Natural killer cells inhibit hepatitis C virus expression

Unraveling the non-fitness status of NK cells: Examining the NKp30 receptor and its isoforms distribution in HIV/HCV coinfected patients

BACKGROUND

HIV/HCV coinfection is associated with a rapid progression to liver damage. Specifically, NK cell population dysregulation is of particular interest, as these cells have been shown to block HCV replication effectively and have an anti-fibrogenic activity. The NKp30 receptor is linked to tumor cell lysis and has a crucial role during viral infections. In the present study, we determined the subpopulations of NK cells based on CD56 and CD16 expression, NKp30 receptor expression, its isoforms A, B, and C, along with the cytotoxicity molecules in patients with HIV/HCV.

RESULTS

evidenced by the APRI and FIB-4 indices, the HCV-infected patients presented greater liver damage than the HIV and HIV/HCV groups. The HCV group presented a decreased expression of NKp30 isoform A, and NK cell frequency was not different between groups; however, CD56brigth subpopulation, NKp30 receptor, and CD247 adaptor chain were decreased in HIV/HCV patients; further, we described increased levels of soluble IL-8, IL-10, IL-12, and IL-23 in the serum of HIV/HCV patients.

CONCLUSIONS

HCV and HIV/HCV patients have multiple parameters of non-fitness status in NK cells; awareness of these dysfunctional immunological parameters in HIV/HCV and HCV patients can elucidate possible novel therapeutics directed towards the improvement of NK cell fitness status, in order to improve their function against liver damage.

Biomarkers in Detection of Hepatitis C Virus Infection

The hepatitis C virus (HCV) infection affects 58 million people worldwide. In the United States, the incidence rate of acute hepatitis C has doubled since 2014; during 2021, this increased to 5% from 2020. Acute hepatitis C is defined by any symptom of acute viral hepatitis plus either jaundice or elevated serum alanine aminotransferase (ALT) activity with the detection of HCV RNA, the anti-HCV antibody, or hepatitis C virus antigen(s). However, most patients with acute infection are asymptomatic. In addition, ALT activity and HCV RNA levels can fluctuate, and a delayed detection of the anti-HCV antibody can occur among some immunocompromised persons with HCV infection. The detection of specific biomarkers can be of great value in the early detection of HCV infection at an asymptomatic stage. The high rate of HCV replication (which is approximately 1010 to 1012 virions per day) and the lack of proofreading by the viral RNA polymerase leads to enormous genetic diversity, creating a major challenge for the host immune response. This broad genetic diversity contributes to the likelihood of developing chronic infection, thus leading to the development of cirrhosis and liver cancer. Direct-acting antiviral (DAA) therapies for HCV infection are highly effective with a cure rate of up to 99%. At the same time, many patients with HCV infection are unaware of their infection status because of the mostly asymptomatic nature of hepatitis C, so they remain undiagnosed until the liver damage has advanced. Molecular mechanisms induced by HCV have been intensely investigated to find biomarkers for diagnosing the acute and chronic phases of the infection. However, there are no clinically verified biomarkers for patients with hepatitis C. In this review, we discuss the biomarkers that can differentiate acute from chronic hepatitis C, and we summarize the current state of the literature on the useful biomarkers that are detectable during acute and chronic HCV infection, liver fibrosis/cirrhosis, and hepatocellular carcinoma (HCC).

HLA-E*01:01 allele is associated with better response to anti-HCV therapy while homozygous status for HLA-E*01:03 allele increases the resistance to anti-HCV treatments in frequently transfused thalassemia patients

BACKGROUND

HLA-E binding to NKG2A/CD94 induces inhibitory signals that modulate NK cells cytotoxicity against infected targets. HCV-derived peptides stabilize HLA-E molecule that favours its higher expression. However, HLA-E stability and expression vary in different genotypes where the presence of HLA-E*01:03 allele is associated with higher HLA-E expression on targets that enhances NK cells inhibition and increases the chance of virus to escape from innate immune system. Here, we aimed to investigate whether HLA-E polymorphism affects HCV infection status or its treatment in major thalassemia patients who are more vulnerable to hepatitis C.

METHODS AND MATERIALS

Study included 89 cases of major thalassemia positive for HCV-antibody; of those 17 patients were negative for HCV-PCR (spontaneously cleared) and 72 patients were HCV-PCR positive (persistent hepatitis under different anti-viral treatment). 16 major thalassemia patients without hepatitis, negative for HCV-antibody were also considered as patients control group. Genomic DNAs extracted from whole bloods were genotyped for HLA-E locus using a sequence specific primer-PCR strategy.

RESULTS

In thalassemia patients, HLA-E*01:03 allele increased susceptibility to HCV infection [p = 0.02; 4.74(1.418-15.85)]. In addition, HLA-E*01:03/*01:03 genotype predicted more resistance to HCV treatment compared to other genotypes [p = 0.037; 3.5(1.1-11.4)]. In other words, we found that the presence of HLA-E*01:01 allele favors better response to anti-HCV therapy [p = 0.037; 3.5(1.1-11.4)].

CONCLUSION

From a mechanistic point of view, the associations between HLA-E polymorphisms and susceptibility to HCV infection or its therapeutic resistance in thalassemia patients may suggest potential roles for the innate and adaptive immune responses to this infection, which are manifested by the acts of HLA-E - NKG2A/CD94 axis in the modulation of NK cell inhibitory function as well as HLA-E associated CD8+ T cell cytolytic activity against HCV, respectively. Notably, from a clinical point of view, paying attention to these associations may not only be useful in increasing the effectiveness of current anti-HCV regimens comprising direct acting antivirals (DAAs) in more complicated patients, but may also suggest antiviral prophylaxis for patients more vulnerable to HCV infection.

Natural Killer Cell Line NK-92-Mediated Damage of Medically Important Fungi

Invasive fungal disease (IFD) in hematopoietic stem cell transplantation is associated with high morbidity and mortality. As the antifungal host response determines risk and outcome of IFD, there is growing interest in adoptive immunotherapy using T cells or natural killer (NK) cells. Although the NK-92 cell line has been tested as anticancer therapy in clinical trials, data on the antifungal activity of NK-92 cells are lacking. Here, we show that the NK-92 cell line exhibits considerable fungal damage on all medically important fungi tested, such as different species of Aspergillus, Candida, mucormycetes, and Fusarium. The extent of fungal damage differs across various species of mucormycetes and Fusarium, whereas it is comparable across different species of Aspergillus and Candida. Interferon (IFN)-γ levels in the supernatant were lower when NK-92 cells are co-incubated with Aspergillus fumigatus, Candida albicans, or Rhizopus arrhizus compared to the levels when NK-92 cells are incubated alone. Different to primary human NK cells, no increase of perforin levels in the supernatant was observed when the fungi were added to NK-92 cells. Our in vitro data demonstrated that the NK-92 cell line could be a feasible tool for antifungal immunotherapy, but data of animal models are warranted prior to clinical trials.

The immunogenetics of neurological disease

Genes encoding antigen-presenting molecules within the human major histocompatibility complex (MHC) account for the highest component of genetic risk for many neurological diseases, such as multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. Myriad genetic, immunological and environmental factors may contribute to an individual's susceptibility to neurological disease. Here, we review and discuss the decades long research on the influence of genetic variation at the MHC locus and the role of immunogenetic killer cell immunoglobulin-like receptor (KIR) loci in neurological diseases, including multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. The findings of immunogenetic association studies are consistent with a polygenic model of inheritance in the heterogeneous and multifactorial nature of complex traits in various neurological diseases. Future investigation is highly recommended to evaluate both coding and non-coding variation in immunogenetic loci using high-throughput high-resolution next-generation sequencing technologies in diverse ethnic groups to fully appreciate their role in neurological diseases.

Hepatitis C virus-induced natural killer cell proliferation involves monocyte-derived cells and the OX40/OX40L axis

BACKGROUND & AIMS

Natural killer (NK) cells are found at increased frequencies in patients with hepatitis C virus (HCV). NK cell activation has been shown to correlate with HCV clearance and to predict a favourable treatment response. The aim of our study was to dissect mechanisms leading to NK cell activation and proliferation in response to HCV.

METHODS

NK cell phenotype, proliferation, and function were assessed after the 6-day co-culture of human peripheral blood mononuclear cells with either HCV replicon-containing HuH6 hepatoblastoma cells or HCV-infected HuH7.5 cells. The results obtained were confirmed by immunohistochemistry of liver biopsies from patients with HCV and from HCV-negative controls.

RESULTS

In HCV-containing co-cultures, a higher frequency of NK cells upregulated the expression of the high-affinity IL-2 receptor chain CD25, proliferated more rapidly, and produced higher amounts of interferon γ compared with NK cells from control co-cultures. This NK cell activation was dependent on IL-2, cell-cell contact-mediated signals, and HCV replicon-exposed monocytes. The tumour necrosis factor-receptor superfamily member OX40 was induced on the activated CD25^± NK cell subset and this induction was abrogated by the depletion of CD14⁺ monocytes. Moreover, OX40L was upregulated on CD14^± monocyte-derived cells co-cultured with HCV-containing cells and also observed in liver biopsies from patients with HCV. Importantly, blocking of the OX40/OX40L interaction abolished both NK cell activation and proliferation.

CONCLUSIONS

Our results uncover a previously unappreciated cell-cell contact-mediated mechanism of NK cell activation and proliferation in response to HCV, mediated by monocyte-derived cells and the OX40/OX40L axis. These results reveal a novel mode of crosstalk between innate immune cells during viral infection.

LAY SUMMARY

Using a cell-culture model of hepatitis C virus (HCV) infection, our study revealed that natural killer (NK) cells become activated and proliferate when they are co-cultured with HCV-containing liver cells. The mechanism of this activation involves crosstalk with other innate immune cells and a cell-cell contact interaction mediated by the cell surface molecules OX40 and OX40L. Our study reveals a novel pathway leading to NK cell proliferation and activation against virus-infected cells that might be of relevance in antiviral immunity.

Spontaneous clearance of chronic hepatitis C is rare in HIV-infected patients after effective use of combination antiretroviral therapy

Objective

To evaluate the rate of spontaneous resolution of chronic hepatitis C (CHC) infection in a cohort of HIV-infected patients.

Methods

A retrospective analysis of 509 HIV-infected patients with chronic HCV infection was performed at two reference hospitals in Andalusia. The main variable of the study was spontaneous clearance of CHC, defined as a negative HCV RNA result after at least two previous quantitative measurements of HCV RNA separated by a minimum of 12 months.

Results

Of 509 patients, 3 (0.59%; 95% CI: 0.15%-1.6%) experienced spontaneous clearance of CHC. After combination antiretroviral therapy (cART) initiation, two of three cases experienced an increased CD4⁺ count, coinciding with HCV viral clearance. All patients were IL28B CC carriers, 2 were co-infected with HCV genotype 3 (the HCV genotype of the remaining patient was not available).

Conclusions

Spontaneous clearance of CHC is a rare event in the context of HIV/HCV co-infected patients and may be associated with the effective use of cART and thus HIV suppression.

Alterations of the NK cell pool in HIV/HCV co-infection

BACKGROUND

A relevant proportion of human immunodeficiency virus (HIV) infected patients is co-infected with the hepatitis C virus (HCV). HCV co-infection in HIV-positive patients is associated with faster progression of liver disease in comparison to HCV mono-infection. Natural killer (NK) cells critically modulate the natural course of HCV infection. Both HIV and HCV mono-infection are associated with alterations of the NK cell pool. However, little data is available concerning phenotype and function of NK cells in HIV/HCV co-infection.

METHODS

A total of 34 HIV/HCV co-infected, 35 HIV and 39 HCV mono-infected patients and 43 healthy control persons were enrolled into this study. All HIV-positive patients were under effective antiretroviral therapy. NK cell phenotype, IFN-γ production and degranulation were studied by flow cytometry.

RESULTS

NK cell frequency in HIV/HCV co-infection was significantly lower than in healthy individuals but did not differ from HIV and HCV mono-infection. HIV/HCV co-infection was associated with significantly decreased expression of the maturation/differentiation markers CD27/62L/127 on NK cells but increased expression of CD57 compared to healthy controls. Of note, expression also differed significantly from HCV mono-infection but was similar to HIV mono-infection, suggesting a pronounced impact of HIV on these alterations. Similar findings were made with regard to the NK cell receptors NKG2A/C and NKp30. More importantly, NK cells in co-infection displayed a highly impaired functional activity with significantly lower IFN-γ production and degranulation than in healthy donors as well as HIV and HCV mono-infection, suggesting a synergistic effect of both viruses.

CONCLUSIONS

Our data indicate that HIV/HCV co-infection is associated with significant alterations of the NK cell pool, which might be involved in the rapid progression of liver disease in co-infected patients and which mainly reflect alterations observed in HIV mono-infection.

Genetic diversity of the KIR/HLA system and susceptibility to hepatitis C virus-related diseases

Background

The variability in the association of host innate immune response to Hepatitis C virus (HCV) infection requires ruling out the possible role of host KIR and HLA genotypes in HCV-related disorders: therefore, we therefore explored the relationships between KIR/HLA genotypes and chronic HCV infection (CHC) as they relate to the risk of HCV-related hepatocarcinoma (HCC) or lymphoproliferative disease progression.

Methods and Findings

We analyzed data from 396 HCV-positive patients with CHC (n = 125), HCC (118), and lymphoproliferative diseases (153), and 501 HCV-negative patients. All were HIV and HBV negative. KIR-SSO was used to determine the KIR typing. KIR2DL5 and KIR2DS4 variants were performed using PCR and GeneScan analysis. HLA/class-I genotyping was performed using PCR-sequence-based typing. The interaction between the KIR gene and ligand HLA molecules was investigated. Differences in frequencies were estimated using Fisher’s exact test, and Cochran-Armitage trend test. The non-random association of KIR alleles was estimated using the linkage disequilibrium test. We found an association of KIR2DS2/KIR2DL2 genes, with the HCV-related lymphoproliferative disorders. Furthermore, individuals with a HLA-Bw6 KIR3DL1+ combination of genes showed higher risk of developing lymphoma than cryoglobulinemia. KIR2DS3 gene was found to be the principal gene associated with chronic HCV infection, while a reduction of HLA-Bw4 + KIR3DS1+ was associated with an increased risk of developing HCC.

Conclusions

Our data highlight a role of the innate-system in developing HCV-related disorders and specifically KIR2DS3 and KIR2D genes demonstrated an ability to direct HCV disease progression, and mainly towards lymphoproliferative disorders. Moreover the determination of KIR3D/HLA combination of genes direct the HCV progression towards a lymphoma rather than an hepatic disease. In this contest IFN-α therapy, a standard therapy for HCV-infection and lymphoproliferative diseases, known to be able to transiently enhance the cytotoxicity of NK-cells support the role of NK cells to counterstain HCV-related and lymphoproliferative diseases.

Extracellular HCV-core protein induces an immature regulatory phenotype in NK cells: implications for outcome of acute infection

Background

Hepatitis C viral (HCV) proteins, including core, demonstrate immuno-modulatory properties; however, the effect of extracellular core on natural killer (NK) cells has not previously been investigated.

Aims

To characterise NKs in acute HCV infection over time, and, to examine the effect of exogenous HCV-core protein on NK cell phenotype and function.

Methods

Acute HCV patients (n = 22), including 10 subjects who spontaneously recovered, were prospectively studied. Flow-cytometry was used to measure natural cytotoxicity and to phenotype NKs directly ex vivo and after culture with HCV-core protein. Microarray analysis was used to identify pathways involved in the NK cell response to exogenous HCV-core.

Results

Direct ex vivo analysis demonstrated an increased frequency of immature/regulatory CD56^bright NKs early in acute HCV infection per se which normalized with viral clearance. Natural cytotoxicity was reduced and did not recover after viral clearance. There was a statistically significant correlation between the frequency of CD56^bright NKs and circulating serum levels of HCV core protein. In vitro culture of purified CD56^bright NK cells with HCV-core protein in the presence of IL-15 maintained a significant proportion of NKs in the CD56^bright state. The in vitro effect of core closely correlates with NK characteristics measured directly ex vivo in acute HCV infection. Pathway analysis suggests that HCV-core protein attenuates NK interferon type I responses.

Conclusions

Our data suggest that HCV-core protein alters NK cell maturation and may influence the outcome of acute infection.

An effective interferon-gamma-mediated inhibition of hepatitis C virus replication by natural killer cells is associated with spontaneous clearance of acute hepatitis C in human immunodeficiency virus-positive patients

Hepatitis C virus (HCV) coinfection is an increasing health problem in human immunodeficiency virus-positive (HIV(+) ) individuals. However, a considerable proportion of HIV(+) patients manage to overcome acute hepatitis C (AHC) spontaneously. In the present study, we analyzed the role of natural killer (NK) cells in modulating the course of AHC in HIV(+) patients. Twenty-seven HIV(+) patients with AHC (self-limited course: n = 10; chronic course: n = 17), 12 HIV(+) patients with chronic hepatitis C (CHC), 8 HIV monoinfected individuals, and 12 healthy controls were studied. NK cells were phenotypically analyzed by flow cytometry. Interferon-gamma (IFN-γ) secretion, degranulation (CD107a), and anti-HCV (= inhibition of HCV replication) activity of NK subpopulations were analyzed using the HuH7A2 HCVreplicon cell system. NK cell frequency did not differ significantly between HIV(+) patients with chronic and self-limited course of AHC. However, we found NK cells from patients with self-limiting infection to be significantly more effective in inhibiting HCV replication in vitro than NK cells from patients developing CHC. Of note, antiviral NK cell activity showed no significant correlation with NK cell degranulation, but was positively correlated with IFN-γ secretion, and blocking experiments confirmed an important role for IFN-γ in NK cell-mediated inhibition of HCV replication. Accordingly, NK cells from patients that spontaneously cleared the virus displayed a stronger IFN-γ secretion than those developing chronic infection. Finally, we observed high expression of NKG2D and NKp46, respectively, to be associated with self-limiting course of aHCV. Accordingly, we found that blocking of these NK cell receptors significantly impaired antiviral NK cell activity.

CONCLUSION

Our data suggest a strong IFN-γ-mediated antiviral NK cell response to be associated with a self-limited course of AHC in HIV(+) patients.

Cyclosporine and tacrolimus have inhibitory effects on toll-like receptor signaling after liver transplantation

Toll-like receptors (TLRs) play a key role in transplantation biology. The effect of immunosuppression on TLR function after liver transplantation is unknown. Peripheral blood mononuclear cells (PBMCs) from 113 post-liver transplant patients and 13 healthy controls were stimulated with TLR-specific ligands [lipopolysaccharide (TLR4), pan-3-cys (P3C) (TLR2), Poly (I:C) (PIC) (TLR3), R848 (TLR7/8), and CpG (TLR9)] for 24 hours. PBMCs from 5 healthy controls were also cultured with therapeutic concentrations of cyclosporine A (CYA) and tacrolimus (TAC). Cytokine production was measured with enzyme-linked immunosorbent assays and flow cytometry. PBMCs from patients on calcineurin inhibitors after liver transplantation produced less interleukin-6 (IL-6) and tumor necrosis factor α (TNFα) in response to TLR2 stimulation (IL-6: P=0.02; TNFα: P=0.01), TLR4 stimulation (IL-6: P=0.02; TNFα: P=0.01), and TLR7/8 stimulation (IL-6: P=0.02; TNFα: P=0.02), compared with healthy controls. Both CD56(bright) and CD56(dim) natural killer (NK) cells from patients on calcineurin inhibitors also produced less interferon-γ (IFNγ) with TLR7/8 stimulation compared with healthy controls (CD56(bright) : P=0.002; CD56(dim) : P=0.004). Similar findings were demonstrated in healthy PBMCs cultured with CYA (PBMCs: TLR2, IL-6: P=0.005; TLR4, IL-6: P=0.03, TNFα: P=0.03; TLR7/8, IL-6: P=0.02, TNFα: P=0.01; CD56(dim) NK cells: TLR7/8, IFNγ: P=0.03). TAC impaired TLR4-mediated IL-6 and TNFα production by PBMCs (IL-6; P = 0.02; TNFα P = 0.009). In conclusion, patients on calcineurin inhibitors had impaired inflammatory cytokine production in response to TLR2, TLR4, and TLR7/8 stimulation compared comparison with healthy controls. Importantly, TAC and CYA appear to have different effects on TLR signaling. Impaired TLR function has important repercussions for risk of infection, graft rejection, and disease recurrence after transplantation, and the different immunosuppressive profiles of CYA and TAC may guide the choice of therapy to improve disease outcomes.

The role of natural killer cells in hepatitis C infection

HCV infection is an exponentially growing health burden worldwide, with an estimated 170 million people infected. Although therapies for HCV are continually improving, there remain a considerable proportion of patients who do not achieve viral eradication and develop liver disease. Natural killer (NK) cells are crucial for T-cell activation and are one of the first-line sentinel cell responders to viral infection. A recent explosion in studies exploring the role of NK cells in HCV infection has yielded important mechanistic information and intriguing potential therapeutic options for HCV infection. This review provides a general overview of normal NK cell function and outlines some of the important mechanisms characterizing the immune interplay between NK cells and HCV infection.

Toll-like receptor 3 and 7/8 function is impaired in hepatitis C rapid fibrosis progression post-liver transplantation

Recurrence of hepatitis C (HCV) postliver transplant is universal, with a subgroup developing rapid hepatic fibrosis. Toll-like receptors (TLRs) are critical to innate antiviral responses and HCV alters TLR function to evade immune clearance. Whether TLRs play a role in rapid HCV recurrence posttransplant is unknown. We stimulated peripheral blood mononuclear cells (PBMCs) from 70 patients with HCV postliver transplant with TLR subclass-specific ligands and measured cytokine production, TLR expression and NK cell function. Rate of fibrosis progression was calculated using posttransplant liver biopsies graded by Metavir scoring (F0-4; R=fibrosis stage/year posttransplant; rapid fibrosis defined as >0.4 units/year). Thirty of 70 (43%) patients had rapid fibrosis progression. PBMCs from HCV rapid-fibrosers produced less IFNα with TLR7/8 stimulation (p=0.039), less IL-6 at baseline (p=0.027) and with TLR3 stimulation (p=0.008) and had lower TLR3-mediated monocyte IL-6 production (p=0.028) compared with HCV slow fibrosers. TLR7/8-mediated NKCD56 dim cell secretion of IFNγ was impaired in HCV rapid fibrosis (p=0.006) independently of IFNα secretion and TLR7/8 expression, while cytotoxicity remained preserved. Impaired TLR3 and TLR7/8-mediated cytokine responses may contribute to aggressive HCV recurrence postliver transplantation through impaired immune control of HCV and subsequent activation of fibrogenesis.

Killer cell immunoglobulin-like receptor (KIR) gene content variation in the HGDP-CEPH populations

In the present study, we investigate patterns of variation in the KIR cluster in a large and well-characterized sample of worldwide human populations in the Human Genome Diversity Project—Centre d'Etude du Polymorphisme Humain (HGDP-CEPH) panel in order to better understand the patterns of diversity in the region. Comparison of KIR data with that from other genomic regions allows control for strictly demographic factors; over 500,000 additional genomic markers have been typed in this panel by other investigators and the data made publicly available. Presence/absence frequencies and haplotypic associations for the KIR region are analyzed in the 52 populations comprising the panel and in accordance with major world regions (Africa, Middle East, Central Asia, East Asia, Europe, Americas, and Oceania). These data represent the first overview of KIR population genetics in the well-documented HGDP-CEPH panel and suggest different evolutionary histories and recent selection in the KIR gene cluster.

Analytical methods for disease association studies with immunogenetic data

Disease association studies involving highly polymorphic immunogenetic data may involve analyses at one or many units of analysis, including amino acid, allele, genotype and haplotype levels, as well as consideration of gene-gene or gene-environment interactions. The selection of the appropriate statistical tests is critical and will be dependent on the nature of the dataset (e.g., case-control vs. family data) as well as the specific research hypotheses being tested. This paper describes the various study and analysis categories used for such analyses, including the advantages and limitations of such techniques.

Activation of natural killer cells by hepatitis C virus particles in vitro

Little is known about the ability of hepatitis C virus (HCV) to alter early innate immune responses in infected patients. Previous studies have shown that natural killer (NK) cells are functionally impaired after interaction of recombinant HCV glycoprotein E2 with the co-stimulatory CD81 molecule in vitro; however, the functional consequences of a prolonged contact of NK cells with HCV particles have remained unclear. We have examined the phenotypes of purified, interleukin-2-activated NK cells from healthy donors and HCV genotype 1b patients after culture for 5 days with HCV pseudoparticles (HCVpp) and serum samples containing HCV genotype 1b. NK cells from healthy donors and chronic HCV patients were found to up-regulate receptors associated with activation (NKp46, NKp44, NKp30, NKG2D), while NK receptors from the killer cell immunoglobulin-like receptor family (KIR/CD158), predominantly having an inhibitory function, were significantly down-modulated after culture in the presence of HCV particles compared with control cultures of NK cells. HCV-infected sera and HCVpp elicited significantly higher secretion of the NK effector lymphokines interferon-γ and tumour necrosis factor-α. Furthermore, HCV stimulated the cytotoxic potential of NK cells from normal donors and patients. The enhanced activation of NK cells after prolonged culture with HCVpp or HCV-containing sera for 5 days suggests that these innate effector cells may play an important role in viral control during early phases of HCV infection.

NK cells require type I IFN receptor for antiviral responses during genital HSV-2 infection

Type I interferon (IFN) signalling, NK cells and NK cell-derived IFN-γ are critical in the early control of genital HSV-2 infection. We have recently reported that NK cells are the source of early IFN-γ in the genital tract in response to HSV-2. However, the response of NK cells to genital HSV-2 infection is not well defined in the context of type I IFN signalling. Here we show that HSV-2 replication was significantly higher in mice deficient in the type I IFN receptor or NK cells compared to wild type controls. There was no detectable IFN-γ production in the genital washes from IFN-α/βR(-/-) mice or NK cell depleted mice in response to HSV-2 infection compared to control mice. Absence of the type I IFN receptor does not alter homing of NK cells to the genital mucosa. Moreover, the absence of IL-12 had no significant effect on NK cell-derived IFN-γ. Surprisingly, IFN-α/βR(-/-) mice had more IL-15 positive cells in the genital mucosa in response to HSV-2 infection compared to control mice. We then examined the expression of IL-15 receptors on NK cells. There was no significant differences in the levels of IL-15 receptor expression on NK cells from IFN-α/βR(-/-) or control mice. Our data clearly suggest that type I IFN receptor signalling is essential for NK cell activation in response to genital HSV-2 infection, and propose that NK cell activation by IL-15 may involve type I IFNs.

Experimental models to study the immunobiology of hepatitis C virus

Effective host immune responses are essential for the control of hepatitis C virus (HCV) infection and persistence of HCV has indeed been attributed to their failure. In recent years, several in vitro and in vivo experimental models have allowed studies of host immune responses against HCV. Numerous observations derived from these models have improved our understanding of the mechanisms responsible for the host's ability to clear the virus as well as of the mechanisms responsible for the host's failure to control HCV replication. Importantly, several findings obtained with these model systems have been confirmed in studies of acutely or chronically HCV-infected individuals. Collectively, several mechanisms are used by HCV to escape host immune responses, such as poor induction of the innate immune response and escaping/impairing adaptive immunity. In this review, we summarize current findings from experimental models available for studies of the immune response targeting HCV and discuss the relevance of these findings for the in vivo situation in HCV-infected humans.

Increased natural killer cell cytotoxicity and NKp30 expression protects against hepatitis C virus infection in high-risk individuals and inhibits replication in vitro

CD56(pos) natural killer (NK)/natural T (NT) cells are important innate effectors providing the first line of defense against viral infection. Enhanced NK activity has been shown to protect from human immunodeficiency virus-1 infection. However, the role played by these innate effectors in protection against or development of hepatitis C virus (HCV) infection is unknown. We characterized CD56(pos) populations in 11 injection drug users (IDUs) who remained uninfected despite being repeatedly exposed to HCV. NK profiles in exposed but uninfected (EU) individuals were compared with preinfection samples (median 90 days prior to HCV seroconversion) collected from 14 IDUs who were exposed and subsequently became infected (EI) and unexposed normal control subjects (n = 8). Flow cytometric analysis of CD56(pos) populations demonstrated that EUs had a higher proportion of CD56(low) mature (P = 0.0011) NK cells compared with EI subjects. Bead-isolated NKs ( > 90% purity) from EUs had significantly higher interleukin-2 (IL-2)-induced cytolytic activity against the NK-sensitive cell line K562 at an effector-to-target ratio of 10:1 (P < 0.0001). NKp30, a natural cytotoxicity receptor involved in NK activation, is highest on NK/NT cells in EUs relative to infected subjects. Using the JFH-1 infection system, we demonstrated that NKp30(high) cells in the absence of exogenous stimulation significantly reduce infection of hepatocytes.

CONCLUSION

CD56(pos) populations in EUs are enriched for effector NKs displaying enhanced IL-2-induced cytolytic activity and higher levels of the natural cytotoxicity receptor NKp30-activating receptor. In addition, NKp30(high) cells are more effective in preventing infection of Huh-7.5 cells than their NKp30(low/neg) counterparts. These data support the hypothesis that NK cells contribute to anti-HCV defense in vivo in the earliest stages of infection, providing innate protection from HCV acquisition.

Cyclosporin A inhibits hepatitis C virus replication and restores interferon-alpha expression in hepatocytes

Hepatitis C virus (HCV) infection is the leading indication for liver transplantation and a major cause of graft failure. This study investigated whether cyclosporin A (CsA), a widely used immunosuppressant for organ transplantation, inhibits full cycle HCV replication and restores type I interferon (IFN) signaling pathway in human hepatocytes. CsA treatment of hepatocytes before, during, and after HCV infection significantly inhibited full cycle viral replication, which is evidenced by decreased expression of HCV RNA, protein, and infectious viruses in human hepatocytes. The suppression of HCV replication by CsA was associated with elevated levels of endogenous IFN-α in infected hepatocytes. Although CsA had little effect on IFN-α signaling pathway in uninfected hepatocytes, CsA treatment of HCV-infected hepatocytes specifically upregulated the expression of IFN regulatory factor-1 and inhibited the expression of suppressor of cytokine signaling-1 and protein inhibitor of activated signal transducers and activators of transcription-x, the primary negative regulators of IFN signaling pathway. These findings provide additional evidence to support the development of CsA-based prevention/treatment of HCV infection for transplant recipients.

Chronic hepatitis C viral infection reduces NK cell frequency and suppresses cytokine secretion: Reversion by anti-viral treatment

Impaired activity of NK (natural killer) cells has been proposed as a mechanism contributing to viral persistence and chronic infection in hepatitis C (HCV) infection. We aimed to assess the impact of HCV infection on NK cells regarding frequency, subset distribution, and cytotoxic and cytokine secretion functions, as well as IFN-alpha and ribavirin therapeutic effects on NK cells. Significant reduction of total NK frequency and the CD56(dim)16(+) subset was observed in chronic HCV patients. IFN-gamma expression upon stimulation with K562 was severely suppressed but cytotoxicity measured by CD107a expression was maintained. These adverse effects were reversed after treatment with pegylated IFN-alpha and ribavirin; however, these skewed functions were not recovered in treatment-resistant patients. Thus, HCV chronic infection severely affects NK functions, except for cytotoxicity. Altered NK cell frequency and cytokine secretion by HCV infection may contribute to impaired cellular immune response and virus persistence.

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.

Liver natural killer and natural killer T cells: immunobiology and emerging roles in liver diseases

Hepatic lymphocytes are enriched in NK and NKT cells that play important roles in antiviral and antitumor defenses and in the pathogenesis of chronic liver disease. In this review, we discuss the differential distribution of NK and NKT cells in mouse, rat, and human livers, the ultrastructural similarities and differences between liver NK and NKT cells, and the regulation of liver NK and NKT cells in a variety of murine liver injury models. We also summarize recent findings about the role of NK and NKT cells in liver injury, fibrosis, and repair. In general, NK and NKT cells accelerate liver injury by producing proinflammatory cytokines and killing hepatocytes. NK cells inhibit liver fibrosis via killing early-activated and senescent-activated stellate cells and producing IFN-gamma. In regulating liver fibrosis, NKT cells appear to be less important than NK cells as a result of hepatic NKT cell tolerance. NK cells inhibit liver regeneration by producing IFN-gamma and killing hepatocytes; however, the role of NK cells on the proliferation of liver progenitor cells and the role of NKT cells in liver regeneration have been controversial. The emerging roles of NK/NKT cells in chronic human liver disease will also be discussed.Understanding the role of NK and NKT cells in the pathogenesis of chronic liver disease may help us design better therapies to treat patients with this disease.

Adoptive immunotherapy with liver allograft-derived lymphocytes induces anti-HCV activity after liver transplantation in humans and humanized mice

After liver transplantation in HCV-infected patients, the virus load inevitably exceeds pre-transplantation levels. This phenomenon reflects suppression of the host-effector immune responses that control HCV replication by the immunosuppressive drugs used to prevent rejection of the transplanted liver. Here, we describe an adoptive immunotherapy approach, using lymphocytes extracted from liver allograft perfusate (termed herein liver allograft-derived lymphocytes), which includes an abundance of NK/NKT cells that mounted an anti-HCV response in HCV-infected liver transplantation recipients, despite the immunosuppressive environment. This therapy involved intravenously injecting patients 3 days after liver transplantation with liver allograft-derived lymphocytes treated with IL-2 and the CD3-specific mAb OKT3. During the first month after liver transplantation, the HCV RNA titers in the sera of recipients who received immunotherapy were markedly lower than those in the sera of recipients who did not receive immunotherapy. We further explored these observations in human hepatocyte-chimeric mice, in which mouse hepatocytes were replaced by human hepatocytes. These mice unfailingly developed HCV infections after inoculation with HCV-infected human serum. However, injection of human liver-derived lymphocytes treated with IL-2/OKT3 completely prevented HCV infection. Furthermore, an in vitro study using genomic HCV replicon-containing hepatic cells revealed that IFN-gamma-secreting cells played a pivotal role in such anti-HCV responses. Thus, our study presents what we believe to be a novel paradigm for the inhibition of HCV replication in HCV-infected liver transplantation recipients.

Fine characterization of intrahepatic NK cells expressing natural killer receptors in chronic hepatitis B and C

BACKGROUND/AIMS

The fate of intrahepatic NK cell subsets in the course of HCV and HBV infections is not clearly understood.

METHODS

Blood and intrahepatic CD56(+) NK cell subsets (expressing NKG2A, CD158a,h or CD158b,j receptors) from HCV or HBV patients were quantified by flow cytometry and localized by immunohistochemistry in liver biopsies.

RESULTS

A significant reduction in NK cell frequency and a quantitative imbalance between CD56(bright) and CD56(dim) subsets were observed in chronic HCV patients as compared to HBV patients, underlining that the inflammatory environment is not the only cause of these phenomena. The proportions of intrahepatic NK cells expressing either NKG2A, and/or CD158a,h, CD158b,j differed significantly between HCV and HBV patients. A higher frequency of perforin among intrahepatic CD56(+)CD3(-) cells was observed in HCV compared to HBV patients. Double immunohistochemical staining showed that CD56(+)CD3(-) cells were localized within necrotic areas. Immune monitoring of circulating CD56 subsets revealed that CD3(-)CD56(bright)NKG2A(+) and CD3(-)CD56(dim)NKG2A(+) cells were positively correlated with the necroinflammatory score and inversely correlated with viral load, respectively, in HCV patients.

CONCLUSIONS

HCV and HBV affect NK cell subsets according to the status of the diseases, especially CD3(-)CD56(dim)NKG2A(+) and CD3(-)CD56(bright)NKG2A(+) cells, may be of interest for disease monitoring.

CD56+ T cells inhibit hepatitis C virus replication in human hepatocytes

CD56(+) T cells are abundant in liver and play an important role in defense against viral infections. However, the role of CD56(+) T cells in control of hepatitis C virus (HCV) infection remains to be determined. We investigated the noncytolytic anti-HCV activity of primary CD56(+) T cells in human hepatocytes. When HCV Japanese fulminant hepatitis-1 (JFH-1)-infected hepatocytes were co-cultured with CD56(+) T cells or incubated in media conditioned with CD56(+) T cell culture supernatants (SN), HCV infectivity and replication were significantly inhibited. The antibodies to interferon (IFN)-gamma or IFN-gamma receptor could largely block CD56(+) T cell-mediated anti-HCV activity. Investigation of mechanism(s) responsible for CD56(+) T cell-mediated noncytolytic anti-HCV activity showed that CD56(+) T SN activated the multiple elements of janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway and enhanced the expression of IFN regulatory factors (IRFs) 1, 3, 7, 8, and 9, resulting in the induction of endogenous IFN-alpha/beta expression in hepatocytes. Moreover, CD56(+) T SN treatment inhibited the expression of HCV-supportive micro RNA (miRNA)-122 and enhanced the levels of anti-HCV miRNA-196a in human hepatocytes.

CONCLUSION

These findings provide direct in vitro evidence at cellular and molecular levels that CD56(+) T cells may have an essential role in innate immune cell-mediated defense against HCV infection. (HEPATOLOGY 2009.).

A synergistic interferon-gamma production is induced by mouse hepatitis virus in interleukin-12 (IL-12)/IL-18-activated natural killer cells and modulated by carcinoembryonic antigen-related cell adhesion molecules (CEACAM) 1a receptor

The production of interferon-gamma (IFN-gamma) by infiltrating natural killer (NK) cells in liver is involved in the control of mouse hepatitis virus (MHV) infection. The objectives of this study were to identify the mechanisms used by MHV type 3 to modulate the production of IFN-gamma by NK cells during the acute hepatitis in susceptible C57BL/6 mice. Ex vivo and in vitro experiments revealed that NK cells, expressing carcinoembryonic antigen-related cell adhesion molecules (CEACAM) 1a (the MHV receptor), can produce a higher level of IFN-gamma in the presence of both L2-MHV3 and interleukin-12 (IL-12)/IL-18. The synergistic production of IFN-gamma by NK cells depends on viral replication rather than viral fixation only, because it is inhibited or not induced in cells infected with ultraviolet-inactivated viruses and in cells from Ceacam1a(-/-) mice infected with virulent viruses. The synergistic IFN-gamma production involves the p38 mitogen-activated protein kinase (MAPK) rather than the extracellular signal-regulated kinase-1/2 MAPK signalling pathway. However, the signal triggered through the engagement of CEACAM1a decreases the production of IFN-gamma, when these molecules are cross-linked using specific monoclonal antibodies. These results suggest that control of acute hepatitis by IFN-gamma-producing NK cells may depend on both production of IL-12 and IL-18 in the liver environment and viral infection of NK cells.

Natural killer cells suppress full cycle HCV infection of human hepatocytes

The role of natural killer (NK) cells in controlling hepatitis C virus (HCV) infection and replication has not been fully delineated. We examined NK cell-mediated noncytolytic effect on full cycle HCV infection of human hepatocytes. Human hepatocytes (Huh7.5.1 cells) co-cultured with NK cells or treated with supernatants (SN) from NK cells cultures had significantly lower levels of HCV RNA and protein than control cells. This NK cell-mediated anti-HCV activity could be largely abolished by antibody to interferon-gamma (IFN-gamma). The investigation of the mechanisms for NK cell-mediated anti-HCV activity showed that NK SN-treated hepatocytes expressed higher levels of IFN-alpha/beta than the control cells. NK SN also enhanced IFN regulatory factor-3 and 7 expression in the hepatocytes. In addition, NK SN enhanced the expression of signal transducer and activator of transcription 1 and 2, the nuclear factors that are essential for the activation of IFN-mediated antiviral pathways. These data provide direct evidence at cellular and molecular levels that NK cells have a key role in suppressing HCV infection of and replication in human hepatocytes.

NK and NKT cells in liver injury and fibrosis

The innate immune mechanisms of the liver represent an important first line of defense against bacterial products, toxins, and food antigens coming from the intestine. Natural Killer (NK) and Natural Killer T cells (NKT) are components of the innate immune system with increased presence in the liver compared to other organs and have been reported to participate in the inflammatory processes during hepatic diseases. However significant confusion has been noted in this field mainly due to changes in the characterization of these cells as new knowledge accumulates and due to differences in the approaches used for their study. Both cell types can mediate hepatic injury in several models but studies in human liver diseases have not managed to fully explain their functions. However accumulating evidence supports an antifibrotic role of NK cells mainly via an inhibitory effect on hepatic stellate cells by inducing apoptosis and via production of interferon-gamma. Therefore, downregulation of NK cells during most types of liver injury may facilitate liver fibrosis. Data about the role of NKT cells in liver fibrosis are limited. This review will summarize the studies about the role of NK and NKT cells in liver diseases with a special interest in hepatic injury and liver fibrosis.

A novel role for adiponectin in regulating the immune responses in chronic hepatitis C virus infection

Adipose tissue releases pro-inflammatory and anti-inflammatory mediators, including adiponectin, which elicit a broad range of metabolic and immunological effects. The study aim was to determine in subjects infected with chronic hepatitis C virus (HCV) the effects of total adiponectin and its high-molecular-weight (HMW) and low-molecular-weight isoforms on HCV-specific immune responses. Serum levels of total adiponectin and its isoforms were determined by immunoassay. The ex vivo effect of adiponectin on the HCV-specific T-cell response was examined by interferon gamma (IFN-gamma) enzyme-linked immunosorbent spot and enzyme-linked immunosorbent assay cytokine assays. The role of the mitogen-activated protein kinase (MAPK) signaling pathway in mediating the adiponectin effect on T cells was also evaluated. We found that serum levels of total and HMW adiponectin were significantly decreased in subjects with chronic HCV and increased body mass index (BMI) compared with HCV-infected lean subjects. The presence of an anti-HCV specific immune response was strongly associated with lower BMI (P = 0.004) and higher serum total (P = 0.01) and HMW (P = 0.02) adiponectin. In ex vivo assays, total adiponectin and the HMW adiponectin isoform enhanced HCV-specific IFN-gamma production (P = 0.02 and 0.03, respectively). Adiponectin-R1 receptors were expressed on T cells and monocytes. In depletion experiments, the IFN-gamma response to adiponectin was entirely dependent on the simultaneous presence of both CD4 and CD8 T cells, and to a lesser extent, natural killer cells. Selective inhibition of p38MAPK activity by SB203580 abrogated the IFN-gamma response to adiponectin, whereas extracellular signal-regulated kinase 1/2 inhibition by PD98059 did not affect the response.

CONCLUSION

In chronic HCV, a reciprocal association exists between BMI, adiponectin, and the anti-HCV immune responses, emphasizing the important role played by adiposity in regulating the immune response in HCV infection.

Centrifugal enhancement of hepatitis C virus infection of human hepatocytes

Hepatitis C virus (HCV) is a human pathogen associated with chronic liver disease. Recently, the cell culture systems supporting complete replication and production of HCV genotype 2a (JFH1) have been established. This study investigated the effect of low-speed centrifugation on HCV JFH1 infection of human hepatocytes (Huh7.5.1). Higher levels of HCV RNA expression were observed in Huh7.5.1 cells infected with centrifugal inoculation of HCV JFH1 than those in the control cells. This increased HCV RNA expression was associated with the elevated expression of HCV NS3 protein in the hepatocytes. The centrifugal enhancement of HCV infection was time and speed dependent. However, the enhancement was not observed when centrifugation was performed before or after HCV infection. In addition, there was no association between centrifugal enhancement and the expression of HCV entry receptors (CD81 and claudin-1) and intracellular IFN-alpha in the hepatocytes. These data indicate that centrifugal inoculation is a useful tool for increasing the efficiency of HCV infection and replication in the target cells in vitro.

Methamphetamine enhances Hepatitis C virus replication in human hepatocytes

Very little is known about the interactions between hepatitis C virus (HCV) and methamphetamine, which is a highly abused psychostimulant and a known risk factor for human immunodeficiency virus (HIV)/HCV infection. This study examined whether methamphetamine has the ability to inhibit innate immunity in the host cells, facilitating HCV replication in human hepatocytes. Methamphetamine inhibited intracellular interferon alpha expression in human hepatocytes, which was associated with the increase in HCV replication. In addition, methamphetamine also compromised the anti-HCV effect of recombinant interferon alpha. Further investigation of mechanism(s) responsible for the methamphetamine action revealed that methamphetamine was able to inhibit the expression of the signal transducer and activator of transcription 1, a key modulator in interferon-mediated immune and biological responses. Methamphetamine also down-regulated the expression of interferon regulatory factor-5, a crucial transcriptional factor that activates the interferon pathway. These in vitro findings that methamphetamine compromises interferon alpha-mediated innate immunity against HCV infection indicate that methamphetamine may have a cofactor role in the immunopathogenesis of HCV disease.

Interferon-Induced Effector Proteins and Hepatitis C Virus Replication

Hepatitis C virus (HCV) is a small, enveloped RNA virus that is often capable of establishing a persistent infection, which may lead to chronic liver disease, cirrhosis, hepatocellular carcinoma, and eventually death. For more than 20 years, hepatitis C patients have been treated with interferon-alpha (IFN-α). Current treatment usually consists of polyethylene glycol-conjugated IFN-α that is combined with ribavirin, but even the most advanced IFN-based therapies are still ineffective in eliminating the virus from a large proportion of individuals. Therefore, a better understanding of the IFN-induced innate immune response is urgently needed. By using selectable self-replicating RNAs (replicons) and, more recently, recombinant full-length genomes, many groups have tried to elucidate the mechanism(s) by which IFNs inhibit HCV replication. This chapter attempts to summarize the current state of knowledge in this interesting field of HCV research.

Activation of natural killer cells inhibits liver fibrosis: a novel strategy to treat liver fibrosis

Liver lymphocytes are enriched in natural killer (NK) cells, which are involved in innate immune defenses against viral infection and tumor transformation in the liver. Recent evidence indicates that NK cell activation by IFN-alpha, IFN-gamma or dsRNA attenuates liver fibrosis through the direct killing of activated hepatic stellate cells (HSCs). Interestingly, NK cells do not kill quiescent or fully activated HSCs, but only early-activated HSCs, as only these cells express elevated levels of the NK cell-activating ligand retinoic acid-induced early transcript (RAE)-1 and TNF-related apoptosis-inducing ligand receptors, in addition to downregulated levels of the NK-cell inhibitory ligand, MHC-I. Inhibition of liver fibrosis by NK cells can also be achieved through production of IFN-gamma, which induces HSC cell cycle arrest and apoptosis in a STAT1-dependent manner. Clinically, it has also been observed that NK cell activity is negatively correlated with liver fibrosis in patients with chronic hepatitis C infection. Therefore, since NK cells inhibit liver fibrosis, stimulating NK activity could potentially be a novel strategy to treat liver fibrosis. Clinical studies will be required to confirm whether stimulating NK cell activity is effective and safe in treating human liver fibrosis.

Cdc42-interacting protein-4 functionally links actin and microtubule networks at the cytolytic NK cell immunological synapse

An essential function of the immunological synapse (IS) is directed secretion. NK cells are especially adept at this activity, as they direct lytic granules to the synapse for secretion, which enables cytotoxicity and facilitates host defense. This initially requires rearrangement of the actin cytoskeleton and, subsequently, microtubule-dependent trafficking of the lytic granules. As these two steps are sequential, specific linkages between them are likely to serve as critical regulators of cytotoxicity. We studied Cdc42-interacting protein-4 (CIP4), which constitutively interacts with tubulin and microtubules but focuses to the microtubule organizing center (MTOC) after NK cell activation, when it is able to associate with Wiskott-Aldrich syndrome protein (WASp) and the actin filament-rich IS. WASp deficiency, overexpression of CIP4, or parts of CIP4 interfere with this union and block normal CIP4 localization, MTOC polarization to the IS, and cytotoxicity. Reduction of endogenous CIP4 expression using small interfering RNA similarly inhibits MTOC polarization and cytotoxic activity but does not impair actin filament accumulation at the IS, or Cdc42 activation. Thus, CIP4 is an important cytoskeletal adaptor that functions after filamentous actin accumulation and Cdc42 activation to enable MTOC polarization and NK cell cytotoxicity.

Immunopathogenesis of hepatitis C virus infection and hepatic fibrosis: New insights into antifibrotic therapy in chronic hepatitis C

Fibrosis and cirrhosis represent the consequences of a sustained wound-healing response to chronic liver injury of any cause. Chronic hepatitis C virus (HCV) has emerged as a leading cause of cirrhosis in the USA and throughout the world. HCV may induce fibrogenesis directly by hepatic stellate cell activation or indirectly by promoting oxidative stress and apoptosis of infected cells. The ultimate result of chronic HCV injury is the accumulation of extracellular matrix with high density type I collagen within the subendothelial space of Disse, culminating in cirrhosis with hepatocellular dysfunction. The treatment of hepatitis C with the combination of pegylated interferon and ribavirin is still both problematic and costly, has suboptimal efficacy, serious side effects and a high level of intolerance, and is contraindicated in many patients. Hence, new approaches have assumed greater importance, for which there is an urgent need. The sustained progress in understanding the pathophysiology of hepatic fibrosis in the past two decades has increased the possibility of developing drugs specifically targeting the fibrogenic process. Future efforts should identify genetic markers associated with fibrosis risk in order to tailor the treatment of HCV infection based on genetically regulated pathways of injury and/or fibrosis. Such advances will expand the arsenal to overcome liver fibrosis, particularly in patients with hepatic diseases who have limited treatment options, such as those patients with chronic hepatitis C who have a high risk of fibrosis progression and recurrent HCV disease after liver transplantation.

Phenotypic and functional changes of cytotoxic CD56pos natural T cells determine outcome of acute hepatitis C virus infection

Innate CD56(pos) natural killer (NK) and natural T (NT) cells comprise important hepatic antiviral effector lymphocytes whose activity is fine-tuned through surface NK receptors (NKRs). Dysregulation of NKRs in patients with long-standing hepatitis C virus (HCV) infection has been shown, but little is known regarding NKRs in acute infection. Treatment-naïve patients with acute HCV (n = 22), including 10 with spontaneous recovery, were prospectively studied. CD56(pos) NT levels were reduced early in acute HCV infection and did not fluctuate over time. In resolving HCV infection, NT cells with a more activated phenotype (lower CD158A and higher natural cytotoxicity receptor expression) at baseline predated spontaneous recovery. Moreover, NKG2A expression on CD56(+) NT cells correlated directly with circulating HCV RNA levels. Deficient interleukin-13 (IL-13) production by NT cells and reduced IL-2-activated killing (LAK) at baseline were associated with the ultimate development of persistence. These results indicate a previously unappreciated role for NT cells in acute HCV infection and identify a potential target for pharmacologic manipulation.

Natural killer cells play a key role in the antitumor immunity generated by chaperone-rich cell lysate vaccination

Tumor derived chaperone-rich cell lysate (CRCL) when isolated from tumor tissues is a potent vaccine that contains at least 4 of the highly immunogenic heat shock proteins (HSP) such as HSP70, HSP90, glucose related protein 94 and calreticulin. We have previously documented that CRCL provides both a source of tumor antigens and danger signals triggering dendritic cell (DC) activation. Immunization with tumor derived CRCL elicits tumor-specific T cell responses leading to tumor regression. In the current study, we further dissect the mechanisms by which CRCL simulates the immune system, and demonstrate that natural killer (NK) cells are required for effective antitumor effects to take place. Our results illustrate that CRCL directly stimulates proinflammatory cytokine and chemokine production by NK cells, which may lead to activation and recruitment of macrophages at the tumor site. Thus, this report provides further insight into the function of CRCL as an immunostimulant against cancer.

Cytokine-Activated Natural Killer Cells Exert Direct Killing of Hepatoma Cells Harboring Hepatitis C Virus Replicons

Hepatitis C virus (HCV)-specific impairments in host immunity have been described at multiple levels of the innate and adaptive response, which may lead to viral persistence in the majority of infections. Understanding of HCV-associated immune defects could lead to novel therapeutic advances. Natural killer (NK) cells, the major effector cells of the innate immune system, are functionally impaired in chronic HCV infection. It has been suggested that this phenotype is a result of virus-specific defects in antigen-presenting cells (APCs) that regulate NK cell activity, as normal NK function is restored when they are stimulated ex vivo. In this study, we used human NK cell cytotoxicity assays to evaluate the activation-induced effects of NK cells on the HCV replicon-containing hepatic cells. We found that cytokine-activated NK cells were capable of inducing an HCV-associated, perforin/granzyme-dependent lysis of human hepatoma cells and that this required direct cellular contact and was independent of MHC class I expression levels. In contrast, on removal of cytokine stimulation, NK cells failed to exert any direct cytolytic effect on replicon targets. These findings suggest an important underlying mechanism by which NK cells control HCV infection and, with appropriate understanding of HCV-associated immune defects, could lead to novel therapeutic advances.

Natural killer cells in viral infection: more than just killers

Innate immunity was believed originally to serve simply as the first-line defense against infection and malignancy, with adaptive immunity imposing specificity and ensuring that appropriate responses are mounted against chronic or reoccurring challenges. In this model of immunity, innate and adaptive immune responses are sequential, essentially non-overlapping, and interactions between components of each response limited or non-existent. Over the last 5 years, it has become increasingly evident that interactions between elements of the innate and adaptive immune systems are common. Indeed, it is now clear that the generation and maintenance of effective immunity require an extensive array of interactions between multiple components of the immune system. This review discusses recent advances in this area with particular emphasis on the role of natural killer cells in shaping the adaptive immune response to viral infection.

Natural killer cell inhibits human immunodeficiency virus replication in chronically infected immune cells

Natural killer (NK) cells are a crucial component of the host innate immune system. We investigated the noncytolytic anti-human immunodeficiency virus (HIV) activity of NK cells in chronically HIV-infected immune cells. Supernatants collected from NK cell cultures (both primary NK cells and NK cell lines, YTS and NK 92) inhibited HIV activation in peripheral blood mononuclear cells (PBMCs) from HIV-infected subjects. NK supernatants (NK SN) also suppressed tumor necrosis factor (TNF)-alpha-induced HIV activation in chronically infected cell lines (U1 and ACH-2 cells). The antibody to interferon (IFN)-gamma blocked NK SN-mediated anti-HIV effect, while the antibodies to CC-chemokines had no impact on NK SN-mediated HIV inhibition in U1 and ACH-2 cells. Investigation of mechanism(s) responsible for the NK action showed that NK SN inhibited TNF-alpha-mediated activation of HIV-long-terminal repeat (LTR), and upregulated the expression of signal transducer and activator of transcription (STAT)-1 and phosphorylated P38 mitogen-activated protein kinase (MAPK). The P38 MAPK inhibitor (SB 203580) blocked NK SN-mediated HIV inhibition. These data provide compelling evidence that NK cells have a critical role in controlling HIV activation in the reservoirs.

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.