HCV immunopathogenesis: virus-induced strategies against host immunity

Immunopathogenesis of Liver Injury During Hepatitis C Virus Infection

The present report describes current concepts about the mechanism of liver cell injury caused by host immune response against hepatitis C virus (HCV) infection in human beings. This report is based on the observations from experimental studies and follow-up actions on human liver diseases. The results from different investigations suggest that liver injury depends on the presentation of viral antigen and the level of host immune response raised against HCV-related peptides. Both innate and adaptive immunity are triggered to counter the viral onset. During development of host immunity, the cell-mediated immune response involving CD4⁺ Th1 cells and CD8⁺ cytotoxic T-lymphocyte (CTL) cells were found to play a major role in causing liver damage. The hepatic Innate lymphoid cells (ILCs) subsets are involved in the immune regulation of different liver diseases: viral hepatitis, mechanical liver injury, and fibrosis. Humoral immunity and natural killer (NK) cell action also contributed in liver cell injury by antibody-dependent cellular cytotoxicity (ADCC). In fact, immunopathogenesis of HCV infection is a complex phenomenon where regulation of immune response at several steps decides the possibility of viral elimination or persistence. Regulation of immune response was noted starting from viral-host interaction to immune reaction cascade engaged in cell damage. The activation or suppression of interferon-stimulated genes, NK cell action, CTL inducement by regulatory T cells (Treg), B cell proliferation, and so on was demonstrated during HCV infection. Involvement of HLA in antigen presentation, as well as types of viral genotypes, also influenced host immune response against HCV peptides. The combined effect of all these effector mechanisms ultimately decides the progression of viral onset to acute or chronic infection. In conclusion, immunopathogenesis of liver injury after HCV infection may be ascribed mainly to host immune response. Second, it is cell-mediated immunity that plays a predominant role in liver cell damage.

The role of the NLRP3 inflammasome and the activation of IL-1β in the pathogenesis of chronic viral hepatic inflammation

BACKGROUND AND AIMS

Chronic viral hepatitis is a prevalent disease with major health implications. Its underlying pathophysiological mechanisms are not fully understood. IL-1β and the NLRP3 inflammasome involvement has been suggested in recent years, from in vitro data and data from peripheral blood samples. Therefore, we investigated IL-1β and the NLRP3 inflammasome in liver tissues in an effort to clarify their role in the pathophysiology of chronic viral hepatitis.

METHODS

We studied liver biopsies from patients with a new diagnosis of either chronic hepatitis B (CHB) and chronic hepatitis C (CHC) or patients with chronic hepatitis B in remission (CHB-rem). The biopsies were separated in two parts. The first part was sent to histology to determine the grade of inflammation and fibrosis. From the second part, RNA was extracted and converted to cDNA used in semi-quantitative Real-Time PCR to measure the levels of IL1B, CASP1, NLRP3, ASC and IL1RA. The cell lines used in the in vitro experiments were Huh7.5, LX2 and THP-1 in variety of combinations of monocultures, co-cultures and triple cultures with one of the cell lines infected with the JFH-1 HCV clone. From the cell cultures RNA was extracted and converted to cDNA. For cell lines, we focused in the expression of IL1B and NLRP3.

RESULTS

The expression of IL1B, CASP1 and NLRP3 were found significantly different between our groups (p = 0.001, p = 0.001 and p = 0.038, respectively). CHB patients displayed significantly higher IL1B and CASP1 mRNA levels compared to both CHB-rem and CHC patients. IL1B expression significantly correlates with liver biochemical data in CHB patients (AST: p = 0.006, r = 0.457; ALT p = 0.002, r = 0.497). Finally, mRNA levels of IL1B in CHB patients significantly correlate with the degree of inflammation (p = 0.016) but not the stage of fibrosis (p = 0.362). Interestingly, the relative expression of IL1B in triple culture experiments in vitro was below of 1.5-fold, suggesting no activation of IL1B. Moreover, no activation of NLRP3 was demonstrated in all investigated in vitro conditions.

CONCLUSION

IL-1β might play an important role in the pathogenesis of chronic hepatic inflammation from HBV, but not from HCV.

Inflammatory cells in minor salivary glands of patients with chronic hepatitis C: immunophenotype, pattern of distribution, and comparison with liver samples

OBJECTIVES

To characterize the immunophenotype and the distribution of the inflammatory infiltrate (INF) in salivary glands (SG) of patients with chronic hepatitis C, comparing with laboratorial data (genotype, viral load, METAVIR, and HCV RNA in SG), and liver.

METHODS

INF was classified as diffuse or focal. Immunohistochemistry for CD3, CD20, CD8, CD4, CD57, CD68, and S100 was performed in 61 SG and 59 livers.

RESULTS

Diffuse INF was more common in SG than in liver. CD3(+), CD20(+), and CD8(+) were the most frequent cells in both tissues, with few CD57(+), CD68(+), and S100(+) cells. CD4(+) cells were common in liver, but rare in SG. Liver presented higher indexes for all markers, except S100(+) (p<0.05). Higher CD3(+), CD20(+), and CD8(+) (p<0.05) were observed in SG with focal infiltrate than with diffuse infiltrate. In liver, CD20(+) and CD3(+) were higher in focal infiltrate, and CD68(+) in diffuse infiltrate (p<0.05). Comparisons with laboratorial data did not show statistical significance.

CONCLUSIONS

The INF in SG was mainly composed by T and B lymphocytes, mostly cytotoxic T cells. The glandular INF can present differences in composition according to its distribution. A more intense inflammation was observed in liver, but similar cell types were identified in SG, except for CD4(+).

Interplay among cellular polarization, lipoprotein metabolism and hepatitis C virus entry

Hepatitis C virus (HCV) infects more than three million new individuals worldwide each year. In a high percentage of patients, acute infections become chronic, eventually progressing to fibrosis, cirrhosis, and hepatocellular carcinoma. Given the lack of effective prophylactic or therapeutic vaccines, and the limited sustained virological response rates to current therapies, new approaches are needed to prevent, control, and clear HCV infection. Entry into the host cell, being the first step of the viral cycle, is a potential target for the design of new antiviral compounds. Despite the recent discovery of the tight junction-associated proteins claudin-1 and occludin as HCV co-receptors, which is an important step towards the understanding of HCV entry, the precise mechanisms are still largely unknown. In addition, increasing evidence indicates that tools that are broadly employed to study HCV infection do not accurately reflect the real process in terms of viral particle composition and host cell phenotype. Thus, systems that more closely mimic natural infection are urgently required to elucidate the mechanisms of HCV entry, which will in turn help to design antiviral strategies against this part of the infection process.

Replication of subgenomic hepatitis C virus replicons in mouse fibroblasts is facilitated by deletion of interferon regulatory factor 3 and expression of liver-specific microRNA 122

Hepatitis C virus (HCV) infection causes significant morbidity, and efficient mouse models would greatly facilitate virus studies and the development of effective vaccines and new therapeutic agents. Entry factors, innate immunity, and host factors needed for viral replication represent the initial barriers that restrict HCV infection of mouse cells. Experiments in this paper consider early postentry steps of viral infection and investigate the roles of interferon regulatory factors (IRF-3 and IRF-9) and microRNA (miR-122) in promoting HCV replication in mouse embryo fibroblasts (MEFs) that contain viral subgenomic replicons. While wild-type murine fibroblasts are restricted for HCV RNA replication, deletion of IRF-3 alone can facilitate replicon activity in these cells. This effect is thought to be related to the inactivation of the type I interferon synthesis mediated by IRF-3. Additional deletion of IRF-9 to yield IRF-3(-/-) IRF-9(-/-) MEFs, which have blocked type I interferon signaling, did not increase HCV replication. Expression of liver-specific miR-122 in MEFs further stimulated the synthesis of HCV replicons in the rodent fibroblasts. The combined effects of miR-122 expression and deletion of IRF-3 produced a cooperative stimulation of HCV subgenome replication. miR-122 and IRF-3 are independent host factors that are capable of influencing HCV replication, and our findings could help to establish mouse models and other cell systems that support HCV growth and particle formation.

Secreted protein acidic and rich in cysteine (SPARC) gene polymorphism association with hepatocellular carcinoma in Italian patients

BACKGROUND AND AIM

Hepatocellular carcinoma (HCC) is a multifactorial disease driven by both genetic and epigenetic factors. Infection, inflammation and the immune response against hepatitis B virus and hepatitis C virus have been shown to play an important role in increasing cancer risk and promoting tumor development. In order to investigate the genetic component influencing HCC development, we analyzed 50 single nucleotide polymorphisms (SNP) spanning 34 different genes in 230 Italian patients affected by HCC and 230 controls.

METHODS

Genes were selected on the basis of their known biological function and their possible involvement in the progression or in the susceptibility to HCC was considered. SNP genotyping was performed using allelic-specific fluorescent probes.

RESULTS

For most SNP, no differences were identified between HCC patients and controls, with the exception of rs2304052, localized on the secreted protein acidic and rich in cysteine (SPARC) gene, which was significantly associated to the disease. The C allele was significantly more frequent in the HCC patients than in the healthy controls (23% vs 10%, corrected P < 0.001), as well as the CC genotype (13% vs 1%, corrected P < 0.001).

CONCLUSION

Since the presence of the rs2304052 C allele is associated with an increased risk (odds ratio: 2.76) of developing hepatocarcinoma, our results allowed us to identify a SNP in the SPARC gene correlating to HCC susceptibility.

Hepatitis C and innate immunity: recent advances

Eradication of hepatitis C virus (HCV) infection requires a complex and coordinated interplay between innate and adaptive immune responses that, when it fails, leads to chronic infection. In this review, the innate immune mechanisms by which HCV is sensed and by which HCV undermines host defense are discussed. The critical role of dendritic cells in antigen presentation and T-cell activation in addition to type I interferon production and interference of HCV with innate immune cell functions are reviewed. Finally, current and emerging therapeutic approaches targeting innate immune pathways are evaluated.