Intrahepatic IL-8 producing Foxp3⁺CD4⁺ regulatory T cells and fibrogenesis in chronic hepatitis C

Interleukin-8: A critical chemokine in biliary atresia

Biliary atresia (BA) is characterized by periductular inflammation and fibrosis and is associated with the progressive obliteration of the bile ducts. The induction and maintenance of systemic and local inflammatory responses plays a pivotal role in this process. Interleukin-8 (IL-8) is an important mediator of inflammation and the immune response in human disease. IL-8 is overexpressed in BA, and its expression positively correlates with inflammation and liver fibrosis. In this review, we focus on the available evidence, recent insights, and future clinical and preclinical possibilities regarding the role of IL-8 in BA.

Paeoniflorin diminishes ConA-induced IL-8 production in primary human hepatic sinusoidal endothelial cells in the involvement of ERK1/2 and Akt phosphorylation

Liver diseases are closely associated with elevated levels of interleukin-8 (IL-8), suggesting the ability to inhibit IL-8 production could enhance the treatment of liver diseases. Paeoniflorin is a major active constituent of dried Paeoniae Radix Alba root (Baishao in Chinese) which is widely used in China to treat liver diseases. We examined the effects and underlying mechanisms of paeoniflorin on IL-8 production in primary human hepatic sinusoidal endothelial cells (HHSECs). Concanavalin A (ConA) at 20 μg/mL produced a 5.2-fold increase in IL-8 mRNA by 8h, and a 14.2-fold rise in IL-8 levels by 16 h. Inhibition of MEK (ERK kinase) and extracellular signal-regulated kinase (ERK) by PD98059 and U0126, or inhibition of phosphatidylinositol 3-kinase (PI3K) by LY294002 blocked both ConA-induced IL-8 mRNA expression and IL-8 secretion. Paeoniflorin reduced ConA-induced IL-8 mRNA expression and IL-8 release by 57.9% and 52.8%, respectively, and also decreased ConA-stimulated phosphorylation of ERK1/2 and Akt, suggesting paeoniflorin inhibits IL-8 expression and release by inhibiting the ERK1/2 and Akt pathways. Combining paeoniflorin with U0126 or LY294002 at low doses showed supra-additive inhibition of not only phospho-ERK1/2 and phospho-Akt by 46.4% and 35.0%, but also IL-8 release by 42.4% and 36.1% and IL-8 mRNA expression by 43.5% and 31.8%, respectively. In conclusion, paeoniflorin most likely contributes to the therapy for liver disease by exerting anti-inflammatory effects on HHSECs through blocking IL-8 secretion via downregulation of ERK1/2 and Akt phosphorylation.

Hepatic inflammation and fibrosis: functional links and key pathways

Inflammation is one of the most characteristic features of chronic liver disease of viral, alcoholic, fatty, and autoimmune origin. Inflammation is typically present in all disease stages and associated with the development of fibrosis, cirrhosis, and hepatocellular carcinoma. In the past decade, numerous studies have contributed to improved understanding of the links between hepatic inflammation and fibrosis. Here, we review mechanisms that link inflammation with the development of liver fibrosis, focusing on the role of inflammatory mediators in hepatic stellate cell (HSC) activation and HSC survival during fibrogenesis and fibrosis regression. We will summarize the contributions of different inflammatory cells, including hepatic macrophages, T and B lymphocytes, natural killer cells and platelets, as well as key effectors, such as cytokines, chemokines, and damage-associated molecular patterns. Furthermore, we will discuss the relevance of inflammatory signaling pathways for clinical liver disease and for the development of antifibrogenic strategies.

Regulatory CD4+ T cells modulate the interaction between NK cells and hepatic stellate cells by acting on either cell type

BACKGROUND & AIMS

NK cells regulate liver fibrosis by killing activated hepatic stellate cells (HSCs) and are controlled themselves by immune cells and/or soluble factors. Here, we analysed if CD4(+) regulatory T cells (Tregs) modify the interaction between NK cells and HSCs.

METHODS

The modification of NK cell activity against HSCs was studied in CD56(high)CD16(-) NK cells, using a flow cytometric CD107a degranulation assay and co-cultures with Tregs from healthy donors and patients with hepatitis C, respectively. We studied the underlying mechanisms in detail, applying Treg supernatants, Treg pretreated HSCs, and recombinant IL-8, TGF-ß1, and IL-10 as well as blocking experiments with neutralizing antibodies and analysed Treg-associated changes in the expression of NK cell receptor ligands on HSCs.

RESULTS

Tregs suppressed NK cell activation during HSC co-culture in a cell-contact-dependent manner involving the cytotoxic T-lymphocyte antigen 4 (CTLA-4). NK cell degranulation was further reduced, when HSCs had been pretreated with Tregs (p=0.043), Treg supernatants (p=0.001) or recombinant IL-8 (R=0.630, p=0.001) and TGF-ß1 (R=0.608, p=0.002), respectively. This additional inhibitory effect corresponded to the IL-8/TGF-ß1-mediated downregulation of MIC-A/B and HLA class-I on HSCs. Tregs from hepatitis C likewise inhibited NK cell activity, which was reversed significantly in specific blocking experiments.

CONCLUSIONS

Our data indicate that Tregs interfere with NK cell regulation of fibrogenesis via both direct cell-contact-dependent inhibition of NK cells and release of soluble factors, downregulating activating NK cell receptor ligands on HSCs. Our data may be particularly relevant for the intrahepatic accumulation of Tregs in chronic hepatitis C because downregulated NK cell activity against HSCs may blunt their control of fibrogenesis.

Molecular Links between Alcohol and Tobacco Induced DNA Damage, Gene Polymorphisms and Patho-physiological Consequences: A Systematic Review of Hepatic Carcinogenesis

Chronic alcohol and tobacco abuse plays a crucial role in the development of different liver associated disorders. Intake promotes the generation of reactive oxygen species within hepatic cells exposing their DNA to continuous oxidative stress which finally leads to DNA damage. However in response to such damage an entangled protective repair machinery comprising different repair proteins like ATM, ATR, H2AX, MRN complex becomes activated. Under abnormal conditions the excessive reactive oxygen species generation results in genetic predisposition of various genes (as ADH, ALDH, CYP2E1, GSTT1, GSTP1 and GSTM1) involved in xenobiotic metabolic pathways, associated with susceptibility to different liver related diseases such as fibrosis, cirrhosis and hepatocellular carcinoma. There is increasing evidence that the inflammatory process is inherently associated with many different cancer types, including hepatocellular carcinomas. The generated reactive oxygen species can also activate or repress epigenetic elements such as chromatin remodeling, non-coding RNAs (micro-RNAs), DNA (de) methylation and histone modification that affect gene expression, hence leading to various disorders. The present review provides comprehensive knowledge of different molecular mechanisms involved in gene polymorphism and their possible association with alcohol and tobacco consumption. The article also showcases the necessity of identifying novel diagnostic biomarkers for early cancer risk assessment among alcohol and tobacco users.

Hypoxia inducible factors in liver disease and hepatocellular carcinoma: current understanding and future directions

Hypoxia inducible transcription factors (HIFs) activate diverse pathways that regulate cellular metabolism, angiogenesis, proliferation, and migration, enabling a cell to respond to a low oxygen or hypoxic environment. HIFs are regulated by oxygen-dependent and independent signals including: mitochondrial dysfunction, reactive oxygen species, endoplasmic reticular stress, and viral infection. HIFs have been reported to play a role in the pathogenesis of liver disease of diverse aetiologies. This review explores the impact of HIFs on hepatocellular biology and inflammatory responses, highlighting the therapeutic potential of targeting HIFs for an array of liver pathologies.

Distinctive intrahepatic characteristics of paediatric and adult pathogenesis of chronic hepatitis C infection

Mechanisms leading to liver damage in chronic hepatitis C (CHC) are being discussed, but both the immune system and the virus are involved. The aim of this study was to evaluate intrahepatic viral infection, apoptosis and portal and periportal/interface infiltrate in paediatric and adult patients to elucidate the pathogenesis of chronic hepatitis C. HCV-infected, activated caspase-3(+) and TUNEL(+) hepatocytes, as well as total, CD4(+), CD8(+), Foxp3(+) and CD20(+) lymphocytes infiltrating portal and periportal/interface tracts were evaluated in 27 paediatric and 32 adult liver samples by immunohistochemistry or immunofluorescence. The number of infected hepatocytes was higher in paediatric than in adult samples (p 0.0078). In children, they correlated with apoptotic hepatocytes (activated caspase-3(+) r = 0.74, p < 0.0001; TUNEL(+) r = 0.606, p 0.0017). Also, infected (p = 0.026) and apoptotic hepatocytes (p = 0.03) were associated with the severity of fibrosis. In adults, activated caspase-3(+) cell count was increased in severe hepatitis (p = 0.009). Total, CD4(+), CD8(+) and Foxp3(+) lymphocyte count was higher in adult samples (p < 0.05). Paediatric CD8(+) cells correlated with infected (r = 0.495, p 0.04) and TUNEL(+) hepatocytes (r = 0.474, p = 0.047), while adult ones correlated with activated caspase-3(+) hepatocytes (r = 0.387, p 0.04). In adults, CD8(+) was associated with hepatitis severity (p < 0.0001) and correlated with inflammatory activity (CD8(+) r = 0.639, p 0.0003). HCV, apoptosis and immune response proved to be involved in CHC pathogenesis of both paediatric and adult patients. However, liver injury in paediatric CHC would be largely associated with a viral cytopathic effect mediated by apoptosis, while in adults it would be mainly associated with an exacerbated immune response.

Liver fibrosis and repair: immune regulation of wound healing in a solid organ

Fibrosis is a highly conserved and co-ordinated protective response to tissue injury. The interaction of multiple pathways, molecules and systems determines whether fibrosis is self-limiting and homeostatic, or whether it is uncontrolled and excessive. Immune cells have been identified as key players in this fibrotic cascade, with the capacity to exert either injury-inducing or repair-promoting effects. A multi-organ approach was recently suggested to identify the core and regulatory pathways in fibrosis, with the aim of integrating the wealth of information emerging from basic fibrosis research. In this Review, we focus on recent advances in liver fibrosis research as a paradigm for wound healing in solid organs and the role of the immune system in regulating and balancing this response.

Between Scylla and Charybdis: The role of the human immune system in the pathogenesis of hepatitis C

Hepatitis C virus (HCV) frequently elicits only mild immune responses so that it can often establish chronic infection. In this case HCV antigens persist and continue to stimulate the immune system. Antigen persistence then leads to profound changes in the infected host’s immune responsiveness, and eventually contributes to the pathology of chronic hepatitis. This topic highlight summarizes changes associated with chronic hepatitis C concerning innate immunity (interferons, natural killer cells), adaptive immune responses (immunoglobulins, T cells, and mechanisms of immune regulation (regulatory T cells). Our overview clarifies that a strong anti-HCV immune response is frequently associated with acute severe tissue damage. In chronic hepatitis C, however, the effector arms of the immune system either become refractory to activation or take over regulatory functions. Taken together these changes in immunity may lead to persistent liver damage and cirrhosis. Consequently, effector arms of the immune system will not only be considered with respect to antiviral defence but also as pivotal mechanisms of inflammation, necrosis and progression to cirrhosis. Thus, avoiding Scylla - a strong, sustained antiviral immune response with inital tissue damage - takes the infected host to virus-triggered immunopathology, which ultimately leads to cirrhosis and liver cancer - the realm of Charybdis.