Toll-like Receptor Expression and Signaling in Peripheral Blood Mononuclear Cells Correlate With Clinical Outcomes in Acute Hepatitis C Virus Infection

Toll-like Receptor Response to Hepatitis C Virus Infection: A Recent Overview

Hepatitis C virus (HCV) infection remains a major global health burden, causing chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that detect pathogen-associated molecular patterns and activate downstream signaling to induce proinflammatory cytokine and chemokine production. An increasing number of studies have suggested the importance of TLR responses in the outcome of HCV infection. However, the exact role of innate immune responses, including TLR response, in controlling chronic HCV infection remains to be established. A proper understanding of the TLR response in HCV infection is essential for devising new therapeutic approaches against HCV infection. In this review, we discuss the progress made in our understanding of the host innate immune response to HCV infection, with a particular focus on the TLR response. In addition, we discuss the mechanisms adopted by HCV to avoid immune surveillance mediated by TLRs.

Toll-like receptors and hepatitis C virus infection

BACKGROUND

Hepatitis C virus (HCV) infection is a worldwide issue. However, the current treatment for hepatitis C has many shortcomings. Toll-like receptors (TLRs) are pattern recognition receptors involved in HCV infection, and an increasing number of studies are focusing on the role of TLRs in the progression of hepatitis C.

DATA SOURCES

We performed a PubMed search up to January 2021 with the following keywords: hepatitis C, toll-like receptors, interferons, inflammation, and immune evasion. We also used terms such as single-nucleotide polymorphisms (SNPs), susceptibility, fibrosis, cirrhosis, direct-acting antiviral agents, agonists, and antagonists to supplement the query results. We reviewed relevant publications analyzing the correlation between hepatitis C and TLRs and the role of TLRs in HCV infection.

RESULTS

TLRs 1-4 and 6-9 are involved in the process of HCV infection. When the host is exposed to the HCV, TLRs, as important participants in HCV immune evasion, trigger innate immunity to remove the virus and also promote inflammation and liver fibrosis. TLR gene SNPs affect hepatitis C susceptibility, treatment, and prognosis. The contribution of each TLR to HCV is different. Drugs targeting various TLRs are developed and validated, and TLRs can synergize with classic hepatitis C drugs, including interferon and direct-acting antiviral agents, constituting a new direction for the treatment of hepatitis C.

CONCLUSIONS

TLRs are important receptors in HCV infection. Different TLRs induce different mechanisms of virus clearance and inflammatory response. Although TLR-related antiviral therapy strategies exist, more studies are needed to explore the clinical application of TLR-related drugs.

Hepatitis C Virus-Induced Exosomal MicroRNAs and Toll-Like Receptor 7 Polymorphism Regulate B-Cell Activating Factor

There are large gaps in understanding the molecular machinery accounting for the association of hepatitis C virus (HCV) infection with autoimmunity. Mixed cryoglobulinemia (MC) is the most common HCV-associated extrahepatic manifestation, which is characterized by B-cell lymphoproliferation and autoantibody production. B-cell activating factor (BAFF) is a member of the tumor necrosis factor family and plays an important role in B-cell proliferation. We explored the roles of hepatocyte-derived exosomal microRNAs (exo-miRNAs) and BAFF in the extrahepatic diseases of HCV infection. The exo-miRNA profiles were explored using a next-generation sequencing approach, followed by quantitative reverse transcription-PCR validation. The Toll-like receptor 7 (TLR7) polymorphism were analyzed using quantitative PCR. The biological function of exo-miRNAs and TLR7 polymorphism in BAFF expression was evaluated by using immunoblotting and enzyme-linked immunosorbent assay. Significantly increased levels of BAFF, exosomes, and TLR7 were found in HCV patients, particularly in those with MC (P < 0.005). HCV-infected hepatocyte-derived miR-122/let-7b/miR-206 upregulated BAFF expression in human macrophages through exosome transmission and TLR7 activation. Analysis of a TLR7 single-nucleotide polymorphism (rs3853839) revealed that G-allele carriers had increased TLR7 transcripts, resulting in more BAFF expression induced by hepatocyte-derived exo-miR-122, compared to those in C-allele carriers (P < 0.005). We identified HCV-infected hepatocyte-derived GU-enriched miRNAs (e.g., miR-122/let-7b/miR-206) as a TLR7 ligand that could induce BAFF production in macrophages through exosome transmission. The polymorphism in TLR7 is associated with the BAFF levels induced by exo-miR-122. It may be a potential predisposing factor of MC syndrome development.

Successful Direct Acting Antiviral Therapy in Chronic Hepatitis C Normalizes IFNγ and IL2 Production in T Cells Together with TLR8 Expression and Functionality in Peripheral Blood Mononuclear Cells

Chronic hepatitis C infection (HCV) activates a systemic cell-mediated immune response characterized by the production of IFNγ and an innate immune response addressed by the activation of TLR signaling. We aimed to investigate whether HCV eradication by direct acting antivirals (DAA) leads to a recovery in cell-mediated immune response and TLR expression and functionality. Blood samples were obtained in HCV infected patients before DAA treatment and at week +48 after the end of treatment. Results were compared to healthy controls. Cell surface expression of TLR8 was assessed on peripheral blood mononuclear cells (PBMCs) by flow cytometry. Freshly isolated PBMCs were cultured with specific TLR8 agonists and intracellular production of cytokines was determined by flow-cytometry after ex vivo TLR8 activation with ssRNA 40. Production of IFNγ, IL2 and IL17 was assessed by flow cytometry in T cells after polyclonal activation. Included were 50 HCV-infected patients and 15 controls. TLR8 expression in PBMCs was significantly increased before treatment and recovered normal levels at week +48. Production of IL1b, IL6 and TNFα dependent on the activation of TLR8 in PBMCs was also increased in patients before DAA treatment, with a significant reduction at week +48. Combined expression of IFNγ and IL2 in CD4+ T cells in HCV-infected patients was significantly increased compared to controls and recovered normal levels at week +48. DAA-mediated clearance of HCV is associated with a decreased expression and activation of TLR8 in PBMCs until healthy control levels which is accompanied by a reduction in the Th1 response.

Hepatic TLR4, MBL and CRP gene expression levels are associated with chronic hepatitis C

Contact with HCV triggers the activation of innate mechanisms responsible for initial infection control. Host cells expressed extra- or intracellularly molecules that promote recognition of pathogen-associated molecular patterns (PAMPs). Toll-like receptor 4 (TLR4), mannose-binding lectin (MBL) and C-reactive protein (CRP) are molecules available for HCV PAMP recognition. The present study evaluated TLR4, MBL and CRP gene expression in the hepatic tissue of chronic HCV carriers (n = 22) and the association of that expression with the pathogenesis of HCV as well as the progression of liver fibrosis. Liver biopsy specimens from the HCV group were divided according to the METAVIR classification: without fibrosis and/or mild fibrosis (F0-F1), moderate fibrosis (F2), and severe fibrosis and/or cirrhosis (F3-F4) and A0-A1 (absent or mild inflammation) and A2 (moderate inflammation); normal liver samples were used as a control (n = 8). The mRNA levels of the genes studied were quantified by real-time PCR, and plasma CRP and liver enzymes were measured using an automated system. CRP and MBL expression was significantly lower in the HCV group compared to that in the control group (p < .0001 and p = .0242, respectively). TLR4 expression was higher in the HCV group than in the control group (p = .0448) and was also significantly higher (p = .0314) with lower levels of necroinflammatory activity (A0-A1), with a significant correlation between the expression of MBL with TLR4 as well as a positive correlation between plasma levels and CRP expression in the HCV group (p = .0431). Hepatic TLR4, MBL and CRP expression showed no significant association with liver enzymes nor plasma viral load. Mechanisms of HCV escape seem to influence hepatic TLR4, MBL and CRP expression, resulting in a change in the transcription profile of these proteins of innate immunity, which may contribute to virus persistence, liver fibrogenesis and loss of normal liver function.

S100A14 Is Increased in Activated NK Cells and Plasma of HIV-Exposed Seronegative People Who Inject Drugs and Promotes Monocyte-NK Crosstalk

BACKGROUND

HIV-exposed seronegative people who inject drugs (HESN-PWID) have been shown to have increased natural killer (NK) cell and myeloid activation when compared with control donors.

METHODS

We investigated potential mechanisms maintaining NK activation by conducting quantitative proteome comparisons of NK cells from HESN-PWID subjects and control donors. Proteins upregulated in NK cells were measured in the plasma of HESN-PWID subjects by ELISA and further investigated for their ability to induce innate immune activation in vitro.

RESULTS

The NK cell proteome comparison showed markedly higher levels of interferon-stimulated proteins and S100 proteins, including S100A14. Consistent with these results, we observed significantly higher levels of S100A14 in the plasma of HESN-PWID subjects compared with controls (P = 0.033, n = 25). In vitro, the addition of recombinant S100A14 protein significantly activated NK cells in a peripheral blood mononuclear cell mixture (P = 0.011, n = 9), but not purified NK cells alone. Treatment of purified monocytes with recombinant S100A14 protein induced secretion of TNF-alpha and led to significantly higher NK CD69 activation (P = 0.0156, n = 7) in a co-culture through a TLR4-dependent interaction.

CONCLUSIONS

Our study identified S100A14 as a novel protein increased within NK cells and plasma of HESN-PWID subjects with the capacity to sustain NK activation through TLR4-dependent activation of myeloid cells.

The associations between Toll-like receptor 4 gene polymorphisms and hepatitis C virus infection: a systematic review and meta-analysis

Background and objective: The hepatitis C virus (HCV) is able to cause a life-threatening disease relating to lethal hepatocellular carcinoma. Previous, Toll-like receptor polymorphisms were proposed as promising biomarker for HCV-related hepatocellular carcinoma and disease progression. This study aimed to summarize the association of TLR4 polymorphisms and HCV infection through meta-analysis.

Methods: We applied a systematic review and meta-analysis performed by using PubMed, EMBASE and Web of Science searches. The Modified Newcastle-Ottawa scale was used for quality assessment. The odd-ratio (OR) and 95% confidence interval (CI) were calculated to assess the association. In silico analysis was applied for proposing the function as microRNA (miRNA) of non-coding polymorphism. Finally, the miRNA target was predicted and annotated to suggest the possible relationship between polymorphism and HCV infection.

Results: Our meta-analysis incorporated seven studies involving rs4986791, rs4986790 and rs2149356. No association exists between rs4986791 and HCV infection. However, the heterozygous model (AG vs GG) of rs4986790 significantly associates with HCV infection (OR = 0.33, 95% CI = 0.21–0.49, P<0.0001). Moreover, the rs2149356 TG genotype also associates with HCV infection in the over-dominant model (TG vs TT+TG: OR = 0.54, 95% CI = 0.40–0.75). In silico analysis of rs2149356G allele showed that this mutation is siRNA, which targets the set of genes, especially in the autophagy pathway.

Conclusion: We demonstrated that rs4986790 and rs2149356 are associated with HCV infection.

IL-28B Genetic Variants Determine the Extent of Monocyte-Induced Activation of NK Cells in Hepatitis C

BACKGROUND

Immuno-genetic studies suggest a functional link between NK cells and λ-IFNs. We recently showed that NK cells are negative for the IFN-λ receptor IFN-λR1 and do not respond to IFN-λ, suggesting a rather indirect association between IL-28B genotype and NK cell activity.

METHODS

A total of 75 HCV(+) patients and 67 healthy controls were enrolled into this study. IL-28B (rs12979860) and IFNL-4 (rs368234815) genotypes were determined by rtPCR. Total PBMC, monocytes, and NK cells were stimulated with IL-29, the TLR-7/8 agonist R848, or a combination of both. NK cell IFN-γ response was analysed by FACS. IL-12 and IL-18 secretion of monocytes was studied by ELISA. In blocking experiments anti-IL-12/anti-IL-18 were used.

RESULTS

Following stimulation of total PBMCs with R848 we found NK cell IFN- γ responses to vary with the IL-28B genotype, with carriers of a T/T genotype displaying the lowest frequency of IFN-γ(+)NK cells. When isolated NK cells were studied no such associations were observed, indicating an indirect association between IL-28B genotype and NK cell activity. Accordingly, we found R848-stimulated monocytes of patients with a T/T genotype to be significantly less effective in triggering NK cell IFN- γ production than monocytes from carriers of a non-T/T genotype. In line with these findings we observed monocytes from T/T patients to secrete significantly lower concentrations of IL-12 than monocytes from non-T/T individuals.

CONCLUSIONS

Our data indicate that monocytes from carriers of an IL-28B T/T genotype display a reduced ability to stimulate NK cell activity and, thus, provide a link between IL-28B genotype and NK functions.