Dynamic decrease in PD-1 expression correlates with HBV-specific memory CD8 T-cell development in acute self-limited hepatitis B patients

BACKGROUND/AIMS

Programmed death-1 (PD-1) upregulation can impair virus-specific CD8 T-cell responses during chronic viral infection. Whether and how PD-1 affects virus-specific memory CD8 T cells in humans with acute viral infection, however, remains largely undefined.

METHODS

The association between PD-1 expression and HBV-specific memory CD8 T-cell responses were longitudinally analyzed in eighteen patients with acute hepatitis B virus (HBV) infection, including ten patients with human leucocyte antigen (HLA)-A201 and eight with other HLA-A2 subtypes.

RESULTS

At clinical onset, PD-1 was significantly up-regulated and subsequently led to the functional suppression of HBV-specific effector CD8 T cells, as blocking PD-1/PD-L1 interactions in vitro enhanced their proliferation and IFN-gamma production. Following disease resolution, HBV-specific effector CD8 T cells developed into memory T cells. During this period, the dynamic PD-1 decrease was numerically correlated with the reduction of HBV-specific CD8 T-cell frequency, phenotypically with an acquisition of CCR7, CD45RA and CD127 expressions, and functionally with the increase in proliferation and IFN-gamma production of the memory T cells.

CONCLUSIONS

PD-1-mediated inhibitory signaling not only attenuates HBV-specific CD8 T-cell effector function during the acute phase of infection but also correlates with the development of HBV-specific memory CD8 T cells following disease resolution.

Toll-like receptors and their role in gastrointestinal disease

The innate immune response to invading pathogens is centred upon a family of non-clonal, germline-encoded pattern recognition receptors (PRRs), the Toll-like receptors (TLRs). These provide specificity for a vast range of microbial pathogens, and offer an immediate anti-microbial response system. Thirteen mammalian TLRs have been described; 10 are expressed in humans, each responsible for the recognition of distinct, invariant microbial structures originating from bacteria, viruses, fungi and protozoa. The two most thoroughly studied are TLR4 and TLR2, the PRRs for Gram-negative and Gram-positive bacterial products, respectively. TLR4 is also the major receptor recognising endogenous ligands released from damaged or dying cells. Activation of a TLR by its relevant ligand rapidly ignites a complex intracellular signaling cascade that ultimately results in upregulation of inflammatory genes and production of proinflammatory cytokines, interferons and recruitment of myeloid cells. It also stimulates expression, upon antigen presenting cells, of co-stimulatory molecules required to induce an adaptive immune response. Whilst a robust TLR response is critical for survival and defence against invading pathogens, inappropriate signaling in response to alterations in the local microflora environment can be detrimental. Such 'unhelpful TLR responses' could form the basis for a large number of gastrointestinal and liver disorders, including inflammatory bowel disease, viral hepatitis, autoimmune liver diseases and hepatic fibrosis. As our understanding of TLRs expands, the pathogenesis of a number of gastrointestinal disorders will be further elucidated, and this offers potential for specific therapies aimed directly at TLR signaling.

Regulatory T cells in the control of host-microorganism interactions (*)

Each microenvironment requires a specific set of regulatory elements that are finely and constantly tuned to maintain local homeostasis. Various populations of regulatory T cells contribute to the maintenance of this equilibrium and establishment of controlled immune responses. In particular, regulatory T cells limit the magnitude of effector responses, which may result in failure to adequately control infection. However, regulatory T cells also help limit collateral tissue damage caused by vigorous antimicrobial immune responses against pathogenic microbes as well as commensals. In this review, we describe various situations in which the balance between regulatory T cells and effector immune functions influence the outcome of host-microorganism coexistence and discuss current hypotheses and points of polemic associated with the origin, target, and antigen specificity of both endogenous and induced regulatory T cells during these interactions.

Toll-like receptors as targets in chronic liver diseases

Toll-like receptors (TLRs) recognise pathogen-associated molecular patterns (PAMPs) to detect the presence of pathogens. In addition to their role in innate immunity, TLRs also play a major role in the regulation of inflammation, even under sterile conditions such as injury and wound healing. This involvement has been suggested to depend, at least in part, on the ability of TLRs to recognise several endogenous TLR ligands termed damage-associated molecular patterns (DAMPs). The liver not only represents a major target of bacterial PAMPs in many disease states but also upregulates several DAMPs following injury. Accordingly, TLR-mediated signals have been implicated in a number of chronic liver diseases. Here, we will summarise recent findings on the role TLRs and TLR ligands in the pathophysiology of liver fibrosis and cirrhosis, viral hepatitis, alcoholic liver disease, non-alcoholic fatty liver disease and hepatocellular carcinoma, and highlight the potential role of TLR agonists, antagonists and probiotics for the treatment of chronic liver disease.

Dendritic cells and chronic hepatitis B

The immune function disorders in patients with chronic hepatitis B (CHB) lead to persistent damage of their liver cells and have impact on the ability to clear the virus. Dendritic cells (DCs) are the most important antigen-presenting cells in body. They help to generate sufficient immune response by the invasion of pathogens. The quantity and functionality of DCs directly correlate with the normal function of the host's immune response. Not only can DCs be resistant to the virus, but also serve as vehicles for the virus to spread and escape immune injury. Therefore the research on DCs and improving their function under the state of CHB is quite significant.

Hepatitis B virus suppresses toll-like receptor-mediated innate immune responses in murine parenchymal and nonparenchymal liver cells

We have previously shown that Toll-like receptor (TLR)-activated murine nonparenchymal liver cells [(NPC); Kupffer cells (KC), liver sinusoidal endothelial cells (LSEC)] can suppress hepatitis B virus (HBV) replication. Therefore, the aim of this study was to investigate whether HBV has the ability to counteract the TLR-mediated control of its replication. Freshly purified murine hepatocytes and NPCs obtained from C57BL6 mice were stimulated by TLR 1-9 ligands in the presence or absence of hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), HBV virions, or supernatants from HBV-producing HBV-Met cells, and HBV replication was suppressed by anti- hepatitis B virus X protein (HBx) small interfering RNA (siRNA) in HBV-Met cells. Supernatants were collected and tested for antiviral cytokines by viral protection assay. HBV gene expression and replication was analyzed by southern blot. RNA and proteins were analyzed by quantitative reverse transcription polymerase chain reaction (RT-PCR) or western blot and enzyme-linked immunosorbent assay, respectively. Pretreatment of hepatocytes and NPCs with HBV-Met cells supernatants, HBsAg, HBeAg, or HBV virions almost completely abrogated TLR-induced antiviral activity, which correlated with suppression of interferon beta (IFN-beta) production and subsequent interferon-stimulated gene induction as well as suppressed activation of interferon regulatory factor 3 (IRF-3), nuclear factor kappa B (NF-kappaB), and extracellular signal-regulated kinase (ERK) 1/2. In HBV-infected HBV-Met cells, TLR stimulation did not induce antiviral cytokines in contrast to primary hepatocytes. TLR-stimulated expression of proinflammatory cytokines [tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6)], and activation of IRF-3 was suppressed after up-regulation of HBV replication in HBV-Met cells. Accordingly, suppression of HBV replication by siRNA led to activation or expression of proinflammatory transcription factors and cytokines.

CONCLUSION

Our data indicate that HBV can suppress the TLR-induced antiviral activity of liver cells. This has major implications for the interaction between HBV and the immune system.

Analysis of CD8+ T-cell-mediated inhibition of hepatitis C virus replication using a novel immunological model

BACKGROUND & AIMS

Virus-specific CD8+ T cells are required for the control of hepatitis C virus (HCV) infection. We investigated the extent to which different effector functions of CD8+ T cells contribute to the inhibition of viral replication.

METHODS

We developed a novel immunologic model by stably transducing the HLA-A2 gene into the replicon system, matching the epitope sequence of the replicon to the sequence targeted by an HCV-specific CD8+ T-cell clone. Luciferase activity was then measured to quantitate HCV RNA replication.

RESULTS

HCV-specific CD8+ T cells strongly inhibited viral replication, through cytolytic and noncytolytic mechanisms, in a dose-dependent manner. HCV replication was almost completely inhibited at an effector-to-target ratio of 1:1 with significant cytotoxicity; however, >95% viral inhibition occurred at ratios as low as 1:100. Importantly, no cytotoxicity was observed at low effector-to-target ratios, indicating a dominant effect of noncytolytic effector functions that was confirmed by Transwell experiments. Neutralization experiments revealed that interferon gamma mediates the noncytolytic inhibition.

CONCLUSIONS

Only a very few HCV-specific CD8+ T cells are required to inhibit HCV replication; inhibition occurs primarily by noncytolytic effector functions.

The diversity of costimulatory and inhibitory receptor pathways and the regulation of antiviral T cell responses

T cell responses are regulated by integrating positive and negative signals from costimulatory and inhibitory receptors. While the function of specific T cell costimulatory molecules during infections has been appreciated for some time, recent observations have now revealed a crucial role for inhibitory receptors in regulating T cell responses to pathogens, especially during chronic infections. A key emerging principle is that there is considerable diversity in the number and type of inhibitory receptors that can be expressed by T cells during both acute and chronic infections. These distinct inhibitory pathways appear to cooperate in regulating T cell function, could have distinct mechanisms of action, and are likely to provide novel therapeutic targets during persisting infections and other diseases.

Activation of toll-like receptor signaling pathway for protection against influenza virus infection

This study aims to evaluate the antiviral role of nucleic acid-based agonists for the activation of toll-like receptor (TLR) signaling pathways, and its protective role in respiratory influenza A virus infections. TLR-3 is expressed on myeloid dendritic cells, respiratory epithelium, and macrophages, and appears to play a central role in mediating both the antiviral and inflammatory responses of the innate immunity in combating viral infections. Influenza viruses can effectively inhibit the host's ability to produce interferons, and thereby suppress the immune system's antiviral defence mechanisms. Poly ICLC is a synthetic double stranded RNA comprising of polyriboinosinic-poly ribocytidylic acid (Poly IC) stabilized with l-lysine (L) and carboxymethylcellulose (C). Poly ICLC and liposome-encapsulated Poly ICLC (LE Poly ICLC) are TLR-3 agonists and are potent inducer of interferons and natural killer cells. Intranasal pre-treatment of mice with Poly ICLC and LE Poly ICLC provided high level of protection against lethal challenge with a highly lethal avian H5N1 influenza (HPAI) strain (A/H5N1/chicken/Henan clade 2), and against lethal seasonal influenza A/PR/8/34 [H1N1] and A/Aichi/2 [H3N2] virus strains. The duration of protective antiviral immunity to multiple lethal doses of influenza virus A/PR/8/34 virus had been previously found to persist for up to 3 weeks in mice for LE Poly ICLC and 2 weeks for Poly ICLC. Similarly, pre-treatment of mice with CpG oligonucleotides (TLR-9 agonist) was also found to provide complete protection against influenza A/PR/8/34 infection in mice. RT-PCR analysis of lung tissues of mice treated with Poly ICLC and LE Poly ICLC revealed upregulation of TLR-3 mRNAs gene expression. Taken together, these results do support the potential role of TLR-3 and TLR-9 agonists such as Poly ICLC and LE Poly ICLC in protection against lethal seasonal and HPAI virus infection.

Upregulation of indoleamine 2,3-dioxygenase in hepatocyte during acute hepatitis caused by hepatitis B virus-specific cytotoxic T lymphocytes in vivo

BACKGROUND/AIMS

Indoleamine-2,3-dioxygenase (IDO) is a tryptophan-catabolizing enzyme inducing suppression of T-cell function and immune tolerance. In hepatitis B virus (HBV) transgenic (Tg) mice, the adoptive transfer of HBV-specific cytotoxic T lymphocytes (CTL) causes a necroinflammatory liver disease that is histologically similar to acute viral hepatitis in man. The present study aimed to determine IDO expression in the liver and hepatocytes during an acute hepatitis model.

METHODS

Serum l-kynurenine (l-Kyn) concentration in HBV Tg mice administered with HBV-specific CTL was measured over time, together with serum levels of alanine aminotransferase (ALT). Furthermore, we examined the expression of IDO in the total liver and isolated hepatocytes of HBV Tg mice after CTL injection using immunohistochemical analysis and reverse-transcription polymerase chain reaction (PCR).

RESULTS

In HBV Tg mice, HBV-specific CTL induced, over the course of several days, a chronic increase in serum l-Kyn levels, which was associated with a sustained enhancement of liver IDO activity. In particular, IDO expression was enhanced in the liver parenchymal cells (hepatocytes) after HBV-specific CTL injection both in immunohistochemical analysis and in reverse-transcription PCR. Moreover, murine recombinant interferon-gamma (IFN-gamma) directly increased the IDO expression in primary hepatocytes in vitro.

CONCLUSIONS

Cytotoxic T lymphocytes transduction results in the upregulation of IDO, which might downregulate T-cell responsiveness. Our findings provide evidence that hepatocyte itself expresses IDO and increases levels of l-Kyn in the blood in acute lethal hepatitis of mice. These data indicate that HBV infection facilitates the induction of IDO in response to proinflammatory cytokines, particularly IFN-gamma.

The novel CD4+CD25+ regulatory T cell effector molecule fibrinogen-like protein 2 contributes to the outcome of murine fulminant viral hepatitis

Fulminant viral hepatitis (FH) remains an important clinical problem in which the underlying pathogenesis is not well understood. Here, we present insight into the immunological mechanisms involved in FH caused by murine hepatitis virus strain 3 (MHV-3), indicating a critical role for CD4(+)CD25(+) regulatory T cells (Tregs) and production of the novel Treg effector molecule FGL2. Before infection with MHV-3, susceptible BALB/cJ mice had increased numbers of Tregs and expression of fgl2 messenger RNA (mRNA) and FGL2 protein compared with resistant A/J mice. After MHV-3 infection, plasma levels of FGL2 in BALB/cJ mice were significantly increased, correlating with increased percentage of Tregs. Treatment with anti-FGL2 antibody completely inhibited Treg activity and protected susceptible BALB/cJ mice against MHV-3-liver injury and mortality. Adoptive transfer of wild-type Tregs into resistant fgl2(-/-) mice increased their mortality caused by MHV-3 infection, whereas transfer of peritoneal exudate macrophages had no adverse effect.

CONCLUSION

This study demonstrates that FGL2 is an important effector cytokine of Tregs that contributes to susceptibility to MHV-3-induced FH. The results further suggest that targeting FGL2 may lead to the development of novel treatment approaches for acute viral hepatitis infection.

Co-immunization of mice with a retroviral DNA vaccine and GITRL-encoding plasmid augments vaccine-induced protection against retrovirus infection

After more than 30 years of research a HIV vaccine is still not at hand. DNA vectors expressing viral antigens are very safe vaccines, but so far they have not been efficient enough to induced broad protective immunity against retroviruses. One strategy to enhance the efficiency of DNA vaccines is to augment effector T-cell priming against viral components by manipulating regulatory T-cell functions (Treg). Glucocorticoid-induced tumor necrosis factor receptor (GITR) is a molecule that is constitutively expressed on CD4(+) Treg cells, and antibodies or natural ligands binding this molecule can impair Treg cell suppression. Here we demonstrate using the retroviral Friend virus (FV) mouse model, that co-immunization of FV antigens along with GITR-ligand (GITRL) encoding plasmids protected mice efficiently against a FV challenge. On the other hand, treatment of DNA-vaccinated mice with alpha-GITR antibody did not improve vaccine-induced protection at all. Thus, for an effective priming of immunity against FV, GITRL and viral antigens might have to be expressed within the same local environment. The data suggest that limitations in DNA vaccination can be overcome by co-expressing co-stimulatory molecules that potentially manipulate the function of Treg cells during priming of anti-retroviral immunity.

Enhancing therapeutic HPV DNA vaccine potency through depletion of CD4+CD25+ T regulatory cells

Therapeutic human papillomavirus (HPV) vaccines targeting E6 and/or E7 antigens represent an opportunity to control HPV-associated lesions. We have previously generated several therapeutic DNA vaccines targeting HPV-16 E7 antigen and generated significant antitumor effects. Since regulatory T cells (Tregs) play an important role in suppressing immune responses against tumors by immunotherapy, such as DNA vaccines, we tested if the therapeutic effects of a DNA vaccine encoding E7 linked to heat shock protein 70 (Hsp70) can be improved by a strategy to deplete Tregs using a anti-CD25 monoclonal antibody (PC61) in vaccinated mice. We found that administration of PC61 prior to vaccination with E7/Hsp70 DNA was capable of generating higher levels of E7-specific CD8(+) T cells compared to the control antibody, leading to significantly improved therapeutic and long-term protective antitumor effects against an E7-expressing tumor, TC-1. Thus, a strategy to deplete CD4(+)CD25(+) Tregs in conjunction with therapeutic tumor antigen-specific DNA vaccine may represent a potentially promising approach to control tumor. The clinical implications of our study are discussed.

A frequent functional toll-like receptor 7 polymorphism is associated with accelerated HIV-1 disease progression

OBJECTIVES

Toll-like receptors (TLRs) play an important role in the innate immune response to pathogens. TLR7 recognizes RNA of various viruses including HIV. The objective of this study was to examine the influence of individual genetic variations of TLR7 on the susceptibility to and progression of HIV disease.

METHOD

We genotyped a population of 734 HIV-positive adults and 545 healthy controls for three TLR7 single nucleotide polymorphisms. The frequency of TLR7 genetic variations was assessed and related to HIV disease progression. Furthermore, we analyzed peripheral blood mononuclear cells obtained from healthy individuals differing in their TLR7 genotype and assessed their response to a TLR7-specific ligand ex vivo.

RESULTS

Presence of the most frequent TLR7 polymorphism, TLR7 Gln11Leu, was associated with higher viral loads and accelerated progression to advanced immune suppression in HIV patients. Furthermore, in women this polymorphism may be associated with increased HIV-1 susceptibility as it was found more frequently among patients as compared with controls. Peripheral blood mononuclear cells from polymorphism carriers secreted significantly less IFN-alpha following TLR7 activation, whereas IL-6 production remained unaltered.

CONCLUSION

This is the first report of a functional TLR7 variant to be associated with susceptibility to and a more severe clinical course of HIV-1 disease. These results may have implications for the risk assessment of individual patients as well as for HIV-1 therapy and vaccination strategies in the future.

Regulatory T cells promote early influx of CD8+ T cells in the lungs of respiratory syncytial virus-infected mice and diminish immunodominance disparities

In addition to regulating autoimmunity and antitumor immunity, CD4(+) CD25(+) FoxP3(+) natural regulatory T (Treg) cells are global regulators of adaptive immune responses. Depletion of these cells with the anti-CD25 antibody PC61 prior to primary respiratory syncytial virus (RSV) infection was partial but had several effects on the RSV-specific CD8(+) response in a hybrid mouse model. Mediastinal lymph node and spleen epitope-specific CD8(+) T-cell responses were enhanced in Treg-cell-depleted mice at all time points following infection, but responses of Treg-cell-depleted lung show a strikingly different pattern than lymphoid organ responses, with an initial delay in the CD8(+) T-cell response. The delay in the CD8(+) T-cell response correlated with a delay both in the early phase of viral clearance and in illness in Treg-cell-depleted mice compared to isotype-treated controls. The lungs of Treg-cell-depleted mice were shown to have increased lung chemokine and cytokine levels 7 days postinfection despite lower CD8(+) T-cell responses. Following the early delay in the lung response, CD8(+) T-cell responses at later infection time points were enhanced and increased the severity of illness in depleted mice. Finally, decreasing regulatory T-cell control of the CD8(+) T-cell response had a greater effect on response of the dominant K(d)-restricted M2 epitope consisting of amino acids 82 to 90 (K(d)M2(82-90)) than on the subdominant D(b)M(187-195) epitope response, indicating that regulatory T cells modulate immunodominance disparities in epitope-specific CD8(+) T-cell responses following primary RSV infection.

Decreased parietal cortex activity during mental rotation in children with congenital hypothyroidism

BACKGROUND

The ability to detect the spatial characteristics of objects and to rotate them mentally is frequently impaired in early treated congenital hypothyroidism (CH) children.

AIMS

To explore the neural substrate of the visuospatial difficulty in children with CH, we studied 15 children with CH (8-10 years) and 13 age-matched control children with functional magnetic resonance imaging (fMRI) using a mental rotation task (VST).

RESULTS

Performance at VST was significantly different between the two groups. Moreover, fMRI data showed greater activation in the superior parietal cortex in control children while children with CH had greater activation in the bilateral SMA and the opercular region of the precentral gyrus, the adjacent insula and the left somatosensory parietal cortex. Furthermore, children with CH deactivated the inferior parietal cortex (Brodmann area 40) more than controls.

CONCLUSION

We suggest that the poorer performance of children with CH on VST task is related to the decreased activation in brain areas important for the mental representation of the objects' spatial characteristics, with increased recruitment of regions involved in the representation of somatosensory whole-body information. More studies will be necessary to understand if this different effectiveness in VST reflects immaturity of the neural system or its actual impairment.

Characterization of the innate immune signalling pathways in hepatocyte cell lines

Hepatitis B virus (HBV) infection is a major cause of liver-related morbidity and mortality. Toll-like receptors (TLRs) have recently been recognized to play an important role in the pathogenesis of chronic hepatitis B (CH-B). Furthermore, manipulation of TLR signalling pathways shows potential as an antiviral therapeutic strategy. Whether hepatocytes themselves possess intact TLR signalling pathways remains controversial. It is critical that cell culture models be developed to allow investigation of the interaction between HBV and the TLR signalling pathways. We have screened three hepatocyte cell lines for the integrity of pro-inflammatory responses and antiviral cytokines following stimulation with interleukin-1 (IL-1) and different TLR ligands. We observed that Huh-7, HepG2 and PH5CH8 cells selectively responded to IL-1 and TLR2 ligands, leading to the activation of NF-kappaB. In addition, the PH5CH8 cell lines were able to induce type 1 interferon (IFN) via both TLR3 and RIG-I following stimulation with poly I:C, HepG2 cells mounted an IFN response via RIG-I only, whereas Huh-7 cells were unresponsive. We conclude that the hepatocyte cell lines investigated display a repertoire of TLR signalling, albeit limited, suggesting that hepatocytes may themselves play an active role in innate immune responses to viruses such as HBV. Furthermore, particular hepatoma cell lines are suitable for investigating the interaction between HBV and hepatocyte-expressed pattern recognition receptors.

[RIG-I mediated hepatic innate immune signaling that controls HCV infection]

Hepatitis C virus (HCV) infection is one of the most serious public health problems in the world. HCV leads patients to develop hepatic cirrhosis and precipitates hepatocellular carcinoma. HCV establishes persistent infection by impairing host innate and adaptive immune responses. HCV infected hepatocytes sense the infection through Pathogen Associated Molecular Patterns (PAMPs). The sensor molecules, Pattern Recognition Receptors (PRRs) contain two distinct categories, toll like receptors (TLR) and cytoplasmic Retinoic Acid inducible Gene I (RIG-I) like helicases (RLHs). In the hepatocyte, the cytoplasmic PRR, Retinoic Acid inducible Gene I (RIG-I) plays the central role of HCV viral genome recognition, resulting in activation of signaling to induce type I interferon and proinflammatory cytokines. Type I IFN induces more than 300 effector molecules known as interferon stimulated genes (ISGs) that establish an antiviral state in infected cells and neighboring cells. The activation of innate immunity is also critical for the mounting of innate and adaptive immunity. However, a variety of viral strategies of HCV disrupt host innate immune signaling and ISG function, resulting in a dysfunctional immune response against HCV and poor responses to the current type I IFN based therapy. Many studies have reported immune dysfunction during HCV infection in cell culture, animal models and patients. This review article focuses on understanding how the hepatic innate immunity sensor, PRR, associates with HCV PAMPs, and how HCV escapes from host immunity.

Toll-like receptor 4 mediates innate immunity to Kaposi sarcoma herpesvirus

The involvement of Toll-like receptor 4 (TLR4) in immunity against human herpesviruses has not been previously demonstrated. We show that infection of endothelial cells with Kaposi sarcoma herpesvirus (KSHV), a human oncogenic virus, leads to rapid suppression of TLR4 expression. This is a mechanism of immune escape as TLR4 mediates innate immunity against KSHV. In vitro, cells lacking TLR4 are more susceptible to KSHV infection, whereas activation of TLR4 protects cells from infection. In vivo, HIV-1-infected individuals carrying a mutant TLR4 allele appear more likely to have multicentric Castleman's disease, a lymphoproliferation associated with enhanced KSHV replication. ERK activation by KSHV structural proteins and the KSHV-encoded vGPCR plays a key role in the TLR4 downregulation, whereas the KSHV vIRF1 also contributes to this effect. Our findings reveal a role for TLR4 in innate immunity against herpesviruses and suggest the potential use of TLR4 agonists for the treatment of KSHV-related neoplasms.

Activation of pattern recognition receptor-mediated innate immunity inhibits the replication of hepatitis B virus in human hepatocyte-derived cells

Recognition of virus infections by pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs), retinoic acid-inducible gene I (RIG-I), and melanoma differentiation associated gene 5 (MDA5), activates signaling pathways, leading to the induction of inflammatory cytokines that limit viral replication. To determine the effects of PRR-mediated innate immune response on hepatitis B virus (HBV) replication, a 1.3mer HBV genome was cotransfected into HepG2 or Huh7 cells with plasmid expressing TLR adaptors, myeloid differentiation primary response gene 88 (MyD88), and TIR-domain-containing adaptor-inducing beta interferon (TRIF), or RIG-I/MDA5 adaptor, interferon promoter stimulator 1 (IPS-1). The results showed that expressing each of the three adaptors dramatically reduced the levels of HBV mRNA and DNA in both HepG2 and Huh7 cells. However, HBV replication was not significantly affected by treatment of HBV genome-transfected cells with culture media harvested from cells transfected with each of the three adaptors, indicating that the adaptor-induced antiviral response was predominantly mediated by intracellular factors rather than by secreted cytokines. Analyses of involved signaling pathways revealed that activation of NF-kappaB is required for all three adaptors to elicit antiviral response in both HepG2 and Huh7 cells. However, activation of interferon regulatory factor 3 is only essential for induction of antiviral response by IPS-1 in Huh7 cells, but not in HepG2 cells. Furthermore, our results suggest that besides NF-kappaB, additional signaling pathway(s) are required for TRIF to induce a maximum antiviral response against HBV. Knowing the molecular mechanisms by which PRR-mediated innate defense responses control HBV infections could potentially lead to the development of novel therapeutics that evoke the host cellular innate antiviral response to control HBV infections.

Selective expansion of a subset of exhausted CD8 T cells by alphaPD-L1 blockade

Programmed death-1 (PD-1) regulates T cell exhaustion during chronic infections. Blocking the PD-1:PD-ligand (PD-L) pathway reinvigorates exhausted CD8 T cells. Exactly how blocking PD-1:PD-L interactions improves T cell immunity, however, remains unclear. PD-1:PD-L blockade could reprogram all exhausted T cells to become antiviral effectors. Alternatively, this blockade might selectively expand a subset of exhausted T cells. We have identified two subpopulations of exhausted CD8 T cells during chronic viral infection in mice. One subset of exhausted CD8 T cells is rescued by alphaPD-L1 blockade, whereas the other subset appears more terminally differentiated and responds poorly to PD-1:PD-L blockade. Blocking PD-1:PD-L interactions reduces spontaneous apoptosis and enhances expansion and protective immunity of the rescuable subset, but not the more terminally differentiated subset of exhausted CD8 T cells. These results have implications for predicting clinical responses to PD-1-based therapeutic interventions and for understanding T cell dynamics during persisting infections.

A subset of IL-10-producing gammadelta T cells protect the liver from Listeria-elicited, CD8(+) T cell-mediated injury

Although gammadelta T cells play a role in protecting tissues from pathogen-elicited damage to bacterial, viral and parasitic pathogens, the mechanisms involved in the damage and in the protection have not been clearly elucidated. This has been addressed using a murine model of listeriosis, which in mice lacking gammadelta T cells (TCRdelta(-/-)) is characterised by severe and extensive immune-mediated hepatic necrosis. We show that these hepatic lesions are caused by Listeria-elicited CD8(+) T cells secreting high levels of TNF-alpha that accumulate in the liver of Listeria-infected TCRdelta(-/-) mice. Using isolated populations of gammadelta T cells from wild-type and cytokine-deficient strains of mice to reconstitute TCRdelta(-/-) mice, the TCR variable gene 4 (Vgamma4)(+) subset of gammadelta T cells was shown to protect against liver injury. Hepatoprotection was dependent upon their ability to produce IL-10 after TCR-mediated interactions with Listeria-elicited macrophages and CD8(+) T cells. IL-10-producing Vgamma4(+) T cells also contribute to controlling CD8(+) T cell expansion and to regulating and reducing TNF-alpha secretion by activated CD8(+) T cells. This effect on TNF-alpha production was directly attributed to IL-10. These findings identify a novel mechanism by which pathogen-elicited CD8(+) T cells are regulated via interactions with, and activation of, IL-10-producing hepatoprotective gammadelta T cells.

Expression and function of PDCD1 at the human maternal-fetal interface

The failure to reject the semiallogenic fetus by maternal T lymphocytes suggests that potent mechanisms regulate these cells. PDCD1 is a CD28 family receptor expressed by T cells, and its ligand CD274 is strongly expressed by trophoblast cells of the human placenta. In this study, we examined whether human maternal T cells express PDCD1. Immunofluorescence examination of uterine tissues revealed PDCD1 expression on CD3+ cells was low in nonpregnant endometrium but increased in first-trimester decidua and remained elevated in term decidua (P < 0.05). In addition, higher relative proportions of term decidual CD8 bright, CD4+, and regulatory T cells expressed PDCD1 in comparison to autologous peripheral blood (P < 0.05). Term decidual T cells also expressed full-length and soluble PDCD1 mRNA isoforms more abundantly than their peripheral blood counterparts (P Collapse

Key Words

• b7-h1
• cd274
• cd279
• decidua
• pd-1
• pdl1
• pdcd1
• placenta
• t cells

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MESH Headings

• Adult
• Antigens, CD/genetics
• Antigens, CD/metabolism
• Antigens, CD/physiology
• Apoptosis Regulatory Proteins/genetics
• Apoptosis Regulatory Proteins/metabolism
• Apoptosis Regulatory Proteins/physiology
• B7-H1 Antigen
• Cells, Cultured
• Cytokines/metabolism
• Decidua/immunology
• Decidua/metabolism
• Female
• Humans
• Maternal-Fetal Exchange/genetics
• Maternal-Fetal Exchange/immunology
• Middle Aged
• Pregnancy
• Programmed Cell Death 1 Receptor
• Protein Isoforms/metabolism
• RNA, Messenger/metabolism
• Signal Transduction/immunology
• T-Lymphocytes/metabolism
• Term Birth/immunology

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Grants

• P20 RR017686 NCRR NIH HHS
• P20 RR016475 NCRR NIH HHS
• HD02528 NICHD NIH HHS
• P20 RR024214 NCRR NIH HHS
• HD049480 NICHD NIH HHS
• P20RR016475 NCRR NIH HHS
• P20RR024214 NCRR NIH HHS
• P20RR017686 NCRR NIH HHS
• P01 HD049480 NICHD NIH HHS
• P30 HD002528 NICHD NIH HHS
• HD45611 NICHD NIH HHS
• R01 HD045611 NICHD NIH HHS

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Affiliation(s)

Elizabeth S. Taglauer Department of Anatomy and Cell Biology, and Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City, Kansas 66160
Ann S. Trikhacheva University of Kansas, Lawrence, Kansas 66045
Joyce G. Slusser Department of Anatomy and Cell Biology, and Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City, Kansas 66160
Margaret G. Petroff Department of Anatomy and Cell Biology, and Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City, Kansas 66160

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Collaborators Collapse

Toll-like receptors and adaptor molecules in liver disease: update

Toll-like receptors (TLRs) are pattern recognition receptors that recognize pathogen-associated molecular patterns and signal through adaptor molecules, myeloid differentiation factor 88 (MyD88), Toll/IL-1 receptor domain containing adaptor protein (TIRAP), Toll/IL-1 receptor domain containing adaptor inducing interferon-beta (TRIF), and TRIF-related adaptor molecule (TRAM) to activate transcription factors, nuclear factor (NF)-kappaB, activator protein 1 (AP-1), and interferon regulatory factors (IRFs) leading to the initiation of innate immunity. This system promptly initiates host defenses against invading microorganisms. Endogenous TLR ligands such as the products from dying cells may also engage with TLRs as damage-associated molecular patterns. Although Kupffer cells are considered the primary cells to respond to pathogen associated molecular patterns in the liver, recent studies provide evidence of TLR signaling in hepatic nonimmune cell populations, including hepatocytes, biliary epithelial cells, endothelial cells, and hepatic stellate cells. This review highlights advances in TLR signaling in the liver, the role of TLRs in the individual hepatic cell populations, and the implication of TLR signaling in acute and chronic liver diseases. We further discuss recent advances regarding cytosolic pattern recognition receptors, RNA helicases that represents a new concept in chronic hepatitis C virus infection.

Understanding the immunopathogenesis of chronic hepatitis B virus: an Asian prospective

The study of hepatitis B virus (HBV) immunity has been mainly focused on understanding the differences between subjects who are able to control HBV infection and patients with persistent infection. These studies have been instrumental in increasing our knowledge on the pathogenesis of the disease caused by HBV. However, it is possible that heterogeneity of host and virus factors which segregate in ethnically distinct HBV infected populations might modify important aspects of the immune response against HBV. In this review, we reexamine the kinetics and the pattern of HBV-specific immunity associated with control or persistence of infection. We then discuss how the epidemiological, genetic and viral characteristics peculiar to Asian patients can impact the profile of HBV-specific immunity.

Dynamic programmed death 1 expression by virus-specific CD8 T cells correlates with the outcome of acute hepatitis B

BACKGROUND & AIMS

Recent studies have shown that programmed death 1 (PD-1) expression can impair virus-specific CD8 T-cell responses during chronic viral infection, including hepatitis B virus (HBV). This study aimed to characterize the PD-1 expression during acute hepatitis B (AHB) and further address whether and how the PD-1-mediated pathway balances antiviral immunity versus immunopathology, possibly contributing to disease progression.

METHODS

Peripheral and intrahepatic PD-1 expression was investigated longitudinally in 23 human HLA-A2-positive patients with acute hepatitis B. Four patients with HBV-related acute liver failure, 13 patients with chronic hepatitis B, and 9 healthy individuals were enrolled as controls. Flow cytometric, immunohistochemical, and immunofunctional assays were performed to analyze the impact of PD-1 expression.

RESULTS

PD-1 expression was significantly up-regulated on HBV-specific CD8 T cells in the early phase of acute HBV infection, and successful viral clearance correlated with a subsequent decrease in PD-1 expression. Blocking the PD-1-mediated pathway in vitro enhanced HBV-specific CD8 T-cell proliferation and inflammatory cytokine production, while reducing interleukin-10 production and apoptosis, confirming the essential role of PD-1 in tempering the T-cell response during the acute phase of infection. In contrast, delayed PD-1 expression on HBV-specific CD8 T cells was associated with acute liver failure.

CONCLUSIONS

PD-1 up-regulation may efficiently mitigate pathogenic CD8 T-cell responses and liver damage, correlating with disease progression of acute HBV infection. This study therefore shows how this negative signaling pathway functions in such early HBV infection, which will be important for better clinical management, prognosis, and new HBV treatments.

Toll-like receptors and viruses: induction of innate antiviral immune responses

Induction of antiviral innate immune responses depends on a family of innate immune receptors, the Toll-like receptors (TLR). TLR mediate the antiviral immune responses by recognizing virus infection, activating signaling pathways and inducing the production of antiviral cytokines and chemokines. ssRNA and dsRNA viruses can be recognized by TLR7/8 and TLR3, respectively. TLR receptors are also involved in the recognition of viruses containing genomes rich in CpG DNA motifs as well as envelope glycoproteins. Cytoplasmic recognition of dsRNA by RNA helicases such as RIG-I and MDA5 provides another means of recognizing viral nucleic acid. In order to counteract the innate host immune system viruses evolved mechanisms that block recognition and signaling through pattern recognition receptors, such as TLRs and RNA helicases. Recently, TLR agonists represent a promising approach for the treatment of infectious diseases. This review will focus on the current knowledge of TLR-mediated immune responses to several viral infections.

Restoration of HCV-specific T cell functions by PD-1/PD-L1 blockade in HCV infection: effect of viremia levels and antiviral treatment

BACKGROUND/AIMS

HCV-specific T cells in acute hepatitis C with subsequent chronic evolution are dysfunctional and most of them express PD-1. The aim of the study was to investigate to what extent the antiviral T cell function can be restored by reversing T cell exhaustion by PD-1/PD-L1 blockade and to assess whether this restoration is favored by IFN-alpha treatment.

METHODS

PD-1 and PD-L1 expression was studied on T cells and dendritic cells, respectively, of 14 patients with acute hepatitis C and different evolutions of infection. The effect of anti-PD-L1 was analyzed on proliferation, cytokine production and cytolytic activity of CD4 and CD8 T cells.

RESULTS

While PD-1 expression dropped concurrently with spontaneous or IFN-alpha induced HCV-RNA decline, PD-L1 levels on dendritic cells increased during IFN-alpha treatment. Anti-PD-L1 antibodies improved expansion and cytokine production but not the cytolytic activity of HCV-specific T cells. This restoration tended to be greater at lower levels of viremia and PD-1 expression and during PEG-IFNalpha treatment.

CONCLUSIONS

PD-1/PD-L1 blockade has an immunoregulatory activity which may synergize with the antiviral effect of IFN-alpha therapy and should be thus explored further in long-lasting chronic HCV infections in the perspective of improving the efficacy of available antiviral treatments.

Blockade of PD-1/B7-H1 interaction restores effector CD8+ T cell responses in a hepatitis C virus core murine model

The impaired function of CD8(+) T cells is characteristic of hepatitis C virus (HCV) persistent infection. HCV core protein has been reported to inhibit CD8(+) T cell responses. To determine the mechanism of the HCV core in suppressing Ag-specific CD8(+) T cell responses, we generated a transgenic mouse, core(+) mice, where the expression of core protein is directed to the liver using the albumin promoter. Using a recombinant adenovirus to deliver Ag, we demonstrated that core(+) mice failed to clear adenovirus-LacZ (Ad-LacZ) infection in the liver. The effector function of LacZ-specific CD8(+) T cells was particularly impaired in the livers of core(+) mice, with suppression of IFN-gamma, TNF-alpha, and granzyme B production by CD8(+) T cells. In addition, the impaired CD8(+) T cell responses in core(+) mice were accompanied by the enhanced expression of the inhibitory receptor programmed death-1 (PD-1) by LacZ-specific CD8(+) T cells and its ligand B7-H1 on liver dendritic cells following Ad-LacZ infection. Importantly, blockade of the PD-1/B7-H1 inhibitory pathway (using a B7-H1 blocking antibody) in core(+) mice enhanced effector function of CD8(+) T cells and cleared Ad-LacZ-infection as compared with that in mice treated with control Ab. This suggests that the regulation of the PD-1/B7-H1 inhibitory pathway is crucial for HCV core-mediated impaired T cell responses and viral persistence in the liver. This also suggests that manipulation of the PD-1/B7-H1 pathway may be a potential immunotherapy to enhance effector T cell responses during persistent HCV infection.

New concepts in the immunopathogenesis of chronic hepatitis B: the importance of the innate immune response

Acute and chronic infection with hepatitis B virus (HBV) is associated with an increased risk of developing liver disease including cirrhosis, decompensated liver disease, and hepatocellular carcinoma. The clinical presentation and natural history of HBV infection is mediated through complex interactions between the virus and the host immune response. HBV is not directly cytopathic to heptocytes; however, the interaction between the virus and the host immune response plays a central role in the pathogenesis of necroinflammation and liver fibrosis. Emerging data from immunopathogenesis studies in animal models and in vitro studies of liver biopsies from patients with chronic hepatitis B demonstrate a potentially important interaction between hepatitis B e antigen, HBV, and components of the innate immune response including Toll-like receptors, Kupffer cells, natural killer T-cells, and dendritic cells. These findings suggest that the innate immune response has an important role in influencing the outcome of acute and chronic HBV infection. The current knowledge regarding the interaction between HBV and components of the innate immune response during acute and chronic HBV infection is reviewed.

Efficacy of cationic lipid-DNA complexes (CLDC) on hepatitis B virus in transgenic mice

Cationic lipid-DNA (non-coding) complexes (CLDC) are activators of the innate immune response that increase survival of rodents with some acute viral infections and cancers. CLDC were evaluated for their ability to impact viral DNA levels in transgenic mice carrying an infectious clone of hepatitis B virus (HBV). Mice used in the studies were diet-restricted as nursing pups from solid food, because the expression of HBV DNA in the liver was increased above background levels in some mice with this restriction. Survival surgery was performed on these mice to obtain liver biopsies from which to select animals with suitable levels of liver HBV DNA for entry into the experimental protocols. Intravenous administration of 5 microg/mouse of CLDC on days 1, 7 and 13 reduced liver HBV DNA to similar low levels achieved with the positive control, adefovir dipivoxil. In a subsequent experiment, the same treatment schedule was used to determine that the minimal effective CLDC dose was between 0.5 and 0.05 microg/mouse. Selective cytokines were increased in the livers of CLDC-treated compared to placebo-treated mice in a dose-responsive manner. CLDC were effective in reducing liver HBV DNA and could be considered for further evaluation in other hepatitis models.

Therapeutic applications of synthetic CpG oligodeoxynucleotides as TLR9 agonists for immune modulation

Vertebrate toll-like receptors (TLRs) sense invading pathogens by recognizing bacterial and viral structures and, as a result, activate innate and adaptive immune responses. Ten human functional TLRs have been reported so far; three of these (TLR7, 8, and 9) are expressed in intracellular compartments and respond to single-stranded nucleic acids as natural ligands. The pathogen structure selectively recognized by TLR9 in bacterial or viral DNA was identified to be CpG dinucleotides in specific sequence contexts (CpG motifs). Short phosphorothioate-stabilized oligodeoxynucleotides (ODNs) containing such motifs are used as synthetic TLR9 agonists, and different classes of ODN TLR9 agonists have been identified with distinct immune modulatory profiles. The TLR9-mediated activation of the vertebrate immune system suggests using such TLR9 agonists as effective vaccine adjuvants for infectious disease, and for the treatment of cancer and asthma/allergy. Immune activation by CpG ODNs has been demonstrated to be beneficial in animal models as a vaccine adjuvant and for the treatment of a variety of viral, bacterial, and parasitic diseases. Antitumor activity of CpG ODNs has also been established in numerous mouse models. In clinical vaccine trials in healthy human volunteers or in immunocompromised HIV-infected patients, CpG ODNs strongly enhanced vaccination efficiency. Most encouraging results in the treatment of cancers have come from human phase I and II clinical trials using CpG ODNs as a tumor vaccine adjuvant, monotherapy, or in combination with chemotherapy. Therefore, CpG ODNs represent targeted immune modulatory drugs with a broad range of potential applications.

Role for MyD88 signaling in murine gammaherpesvirus 68 latency

Toll-like receptors (TLRs) are known predominantly for their role in activating the innate immune response. Recently, TLR signaling via MyD88 has been reported to play an important function in development of a B-cell response. Since B cells are a major latency reservoir for murine gammaherpesvirus 68 (MHV68), we investigated the role of TLR signaling in the establishment and maintenance of MHV68 latency in vivo. Mice deficient in MyD88 (MyD88(-/-)) or TLR3 (TLR3(-/-)) were infected with MHV68. Analysis of splenocytes recovered at day 16 postinfection from MyD88(-/-) mice compared to those from wild-type control mice revealed a lower frequency of (i) activated B cells, (ii) germinal-center B cells, and (iii) class-switched B cells. Accompanying this substantial defect in the B-cell response was an approximately 10-fold decrease in the establishment of splenic latency. In contrast, no defect in viral latency was observed in TLR3(-/-) mice. Analysis of MHV68-specific antibody responses also demonstrated a substantial decrease in the kinetics of the response in MyD88(-/-) mice. Analysis of wild-type x MyD88(-/-) mixed-bone-marrow chimeric mice demonstrated that there is a selective failure of MyD88(-/-) B cells to participate in germinal-center reactions as well as to become activated and undergo class switching. In addition, while MHV68 established latency efficiently in the MyD88-sufficient B cells, there was again a ca. 10-fold reduction in the frequency of MyD88(-/-) B cells harboring latent MHV68. This phenotype indicates that MyD88 is important for the establishment of MHV68 latency and is directly related to the role of MyD88 in the generation of a B-cell response. Furthermore, the generation of a B-cell response to MHV68 was intrinsic to B cells and was independent of the interleukin-1 receptor, a cytokine receptor that also signals through MyD88. These data provide evidence for a unique role for MyD88 in the establishment of MHV68 latency.

Novel strategies to eliminate persistent viral infections

Infection with viruses that have the capacity to modulate or evade the immune response can result in persistence, which can lead to a variety of chronic problems including neoplasia, immunosuppression, autoimmune-like syndromes, and selective organ failure. Recently, two promising new treatment approaches that target either the inhibitory receptor programmed cell death 1 (PD-1) or neutralize interleukin-10 (IL-10) during chronic viral infection have been described. We discuss how future combination therapies can be used to inhibit viral synthesis as well as strengthen the antiviral response without increasing immunopathology or the development of autoimmune disease.

Liver: An organ with predominant innate immunity

Blood circulating from the intestines to the liver is rich in bacterial products, environmental toxins, and food antigens. To effectively and quickly defend against potentially toxic agents without launching harmful immune responses, the liver relies on its strong innate immune system. This comprises enrichment of innate immune cells (such as macrophages, natural killer, natural killer T, and gammadelta T cells) and removal of waste molecules and immunologic elimination of microorganisms by liver endothelial cells and Kupffer cells. In addition, the liver also plays an important role in controlling systemic innate immunity through the biosynthesis of numerous soluble pathogen-recognition receptors and complement components.

CONCLUSION

The liver is an organ with predominant innate immunity, playing an important role not only in host defenses against invading microorganisms and tumor transformation but also in liver injury and repair. Recent evidence suggests that innate immunity is also involved in the pathogenesis of liver fibrosis, providing novel therapeutic targets to treat such a liver disorder.

Toll-like receptor 7 and 9 expression in peripheral blood mononuclear cells from patients with chronic hepatitis B and related hepatocellular carcinoma

AIM

The aim of the present study was to investigate the expression of Toll-like receptors (TLR) 7 and 9 in peripheral blood mononuclear cells (PBMC) of patients with chronic hepatitis B virus (HBV) infection and related hepatocellular carcinoma.

METHODS

The study group was comprised of 52 patients: 41 with chronic hepatitis B and 11 healthy controls. The protein and mRNA levels of TLR7 and TLR9 were evaluated using real-time PCR, Western blot analysis, and flow cytometry. We also detected the serum viral load of HBV in the patients and analyzed the correlation between HBV-DNA copies and the TLR expression.

RESULTS

Our results demonstrated a lower TLR7 expression in all HBV infection groups compared to the controls. We found that HBV infection led to a decreased expression of TLR9 mRNA, but an increased expression of the TLR9 protein compared to the healthy group. The TLR protein levels are related to serum HBV-DNA (P<0.01).

CONCLUSION

There are downregulations of TLR7 expression and TLR9 mRNA in PBMC of HBV-infected patients, but an increased TLR9 expression at the protein level.

Phosphorothioate-modified oligodeoxynucleotides inhibit human cytomegalovirus replication by blocking virus entry

Studies in animal models have provided evidence that Toll-like receptor 9 (TLR9) agonists, such as synthetic oligodeoxynucleotides (ODNs) that contain immunostimulatory deoxycytidyl-deoxyguanosine (CpG) motifs (CpG ODNs), protect against a wide range of viral pathogens. This antiviral activity has been suggested to be indirect and secondary to CpG-induced cytokines and inflammatory responses triggered through TLR9 activation. However, few studies have addressed the potential of CpG ODNs as direct antiviral agents. Here, we report on the ability of some CpG ODNs to directly suppress, almost completely, human cytomegalovirus (HCMV) replication in both primary fibroblasts and endothelial cells. Murine CMV replication was inhibited as well, whereas no inhibition was observed for herpes simplex virus type 1, adenovirus, or vesicular stomatitis virus. The antiviral activity of these ODNs was significantly reduced when they were added after virus adsorption, indicating that their action may be primarily targeted to the very early phases of the HCMV cycle. In fact, the B-class prototype CpG ODN 2006 effectively prevented the nuclear localization of pp65 and input viral DNA, which suggests that it inhibits HCMV entry. Moreover, a CpG 2006 control, ODN 2137 without CpG motifs, also showed a potent inhibitory activity on the HCMV entry phase, indicating that the anticytomegaloviral activity is independent of the CpG motif. In contrast, a phosphodiester version of CpG 2006 showed reduced antiviral activity, indicating that the inhibitory activity is dependent on the phosphorothioate backbone of the ODN. These results suggest that this yet-unrecognized activity of CpG ODNs may be of interest in the development of novel anticytomegaloviral molecules.

Association of TLR7 single nucleotide polymorphisms with chronic HCV-infection and response to interferon-a-based therapy

An efficient immune response against hepatitis C virus (HCV) is necessary to clear infection. As HCV is a single-stranded RNA virus, a role for TLR7 in the immune response against HCV is possible, and early clinical studies have demonstrated an antiviral effect of TLR7 stimulation. We tested the hypothesis that genetic variations of TLR7 are associated with chronic HCV-infection and outcome of therapy. The prevalence of three TLR7 variations was analysed in 978 patients with chronic HCV-infection, 898 patients with chronic liver disease of other aetiologies, and in 203 healthy controls. The prevalence of TLR7 variations was correlated with the response to interferon-alpha-based treatment in 544 patients with chronic HCV-infection. We analysed TLR7 polymorphisms by melting curve analysis and reconstructed haplotypes. The c.32A>T variation was over-represented in female patients with chronic HCV-infection compared to patients with other chronic liver diseases and to healthy controls (P < 0.05). In contrast, c.2403 G>A was less prevalent in male patients with chronic HCV-infection (P < 0.05). No association was observed for the third variant, c.1-120T>G. Haplotype analysis confirmed the differential distribution of TLR7 variants between the groups. Within the group of female patients with chronic HCV-infection, c.32T was predictive of an unfavourable outcome of interferon-alpha therapy (P < 0.05). This study reports the association of TLR7 variants with chronic HCV-infection and with the response to interferon-alpha therapy in patients with chronic HCV-infection. Our results suggest that variations of TLR7 impair the immune response to HCV and imply a gender-specific effect of this X-chromosomal variation.

The programmed death-1 and interleukin-10 pathways play a down-modulatory role in LP-BM5 retrovirus-induced murine immunodeficiency syndrome

Pathology due to the immune system's response to viral infections often represents a delicate balance between inhibition of viral pathogenesis and regulation of protective immunity. In susceptible C57BL/6 (B6) mice, the murine retroviral isolate LP-BM5 induces splenomegaly, hypergammaglobulinemia, profound B- and T-cell immunodeficiency, and increased susceptibility to opportunistic pathogens and terminal B-cell lymphomas. Here, we report that B6.PD-1 (programmed death-1) and B6.IL-10 knockout mice are substantially more susceptible to LP-BM5-induced disease than wild-type B6 mice. LP-BM5-infected B6.PD-1(-/-) mice developed more severe splenomegaly, hypergammaglobulinemia, and immunodeficiency than infected B6 mice: PD-1(-/-) mice are more susceptible to lower doses of LP-BM5 and show more exaggerated disease early postinfection. LP-BM5-infected B6.IL-10(-/-) mice also develop exaggerated LP-BM5-induced disease, compared to B6 mice, without a significant change in the retroviral load. By reciprocal reconstitution experiments, comparing wild-type versus PD-1(-/-) sources of the requisite cells for LP-BM5 pathogenesis-CD4 T and B cells, PD-1(+) B cells appear to be crucial in the normal limitation of LP-BM5-induced disease in B6 mice. Also, infected B6 mice have increased CD11b(+) spleen cells that express interleukin-10 (IL-10). However, PD-1(-/-) mice, though showing an even greater expansion of CD11b(+) cells after LP-BM5 inoculation, did not show an equivalent increase in IL-10-producing cells. Thus, it appears that PD-1/PD-L interactions and IL-10 are primarily important in moderating the effects of LP-BM5-induced disease in B6 mice.

Differential inhibition of human cytomegalovirus (HCMV) by toll-like receptor ligands mediated by interferon-beta in human foreskin fibroblasts and cervical tissue

Human cytomegalovirus (HCMV) can be acquired sexually and is shed from the genital tract. Cross-sectional studies in women show that changes in genital tract microbial flora affect HCMV infection and/or shedding. Since genital microbial flora may affect HCMV infection or replication by stimulating cells through Toll-like receptors (TLR), we assessed the effects of defined TLR-ligands on HCMV replication in foreskin fibroblasts and ectocervical tissue. Poly I:C (a TLR3-ligand) and lipopolysaccharide (LPS, a TLR4-ligand) inhibited HCMV and induced secretion of IL-8 and Interferon-beta (IFNbeta) in both foreskin fibroblasts and ectocervical tissue. The anti-HCMV effect was reversed by antibody to IFNbeta. CpG (TLR9 ligand) and lipoteichoic acid (LTA, TLR2 ligand) also inhibited HCMV infection in ectocervical tissue and this anti-HCMV effect was also reversed by anti-IFNbeta antibody. In contrast, LTA and CpG did not inhibit HCMV infection in foreskin fibroblasts. This study shows that TLR ligands induce an HCMV-antiviral effect that is mediated by IFNbeta suggesting that changes in genital tract flora may affect HCMV infection or shedding by stimulating TLR. This study also contrasts the utility of two models that can be used for assessing the interaction of microbial flora with HCMV in the genital tract. Clear differences in the response to different TLR ligands suggests the explant model more closely reflects in vivo responses to genital infections.

Toll-like receptor-mediated control of HBV replication by nonparenchymal liver cells in mice

Hepatitis B virus (HBV) infection is one of the most frequent causes of chronic liver disease worldwide. Because recent studies have suggested that Toll-like receptor (TLR)-based therapies may be a promising approach in the treatment of HBV infection, we studied the role of the local innate immune system of the liver as a possible mediator of this effect. Murine nonparenchymal cells, including Kupffer cells (KCs) and sinusoidal endothelial cells (LSECs), were isolated from C57/BL6 wild-type or MyD88(-/-) mice and stimulated by agonists of TLR1 to TLR9. Supernatants were harvested and assayed for their antiviral activity against HBV in HBV-Met cells. No direct antiviral effect of TLR agonists could be observed. In controls (myeloid dendritic cells), TLR1, TLR3, TLR4, TLR7, and TLR9 activation lead to production of antiviral cytokines. By contrast, only supernatants from TLR3-stimulated and TLR4-stimulated KCs and TLR3-stimulated LSECs from wild-type mice were able to potently suppress HBV replication as assessed via Southern blotting. Similar results were found with cells from MyD88(-/-) mice, indicating that the effect was independent of this signaling pathway. Cellular HBV RNA and hepatitis B surface antigen or hepatitis B e antigen levels in supernatants remained unchanged. Using neutralizing antibodies, we demonstrated that the TLR3-mediated effect but not the TLR4-mediated effect is mediated exclusively through interferon-beta.

CONCLUSION

Our data indicate that the innate immune system of the liver can control HBV replication after activation by TLR agonists. This has implications for the development of TLR-based therapeutic approaches against HBV.

Regulatory T cells and infection: a dangerous necessity

Surviving a given infection requires the generation of a controlled immune response. Failure to establish or restore homeostatic conditions during or following the onset of an infection can lead to tissue damage. Investigation of the immunoregulatory network that arises in response to the infectious process or that is induced by the pathogen itself should provide insight into therapeutic approaches for the control of infection and any subsequent immunopathology. In this Review, I discuss current hypotheses and points of polemic associated with the origin, mode of action and antigen specificity of the various populations of regulatory T cells that arise during infection.

The immunology of hepatitis B

The hepatitis B virus (HBV) is an enveloped, hepatotrophic, oncogenic hepadnavirus that is noncytopathic for hepatocytes. HBV infection results in a variety of outcomes that are determined by the quality, quantity, and kinetics of the host innate and adaptive immune responses. Whether HBV infection is cleared or persists as a progressive or nonprogressive liver disease is determined by both viral and host factors. Replicative intermediates can persist in the liver under immunologic control after resolution of acute or chronic hepatitis B, conferring a risk for reactivation following a course of immunosuppression or chemotherapy.