Intrahepatic mononuclear cell populations and MHC antigen expression in patients with chronic hepatitis C [correction of B]: effect of interferon-alpha

Control of HCV Infection by Natural Killer Cells and Macrophages

Host defense against invading pathogens within the liver is dominated by innate immunity. Natural killer (NK) cells have been implicated at all stages of hepatitis C virus (HCV) infection, from providing innate protection to contributing to treatment-induced clearance. Decreased NK cell levels, altered NK cell subset distribution, activation marker expression, and functional polarization toward a cytolytic phenotype are hallmarks of chronic HCV infection. Interferon α (IFN-α) is a potent activator of NK cells; therefore, it is not surprising that NK cell activation has been identified as a key factor associated with sustained virological response (SVR) to IFN-α-based therapies. Understanding the role of NK cells, macrophages, and other innate immune cells post-SVR remains paramount for prevention of disease pathogenesis and progression. Novel strategies to treat liver disease may be aimed at targeting these cells.

Natural killer cells: multifaceted players with key roles in hepatitis C immunity

Natural killer cells (NKs) are involved in every stage of hepatitis C viral (HCV) infection, from protection against HCV acquisition and resolution in the acute phase to treatment-induced clearance. In addition to their direct antiviral actions, NKs are involved in the induction and priming of appropriate downstream T-cell responses. In the setting of chronic HCV, overall NK cell levels are decreased, subset distribution is altered, and changes in NK receptor (NKR) expression have been demonstrated, although the contribution of individual NKRs to viral clearance or persistence remains to be clarified. Enhanced NK cell cytotoxicity accompanied by insufficient interferon-γ production may promote liver damage in the setting of chronic infection. Treatment-induced clearance is associated with activation of NK cells, and it will be of interest to monitor NK cell responses to triple therapy. Activated NK cells also have anti-fibrotic properties, and the same hepatic NK cell populations that are actively involved in control of HCV may also be involved in control of HCV-associated liver damage. We still have much to learn, in particular: how do liver-derived NKs influence the outcome of HCV infection? Do NK receptors recognize HCV-specific components? And, are HCV-specific memory NK populations generated?

Innate immunity and chronic immune activation in HCV/HIV-1 co-infection

Innate immune responses are critical in the defense against viral infections. NK cells, myeloid and plasmacytoid dendritic cells, and invariant CD1d-restricted NKT cells mediate both effector and regulatory functions in this early immune response. In chronic uncontrolled viral infections such as HCV and HIV-1, these essential immune functions are compromised and can become a double edged sword contributing to the immunopathogenesis of viral disease. In particular, recent findings indicate that innate immune responses play a central role in the chronic immune activation which is a primary driver of HIV-1 disease progression. HCV/HIV-1 co-infection is affecting millions of people and is associated with faster viral disease progression. Here, we review the role of innate immunity and chronic immune activation in HCV and HIV-1 infection, and discuss how mechanisms of innate immunity may influence protection as well as immunopathogenesis in the HCV/HIV-1 co-infected human host.

Hepatitis C virus (HCV) employs multiple strategies to subvert the host innate antiviral response

Hepatitis C virus (HCV) is a serious global health problem which accounts for approximately 40% of chronic liver diseases worldwide. HCV frequently establishes a persistent infection, although it is recognized and targeted by innate immunity as well as cellular and humoral immune mechanisms. This suggests that HCV has developed powerful strategies to escape elimination by innate and adaptive immunity. HCV-induced liver injury is thought to be mainly immune-mediated rather than due to direct cytopathic effects of the virus. Hence, therapeutic strategies should target those mechanisms favoring viral persistence since unspecific enhancement of host antiviral immunity may theoretically also promote liver injury. The present review summarizes our current understanding of how the hepatitis C virus interferes with the innate antiviral host-response to establish persistent infection.

Sustained response to interferon-alpha plus ribavirin therapy for chronic hepatitis C is closely associated with increased dynamism of intrahepatic natural killer and natural killer T cells

AIM

Previous studies have revealed that functional impairment of innate immune cells, including natural killer (NK) and natural killer T (NKT) cells, might be associated with the persistence of hepatitis C virus (HCV) infection. However, the involvement of innate immune cells, which predominate in the liver, in therapeutic HCV clearance is still unclear.

METHODS

To clarify the role of intrahepatic innate immune cells in the clinical outcome of patients with chronic hepatitis C (CHC) treated with interferon-alpha plus ribavirin (IFN/RBV), we prospectively investigated the status of NK and NKT cells in paired liver biopsy and peripheral blood (PB) samples obtained from 21 CHC patients before and immediately after IFN/RBV treatment by flow cytometry. Normal liver and PB samples were obtained from 10 healthy donors for living donor liver transplantation.

RESULTS

Before treatment, intrahepatic NK and NKT cells constituted a significantly lower proportion in CHC patients than in healthy individuals (P < 0.05). After IFN/RBV treatment, the proportions and absolute numbers of CD3(-)CD161(+) NK and CD3(+)CD56(+) NKT cells in the liver, but not in PB, were significantly increased in sustained responders (SR) as compared with poor responders (P < 0.05). The proportion of CD3(+)CD161(+) NKT cells was also increased in the liver of SR after the treatment. Moreover, there was a striking increase of activated CD152(+) cells among CD3(+)CD56(+) NKT cells in the liver of SR (P = 0.041).

CONCLUSION

These findings demonstrate that sustained response to IFN/RBV treatment for patients with CHC is closely associated with increased dynamism of NK and NKT cells in the liver.

Anti-fibrotic activity of NK cells in experimental liver injury through killing of activated HSC

BACKGROUND/AIMS

We have investigated the role of natural killer (NK) cells in hepatic fibrogenesis. Mouse NK cells express both inhibitory/activating-killing-immunoglobulin-related-receptors (iKIR/aKIR) specific for Class-I-molecules.

METHODS

Hepatic fibrosis induced by carbon-tetrachloride (CCl4) was compared between wild-type (WT) male-BALBc; combined-immunodeficiency (SCID, lacking B/T-cells); and SCID-BEIGE-mice (lacking B/T/NK cells), and naive mice.

RESULTS

Hepatic fibrosis significantly increased in all CCl4-treated groups. SCID-BEIGE mice had more fibrosis than SCID-mice (P<0.0001) as assessed by morphometry of sirius-red stained tissue sections. Following fibrosis, hepatic NK cells significantly decreased, the aKIR:iKIR-ratio significantly increased while Class-I expression on HSC decreased (P<0.001). Both freshly isolated and in situ HSC displayed a significant increase in cellular apoptosis following fibrosis induction. Confocal microscopy demonstrated the direct adhesion of NK cells to HSC in mouse liver sections and in vitro human NK/HSC co-culture. In human HSC there was decreased Class-I expression and increased apoptosis as well, which was further increased following blocking of either HSC-related Class-I or NK-related killer inhibitory receptors. Apoptosis was inhibited by pre-incubation of NK cells with the granzyme inhibitor 3,4-dichloroisocoumarin.

CONCLUSIONS

During liver injury, NK cells have an anti-fibrotic activity at least in part through stimulation of HSC killing.

Reduction of virus burden-induced splenectomy in patients with liver cirrhosis related to hepatitis C virus infection

AIM: To examine the hepatitis C virus (HCV) levels and immunological markers in cirrhotic patients after splenectomy.

METHODS: HCV RNA titers as well as cellular and humoral immune markers were determined in 20 cirrhotic patients after splenectomy and in 32 cirrhotic controls with an intact spleen.

RESULTS: Serum HCV RNA titers were lower in the splenectomized patients than in the controls (186  ±  225 × 10³ copies/mL vs 541  ±  417 × 10³ copies/mL, P < 0.01). HCV RNA was judged to have been spontaneously eradicated in 4 splenectomized patients, but in none of the controls. Natural killer cell activity was higher in the splenectomized patients than in the controls (41.2  ±  19.3% vs 24.7  ±  15.3%, P < 0.01), and natural killer cell activity was negatively correlated to HCV RNA titers in the splenectomized patients except in those with serotype 2-related infection. The CD4/CD8 ratio was significantly lower in the splenectomized patients than in the controls.

CONCLUSION: The findings suggest that splenectomy may diminish virus burden in cirrhotic patients with HCV infection at least in part, through augmentation of natural killer cell activity.

Natural killer cells: primary target for hepatitis C virus immune evasion strategies?

Liver cirrhosis and hepatocellular carcinoma secondary to chronic hepatitis C virus (HCV) infection requiring transplantation represents a significant public health problem. The most remarkable feature of hepatitis C virus is the ability to establish chronic infection in the vast majority of cases. Efforts to define clinical correlates of HCV persistence have focused primarily on CD4 and CD8 T cell responses. Until recently, the role of innate immunity in determining the outcome of HCV infection had received relatively little attention. Natural killer (NK) cells are an important antiviral effector population eliminating virus through direct killing and cytokine production. Recent studies highlighting the cross-talk between NK cells, dendritic cells (DCs) and T cells have prompted reevaluation of the important role NK cells play in regulating and maintaining specific immune responses. Like many other viruses, HCV has evolved strategies to evade detection and elimination by NK cells. T cell defects observed in HCV infection may be a consequence of inhibition of NK:DC interactions. We propose a theoretical model for HCV persistence that places the NK cell at the center of HCV immune evasion strategies. While this model is only theoretical, it provides a plausible interpretation of many published observations and a useful working model to test the role of NK cells in HCV persistence. In conclusion, the role of innate immune cells and their regulation of antigen-specific responses by the initial innate response to the virus, in particular NK cells, may prove to be an informative and clinically relevant avenue of investigation.

Role of NK and NKT cells in the immunopathogenesis of HCV-induced hepatitis

Natural killer (NK) cells constitute the first line of host defense against invading pathogens. They usually become activated in an early phase of a viral infection. Liver is particularly enriched in NK cells, which are activated by hepatotropic viruses such as hepatitis C virus (HCV). The activated NK cells play an essential role in recruiting virus-specific T cells and in inducing antiviral immunity in liver. They also eliminate virus-infected hepatocytes directly by cytolytic mechanisms and indirectly by secreting cytokines, which induce an antiviral state in host cells. Therefore, optimally activated NK cells are important in limiting viral replication in this organ. This notion is supported by the observations that interferon treatment is effective in HCV-infected persons in whom it increases NK cell activity. Not surprisingly, HCV has evolved multiple strategies to counter host's NK cell response. Compromised NK cell functions have been reported in chronic HCV-infected individuals. It is ironic that activated NK cells may also contribute toward liver injury. Further studies are needed to understand the role of these cells in host defense and in liver pathology in HCV infections. Recent advances in understanding NK cell biology have opened new avenues for boosting innate and adaptive antiviral immune responses in HCV-infected individuals.

Upregulation of major histocompatibility complex class I on liver cells by hepatitis C virus core protein via p53 and TAP1 impairs natural killer cell cytotoxicity

The mechanisms of immune evasion and the role of the early immune response in chronic infection caused by hepatitis C virus (HCV) are still unclear. Here, we present evidence for a cascade of molecular events that the virus initiates to subvert the innate immune attack. The HCV core protein induced p53-dependent gene expression of TAP1 (transporter associated with antigen processing 1) and consecutive major histocompatibility complex (MHC) class I upregulation. Moreover, in p53-deficient liver cell lines, only reconstitution with wild-type p53, but not mutated p53 lacking DNA binding capacity, showed this effect. As a consequence of increased MHC class I expression, a significantly downregulated cytotoxic activity of natural killer (NK) cells against HCV core-transfected liver cells was observed, whereas lysis by HCV-specific cytotoxic T cells was not affected. These results demonstrate a way in which HCV avoids recognition by NK cells that may contribute to the establishment of a chronic infection.

Histamine and the response to IFN-alpha in chronic hepatitis C

Whole blood concentrations of histamine were examined in 20 patients with chronic hepatitis C after longterm treatment with interferon-alpha (IFN-alpha). In 13 of these patients, a transient (n = 5) or sustained (n = 8) normalization of liver enzymes and elimination of viral RNA were noted at the end of therapy. Seven patients did not respond to IFN-alpha. Nonresponding patients had significantly lower histamine levels in blood than transient (p = 0.0005) or sustained (p = 0.04) responders. Histamine levels were not different in patients with a sustained vs. a transient IFN response. Confounding factors, such as ongoing viral replication or liver cirrhosis, did not account for the differences in histamine levels. Our data suggest that hypohistaminism in peripheral blood may determine a poor response to IFN-alpha in chronic hepatitis C.

Effect of interferon therapy on bile duct inflammation in hepatitis C

Inflammation of the bile ducts was studied in liver biopsies from patients with chronic hepatitis C to determine whether the frequency of inflamed bile ducts changes with therapy and correlates with other histological variables and expression of class I and II MHC antigens on ductal epithelium. Twenty patients treated at UMMC between 1991 and 1994 underwent needle biopsies of the liver before and after therapy with interferon alpha 2B (IFN). A complete response to therapy was defined as a return to normal serum alanine aminotransferase levels occurring and persisting during therapy. The number of inflamed bile ducts/total ducts (%IBDs), presence of piecemeal necrosis and lymphoid aggregates, and grade of inflammation were assessed in each high-power field in all areas with bile ducts. The frequencies of these variables were compared in cirrhotics and non-cirrhotics and in patients with complete or incomplete responses to IFN. Frozen sections of biopsies from 5 patients were immunostained using antibodies to HLA-DR and B-2 microglobulin, and positive staining was noted on bile ducts. Before therapy, the %IBD was slightly greater in patients with cirrhosis. After IFN, both %IBD and serum alkaline phosphatase levels decreased in non-cirrhotics who responded to IFN. The change in frequency of IBD with IFN paralleled the changes in the other histological features. No correlation was noted between bile duct inflammation and expression of class I and II antigens. The conclusion is that inflammation of the bile ducts occurs frequently in chronic hepatitis C, correlates with other features of inflammation in the triads, and decreases in response to IFN therapy.

Monokine production by peripheral whole blood in chronic hepatitis C patients treated with interferon

Using our scoring system, we studied the production of monokines (interleukin-1 alpha, interleukin-1 beta, tumor necrosis factor-alpha, and interleukin-6) by lipopolysaccharide-stimulated peripheral whole blood in 34 patients with chronic hepatitis C during the interferon-alpha/beta therapy. It decreased in 25.7% (9/35 group A), fluctuated in 60.0% (21/35, group B), and increased in 14.3% (5/35, group C). The patients in group A were younger than those in group B (P < 0.05). The histological grade of injury was milder in group A than in group B or C. The rate of sustained response was 66.7% (6/9) in group A, 19.0% (4/21) in group B, and 40.0% (2/5) in group C(P = 0.0184, group A versus group B). In summary, monokine production by peripheral whole blood varied during interferon therapy for chronic hepatitis C patients. No significant change was noted in 60% of the patients. However, patients with decreased monokine production were younger, with a mild histological grade, and likely to respond to the interferon therapy.