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

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.

Polymorphisms of toll-like receptors and their pathways in viral hepatitis

Toll-like receptors (TLRs) are an important part of the innate immune response to a variety of pathogens including hepatic viral infections. Activation of TLRs stimulates a complex intracellular signalling cascade that results in production of proinflammatory cytokines and interferons important for antiviral responses as well as induction of the adaptive arm of the immune system. There is substantial evidence for an important role for TLRs and TLR-mediated signalling in the pathogenesis and outcomes of hepatitis B and C in particular, but it might also influence responses to other viral hepatitis infections. Several single nucleotide polymorphisms (SNPs) of TLRs, relevant adaptor molecules and cytokines mediated by TLR signalling have been described that alter innate immune responses and have been implicated in a variety of human diseases including viral and other infections. There is now significant evidence that a number of TLR SNPs can affect various clinical outcomes in Caucasian patients with chronic HCV. However, the role of these polymorphisms in acute and other chronic hepatitis infections, including HBV as well as in non-Caucasian populations, has not been elucidated. In addition, results for SNPs downstream of TLR activation, such as in relevant cytokines, are inconsistent and their influence requires further investigation to determine the clinical significance of genetic variations in these mediators.

Hepatitis B virus impairs TLR9 expression and function in plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) play a key role in detecting pathogens by producing large amounts of type I interferon (IFN) by sensing the presence of viral infections through the Toll-Like Receptor (TLR) pathway. TLR9 is a sensor of viral and bacterial DNA motifs and activates the IRF7 transcription factor which leads to type I IFN secretion by pDCs. However, during chronic hepatitis B virus (HBV) infection, pDCs display an impaired ability to secrete IFN-α following ex vivo stimulation with TLR9 ligands. Here we highlight several strategies used by HBV to block IFN-α production through a specific impairment of the TLR9 signaling. Our results show that HBV particle internalisation could inhibit TLR9- but not TLR7-mediated secretion of IFN-α by pDCs. We observed that HBV down-regulated TLR9 transcriptional activity in pDCs and B cells in which TLR9 mRNA and protein levels were reduced. HBV can interfere with TLR9 activity by blocking the MyD88-IRAK4 axis and Sendai virus targeting IRF7 to block IFN-α production. Neutralising CpG motif sequences were identified within HBV DNA genome of genotypes A to H which displayed a suppressive effect on TLR9-immune activation. Moreover, TLR9 mRNA and protein were downregulated in PBMCs from patients with HBV-associated chronic hepatitis and hepatocellular carcinoma. Thus HBV has developed several escape mechanisms to avoid TLR9 activation in both pDCs and B lymphocytes, which may in turn contribute to the establishment and/or persistence of chronic infection.

The tug-of-war between dendritic cells and human chronic viruses

The human immune system is under constant challenge from many viruses, some of which the body is successfully able to clear. Other viruses have evolved to escape the host immune responses and thus persist, leading to the development of chronic diseases. Dendritic cells are professional antigen-presenting cells that play a major role in both innate and adaptive immunity against different pathogens. This review focuses on the interaction of different chronic viruses with dendritic cells and the viruses' ability to exploit this critical cell type to their advantage so as to establish persistence within the host.

Reversal of hepatitis B virus-induced immune tolerance by an immunostimulatory 3p-HBx-siRNAs in a retinoic acid inducible gene I-dependent manner

It is extensively accepted that hepatitis B virus (HBV) escapes from innate immunity by inhibiting type I interferon (IFN) production, but efficient intervention to reverse the immune tolerance is still not achieved. Here, we report that 5'-end triphosphate hepatitis B virus X gene (HBx)-RNAs (3p-HBx-short interfering [si]RNAs) exerted significantly stronger inhibitory effects on HBV replication than regular HBx-siRNAs in stably HBV-expressing hepatoplastoma HepG2.2.15 cells through extremely higher expression of type I IFNs, IFN-induced genes and proinflammatory cytokines, and retinoic acid inducible gene I (RIG-I) activation. Also, 3p-HBx-siRNA were more efficient to stimulate type I IFN response than HBx sequence-unrelated 3p-scramble-siRNA in HepG2.2.15 cells, indicating that a stronger immune-stimulating effect may partly result from the reversal of immune tolerance through decreasing HBV load. In RIG-I-overexpressed HepG2.2.15 cells, 3p-HBx-siRNAs exerted stronger inhibitory effects on HBV replication with greater production of type I IFNs; on the contrary, in RIG-I-silenced HepG2.2.15 cells or after blockade of IFN receptor by monoclonal antibody, inhibitory effect of 3p-HBx-siRNAs on HBV replication was largely attenuated, indicating that immunostimulatory function of 3p-HBx-siRNAs was RIG-I and type I IFN dependent. Moreover, in HBV-carrier mice, 3p-HBx-siRNA more strongly inhibited HBV replication and promoted IFN production than HBx-siRNA in primary HBV(+) hepatocytes and, therefore, significantly decreased serum hepatitis B surface antigen and increased serum IFN-β.

CONCLUSION

3p-HBx-siRNAs may not only directly inhibit HBV replication, but also stimulate innate immunity against HBV, which are both beneficial for the inversion of HBV-induced immune tolerance.

Correlation of the expression of toll-like receptors in monocyte-derived dendritic cells with prognosis of chronic severe hepatitis B

OBJECTIVE

This study aims to measure the expression of toll-like receptors (TLR) in monocyte-derived dendritic cells (MoDC) from chronic severe hepatitis B (CSHB), to assess the contribution of TLRs in CSHB.

METHODS

Peripheral blood was collected from 40 CSHB patients, 30 chronic hepatitis B (CHB) patients, and 30 healthy individuals who served as healthy controls (HCs). Purified monocytes were isolated by a combination of Histopaque-1.077 and CD14 Microbeads. MoDCs were induced with granulocyte macrophage colony-stimulating factor and interleukin-4 for 6 days from CD14(+) monocytes. The expression of TLRs in MoDC was measured using real-time PCR and flow cytometry.

RESULTS

The expressions of TLR-1, -2, -7 were significantly higher in MoDC of CSHB than that of HCs, of which the level of TLR-3 was decreased. Particularly in CSHB patients, the TLR-3 expression was further decreased compared to CHB patients. In non-survival CSHB patients, TLR-3 level was significantly decreased, while TLR-2 expression was dramatically increased. Linear correlation analysis demonstrated significant correlations between TLR-3 level and disease severity markers (total bilirubin, prothrombin activity, creatinine, white blood cell count, and maximum volume of ascitic fluid) in individual CSHB patients.

CONCLUSIONS

TLR-2 and TLR-3 may be involved in the pathogenesis of CSHB, and TLR-3 may influence the prognosis of CSHB.

Recent insights into the role of Toll-like receptors in viral infection

Toll-like receptors (TLRs) have a central role in innate immunity as they detect conserved pathogen-associated molecular patterns (PAMPs) on a range of microbes, including viruses, leading to innate immune activation and orchestration of the adaptive immune response. To date, a large number of viruses have been shown to trigger innate immunity via TLRs, suggesting that these receptors are likely to be important in the outcome to viral infection. This suggestion is supported by the observation that many viruses have evolved mechanisms not only to evade the innate immune system, but also to subvert it for the benefit of the virus. In this review we will discuss earlier evidence, mainly from knock-out mice studies, implicating TLRs in the innate immune response to viruses, in light of more recent clinical data demonstrating that TLRs are important for anti-viral immunity in humans.

Hepatitis B virus lacks immune activating capacity, but actively inhibits plasmacytoid dendritic cell function

Chronic hepatitis B virus (HBV) infection is caused by inadequate anti-viral immunity. Activation of plasmacytoid dendritic cells (pDC) leading to IFNα production is important for effective anti-viral immunity. Hepatitis B virus (HBV) infection lacks IFNα induction in animal models and patients and chronic HBV patients display impaired IFNα production by pDC. Therefore, HBV and HBV-derived proteins were examined for their effect on human pDC in vitro. In addition, the in vitro findings were compared to the function of pDC derived from chronic HBV patients ex vivo. In contrast to other viruses, HBV did not activate pDC. Moreover, HBV and HBsAg abrogated CpG-A/TLR9-induced, but not Loxoribine/TLR7-induced, mTOR-mediated S6 phosphorylation, subsequent IRF7 phosphorylation and IFNα gene transcription. HBV/HBsAg also diminished upregulation of co-stimulatory molecules, production of TNFα, IP-10 and IL-6 and pDC-induced NK cell function, whereas TLR7-induced pDC function was hardly affected. In line, HBsAg preferentially bound to TLR9-triggered pDC demonstrating that once pDC are able to bind HBV/HBsAg, the virus exerts its immune regulatory effect. HBV not only directly interfered with pDC function, but also indirectly by interfering with monocyte-pDC interaction. Also HBeAg diminished pDC function to a certain extent, but via another unknown mechanism. Interestingly, patients with HBeAg-positive chronic hepatitis B displayed impaired CpG-induced IFNα production by pDC without significant alterations in Loxoribine-induced pDC function compared to HBeAg-negative patients and healthy controls. The lack of activation and the active inhibition of pDC by HBV may both contribute to HBV persistence. The finding that the interaction between pDC and HBV may change upon activation may aid in the identification of a scavenging receptor supporting immunosuppressive effects of HBV and also in the design of novel treatment strategies for chronic HBV.

Hepatitis B virus lacks immune activating capacity, but actively inhibits plasmacytoid dendritic cell function

Chronic hepatitis B virus (HBV) infection is caused by inadequate anti-viral immunity. Activation of plasmacytoid dendritic cells (pDC) leading to IFNα production is important for effective anti-viral immunity. Hepatitis B virus (HBV) infection lacks IFNα induction in animal models and patients and chronic HBV patients display impaired IFNα production by pDC. Therefore, HBV and HBV-derived proteins were examined for their effect on human pDC in vitro. In addition, the in vitro findings were compared to the function of pDC derived from chronic HBV patients ex vivo. In contrast to other viruses, HBV did not activate pDC. Moreover, HBV and HBsAg abrogated CpG-A/TLR9-induced, but not Loxoribine/TLR7-induced, mTOR-mediated S6 phosphorylation, subsequent IRF7 phosphorylation and IFNα gene transcription. HBV/HBsAg also diminished upregulation of co-stimulatory molecules, production of TNFα, IP-10 and IL-6 and pDC-induced NK cell function, whereas TLR7-induced pDC function was hardly affected. In line, HBsAg preferentially bound to TLR9-triggered pDC demonstrating that once pDC are able to bind HBV/HBsAg, the virus exerts its immune regulatory effect. HBV not only directly interfered with pDC function, but also indirectly by interfering with monocyte-pDC interaction. Also HBeAg diminished pDC function to a certain extent, but via another unknown mechanism. Interestingly, patients with HBeAg-positive chronic hepatitis B displayed impaired CpG-induced IFNα production by pDC without significant alterations in Loxoribine-induced pDC function compared to HBeAg-negative patients and healthy controls. The lack of activation and the active inhibition of pDC by HBV may both contribute to HBV persistence. The finding that the interaction between pDC and HBV may change upon activation may aid in the identification of a scavenging receptor supporting immunosuppressive effects of HBV and also in the design of novel treatment strategies for chronic HBV.

Dendritic cells can effectively be pulsed by HBVsvp and induce specific immune reactions in mice

Eradication of chronic Hepatitis B virus (HBV) infection, marked by HBs seroconversion, is very rarely achieved by treatment with nucleoside and nucleotide analogs. Therapeutic cell based approaches, like interferon therapy, have a higher chance of seroconversion. Dendritic cells (DC) are key players in the cellular immune response and have been shown to play an important role in controlling HBV infection. In this study, the potential of ex vivo activated DC to induce specific immune responses against HBV was examined. DC derived from bone-marrow of BALB/c or C56BL/6 mice were pulsed with HBV subviral particles (HBVsvp), derived from the HepG2.2.15 cell line. HepG2.2.15 produces subviral particles consisting of the HBc and HBs proteins. Thus, the entire "viral surface" is presented to DC to induce an immune reaction. In vitro pulsation with HBVsvp successfully activated bone-marrow derived DC, demonstrated by FACS analysis showing increased MHCII, CD 86 and CCR-7. Immunization of mice, via subcutaneous injection of the activated DC, induced HBV specific immune reactions which were measured by ELISA, ELISPOT and T-cell proliferation analysis. Vaccination with ex vivo activated DC may be a promising tool for therapeutic or prophylactic approaches against the Hepatitis B virus.

Impaired Toll-like receptor 7 and 9 signaling: from chronic viral infections to cancer

HIV-1, hepatitis B virus, hepatitis C virus, and human papillomavirus type 16 cause persistent infections that frequently precede cancer development. Virions of these viruses are weak inducers of interferon-α and impair Toll-like receptor (TLR)9 function. Loss of TLR9 responsiveness also occurs in tumors without viral etiology such as breast, ovary, and head and neck carcinomas. Recent reports have suggested that viruses and components of the tumor microenviroment interact with regulatory receptors on plasmacytoid dendritic cells (pDCs) to impair TLR7 and TLR9 signaling, and to downregulate TLR9 gene expression. The limited responsiveness of pDCs might contribute to reduced innate immune responses during chronic viral infections and oncogenesis, and represent a target for new therapeutic approaches based on TLR agonists.

Innate antiviral immune responses to hepatitis B virus

Hepatitis B virus (HBV) is a major cause of acute and chronic hepatitis in humans. As HBV itself is currently viewed as a non-cytopathic virus, the liver pathology associated with hepatitis B is mainly thought to be due to immune responses directed against HBV antigens. The outcome of HBV infection is the result of complex interactions between replicating HBV and the immune system. While the role of the adaptive immune response in the resolution of HBV infection is well understood, the contribution of innate immune mechanisms remains to be clearly defined. The innate immune system represents the first line of defense against viral infection, but its role has been difficult to analyze in humans due to late diagnosis of HBV infection. In this review, we discuss recent advances in the field of innate immunity to HBV infection.

Functional impairment of human myeloid dendritic cells during Schistosoma haematobium infection

Chronic Schistosoma infection is often characterized by a state of T cell hyporesponsiveness of the host. Suppression of dendritic cell (DC) function could be one of the mechanisms underlying this phenomenon, since Schistosoma antigens are potent modulators of dendritic cell function in vitro. Yet, it remains to be established whether DC function is modulated during chronic human Schistosoma infection in vivo. To address this question, the effect of Schistosoma haematobium infection on the function of human blood DC was evaluated. We found that plasmacytoid (pDC) and myeloid DC (mDC) from infected subjects were present at lower frequencies in peripheral blood and that mDC displayed lower expression levels of HLA-DR compared to those from uninfected individuals. Furthermore, mDC from infected subjects, but not pDC, were found to have a reduced capacity to respond to TLR ligands, as determined by MAPK signaling, cytokine production and expression of maturation markers. Moreover, the T cell activating capacity of TLR-matured mDC from infected subjects was lower, likely as a result of reduced HLA-DR expression. Collectively these data show that S. haematobium infection is associated with functional impairment of human DC function in vivo and provide new insights into the underlying mechanisms of T cell hyporesponsiveness during chronic schistosomiasis.

A look behind closed doors: interaction of persistent viruses with dendritic cells

Persistent infections with HIV, hepatitis B virus and hepatitis C virus are major causes of morbidity and mortality worldwide. As sentinels of the immune system, dendritic cells (DCs) are crucial for the generation of protective antiviral immunity. Recent advances in our understanding of the role of DCs during infection with these viruses provide insights into the mechanisms used by these viruses to exploit DC function and evade innate and adaptive immunity. In this Review we highlight the current knowledge about the interaction between DCs and these viruses and the underlying mechanisms that might influence the outcome of viral infections.

The potential use of Toll-like receptor agonists to restore the dysfunctional immunity induced by hepatitis C virus

Hepatitis C virus (HCV) infection is a major public health concern with approximately 3% of the world's population is infected, posing social, economical and health burden. Less than 20% of the infected individuals clear the virus during the acute infection, while the rest develop chronic infection. The treatment of choice for HCV infection is pegylated interferon-alpha (IFN-alpha) in combination with ribavarin. Despite the cost and side effects of this treatment regimen, many patients fail this therapy and develop persistent HCV infection, leading to cirrhosis and hepatocellular carcinoma. Although the mechanisms underlying the failure to resolve HCV infection are poorly understood, the incapability of patients to develop effective anti-HCV immunity is a potential cause. We hypothesize that the dysfunctional anti-HCV immunity is due to the emergence of immunosuppressive cells coinciding with a decrease in the stimulatory dendritic cells (DCs) and natural killer (NK) cells. We further hypothesize that applying agents that can correct the imbalance between the immunosuppressive cells and stimulatory cells can results in resolution of chronic HCV. In this review article, we will discuss potential approaches, focusing on the use of Toll-like receptor agonists, to block the suppressive effects of the regulatory cells and restore the stimulatory effects of DCs and NK cells.

In liver fibrosis, dendritic cells govern hepatic inflammation in mice via TNF-alpha

Hepatic fibrosis occurs during most chronic liver diseases and is driven by inflammatory responses to injured tissue. Because DCs are central to modulating liver immunity, we postulated that altered DC function contributes to immunologic changes in hepatic fibrosis and affects the pathologic inflammatory milieu within the fibrotic liver. Using mouse models, we determined the contribution of DCs to altered hepatic immunity in fibrosis and investigated the role of DCs in modulating the inflammatory environment within the fibrotic liver. We found that DC depletion completely abrogated the elevated levels of many inflammatory mediators that are produced in the fibrotic liver. DCs represented approximately 25% of the fibrotic hepatic leukocytes and showed an elevated CD11b+CD8- fraction, a lower B220+ plasmacytoid fraction, and increased expression of MHC II and CD40. Moreover, after liver injury, DCs gained a marked capacity to induce hepatic stellate cells, NK cells, and T cells to mediate inflammation, proliferation, and production of potent immune responses. The proinflammatory and immunogenic effects of fibrotic DCs were contingent on their production of TNF-alpha. Therefore, modulating DC function may be an attractive approach to experimental therapeutics in fibro-inflammatory liver disease.