Recent evidence suggests that toll-like receptors (TLRs) recognize certain viruses. We reported that hepatitis C virus (HCV) core and nonstructural 3 (NS3) proteins activate inflammatory pathways in monocytes. The aim of this study was to investigate the role of TLRs in innate immune cell activation by core and NS3 proteins.
Human monocytes, human embryonic kidney cells transfected with TLR2, and peritoneal macrophages from TLR2, MyD88 knockout, and wild-type mice were studied to determine intracellular signaling and proinflammatory cytokine induction by HCV proteins.
HCV core and NS3 proteins triggered inflammatory cell activation via the pattern recognition receptor TLR2 and failed to activate macrophages from TLR2 or MyD88-deficient mice. HCV core and NS3 induced interleukin (IL)-1 receptor-associated kinase (IRAK) activity, phosphorylation of p38, extracellular regulated (ERK), and c-jun N-terminal (JNK) kinases and induced AP-1 activation. Activation of nuclear factor-kappaB by core and NS3 was associated with increased IkappaBalpha phosphorylation. TLR2-mediated cell activation was dependent on the conformation of core and NS3 proteins and required sequences in the regions of aa 2-122 in core and aa 1450-1643 in NS3. Although cellular uptake of core and NS3 proteins was independent of TLR2 expression, cell activation required TLR2. HCV core protein and TLR2 showed intracellular colocalization. The hyper-elevated TNF-alpha induction by TLR2 ligands in monocytes of HCV-infected patients was not due to increased TLR2 expression.
HCV core and NS3 proteins trigger inflammatory pathways via TLR2 that may affect viral recognition and contribute to activation of the innate immune system.
"In a study conducted by Düesberg et al. , synthetic lipopeptide complexes of the HCV core protein were found to stimulate the innate immune response via TLR2 and TLR4. This was confirmed by other studies showing that HCV proteins, such as core and NS3, can activate human monocytes and macrophages via TLR2 [14, 15]. Other studies have also shown that HCV structural and nonstructural proteins interfere with the innate immunity signaling pathway through the interaction of ISGs [16–18]. "
[Show abstract][Hide abstract] ABSTRACT: Hepatitis C virus (HCV) is a single stranded RNA virus. It affects millions of people worldwide and is considered as a leading cause of liver diseases including cirrhosis and hepatocellular carcinoma. A recent study reported that TLR4 gene polymorphisms are good prognostic predictors and are associated with protection from liver fibrosis among Caucasians. This study aims to investigate the implication of genetic polymorphisms of TLR4 gene on the HCV infection in Saudi Arabian patients. Two SNPs in the TLR4 gene, rs4986790 (A/G) and rs4986791 (C/T), were genotyped in 450 HCV patients and 600 uninfected controls. The association analysis confirmed that both SNPs showed a significant difference in their distribution between HCV-infected patients and uninfected control subjects (P < 0.0001; OR = 0.404, 95% CI = 0.281-0.581) and (P < 0.0001; OR = 0.298, 95% CI = 0.201-0.443), respectively. More importantly, haplotype analysis revealed that four haplotypes, AC, GT, GC, and AT (rs4986790, rs4986791), were significantly associated with HCV infection when compared with control subjects. One haplotype AC was more prominently found when chronic HCV-infected patients were compared with cirrhosis/HCC patients (frequency = 94.7% and P = 0.04). Both TLR4 SNPs under investigation were found to be significantly implicated with HCV-infection among Saudi Arabian population.
BioMed Research International 08/2014; 2014:357062. DOI:10.1155/2014/357062 · 3.17 Impact Factor
"Concurrently, HCV suppresses specific intracellular signaling to evade the host immune control (75). HCV core and NS3 proteins trigger TLR1, TLR2, and TLR6 on monocytes to enhance the production of inflammatory cytokines (76, 77). However, NS3/4a proteins degrade TIR-domain-containing adapter-inducing IFN-β (TRIF) and inhibit TLR3-mediated TRIF-dependent IFN-β production (78, 79). "
[Show abstract][Hide abstract] ABSTRACT: 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.
Frontiers in Immunology 05/2014; 5:221. DOI:10.3389/fimmu.2014.00221
"We investigated the effect of limonin pretreatment on the expression of Toll-like receptors because of its importance in the development of liver disorders and in particular viral hepatitis (Dolganiuc et al. 2004). We have found increased expression of both TLR2 and TLR4 genes in hepatic tissues of animals treated with D-GalN, while both limonin and silymarin prevented only the increased expression of TLR4 without affecting the increased expression of TLR2. "
[Show abstract][Hide abstract] ABSTRACT: Toll-like receptors have been implicated in inflammation and injury in various tissues and organs including the liver. We have investigated the effects of limonin isolated from the dichloromethane fraction of the seeds of bittersweet orange (Citrus aurantium var. bigaradia) in two dose levels (50 and 100 mg/kg) against D-galactosamine (D-GalN)-induced liver toxicity in comparison with standard silymarin treatment on Toll-like receptors expression and hepatic injury, using a well-established rat model of acute hepatic inflammation. The limonoids in the seeds of bittersweet orange were identified. Oral administration of limonin before D-GalN injection, significantly attenuated markers of hepatic damage (elevated liver enzyme activities and total bilirubin) and hepatic inflammation (TNF-α, infiltration of neutrophils), oxidative stress and expression of TLR-4 but not TLR-2 in D-GalN-treated rats. Limonin effects were similar in most aspects to that of the lignan silymarin. The higher dose of limonin (100 mg/kg) performed numerically better for AST and bilirubin, and both doses yielded similar results for ALT and GGT. While the lower dose of limonin (50 mg/kg) performed better against oxidative stress and liver structural damage as compared to the higher dose. Limonin exerts protective effects on liver toxicity associated with inflammation and tissue injury via attenuation of inflammation and reduction of oxidative stress.
Archiv für Experimentelle Pathologie und Pharmakologie 11/2013; 387(3). DOI:10.1007/s00210-013-0937-1 · 2.47 Impact Factor
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