Overexpression of Toll-like receptor 2/4 on monocytes modulates the activities of CD4(+)CD25(+) regulatory T cells in chronic hepatitis B virus infection. Virology. 2010;397:34-42. [PMID: 19945134 DOI: 10.1016/j.virol.2009.11.007]

Interleukin-35 Enhances Regulatory T Cell Function by Potentially Suppressing Their Transdifferentiation into a T Helper 17-Like Phenotype in Kawasaki Disease

Interleukin-35 (IL-35) modulates immune cell activity in inflammation and autoimmune disorders. However, its specific effects on regulatory T cells (Tregs) in Kawasaki disease remain ambiguous. We enrolled 37 patients with Kawasaki disease and 20 healthy controls in this study. The percentages of CD4⁺CD25⁺CD127^dim/- Tregs and CD4⁺IL-17A⁺ T helper 17 (Th17) cells were determined via flow cytometry. Tregs were enriched and stimulated by recombinant IL-35. Immunosuppressive activity of Tregs was via co-culture with autologous CD4⁺CD25^- T cells. Purified Tregs were cultured for Th17 polarization, and the influence of IL-35 on Tregs transdifferentiation into a Th17-like phenotype was determined. The percentage of Tregs was elevated in patients with Kawasaki disease and positively correlated with C-reactive protein levels. There was no significant difference in the percentage of Th17 cells between the two groups. IL-35 stimulation increased the percentage of Tregs in both groups, but decreased the percentage of Tregs Th17 cells in affected patients. IL-35 enhanced the immunosuppressive activity of Tregs in both groups, resulting in decreased cellular proliferation and increased IL-35 subunit mRNA relative levels in co-culture system. IL-35 did not affect the immune checkpoint molecule expression in Tregs, but inhibited the transdifferentiation of Tregs into a Th17-like phenotype in affected patients, indicating by the down-regulations of C-C motif chemokine receptor-4/6 expression, retinoid-related orphan nuclear receptor γt mRNA levels, and IL-17 secretion. IL-35 contributes to the immunosuppressive function of Tregs by inhibiting the cellular proliferation and transdifferentiation of Tregs into a Th17-like phenotype, which may be a protective mechanism against Kawasaki disease.

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.

Decreased CD4+CD25+CD127dim/- Regulatory T Cells and T Helper 17 Cell Responsiveness to Toll-Like Receptor 2 in Chronic Hepatitis C Patients with Daclatasvir Plus Asunaprevir Therapy

Direct-acting antivirals (DAAs) not only rapidly inhibited hepatitis C virus (HCV) replication but also modulated innate and adaptive immune response in chronic hepatitis C patients. However, the regulatory activity of DAAs to Toll-like receptor 2 (TLR2) stimulation on CD4⁺CD25⁺CD127^dim/- regulatory T cells (Tregs) and T helper (Th) 17 cells was not completely understood. In the present study, a total of 23 patients with chronic HCV genotype 1b infection were enrolled, and blood samples were collected at baseline (treatment naive), end of therapy (EOT), and 12 weeks after EOT (SVR12) with daclatasvir plus asunaprevir therapy. TLR2 expression on Tregs and Th17 cells was measured by flow cytometry. Cellular proliferation, cytokine production, and suppressive activity were also tested in purified CD4⁺CD25⁺CD127^dim/- Tregs in response to the stimulation of Pam3Csk4, an agonist of TLR2. Inhibition of HCV RNA by daclatasvir and asunaprevir did not affect either percentage of Tregs/Th17 cells or TLR2 expression on Tregs/Th17 cells. Pam3Csk4 stimulation also did not influence either cellular proliferation or Tregs/Th17 proportion at each time point. Stimulation with Pam3Csk4 only enhanced the suppressive function and interleukin (IL)-35 production by Tregs purified from baseline, but not those from EOT or SVR12. Similarly, Pam3Csk4 stimulation only elevated Th17 cell frequency of CD4⁺ T cells from baseline, but not those from EOT or SVR12. Moreover, daclatasvir and asunaprevir therapy did not promote TLR2-induced shift of Tregs toward Th17-like phenotype and function. These data suggested that daclatasvir plus asunaprevir therapy resulted in the decreased responsiveness of Tregs/Th17 cells to TLR2 stimulation in chronic hepatitis C patients, which might provide a novel mechanism underlying DAA-induced immunoregulation.

Crosstalk between Toll-like receptor 3 and Notch signaling contributes to CD14+ monocytes activity in enterovirus 71 infected hand, foot, and mouth disease

Interaction between Toll-like receptor (TLR) and Notch signaling contributes to inflammatory response in nephropathy and fungicidal infection, however, the role of this crosstalk remains not fully elucidated in enterovirus 71 (EV71)-induced hand, foot, and mouth disease (HFMD). The aim of this study was to investigate the crosstalk between TLR and Notch in inflammatory regulation in EV71 infection. Thirty-seven EV-71-indcued HFMD (16 mild and 21 severe cases) and eleven normal control (NC) were enrolled. CD14⁺ monocytes were purified, and were stimulated with either TLR3/4 agonists [poly(I: C) or LPS] or Notch signaling inhibitor. TLRs and Notch receptors expression, proinflammatory cytokines production, and important molecules in signaling pathways were measured by real-time PCR, ELISA, and Western blot. TLR3 and TLR4 was significantly elevated in CD14⁺ monocytes from HFMD patients than NC. Notch1 and Notch2 mRNA was also remarkably increased in CD14⁺ monocytes from severe HFMD. Poly(I: C) stimulation resulted in robust increase of IL-8, IL-6, and TNF-α by CD14⁺ monocytes in severe HFMD compared to NC. Activation of Notch1, Notch2, and target genes, Hes1 and Hes5 was also enhanced upon ploy(I: C) treatment. Although inhibition of Notch signaling did not affect TLR3 expression, poly(I: C)-induced inflammatory response was robustly attenuated, which was accompanied by silencing Src phosphorylation in CD14⁺ monocytes from severe HFMD patients. The current data indicated that crosstalk between TLR3 and Notch signaling modulated CD14⁺ monocytes function and inflammatory responses in the progression of EV71-induced HFMD.

The association of variations in TLR genes and spontaneous immune control of hepatitis B virus

BACKGROUND

Toll-like receptors (TLRs) are suspected to play a critical role in liver diseases and the progression of chronic hepatitis B (CHB) infection. In this study, we investigated the possible association between TLRs and hepatitis B virus (HBV) infection chronicity in Turkish population.

METHODS

TLR4 (+896 A→G) (rs4986790), TLR5 (+1846 T→C) (rs5744174) and TLR9 (-1237T→C) (rs5743836) polymorphisms were screened in 131 CHB patient and 168 individuals by polymerase chain reaction (PCR) - restriction fragment length polymorphism (RFLP) technique.

RESULTS

Of the screened polymorphisms, TT genotype of the missense variant TLR5 (rs5744174) (NM_003268.5:c.1846T>C (p.Phe616Leu) is significantly more frequent in the control group than CHB patients (P<0.001), presence of TT genotype of the upstream variant TLR9 (rs5743836) (NM_017442.3:c.-1237T>C) is more frequent in CHB group (P=0.043). However, no significant association was found for the missense variant TLR4 (rs4986790) NM_138554.4:c.896A>G (p.Asp299Gly) polymorphism and CHB in Turkish population.

CONCLUSIONS

From all three analyzed SNPs association of TLR5 (rs5744174) with CHB is the most significant. Since TLR5 is associated with interferon-γ production, a high frequency of TT at rs5744174 in controls subjects suggests that it represents a protective genotype against CHB plausibly associated with an increased interferon-γ production.

Interleukin-35 Modulates the Imbalance Between Regulatory T Cells and T Helper 17 Cells in Enterovirus 71-Induced Hand, Foot, and Mouth Disease

Interleukin (IL)-35 modulates the imbalance between regulatory T cells (Tregs) and T helper (Th) 17 cells, which played vital roles in the pathogenesis of autoimmune and infectious diseases. However, the role of Tregs/Th17 cell imbalance and the regulatory functions of IL-35 have remained largely unknown in enterovirus 71 (EV71)-induced hand, foot, and mouth disease (HFMD). In this study, a total of 47 HFMD patients (30 with mild HFMD and 17 with severe HFMD) and 13 healthy individuals were enrolled. The frequencies of CD4⁺CD25⁺CD127^dim/- Tregs and CD4⁺IL-17⁺ Th17 cells, as well as IL-35 expression levels, were measured. Cellular proliferation and cytokine production was also determined in purified Tregs following recombinant IL-35 stimulation. An imbalance between Tregs and Th17 cells was observed in children with severe HFMD, which manifested as a reduction in the Tregs population and an elevation in the Th17 population. Serum IL-35 concentrations were also decreased in case of severe HFMD, which correlated with the Tregs:Th17 cell ratios. Recombinant IL-35 stimulation increased the proportion of Tregs, but downregulated that of Th17 cells. Treatment with IL-35 enhanced Tregs suppressive function and IL-35 and IL-10 expression, but reduced IL-22 secretion in both healthy individuals and those with severe HFMD. The Tregs:Th17 cell ratio was increased in the convalescent patients, however, a significant reduction in serum IL-35 was not observed. Our findings indicated that EV71 infection shifted the Tregs:Th17 cell ratio through IL-35 by downregulating inhibitory cytokine production and reducing the cell-to-cell contact inhibition of effector T cells. Regulation of IL-35 as it relates to the Tregs/Th17 balance may play a critical role in the pathogenesis of EV71-associated HFMD.

Interleukin-35 Suppresses Antiviral Immune Response in Chronic Hepatitis B Virus Infection

The mechanisms of hepatitis B virus (HBV) persistent infection are not completely understood. Interleukin (IL)-35, which is a newly identified cytokine belongs to IL-12 family, has been demonstrated to induce immunotolerance. Thus, the aim of current study was to investigate the role of IL-35 during chronic HBV infection. A total of 61 patients with chronic HBV infection [37 chronic hepatitis B (CHB) and 24 asymptomatic HBV carriers (ASC)] and 20 healthy individuals were enrolled. IL-35 concentration as well as the modulatory function of IL-35 on CD4⁺CD25⁺CD127^dim/− regulatory T cells (Tregs) and on HBV antigen-specific CD8⁺ T cells was investigated. IL-35 expression was significantly increased in both CHB and ASC, and was positively correlated with the levels of HBV DNA. Inhibition of viral replication induced the reduction in serum levels of IL-35. IL-35 stimulation led to inhibition of proinflammatory cytokine productions and elevation of apoptosis in peripheral blood mononuclear cells (PBMCs), but not in HepG2.2.15 cells. Moreover, IL-35 stimulation not only robustly inhibited cellular proliferation, but also up-regulated the production of IL-10 and IL-35 in a HBV antigen-specific and non-specific manner in Tregs/CD4⁺CD25⁻ T cells coculture system, which indicated enhancement of suppressive function of Tregs. Furthermore, IL-35 also reduced both cytolytic activity (direct lysis of HepG2.2.15 cells) and noncytolytic function (IFN-γ and TNF-α production) of HBV antigen-specific CD8⁺ T cells. The current data suggested that IL-35 contributed to maintain viral persistence by suppressing antiviral immune responses and reducing inflammatory responses in chronic HBV infection.

Toll-like receptor 2: An important immunomodulatory molecule during Helicobacter pylori infection

Toll like receptors (TLRs) are an essential subset of pathogen recognition receptors (PRRs) which identify the microbial components and contribute in the regulation of innate and adaptive immune responses against the infectious agents. The TLRs, especially TLR2, TLR4, TLR5 and TLR9, participate in the induction of immune response against H. pylori. TLR2 is expressed on a number of immune and non-immune cells and recognizes a vast broad of microbial components due to its potential to form heterodimers with other TLRs, including TLR1, TLR6 and TLR10. A number of H. pylori-related molecules may contribute to TLR2-dependent responses, including HP-LPS, HP-HSP60 and HP-NAP. TLR2 plays a pivotal role in regulation of immune response to H. pylori through activation of NF-κB and induction of cytokine expression in epithelial cells, monocytes/macrophages, dendritic cells, neutrophils and B cells. The TLR2-related immune response that is induced by H. pylori-derived components may play an important role regarding the outcome of the infection toward bacterial elimination, persistence or pathological reactions. The immunomodulatory and immunoregulatory roles of TLR2 during H. pylori infection were considered in this review. TLR2 could be considered as an interesting therapeutic target for treatment of H. pylori-related diseases.

Modulation of Tim-3 Expression by Antigen-Dependent and -Independent Factors on T Cells from Patients with Chronic Hepatitis B Virus Infection

T-cell immunoglobulin domain and mucin domain-containing molecule-3 (Tim-3) was up-regulated on viral specific T cells and contributed to T cells exhaustion during chronic hepatitis B virus (HBV) infection. However, modulation of Tim-3 expression was still not fully elucidated. To evaluate the potential viral and inflammatory factors involved in the inductor of Tim-3 expression on T cells, 76 patients with chronic HBV infection (including 40 chronic hepatitis B [CHB] and 36 asymptomatic HBV carriers [AsC]) and 40 of normal controls (NCs) were enrolled in this study. Tim-3 expressions on CD4⁺ and CD8⁺ T cells were assessed in response to HBV-encoding antigens, HBV peptide pools, and common γ-chain (γc) cytokines stimulation by flow cytometry. HBV peptides and anti-CD3/CD28 directly induced Tim-3 expression on T cells. γc cytokines also drive Tim-3 up-regulations on both CD4⁺ and CD8⁺ T cells in patients with chronic HBV infection. However, γc cytokines did not enhance the Tim-3 inductions by either anti-CD3/CD28 or HBV peptides stimulation. Furthermore, γc cytokines-mediated Tim-3 induction could not be abrogated by γc cytokine receptor-neutralizing antibodies. The current results suggested that elevation of Tim-3 expression on T cells could be regulated by both antigen-dependent and -independent manner in patients with chronic HBV infection. The role of γc cytokines in modulation of inhibitory pathway might be evaluated as immunotherapies in humans.

Hepatitis B Surface Antigen Promotes the Invasion of Hepatitis B Virus-Related Hepatocellular Carcinoma Cells by Upregulation of Toll-Like Receptor 2

Hepatitis B virus (HBV) infection is one of the major risk factors leading to the development of hepatocellular carcinoma (HCC). Hepatitis B surface antigen (HBsAg) plays a pivotal role in HBV-related HCC pathogenesis, and Toll-like receptor (TLR) 2 is also considered to mediate tumor progression. However, the interaction between HBsAg and TLR2 in HCC progression remains unclear. Thus, the aim of the study was to explore the effect of HBsAg-TLR2 pathway on growth and invasion of HBV-related HCC cells and examine the potential mechanisms been involved. The expression of TLR2 was measured in two different HCC cell lines (HepG2 and HepG2.2.15) with or without recombinant HBsAg by real-time reverse polymerase chain reaction and Western blot. Cellular proliferation, invasion, cytokine productions, and downstream signaling pathways were also measured in TLR2-silencing HepG2.2.15 cells in response to HBsAg stimulation. The mRNA and protein levels of TLR2 were significantly elevated in HepG2.2.15 cells than those in HepG2 cells. HBsAg simulation increased proinflammatory cytokine production and invasion of HepG2.2.15 cells, while this process was inhibited by TLR2 silence. However, TLR2 siRNA transfection alone did not affect the bioactivities of tumor cells. Moreover, HBsAg increased expression of MyD88 and phosphorylation of NF-κB p50 and p38MAPK. Downregulation of TLR2 inhibited HBsAg-induced MyD88 and p-NF-κB, but not p-p38MAPK in HepG2.2.15 cells. In conclusion, HBsAg stimulation promotes the invasion of HBV-related HCC cells. TLR2/MyD88/NF-κB signaling pathway may be involved in this procession by upregulation of cytokine production. The interaction between TLR2 and HBsAg may contribute to the poor prognosis of HBV-related HCC.

Toll-Like Receptor 2 Modulates the Balance of Regulatory T Cells and T Helper 17 Cells in Chronic Hepatitis C

Regulatory T cells (Tregs) and interleukin-17-producing T helper (Th17) cells were mutually antagonistic in the pathogenesis of chronic hepatitis C virus (HCV) infection. However, the regulation of imbalance between Tregs and Th17 cells was poorly understood in HCV infection. A recent report revealed the immunomodulatory role of Toll-like receptor (TLR) 2 in regulating the balance of Tregs/Th17 functions in multiple sclerosis. Thus, the aim of the current study was to assess the effect of TLR2 stimulation on the suppressive function of Tregs and Th17 differentiation in chronic hepatitis C. A total of 65 patients with chronic hepatitis C receiving pegylated interferon-a2a and ribavirin therapy for 48 weeks, as well as 20 of normal controls (NCs) were enrolled. Cellular proliferation and cytokine production was tested in purified CD4(+)CD25(+)CD127(dim/-) Tregs in response to the stimulation of Pam3Csk4, an agonist of TLR2. In treatment-naive patients, Tregs, but not Th17 cells, from chronic hepatitis C patients expressed higher levels of TLR2 compared with NCs. Stimulation with Pam3Csk4 enhanced the suppressive function of Tregs and production of IL-10 in chronic hepatitis C more than in NCs. However, TLR2 stimulation did not promote Th17 differentiation of Tregs in chronic hepatitis C patients. Moreover, effective anti-HCV therapy resulted in the induction of IL-17-secreting phenotypic shift of Tregs without loss of inhibitive function upon TLR2 stimulation. These data provided a novel mechanism underlying modulating the balance of Tregs/Th17 cells in chronic hepatitis C. HCV infection shifted Tregs/Th17 cells through TLR2 stimulation by inducing Tregs to produce IL-10 and enhancing inhibitive function of effector T cells, resulting in viral persistence.

Significant roles of regulatory T cells and myeloid derived suppressor cells in hepatitis B virus persistent infection and hepatitis B virus-related HCCs

The adaptive immune system, including type1 helper T cells (Th1 cells), cytotoxic T lymphocytes (CTLs), and dendritic cells (DCs), plays an important role in the control of hepatitis B virus (HBV). On the other hand, regulatory T cells (Tregs) and myeloid derived suppressor cells (MDSCs) suppress the immune reaction in HBV and hepatocellular carcinoma (HCC). Excessive activation of immune suppressive cells could contribute to the persistent infection of HBV and the progression of HCC. The frequency and/or function of Tregs could affect the natural course in chronic hepatitis B patients and the treatment response. In addition to the suppressive function of MDSCs, MDSCs could affect the induction and function of Tregs. Therefore, we should understand in detail the mechanism by which Tregs and MDSCs are induced to control HBV persistent infection and HBV-related HCC. Immune suppressive cells, including Tregs and MDSCs, contribute to the difficulty in inducing an effective immune response for HBV persistent infection and HBV-related HCC. In this review, we focus on the Tregs and MDSCs that could be potential targets for immune therapy of chronic hepatitis B and HBV-related HCC.

A fusion DNA vaccine encoding middle version of HBV envelope protein fused to interleukin-21 did not enhance HBV-specific immune response in mice

DNA vaccination can generate both humoral and cellular immunity, resulting in potential prophylactic and therapeutic vaccines in variety of conditions, including hepatitis B virus (HBV) infection. Fusion of cytokine gene is one of the ways to increase the immunogenicity of DNA vaccine. Interleukin (IL)-21 has been demonstrated to play an immunomodulatory role in HBV infection. Thus, we aimed to investigate the ability of IL-21 in the regulation of middle version of HBV envelop protein (MS) DNA vaccine. Fusion plasmid encoding IL-21 linked with MS was constructed. Normal and HBV transgenic mice were immunized by plasmid. pcDNA-IL-21/S2S induced a comparable level of anti-HBs antibody and HBsAg-specific CD8+ T-cell response with pcDNA-S2S. Furthermore, the level of circulating HBsAg was decreased by induction of anti-HBs antibody and HBsAg-specific CD8+ T-cell response to both pcDNA-IL-21/S2S and pcDNA-S2S vaccination in HBV transgenic mice. Thus, immunization with DNA vaccine encoding HBV MS protein induced both T- and B-cell response by targeting the specific antigen. Furthermore, it was also revealed that MS DNA vaccination could break immune tolerance in HBV transgenic mice. But IL-21 did not strengthen immune response induced by HBV DNA immunization. Our study suggested that MS-expressing plasmid may be useful for both preventive and therapeutic methods in HBV infection. However, IL-21 does not improve the immunogenicity and efficacy of MS DNA vaccination, and thus may not be used as a therapeutic marker for chronic hepatitis B.

Toll-like receptor 4 and hepatitis B infection: molecular mechanisms and pathogenesis

Hepatitis B virus (HBV) infection mainly causes liver disease, including inflammation, cirrhosis, and hepatocellular carcinoma (HCC). It has been documented that prolonged hepatitis B-infected patients are unable to clear HBV from hepatocytes completely. Previous investigations have suggested that various genetic and immunologic parameters may be responsible for the induction of prolonged infection forms. Toll-like receptors (TLRs), as members of pathogen recognition receptors (PRRs), play critical roles in the recognition of viruses and the induction of appropriate immune responses. Thus, TLRs may be considered as essential sensors for the recognition of HBV and the induction of immune responses against this virus. It has been documented that TLR4 plays key roles in the detection of several microbial pathogen-associated molecular pattern molecules, including bacterial lipopolysaccharide (LPS), as well as endogenous ligands (damage-associated molecular pattern molecules) and subsequently activates pro-inflammatory transcription factors in either MYD88 or TRIF dependent pathways. Previous investigations have proposed that TLR4 might be involved in appropriate immune responses against HBV. Therefore, the aim of this review is to present the recent data regarding the important roles of TLR4 in HBV recognition and regulation of immune responses against this virus, and also its roles in the pathogenesis of cirrhosis and HCC as complications of prolonged hepatitis B infections.

Expression profiles of circulating cytokines, chemokines and immune cells in patients with hepatitis B virus infection

BACKGROUND

Immune cells and molecules play a vital role in initiating, maintaining, regulating immunological homeostasis and inflammation in many pathological and physiological processes; however, the changes on expressions and functions of these cells and molecules in hepatitis B virus (HBV) infection have not been elucidated well.

OBJECTIVES

The current study aimed to determine the expression pattern of different cytokines, chemokines, immune cells in HBV infection and their association with disease progression.

PATIENTS AND METHODS

Sixty-nine patients with chronic HBV infection were enrolled. Five immune cell subsets and 46 cytokines and chemokines were analyzed by flow cytometry and Luminex 200.

RESULTS

In comparison to healthy individuals and asymptomatic HBV carriers, expression of CXCL9, CXCL10, CXCL11, and IL-10 were elevated in patients with chronic active HBV and had positive correlation with ALT levels. In contrast, G-CSF, MCP-3, and IFN-γ levels were significantly decreased in patients with chronic active HBV infection in contrast to carriers and healthy individuals; however, these down regulations did not show any correlation with either virological findings or liver inflammation. Although the proportion of CD4(+) CD25 (high) regulatory T cells (Tregs) was higher in patients with HBV infection than in healthy controls, no correlations were found between Tregs and other cytokines or chemokines.

CONCLUSIONS

CXCR3-associated chemokines might contribute to liver inflammation in chronic hepatitis B, while MCP-3 and G-CSF were inhibited by HBV infection. Host immune response was suppressed as manifested by an increase in CD4(+) CD25(high) Tregs and IL-10 as well as a decrease in IFN-γ. Exploiting the expression pattern of cytokine and chemokine may help to develop a better understanding of chronic HBV infection pathogenesis.

Role of toll-like receptors in immune activation and tolerance in the liver

Liver has a unique vascular system receiving the majority of the blood supply from the gastrointestinal tract through the portal vein and faces continuous exposure to foreign pathogens and commensal bacterial products. These gut-derived antigens stimulate liver cells and result in a distinctive immune response via a family of pattern recognition receptors, the Toll-like receptors (TLRs). TLRs are expressed on Kupffer cells, dendritic cells, hepatic stellate cells, endothelial cells, and hepatocytes in the liver. The crosstalk between gut-derived antigens and TLRs on immune cells trigger a distinctive set of mechanisms to induce immunity, contributing to various acute and chronic liver diseases including liver cirrhosis and hepatocellular carcinoma. Accumulating evidence has shown that TLRs stimulation by foreign antigens induces the production of immunoactivating and immunoregulatory cytokines. Furthermore, the immunoregulatory arm of TLR stimulation can also control excessive tissue damage. With this knowledge at hand, it is important to clarify the dual role of disease-specific TLRs as activators and regulators, especially in the liver. We will review the current understanding of TLR signaling and subsequent immune activation and tolerance by the innate immune system in the liver.

Role of innate immunity in the development of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common form of liver cancer worldwide. It is caused by a variety of risk factors, most common ones being infection with hepatitis viruses, alcohol, and obesity. HCC often develops in the background of underlying cirrhosis, and even though a number of interventional treatment methods are currently in use, recurrence is fairly common among patients who have had a resection. Therefore, whole liver transplantation remains the most practical treatment option for HCC. Due to the growing incidence of HCC, intense research efforts are being made to understand cellular and molecular mechanisms of the disease so that novel therapeutic strategies can be developed to combat liver cancer. In recent years, it has become clear that innate immunity plays a critical role in the development of a number of liver diseases, including HCC. In particular, the activation of Toll-like receptor signaling results in the generation of immune responses that often results in the production of pro-inflammatory cytokines and chemokines, and could cause acute inflammation in the liver. In this review, the current knowledge on the role of innate immune responses in the development and progression of HCC is examined, and emerging therapeutic strategies based on molecular mechanisms of HCC are discussed.

Hepatitis B virus induces expression of cholesterol metabolism-related genes via TLR2 in HepG2 cells

AIM: To investigate whether hepatitis B virus (HBV) exacerbates hepatic cholesterol accumulation, and explore the underlying mechanisms.

METHODS: HepG2 cells were infected with adenovirus (Ad) containing 1.3-fold overlength HBV genome. Real-time polymerase chain reaction and Western blotting were used to measure mRNA and protein expression of target genes. Cholesterol accumulation was measured by fluorescence microscopy. Cell toxicity due to Ad-HBV treatment was determined by the mitochondrial tetrazolium assay. The protein levels of toll-like receptors (TLRs) were determined by Western blotting.

RESULTS: Ad-HBV increased hepatic cholesterol accumulation and enhanced the mRNA and protein levels of low-density lipoprotein receptor (LDLR) and 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMGCoAr) mRNA and protein expression in HepG2 cells. In addition, these inductive effects were partly offset by suppressing TLR2 expression levels by small interfering RNA in HepG2 cells.

CONCLUSION: Ad-HBV increases LDLR and HMGCoAr expression, resulting in exacerbated cholesterol accumulation in HepG2 cells, which was mediated via the TLR2 pathway.

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 type 1 infection up-regulates TLR2 and TLR4 expression and function in vivo and in vitro

Toll-like receptors (TLRs) play a critical role in innate immunity against pathogens. Their stimulation induces the activation of NF-κB, an important inducer of HIV-1 replication. In recent years, an increasing number of studies using several cells types from HIV-infected patients indicate that TLRs play a key role in regulating the expression of proinflammatory cytokines and viral pathogenesis. In the present study, the effect of HIV-1 stimulation of monocyte-derived macrophage (MDM) and peripheral blood mononuclear cell (PBMC) subpopulations from healthy donors on the expression and functions of TLR2 and TLR4 was examined. In addition, and to complete the in vitro study, the expression pattern of TLR2 and TLR4 in 49 HIV-1-infected patients, classified according to viral load and the use of HAART, was determined and compared with 25 healthy subjects. An increase of TLR expression and production of proinflammatory cytokines were observed in MDMs and PBMCs infected with HIV-1 in vitro and in response to TLR stimulation, compared to the mock. In addition, an association between TLR expression and up-regulation of CD80 in plasmacytoid dendritic cells (pDCs) was observed. The ex vivo analysis indicated increased expression of TLR2 and TLR4 in myeloid dendritic cells (mDCs), but only of TLR2 in monocytes obtained from HIV-1-infected patients, compared to healthy subjects. Remarkably, the expression was higher in cells from patients who do not use HAART. In monocytes, there was a positive correlation between both TLRs and viral load, but not CD4(+) T cell numbers. Together, our in vitro and ex vivo results suggest that TLR expression and function can be up-regulated in response to HIV-1 infection and could affect the inflammatory response. We propose that modulation of TLRs represents a mechanism to promote HIV-1 replication or AIDS progression in HIV-1-infected patients.

Toll-like receptor and hepatitis B virus clearance in chronic infected patients: a long-term prospective cohort study in Taiwan

BACKGROUND

We sought to elucidate the impacts of the Toll-like receptors (TLRs) on spontaneous hepatitis B virus (HBV) e antigen (HBeAg) and hepatitis B s antigen (HBsAg) seroconversion in chronic HBV-infected patients.

METHODS

Human TLR2, TLR4, TLR5, and TLR9 gene polymorphisms were assessed in 278 HBeAg-positive, chronic HBV-infected patients. Additionally, HBV core antigen (HBcAg) in vitro stimulation using peripheral blood mononuclear cells (PBMCs) from 113 patients was done to assess interferon γ (IFN- γ) production.

RESULTS

Of the study subjects, 204 (73.4%) developed spontaneous HBeAg seroconversion, 21 (7.6%) developed spontaneous HBsAg clearance, and 10 (3.6%) had spontaneous HBsAg seroconversion during the 19.1 ± 9.9 years of follow-up. The T allele at TLR5 rs5744174 (p.Phe616Leu) and the C allele at TLR9 rs5743836 promoter predicted earlier HBeAg seroconversion (hazard ratios [HRs], 2.45 and 3.65; P = .04, and .006, respectively). The TLR5 rs5744174 T allele carriers have higher PBMCs IFN-γ secretion to HBcAg stimulation (P= .0002). The G allele carriers at TLR4 rs4986790 (p.Asp299Gly) predicted spontaneous HBsAg seroclearance (HR, 18.73; P < .001) and seroconversion (HR, 43.45; P < .001).

CONCLUSIONS

Toll-like receptor 5 rs5744174 (p.Phe616Leu) and TLR9 rs5743836 promoter area polymorphism were associated with earlier spontaneous HBeAg seroconversion. Toll-like receptor 4 rs4986790 (p.Asp299Gly) was associated with HBsAg seroclearance/seroconversion in chronic HBV patients. Toll-like receptor 5 rs5744174 (p.Phe616Leu) was associated with higher IFN-γ production in chronic HBV-infected patients.

Toll-like receptors in liver fibrosis: cellular crosstalk and mechanisms

Toll-like receptors (TLRs) are pattern recognition receptors that distinguish conserved microbial products, also known as pathogen-associated molecular patterns (PAMPs), from host molecules. Liver is the first filter organ between the gastrointestinal tracts and the rest of the body through portal circulation. Thus, the liver is a major organ that must deal with PAMPs and microorganisms translocated from the intestine and to respond to the damage associated molecular patterns (DAMPs) released from injured organs. These PAMPs and DAMPs preferentially activate TLR signaling on various cell types in the liver inducing the production of inflammatory and fibrogenic cytokines that initiate and prolong liver inflammation, thereby leading to fibrosis. We summarize recent findings on the role of TLRs, ligands, and intracellular signaling in the pathophysiology of liver fibrosis due to different etiology, as well as to highlight the potential role of TLR signaling in liver fibrosis associated with hepatitis C infection, non-alcoholic and alcoholic steatoheoatitis, primary biliary cirrhosis, and cystic fibrosis.

Inhibition of viral replication downregulates CD4(+)CD25(high) regulatory T cells and programmed death-ligand 1 in chronic hepatitis B

Chronic hepatitis B is characterized by an impaired immune response to hepatitis B virus (HBV). Telbivudine treatment has significantly improved the clinical outcome of chronic HBV infection. However, the underlying mechanism behind the antiviral response of patients treated with nucleoside analogs remains unclear. To gather more evidence about the mechanism responsible for the weak immune response, in this study we analyzed the effects on HBV viral load of treatment with the nucleoside analogue telbivudine and the percentage of Tregs, programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) expression, and related cytokine production. Peripheral blood mononuclear cells (PBMCs) and serum of 28 patients with chronic hepatitis B were collected at baseline, and 3 mo and 6 mo after therapy was begun. In parallel with the decline in viral load and serum ALT normalization, we found a decline in circulating CD4(+)CD25(high) Tregs, PD-L1 on CD4(+) T cells, and IL-9 production. The expression of PD-1 on CD4(+) T cells and the production of IFN-γ did not increase during therapy. Our findings suggest that the antiviral effect of the nucleoside analogs may be attributable not only to their direct effect on virus suppression, but also to their immunoregulatory capabilities.

Changes in the proportions of CD4(+)T cell subsets defined by CD127 and CD25 expression during HBV infection

CD4(+)T cell counts are closely related to the progression of HBV infection. Here, we investigated how the proportions of three CD4(+)T cell subsets - CD127(-)CD25(-), CD127(+)CD25(low/-) and CD127(low)CD25(high) - changed during HBV infection, as is little known. Compared with healthy controls, the proportions of CD127(-)CD25(-) in chronic hepatitis B (CHB) patients and HBV carriers significantly increased, while that of CD127(+)CD25(low/-) significantly decreased. The proportion of CD127(low)CD25(high) in CHB patients was significantly higher than those in HBV carriers or healthy controls. Compared with HBV-DNA negative group, the proportion of CD127(-)CD25(-) in positive group significantly decreased and that of CD127(+)CD25(low/-) significantly increased. In the follow-up study for CHB patients treated with interferon-α2b for 12 weeks or 24 weeks, the proportions of CD127(-)CD25(-) significantly decreased, while that of CD127(low/-)CD25(high) significantly increased. The results suggested that specific changes in the fraction of CD4(+)T cell subsets expressing CD127 and/or CD25 were associated with hepatitis B progression.

Toll-like receptors signaling contributes to immunopathogenesis of HBV infection

Innate and adaptive immune systems have important role in the pathogenesis of acute and chronic infection with hepatitis B virus (HBV). These immune responses are mediated through complex interactions between the innate immune response and adaptive immune response. Toll-like receptors (TLRs) are a family of innate immune-recognition receptors that recognize the molecular patterns associated with microbial pathogens. So far, TLR1 to 13 were found in human or mice and investigated to detect the target molecules and the downstream mechanisms of these unique systems. Stimulation by their ligands initiates the activation of complex networks of intracellular signaling transduction and innate and adaptive immune-related cells (NK, NK-T, monocytes, dendritic cells, T cells, B cells, and Tregs, etc.). However, reports on such relationships between HBV and TLRs have been relatively rare in comparison to those on HCV and TLRs, but have recently been increasing. Thus, a review of TLRs involved in the pathogenesis of HBV infection may be needed toward better understanding of the immunopathogenesis of HBV infection.

Cardiotrophin-1 promotes a high survival rate in rabbits with lethal fulminant hepatitis of viral origin

Rabbit hemorrhagic disease virus (RHDV) causes lethal fulminant hepatitis closely resembling acute liver failure (ALF) in humans. In this study, we investigated whether cardiotrophin-1 (CT-1), a cytokine with hepatoprotective properties, could attenuate liver damage and prolong survival in virus-induced ALF. Twenty-four rabbits were infected with 2 × 10(4) hemagglutination units of RHDV. Twelve received five doses of CT-1 (100 μg/kg) starting at 12 h postinfection (hpi) (the first three doses every 6 h and then two additional doses at 48 and 72 hpi), while the rest received saline. The animals were analyzed for survival, serum biochemistry, and viral load. Another cohort (n = 22) was infected and treated similarly, but animals were sacrificed at 30 and 36 hpi to analyze liver histology, viral load, and the expression of factors implicated in liver damage and repair. All infected rabbits that received saline died by 60 hpi, while 67% of the CT-1-treated animals survived until the end of the study. Treated animals showed improved liver function and histology, while the viral loads were similar. In the livers of CT-1-treated rabbits we observed reduction of oxidative stress, diminished PARP1/2 and JNK activation, and decreased inflammatory reaction, as reflected by reduced expression of tumor necrosis factor alpha, interleukin-1β, Toll-like receptor 4, VCAM-1, and MMP-9. In addition, CT-1-treated rabbits exhibited marked upregulation of TIMP-1 and increased expression of cytoprotective and proregenerative growth factors, including platelet-derived growth factor B, epidermal growth factor, platelet-derived growth factor receptor β, and c-Met. In conclusion, in a lethal form of acute viral hepatitis, CT-1 increases animal survival by attenuating inflammation and activating cytoprotective mechanisms, thus representing a promising therapy for ALF of viral origin.

Up-regulation of TLR2 and TLR4 in dendritic cells in response to HIV type 1 and coinfection with opportunistic pathogens

The ability to trigger an innate immune response against opportunistic pathogens associated with HIV-1 infection is an important aspect of AIDS pathogenesis. Toll-like receptors (TLRs) play a critical role in innate immunity against pathogens, but in HIV-1 patients coinfected with opportunistic infections, the regulation of TLR expression has not been studied. In this context, we have evaluated the expression of TLR2 and TLR4 in monocytes, plasmacytoid dendritic cells, and myeloid dendritic cells of HIV-1 patients with or without opportunistic infections. Forty-nine HIV-1-infected individuals were classified according to viral load, highly active antiretroviral therapy (HAART), and the presence or absence of opportunistic infections, and 21 healthy subjects served as controls. Increased expression of TLR2 and TLR4 was observed in myeloid dendritic cells of HIV-1 patients coinfected with opportunistic infections (without HAART), while TLR4 increased in plasmacytoid dendritic cells, compared to both HIV-1 without opportunistic infections and healthy subjects. Moreover, TLR2 expression was higher in patients with opportunistic infections without HAART and up-regulation of TLR expression in HIV-1 patients coinfected with opportunistic infections was more pronounced in dendritic cells derived from individuals coinfected with Mycobacterium tuberculosis. The results indicate that TLR expression in innate immune cells is up-regulated in patients with a high HIV-1 load and coinfected with opportunistic pathogens. We suggest that modulation of TLRs expression represents a mechanism that promotes HIV-1 replication and AIDS pathogenesis in patients coinfected with opportunistic pathogens.

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.

HBV core region variability: effect of antiviral treatments on main epitopic regions

BACKGROUND

Amino acid (AA) changes in specific hepatitis B core antigen (HBcAg) regions were assessed in patients infected with chronic hepatitis B (CHB) after a 12-month untreated period and after receiving antiviral therapy (interferon, lamivudine or adefovir dipivoxil), and in inactive hepatitis B surface antigen-positive carriers.

METHODS

Samples corresponding to different time points in 76 CHB cases (64 on-treatment) and 4 inactive carriers were included. The main precore mutation, T-helper immunodominant epitope at AA 50-69 (Th50-69), minor T-helper epitope (Th28-47), B-cell immunodominant epitope (B74-84) and a conserved region of HBcAg at AA 1-11 (AA1-11) were directly sequenced. For comparisons, the average number of AA changes in each region was standardized to 12 months (Av12).

RESULTS

AA changes clustered mainly in immunodominant regions (69%). The highest percentage of cases (%n) with changes and highest Av12 changes were detected after interferon treatment (%n=73%, Av12=3.1 in Th50-69 and %n=86%, Av12=2.7 in B74-84). At baseline, immunodominant regions had higher Av12 changes in hepatitis B e antigen-negative patients and those with main precore mutations. Changes in the Th28-47 region were more frequent after nucleoside/nucleotide analogue treatment (40%) than before treatment (9%). Codons 74 and 77 were the most polymorphic, and the double change E64D-N67T was significantly observed. Codon 84 substitutions were mainly associated with interferon treatment (P=0.05).

CONCLUSIONS

Natural and treatment-induced substitutions in HBV core protein, occurring especially with interferon treatment, were characterized. Some immune-stimulating activity related to the minor Th28-47 epitope might be associated with nucleoside/nucleotide analogues; this activity was also seen in inactive carriers.

Opisthorchis viverrini excretory/secretory products induce toll-like receptor 4 upregulation and production of interleukin 6 and 8 in cholangiocyte

Biliary tract infection with the Group I carcinogenic liver fluke Opisthorchis viverrini is associated with severe inflammation leading to cholangiocarcinoma--a major biliary cancer in Southeast Asia. However, mechanism(s) by which the liver fluke induces host mucosal immune/inflammatory responses is unclear. In the present study we address whether a normal immortalized human cholangiocyte cell line (H69 cells) recognizes and responds to O. viverrini excretory/secretory products (OVES). Expression of multiple TLRs, activation of NF-κB, and expression of pro-inflammatory cytokines were monitored in the presence and absence of OVES. Our results showed that OVES induced increased cholangiocyte TLR4 mRNA expression, induced IκB-α degradation in a MyD88-dependent manner, and activated NF-κB nuclear translocation. Moreover, OVES induced expression and secretion of the strong chemoattractant chemokine interleukin 8 (IL-8) and pro-inflammatory cytokine IL-6. These results demonstrate that secreted/excreted products of O. viverrini are recognized by human cholangiocytes and initiate innate mucosal immunity/inflammatory cascades, a primary event in the pathogenesis of opisthorchiasis and cholangiocarcinoma.

Polymorphism in 3'-untranslated region of toll-like receptor 4 gene is associated with protection from hepatitis B virus recurrence after liver transplantation

BACKGROUND

Hepatitis B virus (HBV) recurrence is one of the more severe complications following liver transplantation. Toll-like receptors (TLRs) play a key role in human immunity by recognizing various bacteria, viruses, fungi, and parasites. Single nucleotide polymorphisms (SNPs) in the TLRs are thought to have an impact on the susceptibility to some pathogens. This study focused on the association between polymorphisms in the TLRs and HBV recurrence after liver transplantation in Han Chinese patients.

METHODS

A total of 41 tag SNPs in TLRs were detected by the snapshot technique in 125 patients with primary HBV-related diseases receiving liver transplantation in our center from 2004 to 2008.

RESULTS

By comparing the genetic variations and clinical data between the HBV recurrence patients and nonrecurrence patients, we found that the variant genotype of rs11536889 (TLR4) was significantly associated with HBV recurrence after liver transplantation (P = 0.040, odds ratio was 0.390, 95% confidence interval 0.159-0.957).

CONCLUSION

Our findings indicate that polymorphism in 3'-untranslated regions of the TLR4 gene may be related to protection from HBV recurrence after liver transplantation in Han Chinese patients.