Chemokines in the immunopathogenesis of hepatitis C infection

The hepatitis C virus core protein indirectly induces alpha-smooth muscle actin expression in hepatic stellate cells via interleukin-8

BACKGROUND & AIMS

Progressive deposition of liver fibrosis is a common feature of chronic hepatitis associated with hepatitis C virus (HCV) infection, and it may eventually lead to cirrhosis and liver failure. Although this fibrogenic process appears to be linked to HCV protein expression and replication via indirect mechanisms, i.e., to be mediated by virally-driven inflammation, a direct role of HCV in inducing fibrosis deposition has never been entirely excluded.

METHODS

We established an in vitro system in which the human hepatic stellate cell line LX-2 was cultured in the presence of conditioned medium from human hepatoma Huh-7 cells transduced with a lentiviral vector expressing HCV core proteins of different genotypes.

RESULTS

Treatment of LX-2 cells, with conditioned medium from Huh-7 cells expressing HCV core protein, led to the activation of alpha-smooth muscle actin expression. Among the chemokines secreted by cells transduced with HCV core, interleukin-8 was identified as the strongest inducer of alpha-smooth muscle actin expression in LX-2 and primary hepatic stellate cells. This effect was accompanied by a decrease in cell migration and increased focal contact organisation.

CONCLUSIONS

The expression of the HCV core in hepatocytes may contribute to the establishment of a profibrogenic microenvironment.

Lower copy numbers of the chemokine CCL3L1 gene in patients with chronic hepatitis C

BACKGROUND & AIMS

Recently, variation of gene copy numbers was recognized as a novel type of common genetic diversity, but its impact on viral hepatitis is unknown. Here, we determine the influence of copy number variation on the susceptibility and disease severity in hepatitis C virus (HCV) infection, investigating copy number variants (CNVs) of the chemokine CCL3L1 gene, which encodes a potent CCR5 ligand.

METHODS

CNVs were determined in 254 patients with chronic hepatitis C, 144 HCV/HIV co-infected patients, and 210 HCV negative controls, using quality-controlled real-time fluorescent dye-labeled quantitative PCR. Liver biopsies were obtained from HCV infected patients.

RESULTS

Copy numbers of the CCL3L1 gene range from 0 to 12 (mean 2.7+/-1.4 copies). Patients with two or less copies are over-represented in the HCV infected cohort compared to HCV negative controls (odds ratio [OR] 1.54; p=0.02). CCL3L1 copies are shifted to lower numbers in HCV infected patients (means 2.6 vs. 2.9 in controls; p=0.011). HCV/HIV co-infected patients carry even lower CCL3L1 copy numbers compared to controls (means 2.2 vs. 2.9; p<0.001), with a higher proportion of patients possessing two or less copies (OR=3.42; p<0.001). No association was detected between CCL3L1 copy numbers and histological grades of inflammation or stages of fibrosis.

CONCLUSIONS

Lower CCL3L1 gene copy number compared to the population median is associated with chronic hepatitis C. Copy number variation of host genes represents a novel class of genetic diversity associated with viral hepatitis.

CX3CL1 (fractalkine): a signpost for biliary inflammation in primary biliary cirrhosis

Improvements in the treatment of primary biliary cirrhosis (PBC) may depend upon dissection of mechanisms that determine recruitment of mononuclear cells to intralobular bile ducts, including the role of the chemokine-adhesion molecule CX3CL1 (fractalkine). We submit that there are unique interactions between intrahepatic biliary epithelial cells (BECs), endothelial cells (ECs), liver sinusoidal endothelial cells (LSECs), and liver-infiltrating mononuclear cells (LMCs), and that such interactions will in part dictate the biliary-specific inflammatory response. To address this, we studied fresh explanted livers from pretransplantation patients with PBC and with inflammatory liver disease due to viral infection (disease controls) and biopsy material from patients with a discrete liver tumor (normal controls). Using this clinical material, we isolated and stimulated BECs, ECs, LSECs, and LMCs with a panel of Toll-like receptor ligands. We also studied the interactions of these cell populations with LMCs with respect to adhesion capability and production of tumor necrosis factor alpha (TNF-alpha). Finally, we used fresh biopsy samples to evaluate mononuclear cells around intrahepatic biliary ductules using monoclonal antibodies specific to CD68 or CD154, markers for monocytes/macrophages, and activated T cells, respectively.

CONCLUSION

There are common properties of ECs, LSECs, and BECs, whether derived from PBC or viral hepatitis, but there are also significant differences, particularly in the potential in PBC for LMCs to adhere to ECs and BECs and to produce TNF-alpha; such properties were associated with augmented CX3CL1 production by BEC from PBC liver. The processes defined herein suggest potential novel biotherapies for biliary specific inflammation.

Chemokine transcription in rainbow trout (Oncorhynchus mykiss) is differently modulated in response to viral hemorrhagic septicaemia virus (VHSV) or infectious pancreatic necrosis virus (IPNV)

Chemokines not only act as chemoattractants for immune cells, but also exert immunomodulatory actions, thus modulating the immune functions of their target cells. In rainbow trout (Oncorhynchus mykiss), twenty-four chemokines have been identified to date. Even though their sequences have been reported, their biological role has been scarcely elucidated and the role that these chemokines have on the antiviral response in fish has been poorly studied. In this sense, in the current work, we have determined the levels of expression of several of these rainbow trout chemokines (CXCd, gammaIP, CK1, CK3, CK5B, CK6, CK7A, CK9 and CK12) in head kidney and spleen during the course of a viral infection using two different viruses, viral hemorrhagic septicaemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV), comparing them to the levels induced by poly I:C. We also determined the effects that the two viruses and poly I:C provoked on the levels of expression of these chemokines in vitro in head kidney leucocytes. Overall, VHSV was capable of modulating gammaIP, CXCd, CK1, CK3, CK5B, CK6 and CK12, while IPNV induced a very different chemokine profile and affected CK1, CK5B, CK6, CK7A, CK9 and CK12. On the other hand, a viral mimic such as poly I:C was capable of up-regulating gammaIP, CXCd, CK1, CK3, CK5B, CK7A and CK12. As more information becomes available concerning the immune role and target cells that these chemokines have on rainbow trout, we would be able to better interpret the importance of these differences in the pathogenicity of these two viruses.

The role of chemokines in the recruitment of lymphocytes to the liver

Chemokines direct leukocyte trafficking and positioning within tissues. They thus play critical roles in regulating immune responses and inflammation. The chemokine system is complex involving interactions between multiple chemokines and their receptors that operate in combinatorial cascades with adhesion molecules. The involvement of multiple chemokines and chemokine receptors in these processes brings flexibility and specificity to recruitment. The hepatic vascular bed is a unique low flow environment through which leukocyte are recruited to the liver during homeostatic immune surveillance and in response to infection or injury. The rate of leukocyte recruitment and the nature of cells recruited through the sinusoids in response to inflammatory signals will shape the severity of disease. At one end of the spectrum fulminant liver failure results from a rapid recruitment of leukocytes that leads to hepatocyte destruction and liver failure at the other diseases such as chronic hepatitis C infection may progress over many years from hepatitis to fibrosis and cirrhosis. Chronic hepatitis is charactezised by a T lymphocyte rich infiltrate and the nature and outcome of hepatitis will depend on the T cell subsets recruited, their activation and function within the liver. Different subsets of effector T cells have been described based on their secretion of cytokines and specific functions. These include Th1 and Th2 cells and more recently Th17 and Th9 cells which are associated with different types of immune response and which express distinct patterns of chemokine receptors that promote their recruitment under particular conditions. The effector function of these cells is balanced by the recruitment of regulatory T cells that are able to suppress antigen-specific effectors to allow resolution of immune responses and restoration of immune homeostasis. Understanding the signals that are responsible for recruiting different lymphocyte subsets to the liver will elucidate disease pathogenesis and open up new therapeutic approaches to modulate recruitment in favour of resolution rather than injury.

Role of host genetic factors in the outcome of hepatitis C virus infection

The natural history of hepatitis C virus (HCV) infection is determined by a complex interplay between host genetic, immunological and viral factors. This review highlights genes involved in innate and adaptive immune responses associated with different outcomes of HCV infection. For example, an association of HCV clearance with certain HLA alleles has been demonstrated. The mechanisms responsible for these associations have been linked to specific T cell responses for some particular alleles (e.g., HLA-B27). Genetic associations involved in T cell regulation and function further underline the role of the adaptive immune response in the natural history of HCV infection. In addition, some genes involved in innate NK cell responses demonstrate the complex interplay between components of the immune system necessary for a successful host response to HCV infection.

Antifibrotic effects of CXCL9 and its receptor CXCR3 in livers of mice and humans

BACKGROUND & AIMS

Fibrosis is the hallmark of chronic liver diseases, yet many aspects of its mechanism remain to be defined. Chemokines are ubiquitous chemotactic molecules that mediate many acute and chronic inflammatory conditions, and CXC chemokine genes colocalize with a locus previously shown to include fibrogenic genes. We investigated the roles of the chemokine CXCL9 and its receptor CXCR3 in liver fibrosis.

METHODS

The effects of CXCL variants on fibrogenesis were analyzed using samples from patients with hepatitis C virus infection and by induction of fibrosis in CXCR3(-/-) and wild-type mice. In mice, intrahepatic immune cell subsets were investigated and interferon gamma messenger RNA levels were measured at baseline and after injury. Human serum CXCL9 levels were measured and correlated with CXCL9 variant and fibrosis severity. The effects of stimulation with CXCL9 were investigated on human hepatic stellate cells (LX-2).

RESULTS

Specific CXCL9 variants were associated with liver fibrosis in mice and humans; CXCL9 serum concentrations correlated with genotypes and levels of fibrosis in patients. In contrast to other chemokines, CXCL9 exerted antifibrotic effects in vitro, suppressing collagen production in LX-2 cells. CXCR3(-/-) mice had increased liver fibrosis; progression was associated with decreased numbers of intrahepatic interferon gamma-positive T cells and reduced interferon gamma messenger RNA, indicating that CXCL9-CXCR3 regulates Th1-associated immune pathways.

CONCLUSIONS

This is the first description of a chemokine-based antifibrotic pathway in the liver; antifibrotic therapies might be developed to modulate CXC chemokine levels.