHB in comparison to spontaneously cleared HBV infection. Relative gene expression of 26 genes involved in innate immunity were studied using Real-Time Polymerase Chain Reaction Array. A total of 679 subjects from three different geographical regions of Northeast India (Assam, Arunachal Pradesh, and Tripura) were included in this case-control study. The cases were subdivided into CHB cases with HBeAg(+)(72), CHB with HBeAg(-)(278), spontaneously cleared controls (88), and healthy controls (228). Overall, 28.3% of the subjects had previous exposure with HBV, while 28.6% had protective antibodies IgG/IgM against HBV. There was a statistically higher number of CHB in men (66.4%) compared to women (33.6%) (p = 0.0001). Proto-oncogene FOS has been found to be moderately upregulated in CHB with HBeAg +ve (2.3-fold) and significantly upregulated (4.1-fold upregulation) in hepatocellular carcinoma. Further, FOXP3 was found to be significantly upregulated (3.0-fold, p = 0.01) in CHB with HBeAg (+) compared to spontaneously cleared HBV infection. In conclusion, CHB with HBeAg positivity was found to have disrupted immune response with upregulation of FOS and FOXP3. Thus, early induction of HBeAg seroconversion with interferon-based therapy or oral nucleos(t)ide analogs along with FOS inhibitors can have important clinical implications in the management of CHB and preventing cirrhosis and HCC.

Regulation of Pattern-Recognition Receptor Signaling by HBX During Hepatitis B Virus Infection

As a small DNA virus, hepatitis B virus (HBV) plays a pivotal role in the development of various liver diseases, including hepatitis, cirrhosis, and liver cancer. Among the molecules encoded by this virus, the HBV X protein (HBX) is a viral transactivator that plays a vital role in HBV replication and virus-associated diseases. Accumulating evidence so far indicates that pattern recognition receptors (PRRs) are at the front-line of the host defense responses to restrict the virus by inducing the expression of interferons and various inflammatory factors. However, depending on HBX, the virus can control PRR signaling by modulating the expression and activity of essential molecules involved in the toll-like receptor (TLR), retinoic acid inducible gene I (RIG-I)-like receptor (RLR), and NOD-like receptor (NLR) signaling pathways, to not only facilitate HBV replication, but also promote the development of viral diseases. In this review, we provide an overview of the mechanisms that are linked to the regulation of PRR signaling mediated by HBX to inhibit innate immunity, regulation of viral propagation, virus-induced inflammation, and hepatocarcinogenesis. Given the importance of PRRs in the control of HBV replication, we propose that a comprehensive understanding of the modulation of cellular factors involved in PRR signaling induced by the viral protein may open new avenues for the treatment of HBV infection.

Toll-Like Receptor Response to Hepatitis B Virus Infection and Potential of TLR Agonists as Immunomodulators for Treating Chronic Hepatitis B: An Overview

Chronic hepatitis B virus (HBV) infection remains a major global health problem. The immunopathology of the disease, especially the interplay between HBV and host innate immunity, is poorly understood. Moreover, inconsistent literature on HBV and host innate immunity has led to controversies. However, recently, there has been an increase in the number of studies that have highlighted the link between innate immune responses, including Toll-like receptors (TLRs), and chronic HBV infection. TLRs are the key sensing molecules that detect pathogen-associated molecular patterns and regulate the induction of pro- and anti-inflammatory cytokines, thereby shaping the adaptive immunity. The suppression of TLR response has been reported in patients with chronic hepatitis B (CHB), as well as in other models, including tree shrews, suggesting an association of TLR response in HBV chronicity. Additionally, TLR agonists have been reported to improve the host innate immune response against HBV infection, highlighting the potential of these agonists as immunomodulators for enhancing CHB treatment. In this study, we discuss the current understanding of host innate immune responses during HBV infection, particularly focusing on the TLR response and TLR agonists as immunomodulators.

Type I Interferon Induction and Exhaustion during Viral Infection: Plasmacytoid Dendritic Cells and Emerging COVID-19 Findings

Type I Interferons (IFN-I) are a family of potent antiviral cytokines that act through the direct restriction of viral replication and by enhancing antiviral immunity. However, these powerful cytokines are a caged lion, as excessive and sustained IFN-I production can drive immunopathology during infection, and aberrant IFN-I production is a feature of several types of autoimmunity. As specialized producers of IFN-I plasmacytoid (p), dendritic cells (DCs) can secrete superb quantities and a wide breadth of IFN-I isoforms immediately after infection or stimulation, and are the focus of this review. Notably, a few days after viral infection pDCs tune down their capacity for IFN-I production, producing less cytokines in response to both the ongoing infection and unrelated secondary stimulations. This process, hereby referred to as "pDC exhaustion", favors viral persistence and associates with reduced innate responses and increased susceptibility to secondary opportunistic infections. On the other hand, pDC exhaustion may be a compromise to avoid IFN-I driven immunopathology. In this review we reflect on the mechanisms that initially induce IFN-I and subsequently silence their production by pDCs during a viral infection. While these processes have been long studied across numerous viral infection models, the 2019 coronavirus disease (COVID-19) pandemic has brought their discussion back to the fore, and so we also discuss emerging results related to pDC-IFN-I production in the context of COVID-19.

Molecular Mechanisms during Hepatitis B Infection and the Effects of the Virus Variability

The immunopathogenesis and molecular mechanisms involved during a hepatitis B virus (HBV) infection have made the approaches for research complex, especially concerning the patients’ responses in the course of the early acute stage. The study of molecular bases involved in the viral clearance or persistence of the infection is complicated due to the difficulty to detect patients at the most adequate points of the disease, especially in the time lapse between the onset of the infection and the viral emergence. Despite this, there is valuable data obtained from animal and in vitro models, which have helped to clarify some aspects of the early immune response against HBV infection. The diversity of the HBV (genotypes and variants) has been proven to be associated not only with the development and outcome of the disease but also with the response to treatments. That is why factors involved in the virus evolution need to be considered while studying hepatitis B infection. This review brings together some of the published data to try to explain the immunological and molecular mechanisms involved in the different stages of the infection, clinical outcomes, viral persistence, and the impact of the variants of HBV in these processes.

Identification of miRNAs associated with dendritic cell dysfunction during acute and chronic hepatitis B virus infection

The uptake or expression of hepatitis B virus (HBV) proteins by dendritic cells (DCs) is considered important for disease outcome. Differential expression of microRNA (miRNA) may have a role in viral persistence and hepatocellular injury. The miRNA expression was investigated by microarray in DCs from different stages of HBV infection and liver disease namely, immune active (IA; n = 20); low replicative (LR; n = 20); HBeAg negative (n = 20); acute viral hepatitis (AVH, n = 20) and healthy controls (n = 20). miRNA levels were analyzed by unsupervised hierarchical clustering and principal component analyses and validated by quantitative polymerase Chain Reaction (qPCR). The miRNA-messenger RNA (mRNA)regulatory networks identified 19 miRNAs and 12 target gene interactions in major histocompatibility complex and other immune pathways. miR-2278, miR-615-3p, and miR-3681-3p were downregulated in the IA group compared to healthy control, miR-152-3p and miR-3613-3p in the LR group compared to IA group and miR-152-3p and miR-503-3p in HBe negative compared to LR group. However, miR-7-1-1-3p, miR-192-5p, miR-195-5p, and miR-32-5p in LR, miR-342-3p, and miR-940 in HBe negative, and miR-34a-5p, miR-130b-3p, miR-221-3p, miR-320a, miR-324-5p, and miR-484 in AVH were upregulated. Further, qPCR confirmed changes in miRNA levels and their target genes associated with antigen processing and presentation. Thus, a deregulated network of miRNAs-mRNAs in DCs seems responsible for an impaired immune response during HBV pathogenesis.

Treatment with the Immunomodulator AIC649 in Combination with Entecavir Produces Antiviral Efficacy in the Woodchuck Model of Chronic Hepatitis B

As current interventions for chronic hepatitis B (CHB) rarely induce cure, more effective drugs are needed. Short-term treatment of woodchucks with the novel immunomodulator AIC649, a parapoxvirus-based stimulator of toll-like receptor 9 dependent and independent pathways, has been shown to reduce viral DNA and surface antigen via a unique, biphasic response pattern. The present study evaluated long-term AIC649 treatment in combination with Entecavir for potency and safety in woodchucks. AIC649 monotreatment induced modest reductions in serum viral DNA and surface and e antigens that were associated with the same biphasic response pattern previously observed. Entecavir monotreatment reduced transiently viremia but not antigenemia, while AIC649/Entecavir combination treatment mediated superior viral control. Undetectability of viral antigens and elicitation of antibodies in AIC649/Entecavir-treated woodchucks correlated with the expression of interferons and suppression of viral replication in liver. Combination treatment was well tolerated, and liver enzyme elevations were minor and transient. It was concluded that the AIC649-mediated effects were most likely based on an improvement and/or reconstitution of antiviral immune responses that are typically deficient in CHB. As a combination partner to Entecavir, the antiviral efficacy of AIC649 was markedly enhanced. This preclinical study supports future evaluation of AIC649 for treatment of human CHB.

Hepatitis B virus exploits C-type lectin receptors to hijack cDC1s, cDC2s and pDCs

Objectives

C‐type lectin receptors (CLRs) are key receptors used by DCs to orchestrate responses to pathogens. During infections, the glycan–lectin interactions shape the virus–host interplay and viruses can subvert the function of CLRs to escape antiviral immunity. Recognition of virus/viral components and uptake by CLRs together with subsequent signalling cascades are crucial in initiating and shaping antiviral immunity, and decisive in the outcome of infection. Yet, the interaction of hepatitis B virus (HBV) with CLRs remains largely unknown. As HBV hijacks DC subsets and viral antigens harbour glycan motifs, we hypothesised that HBV may subvert DCs through CLR binding.

Methods

We investigated here the pattern of CLR expression on BDCA1⁺ cDC2s, BDCA2⁺ pDCs and BDCA3⁺ cDC1s from both blood and liver of HBV‐infected patients and explored the ability of HBsAg to bind DC subsets through specific CLRs.

Results

We highlighted for the first time that the CLR repertoire of circulating and intrahepatic cDC2s, cDC1s and pDCs was perturbed in patients with chronic HBV infection and that some CLR expression levels correlated with plasma HBsAg and HBV DNA levels. We also identified candidate CLR responsible for HBsAg binding to cDCs (CD367/DCIR/CLEC4A, CD32/FcɣRIIA) and pDCs (CD369/DECTIN1/CLEC7A, CD336/NKp44) and demonstrated that HBsAg inhibited DC functions in a CLR‐ and glycosylation‐dependent manner.

Conclusion

HBV may exploit CLR pathways to hijack DC subsets and escape from immune control. Such advances bring insights into the mechanisms by which HBV subverts immunity and pave the way for developing innovative therapeutic strategies to restore an efficient immune control of the infection by manipulating the viral glycan–lectin axis.

Infection and cancer suppress pDC derived IFN-I

Plasmacytoid dendritic cells (pDCs) are specialized producers of Type I interferon (IFN-I) that promote anti-viral and anti-tumor immunity. However, chronic infections and cancer inhibit pDC-derived IFN-I. While the mechanisms of this inhibition are multifarious they can be classified broadly into two categories: i) reduction or ablation of pDC IFN-I-production capacity (functional exhaustion) and/or ii) decrease in pDC numbers (altered population dynamics). Recent work has identified many processes that contribute to suppression of pDC-derived IFN-I during chronic infections and cancer, including sustained stimulation through Toll Like Receptors (TLRs), inhibitory microenvironments, inhibitory receptor ligation, and reduced development from bone marrow progenitors and apoptosis. Emerging success leveraging pDCs in treatment of disease through TLR activation illustrates the therapeutic potential of targeting pDCs. Deeper understanding of the systems that limit pDC-derived IFN-I has the potential to improve these emerging therapies as well as help devising new approaches that harness the outstanding IFN-I-production capacity of pDCs.

Pathogenetic Mechanisms of T Cell Dysfunction in Chronic HBV Infection and Related Therapeutic Approaches

A great effort of research has been devoted in the last few years to developing new anti-HBV therapies of finite duration that also provide effective sustained control of virus replication and antigen production. Among the potential therapeutic strategies, immune-modulation represents a promising option to cure HBV infection and the adaptive immune response is a rational target for novel therapeutic interventions, in consideration of the key role played by T cells in the control of virus infections. HBV-specific T cells are severely dysfunctional in chronic HBV infection as a result of several inhibitory mechanisms which are simultaneously active within the chronically inflamed liver. Indeed, the liver is a tolerogenic organ harboring different non-parenchymal cell populations which can serve as antigen presenting cells (APC) but are poorly efficient in effector T cell priming, with propensity to induce T cell tolerance rather than T cell activation, because of a poor expression of co-stimulatory molecules, up-regulation of the co-inhibitory ligands PD-L1 and PD-L2 upon IFN stimulation, and production of immune regulatory cytokines, such as IL10 and TGF-β. They include resident dendritic cells (DCs), comprising myeloid and plasmacytoid DCs, liver sinusoidal endothelial cells (LSECs), Kupffer cells (KCs), hepatic stellate cells (HSCs) as well as the hepatocytes themselves. Additional regulatory mechanisms which contribute to T cell attrition in the chronically infected liver are the high levels of soluble mediators, such as arginase, indoleamine 2,3-dioxygenase (IDO) and suppressive cytokines, the up-regulation of inhibitory checkpoint receptor/ligand pairs, the expansion of regulatory cells, such as CD4+FOXp3+ Treg cells, myeloid-derived suppressor cells and NK cells. This review will deal with the interactions between immune cells and liver environment discussing the different mechanisms which contribute to T cell dysfunction in chronic hepatitis B, some of which are specifically activated in HBV infection and others which are instead common to chronic inflammatory liver diseases in general. Therapeutic interventions targeting dysregulated pathways and cellular functions will be also delineated.

The Management of Glucocorticoid Therapy in Liver Failure

Liver failure is characterized by rapid progression and high mortality. Excessive systemic inflammation is considered as the trigger of liver failure. Glucocorticoids (GCs) can rapidly suppress excessive inflammatory reactions and immune response. GCs have been applied in the treatment of liver failure since the 1970s. However, until now, the use of GCs in the treatment of liver failure has been somewhat unclear and controversial. New research regarding the molecular mechanisms of GCs may explain the controversial actions of GCs in liver failure. More results should be confirmed in a larger randomized clinical trial; this can aid the discovery of better definitions in terms of treatment schedules according to different clinical settings. Meanwhile, the timing and dosing of GCs in the treatment of liver failure should also be explored.

Immune network for viral hepatitis B: Topological representation

The liver is a well-known immunotolerogenic environment, which provides the adequate setting for liver infectious pathogens persistence such as the hepatitis B virus (HBV). Consequently, HBV infection can derive in the development of chronic disease in a proportion of the patients. If this situation persists in time, chronic hepatitis B (CHB) would end in cirrhosis, hepatocellular carcinoma and eventually, the death of the patient. It is thought that this immunotolerogenic environment is the result of complex interactions between different elements of the immune system and the viral biology. Therefore, the purpose of this work is to unravel the mechanisms implied in the development of CHB and to design a tool able to help in the study of adequate therapies. Firstly, a conceptual framework with the main components of the immune system and viral dynamics was constructed providing an overall insight on the pathways and interactions implied in this disease. Secondly, a review of the literature was performed in a modular fashion: (i) viral dynamics, (ii) innate immune response, (iii) humoral and (iv) cellular adaptive immune responses and (v) tolerogenic aspects. Finally, the information collected was integrated into a single topological representation that could serve as the plan for the systems pharmacology model architecture. This representation can be considered as the previous unavoidable step to the construction of a quantitative model that could assist in biomarker and target identification, drug design and development, dosing optimization and disease progression analysis.

Circulating and Hepatic BDCA1+, BDCA2+, and BDCA3+ Dendritic Cells Are Differentially Subverted in Patients With Chronic HBV Infection

Background and aims: Chronic hepatitis B virus (HBV) infection is a major health burden potentially evolving toward cirrhosis and hepatocellular carcinoma. HBV physiopathology is strongly related to the host immunity, yet the mechanisms of viral evasion from immune-surveillance are still misunderstood. The immune response elicited at early stages of viral infection is believed to be important for subsequent disease outcome. Dendritic cells (DCs) are crucial immune sentinels which orchestrate antiviral immunity, which offer opportunity to pathogens to subvert them to escape immunity. Despite the pivotal role of DCs in orientating antiviral responses and determining the outcome of infection, their precise involvement in HBV pathogenesis is not fully explored.

Methods: One hundred thirty chronically HBV infected patients and 85 healthy donors were enrolled in the study for blood collection, together with 29 chronically HBV infected patients and 33 non-viral infected patients that were included for liver biopsy collection. In a pioneer way, we investigated the phenotypic and functional features of both circulating and intrahepatic BDCA1+ cDC2, BDCA2+ pDCs, and BDCA3+ cDC1 simultaneously in patients with chronic HBV infection by designing a unique multi-parametric flow cytometry approach.

Results: We showed modulations of the frequencies and basal activation status of blood and liver DCs associated with impaired expressions of specific immune checkpoints and TLR molecules on circulating DC subsets. Furthermore, we highlighted an impaired maturation of circulating and hepatic pDCs and cDCs following stimulation with specific TLR agonists in chronic HBV patients, associated with drastic dysfunctions in the capacity of circulating DC subsets to produce IL-12p70, TNFα, IFNα, IFNλ1, and IFNλ2 while intrahepatic DCs remained fully functional. Most of these modulations correlated with HBsAg and HBV DNA levels.

Conclusion: We highlight potent alterations in the distribution, phenotype and function of all DC subsets in blood together with modulations of intrahepatic DCs, revealing that HBV may hijack the immune system by subverting DCs. Our findings provide innovative insights into the immuno-pathogenesis of HBV and the mechanisms of virus escape from immune control. Such understanding is promising for developing new therapeutic strategies restoring an efficient immune control of the virus.

Immune function of plasmacytoid dendritic cells, natural killer cells, and their crosstalk in HBV infection

Chronic hepatitis B virus infection is a major health problem, with over 245 million chronic carriers worldwide. This persistent infection is thought to be associated with inefficient innate and adaptive immune responses. Natural killer cells (NK cells) and plasmacytoid dendritic cells (pDCs) are the major innate immune cells which respond to viral infection at the early phase and are considered major components of the antiviral immune response. In this review, we summarize recent findings regarding the role of NK cells, pDCs, and their cross-talk in HBV infection and its chronicity. Although the data regarding the biological function of pDCs and NK cells in HBV infection is still controversial, many studies show that in chronic HBV infection, the cytotoxicity of NK cells is retained, while their capacity to secrete cytokines is strongly impaired. In addition, interferon-α production by pDCs is impaired during chronic HBV infection, and the virus interferes with pDC-NK cell interaction.

Interaction between Toll-Like Receptor 9-CpG Oligodeoxynucleotides and Hepatitis B Virus Virions Leads to Entry Inhibition in Hepatocytes and Reduction of Alpha Interferon Production by Plasmacytoid Dendritic Cells

We previously reported that Toll-like receptor 9 (TLR9)-CpG oligonucleotides could inhibit the establishment of hepatitis B virus (HBV) infections in hepatocytes. Our aim was to uncover the underlying mechanisms of this inhibition. HepaRG cells, RPMI-B lymphoblastoma cells, and primary plasmacytoid dendritic cells (pDCs) exposed to HBV and TLR9 ligands/agonists in various configurations were used. We observed an inhibition of HBV infection upon TLR9 stimulations only when agonist was applied during inoculation. This inhibition was independent of interleukin-6 (IL-6)/interferon-inducible protein 10 (IP-10) production as well as of TLR9 expression in hepatocytes. We further demonstrated an entry inhibition mechanism by showing a noncovalent binding of TLR9 agonist to HBV particles. Besides inhibiting HBV entry into hepatocytes, this biophysical interaction between HBV virions and TLR9 agonist was responsible for a reduction of alpha interferon (IFN-α) expression by pDCs. Interestingly, subviral particles composed of only HBsAg were able to genuinely inhibit the TLR9 pathway, without titrating TLR9 ligands. To conclude, our data suggest that synthetic TLR9-CpG oligonucleotides can strongly inhibit HBV entry by "coating" HBV virions and thereby preventing their interaction with cellular receptor. This titration effect of TLR9 agonist is also artifactually responsible for the inhibition of TLR9 engagement in pDCs, whereas a genuine inhibition of this innate pathway was confirmed with HBsAg subviral particles.

Interaction between Hepatitis B Virus and Toll-Like Receptors: Current Status and Potential Therapeutic Use for Chronic Hepatitis B

Immune defense against infection with the hepatitis B virus (HBV) is complex and involves both host innate and adaptive immune systems. It is well accepted that the development of sufficient HBV-specific T cell and B cell responses are required for controlling an HBV infection. However, the contribution of innate immunity to removing HBV has been explored in recent years. Toll-like receptors (TLRs) are recognized as the first line of antiviral immunity because they initiate intracellular signaling pathways to induce antiviral mediators such as interferons (IFNs) and other cytokines. Recent studies show that the activation of TLR-mediated signaling pathways results in a suppression of HBV replication in vitro and in vivo. However, HBV has also evolved strategies to counter TLR responses including the suppression of TLR expression and the blockage of downstream signaling pathways. Antiviral treatment in chronic HBV-infected patients leads to an upregulation of TLR expression and the restoration of its innate antiviral functions. Thus, TLR activation may serve as an additional immunotherapeutic option for treating chronic HBV infection in combination with antiviral treatment.

Efficacy of a Virus-Like Nanoparticle As Treatment for a Chronic Viral Infection Is Hindered by IRAK1 Regulation and Antibody Interference

Although vaccination has been an effective way of preventing infections ever since the eighteenth century, the generation of therapeutic vaccines and immunotherapies is still a work in progress. A number of challenges impede the development of these therapeutic approaches such as safety issues related to the administration of whole pathogens whether attenuated or inactivated. One safe alternative to classical vaccination methods gaining recognition is the use of nanoparticles, whether synthetic or naturally derived. We have recently demonstrated that the papaya mosaic virus (PapMV)-like nanoparticle can be used as a prophylactic vaccine against various viral and bacterial infections through the induction of protective humoral and cellular immune responses. Moreover, PapMV is also very efficient when used as an immune adjuvant in an immunotherapeutic setting at slowing down the growth of aggressive mouse melanoma tumors in a type I interferon (IFN-I)-dependent manner. In the present study, we were interested in exploiting the capacity of PapMV of inducing robust IFN-I production as treatment for the chronic viral infection model lymphocytic choriomeningitis virus (LCMV) clone 13 (Cl13). Treatment of LCMV Cl13-infected mice with two systemic administrations of PapMV was ineffective, as shown by the lack of changes in viral titers and immune response to LCMV following treatment. Moreover, IFN-α production following PapMV administration was almost completely abolished in LCMV-infected mice. To better isolate the mechanisms at play, we determined the influence of a pretreatment with PapMV on secondary PapMV administration, therefore eliminating potential variables emanating from the infection. Pretreatment with PapMV led to the same outcome as an LCMV infection in that IFN-α production following secondary PapMV immunization was abrogated for up to 50 days while immune activation was also dramatically impaired. We showed that two distinct and overlapping mechanisms were responsible for this outcome. While short-term inhibition was partially the result of interleukin-1 receptor-associated kinase 1 degradation, a crucial component of the toll-like receptor 7 signaling pathway, long-term inhibition was mainly due to interference by PapMV-specific antibodies. Thus, we identified a possible pitfall in the use of virus-like particles for the systemic treatment of chronic viral infections and discuss mitigating alternatives to circumvent these potential problems.

Correlation between low tapasin expression and impaired CD8+ T‑cell function in patients with chronic hepatitis B

Recent studies have demonstrated that chronic hepatitis B virus (HBV) infection is associated with reduced antigen‑presenting capacity and insufficient cytotoxic T lymphocyte (CTL) production. The molecular chaperone tapasin mediates binding of the transporter associated with antigen processing (TAP), and has an important role in endogenous antigen processing and presentation, and the induction of specific CTL responses. The present study aimed to determine whether tapasin is associated with chronic HBV (CHB) infection. The mRNA expression levels of tapasin were detected in peripheral blood mononuclear cells from 27 patients with CHB, 20 patients with acute HBV (AHB) and 26 healthy controls by reverse transcription‑quantitative polymerase chain reaction. In addition, CD8+ T immune responses were evaluated in all groups, and the correlation between tapasin expression and CD8+ responses was analyzed. The results demonstrated that the mRNA expression levels of tapasin were significantly downregulated in patients with CHB compared with in healthy controls and patients with AHB. Furthermore, the apoptotic rate of CD8+ T cells was increased in patients with CHB compared with in the other two groups. The percentage of interferon (IFN)‑γ+CD8+ T cells was reduced in patients with CHB compared with in patients with AHB and healthy controls, and serum cytokine levels (IFN‑γ, interleukin‑2 and tumor necrosis factor‑α) were generally low in patients with CHB. Furthermore, the mRNA expression levels of tapasin were positively correlated with IFN‑γ production by CD8+ T cells, and were inversely correlated with the apoptotic ratio of CD8+ T cells. These results indicate that decreased expression of tapasin may be closely associated with CHB, and suggest an important role for tapasin in the pathogenesis of CHB.

Coxiella burnetii Induces Inflammatory Interferon-Like Signature in Plasmacytoid Dendritic Cells: A New Feature of Immune Response in Q Fever

Plasmacytoid dendritic cells (pDCs) play a major role in antiviral immunity via the production of type I interferons (IFNs). There is some evidence that pDCs interact with bacteria but it is not yet clear whether they are protective or contribute to bacterial pathogenicity. We wished to investigate whether Coxiella burnetii, the agent of Q fever, interacts with pDCs. The stimulation of pDCs with C. burnetii increased the expression of activation and migratory markers (CD86 and CCR7) as determined by flow cytometry and modulated gene expression program as revealed by a microarray approach. Indeed, genes encoding for pro-inflammatory cytokines, chemokines, and type I INF were up-regulated. The up-regulation of type I IFN was correlated with an increase in IFN-α release by C. burnetii-stimulated pDCs. We also investigated pDCs in patients with Q fever endocarditis. Using flow cytometry and a specific gating strategy, we found that the number of circulating pDCs was significantly lower in patients with Q fever endocarditis as compared to healthy donors. In addition, the remaining circulating pDCs expressed activation and migratory markers. As a whole, our study identified non-previously reported activation of pDCs by C. burnetii and their modulation during Q fever.

Host-virus interactions in hepatitis B and hepatitis C infection

Hepatitis B virus (HBV) and hepatitis C virus (HCV) are among the most endemic pathogens worldwide, with more than 500 million people globally currently infected with these viruses. These pathogens can cause acute and chronic hepatitis that progress to liver cirrhosis or hepatocellular carcinoma. Both viruses utilize multifaceted strategies to evade the host surveillance system and fall below the immunological radar. HBV has developed specific strategies to evade recognition by the innate immune system and is acknowledged to be a stealth virus. However, extensive research has revealed that HBV is recognized by dendritic cells (DCs) and natural killer (NK) cells. Indoleamine-2, 3-dioxygenase is an enforcer of sequential immune reactions in acute hepatitis B, and this molecule has been shown to be induced by the interaction of HBV-infected hepatocytes, DCs, and NK cells. The interleukin-28B genotype has been reported to influence HCV eradication either therapeutically or spontaneously, but the biological function of its gene product, a type-III interferon (IFN-λ3), remains to be elucidated. Human BDCA3(+)DCs have also been shown to be a potent producer of IFN-λ3 in HCV infection, suggesting the possibility that BDCA3(+)DCs could play a key role in developing therapeutic HCV vaccine. Here we review the current state of research on immune responses against HBV and HCV infection, with a specific focus on innate immunity. A comprehensive study based on clinical samples is urgently needed to improve our understanding of the immune mechanisms associated with viral control and thus to develop novel immune modulatory therapies to cure chronic HBV and HCV infection.

Tissue-resident dendritic cells and diseases involving dendritic cell malfunction

Dendritic cells (DCs) control immune responses and are central to the development of immune memory and tolerance. DCs initiate and orchestrate immune responses in a manner that depends on signals they receive from microbes and cellular environment. Although DCs consist mainly of bone marrow-derived and resident populations, a third tissue-derived population resides the spleen and lymph nodes (LNs), different subsets of tissue-derived DCs have been identified in the blood, spleen, lymph nodes, skin, lung, liver, gut and kidney to maintain the tolerance and control immune responses. Tissue-resident DCs express different receptors for microbe-associated molecular patterns (MAMPs) and damage-associated molecular patterns (DAMPs), which were activated to promote the production of pro- or anti-inflammatory cytokines. Malfunction of DCs contributes to diseases such as autoimmunity, allergy, and cancer. It is therefore important to update the knowledge about resident DC subsets and diseases associated with DC malfunction.

Host-virus interactions in hepatitis B and hepatitis C infection

Hepatitis B virus (HBV) and hepatitis C virus (HCV) are among the most endemic pathogens worldwide, with more than 500 million people globally currently infected with these viruses. These pathogens can cause acute and chronic hepatitis that progress to liver cirrhosis or hepatocellular carcinoma. Both viruses utilize multifaceted strategies to evade the host surveillance system and fall below the immunological radar. HBV has developed specific strategies to evade recognition by the innate immune system and is acknowledged to be a stealth virus. However, extensive research has revealed that HBV is recognized by dendritic cells (DCs) and natural killer (NK) cells. Indoleamine-2, 3-dioxygenase is an enforcer of sequential immune reactions in acute hepatitis B, and this molecule has been shown to be induced by the interaction of HBV-infected hepatocytes, DCs, and NK cells. The interleukin-28B genotype has been reported to influence HCV eradication either therapeutically or spontaneously, but the biological function of its gene product, a type-III interferon (IFN-λ3), remains to be elucidated. Human BDCA3(+)DCs have also been shown to be a potent producer of IFN-λ3 in HCV infection, suggesting the possibility that BDCA3(+)DCs could play a key role in developing therapeutic HCV vaccine. Here we review the current state of research on immune responses against HBV and HCV infection, with a specific focus on innate immunity. A comprehensive study based on clinical samples is urgently needed to improve our understanding of the immune mechanisms associated with viral control and thus to develop novel immune modulatory therapies to cure chronic HBV and HCV infection.

Crosstalk between innate and adaptive immunity in hepatitis B virus infection

Hepatitis B virus (HBV) infection is a major public health problem worldwide. HBV is not directly cytotoxic to infected hepatocytes; the clinical outcome of infection results from complicated interactions between the virus and the host immune system. In acute HBV infection, initiation of a broad, vigorous immune response is responsible for viral clearance and self-limited inflammatory liver disease. Effective and coordinated innate and adaptive immune responses are critical for viral clearance and the development of long-lasting immunity. Chronic hepatitis B patients fail to mount efficient innate and adaptive immune responses to the virus. In particular, HBV-specific cytotoxic T cells, which are crucial for HBV clearance, are hyporesponsiveness to HBV infection. Accumulating experimental evidence obtained from the development of animal and cell line models has highlighted the importance of innate immunity in the early control of HBV spread. The virus has evolved immune escape strategies, with higher HBV loads and HBV protein concentrations associated with increasing impairment of immune function. Therefore, treatment of HBV infection requires inhibition of HBV replication and protein expression to restore the suppressed host immunity. Complicated interactions exist not only between innate and adaptive responses, but also among innate immune cells and different components of adaptive responses. Improved insight into these complex interactions are important in designing new therapeutic strategies for the treatment HBV infection. In this review, we summarize the current knowledge regarding the cross-talk between the innate and adaptive immune responses and among different immunocytes in HBV infection.

Correlation between Th17 and nTreg cell frequencies and the stages of progression in chronic hepatitis B

Several studies have suggested that the balance of T helper 17 (Th17) and natural regulatory T (nTreg) cells in the Th17‑mediated immune response are critical in the pathogenesis of viral hepatitis. The aim of the present study was to examine the role of circulating Th17 and nTreg cells in the disease progression of hepatitis B virus (HBV) infection. A total of 40 patients with chronic HBV (CHB), 27 patients with HBV‑associated cirrhosis, 20 patients with HBV‑associated liver failure and 20 healthy controls were enrolled in the present study. The frequencies of Th17 and nTreg cells in the peripheral blood were examined using flow cytometry. Th17‑associated serum cytokine levels were measured using an enzyme‑linked immunosorbent assay. The results revealed a significantly higher frequency of circulating Th17 cells in the patients with CHB, cirrhosis and liver failure compared, with the normal controls, particularly in the patients with liver failure. The same trend was observed in the serum levels of interleukin (IL)‑17. The frequency of Th17 cells and the serum levels of IL‑17 were positively correlated with the levels of alanine aminotransferase and the prothrombin times. There was a significantly higher frequency of circulating nTreg cells in the patients with CHB, compared with the normal controls. The nTreg cell frequencies were significantly and positively correlated with plasma HBV DNA load, and were negatively correlated with Th17 frequencies in the cohort of patients with HBV. Taken together, the results suggested that Th17 cell‑mediated inflammation is associated with progression from CHB to cirrhosis, and to liver failure. Peripheral Th17 cell frequency and serum levels of IL‑17 may assisting in predicting the severity of liver damage and fibrosis.

Innate and Adaptive Immune Regulation During Chronic Viral Infections

Chronic viral infections represent a unique challenge to the infected host. Persistently replicating viruses outcompete or subvert the initial antiviral response, allowing the establishment of chronic infections that result in continuous stimulation of both the innate and adaptive immune compartments. This causes a profound reprogramming of the host immune system, including attenuation and persistent low levels of type I interferons, progressive loss (or exhaustion) of CD8(+) T cell functions, and specialization of CD4(+) T cells to produce interleukin-21 and promote antibody-mediated immunity and immune regulation. Epigenetic, transcriptional, posttranscriptional, and metabolic changes underlie this adaptation or recalibration of immune cells to the emerging new environment in order to strike an often imperfect balance between the host and the infectious pathogen. In this review we discuss the common immunological hallmarks observed across a range of different persistently replicating viruses and host species, the underlying molecular mechanisms, and the biological and clinical implications.

TLR9: an important molecule in the fight against hepatitis B virus

Hepatitis B virus (HBV) is the most prevalent infectious agent that can induce severe liver disease. Patients infected with long-term HBV, including chronic, asymptomatic and occult forms, cannot clear HBV from infected hepatocytes completely. It is not clear why some people can clear the infection while others cannot. Furthermore, the main mechanisms responsible for progression of the infections are not fully understood. It has been hypothesised that differences in genetic and immunological parameters between patients and subjects who successfully clear HBV infections are responsible for inducing the long-term forms of the infection. Previous investigations showed that Toll-like receptors (TLRs) play important roles in immune responses, especially innate immunity, against viral infections, including hepatitis B. TLR9 detects intracellular viral dsDNA, which results in the activation of an immune response against HBV. However, defects in this system may result in an attenuated response ultimately leading to long-term HBV infections. Targeting the defects in TLR9 or reactivating the downstream pathways that are normally switched on by TLR9 in response to HBV infection is a new approach to the treatment of long-term HBV infection. However, the pathways and defects seen in patients with long-term HBV need to be thoroughly explored before therapeutics can be applied in the clinical setting. Furthermore, the apparently multigenic nature of long-term HBV infection suggests that treatment of patients may need to be personalised.

Contribution of Toll-like receptors to the control of hepatitis B virus infection by initiating antiviral innate responses and promoting specific adaptive immune responses

It is well accepted that adaptive immunity plays a key role in the control of hepatitis B virus (HBV) infection. In contrast, the contribution of innate immunity has only received attention in recent years. Toll-like receptors (TLRs) sense pathogen-associated molecule patterns and activate antiviral mechanisms, including intracellular antiviral pathways and the production of antiviral effector interferons (IFNs) and pro-inflammatory cytokines. Experimental results from in vitro and in vivo models have demonstrated that TLRs mediate the activation of cellular signaling pathways and the production of antiviral cytokines, resulting in a suppression of HBV replication. However, HBV infection is associated with downregulation of TLR expression on host cells and blockade of the activation of downstream signaling pathways. In primary HBV infection, TLRs may slow down HBV infection, but contribute only indirectly to viral clearance. Importantly, TLRs may modulate HBV-specific T- and B-cell responses in vivo, which are essential for the termination of HBV infection. Thus, TLR agonists are promising candidates to act as immunomodulators for the treatment of chronic HBV infection. Antiviral treatment may recover TLR expression and function in chronic HBV infection and may increase the efficacy of therapeutic approaches based on TLR activation. A combined therapeutic strategy with antiviral treatment and TLR activation could facilitate the restoration of HBV-specific immune responses and thereby, achieve viral clearance in chronically infected HBV patients.

Control of hepatitis B virus replication by interferons and Toll-like receptor signaling pathways

Hepatitis B virus (HBV) infection is one of the major causes of liver diseases, affecting more than 350 million people worldwide. The interferon (IFN)-mediated innate immune responses could restrict HBV replication at the different steps of viral life cycle. Indeed, IFN-α has been successfully used for treatment of patients with chronic hepatitis B. However, the role of the innate immune response in HBV replication and the mechanism of the anti-HBV effect of IFN-α are not completely explored. In this review, we summarized the currently available knowledge about the IFN-mediated anti-HBV effect in the HBV life cycle and the possible effectors downstream the IFN signaling pathway. The antiviral effect of Toll-like receptors (TLRs) in HBV replication is briefly discussed. The strategies exploited by HBV to evade the IFN- and TLR-mediated antiviral actions are summarized.

Regulation of microRNA by hepatitis B virus infection and their possible association with control of innate immunity

Hepatitis B virus (HBV) chronically infects more than 350 million people worldwide. HBV causes acute and chronic hepatitis, and is one of the major causes of cirrhosis and hepatocellular carcinoma. There exist complex interactions between HBV and the immune system including adaptive and innate immunity. Toll-like receptors (TLRs) and TLR-signaling pathways are important parts of the innate immune response in HBV infections. It is well known that TLR-ligands could suppress HBV replication and that TLRs play important roles in anti-viral defense. Previous immunological studies demonstrated that HBV e antigen (HBeAg) is more efficient at eliciting T-cell tolerance, including production of specific cytokines IL-2 and interferon gamma, than HBV core antigen. HBeAg downregulates cytokine production in hepatocytes by the inhibition of MAPK or NF-κB activation through the interaction with receptor-interacting serine/threonine protein kinase. MicroRNAs (miRNAs) are also able to regulate various biological processes such as the innate immune response. When the expressions of approximately 1000 miRNAs were compared between human hepatoma cells HepG2 and HepG2.2.15, which could produce HBV virion that infects chimpanzees, using real-time RT-PCR, we observed several different expression levels in miRNAs related to TLRs. Although we and others have shown that HBV modulates the host immune response, several of the miRNAs seem to be involved in the TLR signaling pathways. The possibility that alteration of these miRNAs during HBV infection might play a critical role in innate immunity against HBV infection should be considered. This article is intended to comprehensively review the association between HBV and innate immunity, and to discuss the role of miRNAs in the innate immune response to HBV infection.

Decreased expressions of Toll-like receptor 9 and its signaling molecules in chronic hepatitis B virus-infected patients

CONTEXT

Toll-like receptors (TLRs) play crucial roles in immune responses, especially innate immunity, against viral infections. Toll-like receptor 9 recognizes intracellular viral double-strand DNA, which leads to the activation of nuclear factor B (NF-κB) through the myeloid differentiation primary response 88 (MYD88) pathway. Defects in the expression of TLR9 and its signaling molecules may cause attenuated immune responses against hepatitis B virus.

OBJECTIVE

To determine expression levels of TLR9 messenger RNA along with MYD88, interleukin 1 receptor-associated kinase 1 (IRAK1), tumor necrosis factor receptor-associated factor 6 (TRAF6), and NF-κB in the peripheral blood mononuclear cells obtained from chronic hepatitis B virus (CHB)-infected patients.

DESIGN

In this study, 60 CHB patients and 60 healthy controls were recruited and the expression of TLR9 and its downstream signaling molecules was examined by real-time polymerase chain reaction techniques using β-actin as a housekeeping gene.

RESULTS

Our results showed that expression of TLR9, MYD88, IRAK1, TRAF6, and NF-κB in peripheral blood mononuclear cells of CHB patients was significantly decreased in comparison with healthy controls.

CONCLUSIONS

According to our results, it appears that CHB patients are unable to appropriately express genes in the TLR9 pathway, which may impede immune responses against hepatitis B virus infection. These results suggest a mechanism that may partially explain the fact that immune responses are disrupted in CHB patients.

Mobilizing monocytes to cross-present circulating viral antigen in chronic infection

Selection of antigens for therapeutic vaccination against chronic viral infections is complicated by pathogen genetic variations. We tested whether antigens present during persistent viral infections could provide a personalized antigenic reservoir for therapeutic T cell expansion in humans. We focused our study on the HBV surface antigen (HBsAg), which is present in microgram quantities in the serum of chronic HBV patients. We demonstrated by quantitative fluorescent microscopy that, out of 6 professional APC populations in the circulation, only CD14 monocytes (MNs) retained an HBsAg depot. Using TCR-redirected CD8+ T cells specific for MHC-I-restricted HBV epitopes, we showed that, despite being constantly exposed to antigen, ex vivo-isolated APCs did not constitutively activate HBV-specific CD8+ T cells. However, differentiation of HBsAg+ CD14 MNs from chronic patients to MN-derived DCs (moDCs) induced cross-presentation of the intracellular reservoir of viral antigen. We exploited this mechanism to cross-present circulating viral antigen and showed that moDCs from chronically infected patients stimulated expansion of autologous HBV-specific T cells. Thus, these data demonstrate that circulating viral antigen produced during chronic infection can serve as a personalized antigenic reservoir to activate virus-specific T cells.

Therapeutic advances in the management of chronic hepatitis B infection

Hepatitis B virus (HBV) is a small nonenveloped DNA virus that is a member of the Hepadnaviridae family. Chronic HBV infection is estimated to effect more than 350 million people worldwide with over 2 billion people being exposed to the virus. Risk factors for chronic infection include age of exposure to the virus, concurrent immunosuppression and HIV infection. Individuals chronically infected are 200 times more likely to develop hepatocellular carcinoma (HCC) than uninfected individuals and are at risk of developing cirrhosis and the risks of decompensated liver disease. This article focuses on the recent therapeutic advances that reduce the risk of developing these complications, those that prevent the spread of HBV and strategies for the prevention of post-liver-transplantation recurrence of HBV.

HIV and co-infections

Despite significant reductions in morbidity and mortality secondary to availability of effective combination anti-retroviral therapy (cART), human immunodeficiency virus (HIV) infection still accounts for 1.5 million deaths annually. The majority of deaths occur in sub-Saharan Africa where rates of opportunistic co-infections are disproportionately high. In this review, we discuss the immunopathogenesis of five common infections that cause significant morbidity in HIV-infected patients globally. These include co-infection with Mycobacterium tuberculosis, Cryptococcus neoformans, hepatitis B virus, hepatitis C virus, and Plasmodium falciparum. Specifically, we review the natural history of each co-infection in the setting of HIV, the specific immune defects induced by HIV, the effects of cART on the immune response to the co-infection, the pathogenesis of immune restoration disease (IRD) associated with each infection, and advances in the areas of prevention of each co-infection via vaccination. Finally, we discuss the opportunities and gaps in knowledge for future research.

Reduced Toll-like receptor 3 expression in chronic hepatitis B patients and its restoration by interferon therapy

BACKGROUND

Toll-like receptor (TLR)3 gene variants may correlate with clinical significance of chronic viral infections including HBV. We aimed to investigate the expression of TLR3 in peripheral blood mononuclear cells (PBMCs) and liver cells of chronic hepatitis B (CHB) patients and its response to pegylated interferon or nucleoside analogue therapy.

METHODS

We consecutively enrolled 127 CHB patients and 64 hepatitis B surface antigen-negative, anti-HCV-negative healthy individuals as controls. We compared the TLR3 expressions on fresh PBMCs and liver cells from patients and controls, before and during pegylated interferon or nucleoside analogue therapy.

RESULTS

Compared to controls, patients had a lower TLR3 mean fluorescence intensity (MFI) on PBMCs (mean ± sd 14.61 ± 13.49 versus 9.70 ± 4.61; P < 0.001), independent of age, gender and alanine aminotransferase (ALT; -13.466, 95% CI -17.202, -9.730; P < 0.001). Patients had limited TLR3 stains on Kupffer cells, whereas controls had diffuse stains on Kupffer and hepatocytes. Hepatic TLR3 messenger RNA was lower in patients than controls (0.47 ± 0.30 versus 1-fold). Using pretreatment TLR3 MFI as a referent, among 5 of 12 pegylated-interferon-treated patients with sustained virological response (SVR), TLR3 MFI was restored to a mean of 1.5- to 1.7-folds immediately after treatment. Among seven non-responders or relapsers, TLR3 MFI reduced to a mean of 0.5- to 0.7-fold. Among 10 entecavir-treated patients with on-treatment virological response, TLR3 MFI gradually was restored to a mean of 1.2-folds during 48-week therapy.

CONCLUSIONS

CHB patients have reduced TLR3 expression on PBMCs, independent of age, gender and ALT, and on liver cells. Patients with pegylated-interferon-induced SVR have a more significant restoration of TLR3 expression than those under entecavir.

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.

HIV-1 gp120 impairs the induction of B cell responses by TLR9-activated plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) play a central role in innate and adaptive immune responses to viral infections, including HIV type 1 (HIV-1). pDCs produce substantial quantities of type I IFN and proinflammatory cytokines upon stimulation via TLRs, specifically TLR7 or TLR9. The HIV-1 envelope glycoproteins, exemplified by the gp120 monomer, are the focus of vaccines aimed at inducing B cell responses. We have studied how the interactions of gp120 with various receptors on human pDCs affect the activation of these cells via TLR9 and their subsequent ability to stimulate B cells. We observed that IFN-α production by pDCs in response to TLR9, but not TLR7, stimulation was reduced by exposure to gp120. Specifically, gp120 inhibited the CpG-induced maturation of pDCs and their expression of TNF-α, IL-6, TLR9, IFN regulatory factor 7, and BAFF. Receptor-blocking and cross-linking studies showed that these inhibitory effects of gp120 were mediated by interactions with CD4 and mannose-binding C-type lectin receptors, but not with the chemokine receptors CCR5 and CXCR4. Of note is that gp120 inhibited the activation of B cells by TLR9-stimulated pDCs. Taken together, our data show that HIV-1 gp120 impairs pDC functions, including activation of B cell responses, and imply that TLR9 ligands may not be good adjuvants to use in combination with envelope glycoprotein vaccines.

PI3K-PKB hyperactivation augments human plasmacytoid dendritic cell development and function

Plasmacytoid dendritic cells (pDCs) are considered potential tools or targets for immunotherapy. However, current knowledge concerning methodologies to manipulate their development or function remains limited. Here, we investigated the role of the phosphatidylinositol 3-kinase (PI3K)-protein kinase B (PKB)-mammalian target of rapamycin (mTOR) axis in human pDC development, survival, and function. In vitro pDC generation from human cord blood-derived CD34(+) hematopoietic progenitors was reduced by pharmacologic inhibition of PI3K, PKB, or mTOR activity, and peripheral blood pDCs required PI3K-PKB-mTOR signaling to survive. Accordingly, activity of this pathway in circulating pDCs correlated with their abundance in peripheral blood. Importantly, introduction of constitutively active PKB or pharmacologic inhibition of negative regulator phosphatase and tensin homolog (PTEN) resulted in increased pDC numbers in vitro and in vivo. Furthermore, MHC class II and costimulatory molecule expression, and production of IFN-α and TNF-α, were augmented, which could be explained by enhanced IRF7 and NF-κB activation. Finally, the numerically and functionally impaired pDCs of chronic hepatitis B patients demonstrated reduced PI3K-PKB-mTOR activity. In conclusion, intact PI3K-PKB-mTOR signaling regulates development, survival, and function of human pDCs, and pDC development and functionality can be promoted by PI3K-PKB hyperactivation. Manipulation of this pathway or its downstream targets could be used to improve the generation and function of pDCs to augment immunity.

Natural killer cells display impaired responses to toll like receptor 9 that support viral persistence in chronic hepatitis B

Toll like receptors (TLR) are crucial mediators of innate immune responses, but their influence on natural killer (NK) cell function in chronic hepatitis B infection (CHB) is not well understood. Here we evaluated the responses of peripheral NK cells from CHB patients to multiple TLR agonists. CHB was associated with an impaired NK cell IFN-γ response to TLR9 stimulation compared to controls. This deficiency corrected with recombinant IFN-alpha, while anti-IFN-alpha neutralizing antibody diminished NK IFN-γ production in controls. NK cell CD69 upregulation in response to TLR9 was maintained in CHB. No differences were noted in responses to the other TLR ligands. Our results demonstrate a dichotomous NK cell response to TLR9 that is mediated by IFN-alpha and reflect the multiple mechanisms involved with NK activation. Consequently, it is possible that when activated these cells are unable to contribute to viral clearance while still having the potential to mediate tissue injury.

HBsAg inhibits IFN-α production in plasmacytoid dendritic cells through TNF-α and IL-10 induction in monocytes

Type I Interferon (IFN) is one of the first lines of defense against viral infection. Plasmacytoid dendritic cells (pDCs) are professional IFN-α-producing cells that play an important role in the antiviral immune response. Previous studies have reported that IFN-α production is impaired in chronic hepatitis B (CHB) patients. However, the mechanisms underlying the impairment in IFN-α production are not fully understood. Here, we report that plasma-derived hepatitis B surface antigen (HBsAg) and HBsAg expressed in CHO cells can significantly inhibit toll like receptor (TLR) 9-mediated Interferon-α (IFN-α) production in peripheral blood mononuclear cells (PBMCs) from healthy donors. Further analysis indicated that monocytes participate in the inhibitory effect of HBsAg on pDCs through the secretion of TNF-α and IL-10. Furthermore, TLR9 expression on pDCs was down-regulated by TNF-α, IL-10 and HBsAg treatment. This down-regulation may partially explain the inhibition of IFN-α production in pDCs. In conclusion, we determined that HBsAg inhibited the production of IFN-α by pDCs through the induction of monocytes that secreted TNF-α and IL-10 and through the down-regulation of TLR9 expression on pDCs. These data may aid in the development of effective antiviral treatments and lead to the immune control of the viral infections.

Downregulation of TLR7/9 leads to deficient production of IFN-α from plasmacytoid dendritic cells in chronic hepatitis B

OBJECTIVE

To investigate whether Toll-like receptor (TLR) 7 and TLR9-mediated interferon α (IFN-α) production in plasmacytoid dendritic cells (pDCs) is compromised in patients with chronic hepatitis B virus (HBV) infection.

MATERIALS AND METHODS

Peripheral blood mononuclear cells (PBMCs) were prepared from 32 chronic HBV patients and 13 healthy volunteers, and treated with loxoribine or cytidine phosphate guanosine (CpG) oligodeoxynucleotides (ODN). Interferon α in the supernatant was measured by sandwich ELISA. PDC frequency and the expression levels of TLR7 and TLR9 in pDCs were quantified by flow cytometry. The serum viral load of HBV was quantified using a highly sensitive real-time PCR kit.

RESULTS

Compared to cells from healthy control group, PBMCs and pDCs from the HBV group showed significantly decreased production of IFN-α in response to ligand for TLR7 (loxoribine) and TLR9 (CpG ODN, P < 0.05). Mechanistically, the number of pDCs in peripheral blood, and the expression of pDC-associated TLR7 and TLR9 were significantly lower in HBV group than in the healthy control group (P < 0.05). In addition, the number of pDCs and the expression of TLR9 on pDCs were correlated inversely with the serum load of HBV.

CONCLUSION

Impaired IFN-α production from pDC may contribute to the immunopathogenesis of chronic HBV infection, which may be the result of a reduced amount of pDCs as well as decreased expression of TLR7 and TLR9 on pDCs.

HIV Infection and TLR Signalling in the Liver

Despite the availability of effective combination antiretroviral therapy (cART), liver disease is one of the leading causes of morbidity and mortality in Human Immunodeficiency Virus (HIV)-infected individuals, specifically, in the presence of viral hepatitis coinfection. HIV, a single stranded RNA virus, can bind to and activate both Toll-like receptor (TLR)7 and TLR8 in circulating blood mononuclear cells, but little is known about the effect of HIV on TLRs expressed in the liver. HIV can directly infect cells of the liver and HIV-mediated depletion of CD4+ T-cells in the gastrointestinal tract (GI tract) results in increased circulating lipopolysaccharide (LPS), both of which may impact on TLR signaling in the liver and subsequent liver disease progression. The potential direct and indirect effects of HIV on TLR signaling in the liver will be explored in this paper.

Hepatitis B virus suppresses the functional interaction between natural killer cells and plasmacytoid dendritic cells

Natural killer cells (NK) are one of the key players in the eradication and control of viral infections. Infections with the hepatitis B virus (HBV) may lead to persistence in a subgroup of patients, and impaired NK cell functions have been observed in these patients. Crosstalk with other immune cells has been shown to modulate the function of NK cells. We studied the functional crosstalk between NK cells and plasmacytoid dendritic cell (pDC) and its modulation by HBV. Healthy human peripheral blood-derived NK cells and pDC were purified and cocultured in the presence or absence of HepG2.2.15-derived HBV under various in vitro conditions. The functionality of NK cells was assessed by evaluation of activation markers, cytokine production and cytotoxicity of carboxyfluorescein succinimidyl ester-labelled K562 target cells by flow cytometry or immunoassays. Additionally, the crosstalk was examined using NK and pDC from patients with chronic HBV. The activation of NK cells in cocultures with pDC, as demonstrated by CD69, CD25 and HLA-DR, was not affected by the presence of HBV. Similarly, when cocultured with pDC, the cytotoxic potential of NK cells was not influenced by HBV. However, HBV significantly inhibited pDC-induced IFN-γ production by NK cells both in the presence and in the absence of CpG. As HBV did not affect cytokine-induced IFN-γ production by NK cells cultured alone, the suppressive effect of HBV on NK cell function was mediated via interference with pDC-NK cell interaction. In contrast to other viruses, HBV does not activate pDC-NK cell interaction but inhibits pDC-induced NK cell function. In parallel with NK cells of patients with chronic HBV, which show diminished cytokine production with normal cytotoxicity, HBV specifically suppressed pDC-induced IFN-γ production by NK cells without affecting their cytolytic ability. These data demonstrate that HBV modulates pDC-NK cell crosstalk, which may contribute to HBV persistence.