Natural killer inhibitory receptor expression associated with treatment failure and interleukin-28B genotype in patients with chronic hepatitis C

Sofosbuvir (+) daclatasvir (+) ribavirin in Egyptian patients with hepatitis C virus: Therapeutic outcomes and the prognostic role of natural killer cells

BACKGROUND

One of the prominent causes of chronic liver disease worldwide is the hepatitis C virus (HCV). HCV believed that innate immunity contributes to a sustained virological response (SVR) to the treatment of Sofosbuvir (SOF) (+) Daclatasvir (DCV) (+) Ribavirin (RBV). This study aimed to evaluate the impact of SOF (+) DCV (+) RBV therapy and persistent HCV infection on the subset of natural killer cells (NK) in HCV genotype four patients from Egypt.

MATERIALS AND METHODS

One hundred and ten patients with persistent HCV infections requiring SOF (+) DCV (+) RBV therapy were grouped, and a flow cytometry (FCM) study of the NK cell subset in peripheral blood was performed. The assessment was performed before and after three and/or six months of the cessation of viral suppression therapy when a patient had a long-term viral response (SVR). One hundred and ten volunteers from the National Liver Institute's (NLI) blood bank were selected as controls.

RESULTS

Patients with chronic HCV infection before therapy had considerably lower CD16+ and CD3- CD56+ cells than controls. Their levels increase during SOF (+) DCV (+) RBV therapy. In patients with SVR during treatment, CD16+ and CD3- CD56+ cells increased significantly compared to those who did not get SVR. Furthermore, CD56+ cells were significantly higher in patients with persistent infection before treatment than controls but diminished with the response to treatment.

CONCLUSION

NK cell activation following SOF (+) DCV (+) RBV therapy and polarization to cytotoxicity occurred early in HCV antiviral therapy and was elevated in the respondents. Our data illustrated that establishing an inhibitory cytotoxic NK profile is related to therapeutic outcomes.

SNPs of the IFNL favour spontaneous clearance of HCV infection in children

BACKGROUND

Both spontaneous and treatment-induced clearance of hepatitis C virus (HCV) in adults have been associated with genetic polymorphisms in the interferon-λ genes. The aim of the present study was to confirm the association between the rs12979860 and evaluate the association between the rs368234815 and the rs4803217 single-nucleotide polymorphisms (SNPs) of the interferon-λ genes and the outcome of the infection in children.

METHODS

Alleles and genotypes frequencies of 32 children, who presented spontaneous clearance of the virus and 135 children, with viral persistence were compared with ethnically matched controls obtained from the 1000 Genomes Project and the International HapMap Project databases.

RESULTS

The frequencies of the C/C genotype of rs12979860, the TT/TT of the rs368234815 and the A/C of the rs4803217 were higher in the clearance group than in children with viral persistence (C/C versus T/T + C/T odds ratio (OR): 2.6; 90% confidence intervals (CI): 1.3-5; p = 0.01; TT/TT versus ΔG/TT + ΔG/ΔG OR: 2.8; 90% CI: 1.4-5.5; p = 0.01; and A/A versus A/C OR: 8.3; 90% CI: 1.5-45.9; p = 0.017, respectively) and with the ethnically matched controls.

CONCLUSIONS

The rs12979860, the rs368234815 and the rs4803217 SNPs are associated with spontaneous clearance of HCV in children.

IMPACT

Innate immune system response has a key role in the outcome of vertically acquired HCV infection in children. The rs12979860, the rs368234815 and the rs4803217 SNPs are associated with spontaneous clearance of HCV in children. Interferons-λ activate the Janus kinase-Stat pathway, which in turn induces several interferon-stimulated genes, leading to suppression of HCV replication both in vivo and in vitro.

Role of KIR Receptor in NK Regulation during Viral Infections

Natural Killer (NK) cells are key effectors of the innate immune system which represent the first line of defense against viral infections. NK cell activation depends on the engagement of a complex receptor repertoire expressed on their surface, consisting of both activating and inhibitory receptors. Among the known NK cell receptors, the family of killer Ig-like receptors (KIRs) consists in activating/inhibitory receptors that interact with specific human leukocyte antigen (HLA) molecules expressed on target cells. In particular, the expression of peculiar KIRs have been reported to be associated to viral infection susceptibility. Interestingly, a significant association between the development and onset of different human pathologies, such as tumors, neurodegeneration and infertility, and a clonal KIRs expression on NK cells has been described in presence of viral infections, supporting the crucial role of KIRs in defining the effect of viral infections in different tissues and organs. This review aims to report the state of art about the role of KIRs receptors in NK cell activation and viral infection control.

A juggernaut of innate & adaptive immune cells in chronic hepatitis C

Hepatitis C virus (HCV) is a small positive-sense, single-stranded RNA virus, the causal organism for chronic hepatitis. Chronic hepatitis leads to inflammation of liver, causing cirrhosis, fibrosis and steatosis, which may ultimately lead to liver cancer in a few cases. Innate and adaptive immune responses play an important role in the pathogenesis of HCV infection, thus acting as an important component in deciding the fate of the disease. Numerous studies have indicated that the derangement of these immune responses results in the persistence of infection leading to chronic state of the disease. Interactions between virus and host immune system generally result in the elimination of virus, but as the virus evolves with different evading mechanisms, it makes environment favourable for its survival and replication. It has been reported that HCV impairs the immune system by functional modulation of the cells of innate as well as adaptive immune responses, resulting in chronic state of the disease, influencing the response to antiviral therapy in these patients. These defects in the immune system lead to suboptimal immune responses and therefore, impaired effector functions. This review highlights the involvement or association of different immune cells such as natural killer cells, B cells, dendritic cells and T cells in HCV infection and how the virus plays a role in manipulating certain regulatory mechanisms to make these cells dysfunctional for its own persistence and survival.

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.

Hepatitis B e Antigen Induces NKG2A+ Natural Killer Cell Dysfunction via Regulatory T Cell-Derived Interleukin 10 in Chronic Hepatitis B Virus Infection

Although persistent hepatitis B virus (HBV) infection is associated with natural killer (NK) cell dysfunction, it remains obscure whether HBV viral antigens are responsible for NK cell dysfunction in patients with chronic hepatitis B (CHB) infection. In this study, we found that the percentage of NK cells expressing the inhibitory receptor, NKG2A, was increased in CHB patients, and NKG2A blockade restored NK cell function. Furthermore, in CHB patients, the frequency of NK cells expressing NKG2A positively correlated with the number of regulatory T cells (Tregs) and production of interleukin-10 (IL-10) in these Tregs. Moreover, exposure of peripheral blood mononuclear cells (PBMCs) isolated from healthy controls to sera from CHB patients resulted in increased proportion of NKG2A⁺ NK cells; IL-10 blockade reduced the frequency of NKG2A⁺ NK cells while increasing the percentage of IFN-γ⁺ NK cells. In addition, stimulation of NK cells and Tregs from healthy controls with CHB sera together with anti-IL-10 antibody increased IFN-γ production in the culture supernatant. The frequencies of NKG2A⁺ NK cells and IL-10⁺ Tregs, along with serum levels of alanine transferase and HBV DNA, were significantly increased in CHB patients positive for the Hepatitis B e antigen (HBeAg, a marker of viral replication) when compared to HBeAg-negative CHB patients. Importantly, exposure of PBMCs from healthy controls to HBeAg resulted in increased IL-10 production but reduced levels of TNF and IFN-γ, and IL-10 blockade rescued the generation of TNF and IFN-γ in this assay. The reduced production of TNF and IFN-γ was also observed in NK cells and Tregs from healthy controls that were stimulated with HBeAg, while IL-10 blockade increased the secretion of these two cytokines. We conclude that HBeAg induces IL-10 production in Tregs, thereby leading to increased expression of NKG2A on NK cells, which contributes to NK cell dysfunction during CHB infection. These data suggest that HBeAg is associated with NK cell dysfunction in CHB.

Genetic Polymorphisms within Interferon-λ Region and Interferon-λ3 in the Human Pathophysiology: Their Contribution to Outcome, Treatment, and Prevention of Infections with Hepatotropic Viruses

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Genetic polymorphisms within the interferon λ (IFN-λ) chromosomal region, mainly rs12979860 of IFN-λ4 gene (IFNL4), are known as associated with spontaneous hepatitis C virus (HCV) resolution and sustained viral response to therapy with pegylated interferon- α and ribavirin. Strong linkage disequilibrium of IFNL4 rs12979860 with IFNL4 rs368234815, which is casually associated with HCV spontaneous and therapeutical eradication, at least partially explains favorable HCV outcomes attributed to major homozygosity in rs12979860. Effects of IFN-based antiviral treatment are associated with pretreatment expression of the IFN-λ1 receptor, expression of hepatic IFN-stimulated genes, production of IFN- λ4, and preactivation of the JAK-STAT signaling. Nowadays direct-acting antivirals (DAAs) became a potent tool in the treatment of hepatitis C, but IFN-λs are still under investigation as potential antivirals and might be an option in HCV infection (DAA resistance, recurrent viremia, adverse effects).

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Patients with altered immunocompetence are especially prone to infections. In uremic subjects, polymorphisms within the IFN-λ chromosomal region associate with spontaneous HCV clearance, similarly like in the non-uremic population. Circulating IFN-λ3 shows a positive correlation with plasma titers of antibodies to surface antigen of hepatitis B virus (anti-HBs), which are crucial for protection against hepatitis B virus. More efficient anti-HBs production in the presence of higher IFN-λ3 levels might occur due to IFN-λ3-induced regulation of indoleamine 2,3-dioxygenase (IDO) expression. IFN-stimulated response element is a part of IDO gene promoter. It is worth further investigation whether IDO gene, circulating IDO, genetic polymorphisms within the IFN-λ region, and circulating IFN-λ3 act in concordance in immunological response to hepatotropic viruses.

The effects of direct-acting antiviral agents on the frequency of myeloid-derived suppressor cells and natural killer cells in patients with chronic hepatitis C

Currently, hepatitis C antiviral therapy is entering a new era with the use of direct-acting antiviral (DAA) agents. However, the precise immunological influences of DAA therapy in patients with chronic hepatitis C (CHC) are insufficiently understood. This study aimed to investigate the effects of DAA therapy on the frequency of myeloid-derived suppressor cells (MDSCs), T lymphocytes, and natural killer (NK) cells in patients with CHC. Thirty-two treatment-naive CHC patients were treated with DAA therapy, and the frequency of immune cells was analyzed by flow cytometry at various time points during and after therapy. Sixteen healthy donors were recruited for comparison. DAA therapy decreased the frequency of MDSCs and monocytic MDSCs in patients with CHC to a normal level. DAA therapy also increased the CD8⁺ T and NK cell levels in patients with CHC. In addition, activation (NKp30 and NKp46) and inhibitory (NKG2A) receptors on NK cells were downregulated to yield an NK cell phenotype resembling that observed in the healthy controls. This study provides insight into the normalization of immune cell levels under DAA therapy and indicates that restoration of the immune system in patients with CHC strongly supports long-term curative hepatitis C virus eradication.

Expression of Natural Killer Cell Inhibitory Receptors is Associated with Significant Liver Injury in Chronic Hepatitis C in Children

INTRODUCTION AND AIM

Natural Killer (NK) cells play an important role in innate immune response to viral infections and their high proportion is situated in the liver. The aim of this study was to analyze possible relation between the expression of NK cell receptors and varied intensity of liver lesions in chronic hepatitis C (CHC) in children.

MATERIAL AND METHODS

Study included 105 children with CHC - 54 boys and 51 girls, age 13.62 ± 3.48 years. Blood specimens were taken at the day of the liver biopsy. Histological evaluation was performed according to METAVIR scoring system. Circulating NK cells were evaluated by flow cytometry. The results were shown as a proportion of cells expressing evaluated receptor and its' mean fluorescent intensity (MFI).

RESULTS

In 58 children with CHC (55.2%) significant liver fibrosis was observed ( ≥F2). Higher proportion of cells expressing CD158e inhibitory receptors was observed in the group of children with ALT > 2UNL (21.11 ± 14.60 vs. 12.22 ± 8.99%; p = 0.037). While higher proportion of cells expressing inhibitory CD158b receptor was observed in children with significant fibrosis (F ≥ 2) compared to minimal fibrosis (F < 2) - (34.14 ± 12.44 vs. 27.48 ± 8.71%; p = 0.049). Children with advanced fibrosis (F ≥ 3) had higher MFI of NK cell CD 158b receptor than children with fibrosis scored F < 3 - (5344.20 ± 3407.49 vs. 2979.67 ± 1190.64; p = 0.049). Proportion of NK cells expressing CD158b was found a predictor of significant fibrosis in univariate analysis - [OR 1.065; 95%CI (1.07-1.15); p = 0.046].

CONCLUSIONS

Higher proportion of NK cells expressing inhibitory CD158b and CD158e receptors is associated with significant liver injury.

Concerted action of IFN-α and IFN-λ induces local NK cell immunity and halts cancer growth

Hepatocellular carcinoma (HCC) is the most prevalent type of liver cancer. No significant improvement has been reported with currently available systemic therapies. IFN-α has been tested in both clinic and animal models and only moderate benefits have been observed. In animal models, similar modest antitumor efficacy has also been reported for IFN-λ, a new type of IFN that acts through its own receptor complex. In the present study, the antitumor efficacy of the combination of IFN-α and IFN-λ was tested in the BNL mouse hepatoma model. This study was accomplished by using either engineered tumor cells (IFN-α/IFN-λ gene therapy) or by directly injecting tumor-bearing mice with IFN-α/IFN-λ. Both approaches demonstrated that IFN-α/IFN-λ combination therapy was more efficacious than IFN monotherapy based on either IFN-α or IFN-λ. In complement to tumor surgery, IFN-α/IFN-λ combination induced complete tumor remission. Highest antitumor efficacy has been obtained following local administration of IFN-α/IFN-λ combination at the tumor site that was associated with strong NK cells tumor infiltration. This supports the use of IFN-α/IFN-λ combination as a new cancer immunotherapy for stimulating antitumor response after cancer surgery.

Higher expression of inhibitory CD158b and CD158e NK cell receptor and age predicts treatment response in children with chronic hepatitis C

Treatment with pegylated interferon-α and ribavirin (PEG-IFN/RBV) is the only choice for chronic hepatitis C (CHC) in children. Natural killer (NK) cells were described to play a vital role in CHC. The aim of this study was to analyze the expression of peripheral blood NK cell receptors in their relation to PEG-IFN/RBV treatment response. Study included 26 children with CHC-13 boys, age range 13.42 ± 3.28 years. Blood for biochemical, virological and cytometric testing was taken for evaluation prior to the antiviral treatment. NK cell receptors were detected by flow cytometry and the results were presented as proportion of cells and mean fluorescence intensity (MFI). Therapy consisted of PEG-IFNα-2b (60 μg/m² s.c 1×/week) and RBV (15 mg/kg p.o. daily). Treatment duration was response-related and varied from 12 to 72 weeks. Rapid virological response (RVR) was evaluated in the 4th week and sustained virological response (SVR) 6 months after completion of the therapy. RVR children were younger (11.67 ± 3.74 vs 15.35 ± 2.42; p = 0.001) and displayed higher CD158b (3.58 ± 0.16 vs 3.45 ± 0.13; p = 0.038) and CD158e expression (4.33 ± 0.21 vs 4.03 ± 0.16; p = 0.039). Density of CD158b (logMFI = 3.68 ± 0.22 vs 3.36 ± 0.16; p = 0.036) and CD158e expression was significantly higher (4.37 ± 0.14 vs 4.12 ± 0.21; p = 0.046) and NKG2D expression significantly lower (97.50 ± 3.46 vs 94.92 ± 5.93; p = 0.049) in SVR children. SVR children were also significantly younger (12.40 ± 3.66 vs 15.13 ± 2.83; p = 0.003). Significance of the age of patients, and expression of CD158b and CD158e were confirmed in univariate and multivariate analysis. Age of patients is negatively related to RVR and SVR. NK cell phenotype with higher expression density of CD158b and CD158e receptor was a positive predictor of SVR.

Hepatitis C virus-induced NK cell activation causes metzincin-mediated CD16 cleavage and impaired antibody-dependent cytotoxicity

BACKGROUND & AIMS

The Fc receptor family for immunoglobulin (Ig)G type III (FcγRIII, CD16) is an activating receptor on natural killer (NK) cells and an essential mediator of antibody-dependent cellular cytotoxicity (ADCC). There is only limited information on its role during chronic hepatitis C virus (HCV) infection. We studied CD16 expression in relation to NK cell functional activity in HCV-infected patients and sought mechanistic insights into virus-induced modulation.

METHODS

NK cell CD16 expression and activation status were evaluated ex vivo by flow cytometry in HCV-infected patients and healthy controls (HC) as well as in vitro after co-culture with HCV-infected HuH7.5 cells. Rituximab-mediated ADCC was assessed in HC and HCV-infected patients using Daudi cells as a target. The role of metzincins in CD16 down-modulation was assessed using specific inhibitory molecules and by evaluating intracellular mRNA levels.

RESULTS

HCV-infected patients exhibited increased frequencies of ex vivo activated NK cells and a concomitantly decreased NK CD16 expression, which resulted in impaired ADCC activity. Moreover, exposure of NK cells to culture-derived HCV recapitulated the ex vivo findings of decreased CD16 expression and increased NK cell activation. Importantly, blockade of metzincin-mediated shedding activity, including selective a disintegrin and metalloproteinase 17 (ADAM-17) inhibition, restored NK CD16 expression. Successful treatment with direct-acting antivirals partially improved NK ADCC function despite delayed CD16 reconstitution.

CONCLUSION

Chronic HCV infection induces NK cell activation resulting in ADAM-17-dependent CD16 shedding and consequent impaired ADCC function. Altered ADCC may contribute to failure to eradicate HCV-infected hepatocytes.

LAY SUMMARY

We show here that hepatitis C virus (HCV) activates natural killer (NK) lymphocytes which, as a consequence, loose their Fc receptor for IgG (CD16), an essential molecule for antibody binding. We show that this occurs through the action of enzymes named metzincins, resulting in altered NK-mediated antibody-dependent killing (ADCC) of target cells. This mechanism may contribute to HCV persistence and may represent a general phenomenon whereby some viruses can escape host's immune responses.

Rapid decrease in hepatitis C viremia by direct acting antivirals improves the natural killer cell response to IFNα

OBJECTIVE

Chronic HCV infection is characterised by innate immune activation with increased interferon-stimulated genes (ISG) expression and by an altered phenotype of interferon-responsive natural killer (NK) cells. Here, we asked whether a rapid reduction in viremia by daclatasvir (DCV) and asunaprevir (ASV) improves the response to pegylated interferon (PegIFN) in patients who had previously failed a standard course of PegIFN/ribavirin (RBV) therapy.

DESIGN

Twenty-two HCV-infected non-responders to previous PegIFN/RBV therapy were studied for IFN-responsiveness of NK cells during quadruple (QUAD) therapy with DCV, ASV, PegIFN and RBV. A direct comparison of early NK cell responses in PegIFN/RBV therapy and QUAD therapy was performed for seven patients using paired cryopreserved peripheral blood mononuclear cells (PBMC) from both treatment courses. As a validation cohort, nine DCV/ASV-treated patients were studied for their NK cell response to in vitro stimulation with IFNα.

RESULTS

The 24 h virological response to QUAD therapy correlated with an increase in signal transducer and activator of transcription 1 (STAT1), phosphorylated STAT1 (pSTAT1) and tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) expression in NK cells, and the STAT1/pSTAT1/TRAIL induction was greater during QUAD therapy than during previous PegIFN/RBV therapy. Successful QUAD therapy as well as successful IFN-free DCV/ASV regimen resulted in an improved functional NK cell response (degranulation and TRAIL expression) to in vitro stimulation with IFNα.

CONCLUSIONS

IFN-responsiveness can be improved by inhibiting HCV replication and reducing the HCV-induced activation of the innate immune response. This may provide a rationale for clinical trials of a brief period of direct acting antiviral therapy followed by PegIFN/RBV therapy to reduce the overall treatment costs in low-income and middle-income countries.

TRIAL REGISTRATION NUMBERS

NCT01888900 and NCT00718172.

Frequency and role of NKp46 and NKG2A in hepatitis B virus infection

Background and Aim

Natural Killer (NK) cells are involved in the control of viral infection. However, the role of NK cells in chronic hepatitis B (CHB) remains unclear. This study investigated the frequencies and roles of NK cells in CHB, with a focus on activating receptor NKp46 and inhibitory receptor NKG2A.

Patients/Method

Peripheral blood lymphocytes were obtained from 71 CHB patients and 37 healthy subjects (HS). The expressions of NKp46 and NKG2A were analyzed using flow cytometry. The role of NKp46-ligand was assessed using an in vitro co-culture system. Cytotoxicity and IFN-γ production in NK cells were evaluated using RT-PCR and flow cytometry.

Results

CHB patients were classified into treatment-naïve patients with low HBV DNA titer (CHB-L; n = 28), high HBV DNA titer (CHB-H; n = 24) by the cut-off level of serum HBV DNA 4 log copies/ml, and patients receiving nucleos(t)ide analogue (CHB-NA; n = 19). The expressions of NKp46 and NKG2A were higher in CHB-H than in HS/CHB-L/CHB-NA. HepG2.2.15 had higher NKp46-ligand expression than HepG2. When NK cells from HS were co-cultured with HepG2.2.15, inhibition of the NKp46 and NKp46-ligand interaction by anti-NKp46 antibody significantly reduced cytolysis of HepG2.2.15 and IFN-γ production. However, those reductions were not observed in co-culture with HepG2. Additionally, NK cells that highly expressed NKp46 also highly expressed NKG2A (NKp46^highNKG2A^high subset). The frequencies of NKp46^highNKG2A^high subset in CHB-H were higher than those in HS/CHB-L/CHB-NA. Among treatment-naïve CHB patients, the frequencies of NKp46^highNKG2A^high subset were positively correlated with serum ALT (P<0.01, r = 0.45) and HBV DNA (P<0.01, r = 0.59) levels. The expressions of Fas-L, STAT1, TRAIL and CD107a were higher and IFN-γ expression was lower in the NKp46^highNKG2A^high subset than in the other subsets.

Conclusion

The NKp46 and NKp46-ligand interaction contributes to NK cell activation. A novel NK cell subset, the NKp46^highNKG2A^high subset, may be associated with liver injury and HBV replication.

Type III Interferons in Hepatitis C Virus Infection

The interferon (IFN)-λ family of type III cytokines includes the closely related interleukin (IL)-28A (IFN-λ2), IL-28B (IFN-λ3), and IL-29 (IFN-λ1). They signal through the Janus kinases (JAK)-signal transducers and activators of transcription pathway and promote an antiviral state by the induction of expression of several interferon-stimulated genes (ISGs). Contrary to type I IFNs, the effect of IFN-λ cytokines is largely limited to epithelial cells due to the restricted pattern of expression of their specific receptor. Several genome-wide association studies have established a strong correlation between polymorphism in the region of IL-28B gene (encoding for IFN-λ3) and both spontaneous and therapeutic IFN-mediated clearance of hepatitis C virus (HCV) infection, but the mechanism(s) underlying this enhanced viral clearance are not fully understood. IFN-λ3 directly inhibits HCV replication, and in vitro studies suggest that polymorphism in the IFN-λ3 and its recently identified overlapping IFN-λ4 govern the pattern of ISGs induced upon HCV infection of hepatocytes. IFN-λ can also be produced by dendritic cells, and apart from its antiviral action on hepatocytes, it can regulate the inflammatory response of monocytes/macrophages, thus acting at the interface between innate and adaptive immunity. Here, we review the current state of knowledge about the role of IFN-λ cytokines in mediating and regulating the immune response during acute and chronic HCV infections.

NKp30+ NK cells are associated with HBV control during pegylated-interferon-alpha-2b therapy of chronic hepatitis B

A pressing need exists for improved therapeutic options for chronic hepatitis B (CHB). Pegylated-interferon-alpha (Peg-IFN-α) achieves sustained off-treatment responses in many cases because of its direct anti-viral effects and regulation of the immune response. However, non-responsiveness to Peg-IFN-α is frequent, and the mechanism is poorly understood. In this study, we found that the frequency and absolute number of NKp30+ natural killer (NK) cells increased markedly, accompanied by enhanced CD107a and IFN-γ production, during Peg-IFN-α-2b monotherapy or combination therapy with adefovir dipivoxil in patients with CHB, especially in responders. The responders and non-responders differed in the frequency of polyfunctional IFN-γ+ CD107+ NK cells. In addition, the increase in NKp30+ NK cells was negatively correlated with the HBV viral load and plasma HBeAg. Moreover, it was found that IL-15 may contribute to the up-regulation of NKp30 on the NK cells, and this up-regulation was not induced in vitro by Peg-IFN-α-2b alone. However, in the non-responders, these NKp30+ NK cells were dysfunctional because of increased NKG2A expression, which partly explains the inactivation of NKp30+ NK cells and the reduced capacity of these cells to produce antiviral cytokines. These findings may provide a new mechanism to explain the variable efficacy of Peg-IFN-α-2b therapy.

Natural Killer Group 2A Expressed on Both Peripheral CD3-CD56+NK Cells and CD3+CD8+T Cells Plays a Pivotal Negative Regulatory Role in the Progression of Hepatitis B Virus-Related Acute-on-Chronic Liver Failure

To explore the role of surface receptors natural killer group 2A (NKG2A) and natural killer group 2D (NKG2D) on CD3⁺CD8⁺T cells and CD3^-CD56⁺NK cells in the progression of hepatitis B virus (HBV)-related acute-on-chronic liver failure (ACLF), we measured the expression of NKG2A and NKG2D on the surface of these 2 types of circulating cells by flow cytometry in 3 groups. One group consists of 36 patients with chronic hepatitis B (CHB), another one consists of 22 patients with HBV-related ACLF, and the last one has 12 normal controls (NC). The experimental result indicated that there was no significant difference in the proportion of CD3⁺CD8⁺T cells in total lymphocytes between the 3 groups. However, the percentage of CD3^-CD56⁺NK cells in ACLF group was evidently higher than that in the CHB group (P < 0.05). In addition, the expression of NKG2D on CD3⁺CD8⁺T cells in the ACLF group was significantly lower than that in the CHB group (P < 0.05), but there were no statistically significant differences in its percentages on CD3^-CD56⁺NK cells between the 3 groups. The expression of NKG2A on CD3⁺CD8⁺T cells in the ACLF group was significantly higher than that in the NC group (P < 0.05), and on NK cells was significantly higher than that in the CHB group (P < 0.05) and NC group (P < 0.01). The increase in ratios of NKG2A to NKG2D on CD3⁺CD8⁺T cells and CD3^-CD56⁺NK cells in the ACLF group was significantly more than that in the CHB group and NC group. The results indicate that the imbalance between NKG2A and NKG2D may contribute to the progression of HBV-related ACLF mediated by CD3^-CD56⁺NK cells and CD3⁺CD8⁺T cells. Compared with NKG2D, NKG2A expressed on both peripheral CD3^-CD56⁺NK cells and CD3⁺CD8⁺T cells plays a more pivotal negative regulatory role in the progression of HBV-related ACLF.

IFN-λ3 polymorphism indirectly influences NK cell phenotype and function during acute HCV infection

Introduction

Polymorphisms in the type III interferon IFN‐λ3 and the killer cell immunoglobulin‐like receptor (KIR) genes controlling the activity of natural killer (NK) cells can predict spontaneous resolution of acute hepatitis C virus (HCV) infection. We hypothesized that IFN‐λ3 polymorphism may modulate NK cell function during acute HCV.

Methods

We monitored the plasma levels of type III IFNs in relation to the phenotype and the function of NK cells in a cohort of people who inject drugs (PWID) during acute HCV infection with different outcomes.

Results

Early acute HCV was associated with high variability in type III IFNs plasma levels and the favorable IFN‐λ3 CC genotype was associated with higher viral loads. Reduced expression of Natural Killer Group Protein 2A (NKG2A) was associated with lower IFN‐λ3 plasma levels and the CC genotype. IFN‐γ production by NK cells was higher in individuals with the CC genotype during acute infection but this did not prevent viral persistence. IFN‐λ3 plasma levels did not correlate with function of NK cells and IFN‐λ3 prestimulation did not affect NK cell activation and function.

Conclusions

These results suggest that IFN‐λ3 polymorphism indirectly influences NK cell phenotype and function during acute HCV but other factors may act in concert to determine the outcome of the infection.

Impact of natural killer cells on chronic hepatitis C and hepatocellular carcinoma

Natural killer (NK) cells are involved in the pathogenesis of hepatitis C viral (HCV) infection and hepatocellular carcinoma (HCC). Recent immunological progresses have revealed the molecular mechanisms of activation or inhibition of NK cells. In patients infected with HCV, the percentages of NK cells are decreased and the NK receptor expression and function of NK cells including cytotoxicity and cytokine production are altered. These alterations in NK cells are associated with persistent infection with HCV, liver injury, liver fibrosis and liver carcinogenesis. In HCV treatment, NK cells play a role in the eradication of HCV in both interferon (IFN)-based therapy and IFN-free therapy using direct-acting antivirals (DAA). In HCC patients, the exhaustion of NK cells that represents lower cytotoxicity and impaired cytokine production may contribute to the progression of HCC. Several immunotherapies targeting NK cells have been reported. NK cell transfer and NK-activating gene therapy have been demonstrated to be effective in mouse liver cancer models and several clinical trials are ongoing. Recently, the role of major histocompatibility complex class I-related chain A (MICA), a human ligand of NKG2D, has attracted attention in the development of HCC. The expression of MICA could be controlled by anti-HCC drugs including sorafenib. A new chemo-immunotherapy may be expected in the treatment of HCC. In this review, we summarize the impact of NK cells on chronic hepatitis C and HCC.

Natural killer cells in hepatitis C: Current progress

Patients infected with the hepatitis C virus (HCV) are characterized by a high incidence of chronic infection, which results in chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. The functional impairment of HCV-specific T cells is associated with the evolution of an acute infection to chronic hepatitis. While T cells are the important effector cells in adaptive immunity, natural killer (NK) cells are the critical effector cells in innate immunity to virus infections. The findings of recent studies on NK cells in hepatitis C suggest that NK cell responses are indeed important in each phase of HCV infection. In the early phase, NK cells are involved in protective immunity to HCV. The immune evasion strategies used by HCV may target NK cells and might contribute to the progression to chronic hepatitis C. NK cells may control HCV replication and modulate hepatic fibrosis in the chronic phase. Further investigations are, however, needed, because a considerable number of studies observed functional impairment of NK cells in chronic HCV infection. Interestingly, the enhanced NK cell responses during interferon-α-based therapy of chronic hepatitis C indicate successful treatment. In spite of the advances in research on NK cells in hepatitis C, establishment of more physiological HCV infection model systems is needed to settle unsolved controversies over the role and functional status of NK cells in HCV infection.

Immunopathogenesis of Hepatitis C Virus Infection

Despite advances in therapy, hepatitis C virus infection remains a major global health issue with 3 to 4 million incident cases and 170 million prevalent chronic infections. Complex, partially understood, host-virus interactions determine whether an acute infection with hepatitis C resolves, as occurs in approximately 30% of cases, or generates a persistent hepatic infection, as occurs in the remainder. Once chronic infection is established, the velocity of hepatocyte injury and resultant fibrosis is significantly modulated by immunologic as well as environmental factors. Immunomodulation has been the backbone of antiviral therapy despite poor understanding of its mechanism of action.

Innate Immune Activity Correlates with CD4 T Cell-Associated HIV-1 DNA Decline during Latency-Reversing Treatment with Panobinostat

The pharmaceutical reactivation of dormant HIV-1 proviruses by histone deacetylase inhibitors (HDACi) represents a possible strategy to reduce the reservoir of HIV-1-infected cells in individuals treated with suppressive combination antiretroviral therapy (cART). However, the effects of such latency-reversing agents on the viral reservoir size are likely to be influenced by host immune responses. Here, we analyzed the immune factors associated with changes in proviral HIV-1 DNA levels during treatment with the potent HDACi panobinostat in a human clinical trial involving 15 cART-treated HIV-1-infected patients. We observed that the magnitude, breadth, and cytokine secretion profile of HIV-1-specific CD8 T cell responses were unrelated to changes in HIV-1 DNA levels in CD4 T cells during panobinostat treatment. In contrast, the proportions of CD3(-) CD56(+) total NK cells and CD16(+) CD56(dim) NK cells were inversely correlated with HIV-1 DNA levels throughout the study, and changes in HIV-1 DNA levels during panobinostat treatment were negatively associated with the corresponding changes in CD69(+) NK cells. Decreasing levels of HIV-1 DNA during latency-reversing treatment were also related to the proportions of plasmacytoid dendritic cells, to distinct expression patterns of interferon-stimulated genes, and to the expression of the IL28B CC genotype. Together, these data suggest that innate immune activity can critically modulate the effects of latency-reversing agents on the viral reservoir and may represent a target for future immunotherapeutic interventions in HIV-1 eradication studies.

IMPORTANCE

Currently available antiretroviral drugs are highly effective in suppressing HIV-1 replication, but the virus persists, despite treatment, in a latent form that does not actively express HIV-1 gene products. One approach to eliminate these cells, colloquially termed the "shock-and-kill" strategy, focuses on the use of latency-reversing agents that induce active viral gene expression in latently infected cells, followed by immune-mediated killing. Panobinostat, a histone deacetylase inhibitor, demonstrated potent activities in reversing HIV-1 latency in a recent pilot clinical trial and reduced HIV-1 DNA levels in a subset of patients. Interestingly, we found that innate immune factors, such as natural killer cells, plasmacytoid dendritic cells, and the expression patterns of interferon-stimulated genes, were most closely linked to a decline in the HIV-1 DNA level during treatment with panobinostat. These data suggest that innate immune activity may play an important role in reducing the residual reservoir of HIV-1-infected cells.

Altered effector functions of NK cells in chronic hepatitis C are associated with IFNL3 polymorphism

Interferon α-mediated effector functions of NK cells may contribute to the control of HCV replication and the pathogenesis of liver disease. The single-nucleotide polymorphism rs12979860 near IFNL3 (previously known as IL28B) is important in response to IFN-α treatment and in spontaneous resolution of acute hepatitis C. The role of the IFNL3 polymorphism in NK cell function is unclear. Thus, we investigated the role of IFNL3 polymorphism in type I IFN-dependent regulation of NK cell functions in patients with cHC and healthy control subjects. We demonstrated a marked polarization of NK cells toward cytotoxicity in response to IFN-α stimulation in patients with hepatitis C. That TRAIL up-regulation was present, particularly in patients with the IFNL3-TT allele, was supported by a shift in the pSTAT-1:pSTAT-4 ratios toward pSTAT-1. In patients bearing the IFNL3-TT allele, NK cell effector function correlated with liver disease activity. In contrast, higher cytokine production of NK cells was observed in healthy individuals with the IFNL3-CC genotype, which may support spontaneous HCV clearance in acute infection. Overall, these findings show that the role of NK cells may differ in chronic infection vs. early antiviral defense and that the IFNL3 genotype differentially influences NK cell function.

Investigation of Pathogenesis of H1N1 Influenza Virus and Swine Streptococcus suis Serotype 2 Co-Infection in Pigs by Microarray Analysis

Swine influenza virus and Streptococcus suis are two important contributors to the porcine respiratory disease complex, and both have significant economic impacts. Clinically, influenza virus and Streptococcus suis co-infections in pigs are very common, which often contribute to severe pneumonia and can increase the mortality. However, the co-infection pathogenesis in pigs is unclear. In the present study, co-infection experiments were performed using swine H1N1 influenza virus and Streptococcus suis serotype 2 (SS2). The H1N1-SS2 co-infected pigs exhibited more severe clinical symptoms, serious pathological changes, and robust apoptosis of lungs at 6 days post-infection compared with separate H1N1 and SS2 infections. A comprehensive gene expression profiling using a microarray approach was performed to investigate the global host responses of swine lungs against the swine H1N1 infection, SS2 infection, co-infection, and phosphate-buffered saline control. Results showed 457, 411, and 844 differentially expressed genes in the H1N1, SS2, and H1N1-SS2 groups, respectively, compared with the control. Noticeably, genes associated with the immune, inflammatory, and apoptosis responses were highly overexpressed in the co-infected group. Pathway analysis indicated that the cytokine–cytokine receptor interactions, MAPK, toll-like receptor, complement and coagulation cascades, antigen processing and presentation, and apoptosis pathway were significantly regulated in the co-infected group. However, the genes related to these were less regulated in the separate H1N1 and SS2 infection groups. This observation suggested that a certain level of synergy was induced by H1N1 and SS2 co-infection with significantly stronger inflammatory and apoptosis responses, which may lead to more serious respiratory disease syndrome and pulmonary pathological lesion.

Hepatitis C viral infection is associated with activated cytolytic natural killer cells expressing high levels of T cell immunoglobulin- and mucin-domain-containing molecule-3

T cell immunoglobulin- and mucin-domain-containing molecule-3 (Tim-3) is an inhibitory receptor implicated in T cell exhaustion characteristic of chronic viral infection. Limited data exist on NK cell Tim-3 expression and functional consequences. In chronic hepatitis C virus (HCV)-infected subjects, we found increased Tim-3 on NKs, which was associated with an activated phenotype. The high level of Tim-3 was not reversed by successful IFN-alpha-based antiviral therapy. Tim-3(high) NK cells up-regulated TRAIL in response to IFN-alpha to a greater extent and demonstrated greater lymphokine-activated killing activity, viral control, and degranulation but similar cytokine production than their Tim-3(low) counterparts. Our results suggest that Tim-3 on NKs is associated with activation of this innate lymphocyte population that is polarized towards cytotoxicity in chronic HCV. These findings reveal roles for Tim-3 in the regulation of NKs that might represent targets for treatment of chronic viral infections.

Natural Killer Cell Characteristics in Patients With Chronic Hepatitis B Virus (HBV) Infection Are Associated With HBV Surface Antigen Clearance After Combination Treatment With Pegylated Interferon Alfa-2a and Adefovir

BACKGROUND

The role of natural killer (NK) cells in the process of hepatitis B virus (HBV) surface antigen (HBsAg) clearance and whether their phenotype is related to treatment outcome in patients with chronic hepatitis B are currently unknown.

METHODS

Patients with chronic hepatitis B (HBV DNA load, >17 000 IU/mL) were treated with pegylated interferon alfa-2a and adefovir for 48 weeks. NK cell phenotype and function were analyzed in 7 responders (defined as individuals with HBsAg clearance by week 72; 3 HBV e antigen [HBeAg]-positive and 4 HBeAg-negative), 7 matched nonresponders, and 7 healthy controls. Subsequently, 34 baseline samples from HBeAg-positive patients with chronic hepatitis B were analyzed.

RESULTS

During treatment, the percentage and absolute number of CD56(bright) NK cells increased significantly, whereas the percentage and absolute number of CD56(dim) NK cells decreased. At baseline, responders had a significantly lower expression of chemokine receptor CX3CR1 on CD56(bright) NK cells and inhibitory receptor NKG2A on CD56(dim) NK cells, compared with nonresponders. In addition, responders had higher CD56(bright) TRAIL expression and interferon γ production at end of treatment. These baseline differences were not found in HBeAg-positive patients who had HBeAg seroconversion without HBsAg clearance.

CONCLUSIONS

Combination therapy significantly influences NK cell phenotype and function. Differences between patients with chronic hepatitis B with HBsAg clearance and nonresponders suggest that NK cells play a role in the clearance of HBsAg during interferon-based combination therapy.

Innate and adaptive immune responses in HCV infections

Hepatitis C virus has been identified a quarter of a decade ago as a leading cause of chronic viral hepatitis that can lead to cirrhosis and hepatocellular carcinoma. Only a minority of patients can clear the virus spontaneously during acute infection. Elimination of HCV during acute infection correlates with a rapid induction of innate, especially interferon (IFN) induced genes, and a delayed induction of adaptive immune responses. However, the majority of patients is unable to clear the virus and develops viral persistence in face of an ongoing innate and adaptive immune response. The virus has developed several strategies to escape these immune responses. For example, to escape innate immunity, the HCV NS3/4A protease can efficiently cleave and inactivate two important signalling molecules in the sensory pathways that react to HCV pathogen-associated molecular patterns (PAMPs) to induce IFNs, i.e., the mitochondrial anti-viral signalling protein (MAVS) and the Toll-IL-1 receptor-domain-containing adaptor-inducing IFN-β (TRIF). Despite these escape mechanisms, IFN-stimulated genes (ISGs) are induced in a large proportion of patients with chronic infection. Of note, chronically HCV infected patients with constitutive IFN-stimulated gene (ISG) expression have a poor response to treatment with pegylated IFN-α (PegIFN-α) and ribavirin. The mechanisms that protect HCV from IFN-mediated innate immune reactions are not entirely understood, but might involve blockade of ISG protein translation at the ribosome, localization of viral replication to cell compartments that are not accessible to anti-viral IFN-stimulated effector systems, or direct antagonism of effector systems by viral proteins. Escape from adaptive immune responses can be achieved by emergence of viral escape mutations that avoid recognition by antibodies and T cells. In addition, chronic infection is characterized by the presence of functionally and phenotypically altered NK and T cell responses that are unable to clear the virus but most likely contribute to the ongoing liver disease. In this review, we will summarize current knowledge about the role of innate and adaptive immune responses in determining the outcome of HCV infection.

Hepatitis C in African Americans

The care of hepatitis C virus (HCV) in African Americans represents an opportunity to address a major health disparity in medicine. In all facets of HCV infection, African Americans are inexplicably affected, including in the prevalence of the virus, which is higher among them compared with most of the racial and ethnic groups. Ironically, although fibrosis rates may be slow, hepatocellular carcinoma and mortality rates appear to be higher among African Americans. Sustained viral response (SVR) rates have historically significantly trailed behind Caucasians. The reasons for this gap in SVR are related to both viral and host factors. Moreover, low enrollment rates in clinical trials hamper the study of the efficacy of anti-viral therapy. Nevertheless, the gap in SVR between African Americans and Caucasians may be narrowing with the use of direct-acting agents. Gastroenterologists, hepatologists, primary care physicians, and other health-care providers need to address modifiable risk factors that affect the natural history, as well as treatment outcomes, for HCV among African Americans. Efforts need to be made to improve awareness among health-care providers to address the differences in screening and referral patterns for African Americans.

NK cells and virus-related cancers

Natural killer (NK) cells become activated during viral infections and can play roles in such infections by attacking virus-infected cells or by regulating adaptive immune responses. Experimental models suggest that NK cells may also have the capacity to restrain virus-induced cancers. Here, we discuss the seven viruses linked to human cancers and the evidence of NK cell involvement in these systems.

Natural killer cell function and dysfunction in hepatitis C virus infection

Viruses must continually adapt against dynamic innate and adaptive responses of the host immune system to establish chronic infection. Only a small minority (~20%) of those exposed to hepatitis C virus (HCV) spontaneously clear infection, leaving approximately 200 million people worldwide chronically infected with HCV. A number of recent research studies suggest that establishment and maintenance of chronic HCV infection involve natural killer (NK) cell dysfunction. This relationship is illustrated in vitro by disruption of typical NK cell responses including both cell-mediated cytotoxicity and cytokine production. Expression of a number of activating NK cell receptors in vivo is also affected in chronic HCV infection. Thus, direct in vivo and in vitro evidence of compromised NK function in chronic HCV infection in conjunction with significant epidemiological associations between the outcome of HCV infection and certain combinations of NK cell regulatory receptor and class I human histocompatibility linked antigen (HLA) genotypes indicate that NK cells are important in the immune response against HCV infection. In this review, we highlight evidence suggesting that selective impairment of NK cell activity is related to establishment of chronic HCV infection.

The association of IL28B genotype with the histological features of chronic hepatitis C is HCV genotype dependent

The interleukin 28B (IL28B) rs12979860 polymorphism is associated with treatment outcome in hepatitis C virus (HCV) genotype 1 and 4 patients. Its association with the histological features of chronic hepatitis C and disease severity needs further clarifications. To assess the correlation between IL28B genotype, HCV genotype and liver biopsy findings in untreated patients.

MATERIALS AND METHODS

Pre-treatment liver biopsies from 335 HCV Caucasian patients (59% males, age 50 years) enrolled in the MIST study were staged for fibrosis and inflammation according to the METAVIR and the Ishak scoring systems; steatosis was dichotomized as <5% or ≥5%. IL28B was typed by Taqman Single Nucleotide Polymorphism (SNP) genotyping assay. HCV genotype was 1 in 151 (45%), 2 in 99 (30%), 3 in 50 (15%) and 4 in 35 (10%) patients. IL28B genotype was CC in 117 (34%), CT in 166 (49%) and TT in 52 (15%). At univariate analysis, the IL28B CC genotype was associated with severe portal inflammation in HCV-1 patients (CC vs.

CT/TT

86% vs. 63%, p = 0.005), severe lobular inflammation in HCV-2 patients (CC vs.

CT/TT

44% vs. 23%, p = 0.03), and less fatty infiltration in HCV-1 patients (CC vs.

CT/TT

72% vs. 51%, p = 0.02). Despite the lack of any association between IL28B and fibrosis stage, in HCV-3 patients IL28B CC correlated with METAVIR F3-F4 (CC vs.

CT/TT

74% vs. 26%, p = 0.05). At multivariate analysis, the genotype CC remained associated with severe portal inflammation in HCV-1, only (Odds Ratio (OR): 95% Confidence Interval (CI): 3.24 (1.23-8.51)). IL28B genotype is associated with the histological features of chronic hepatitis C in a HCV genotype dependent manner, with CC genotype being independently associated with severe portal inflammation.

Alterations in NK cell phenotype in relation to liver steatosis in children with chronic hepatitis C

NK cells were found to play an important role in liver fibrosis, a process commonly seen in a chronic liver disease such as chronic hepatitis C (CHC). The aim of this study was to evaluate potential differences in relation to coexisting liver steatosis in children with chronic hepatitis C. The study group consisted of 31 children with chronic hepatitis, aged 7–18 years (mean = 15 ± 2 years). Blood samples were taken prior to liver biopsy. The METAVIR scale was used for histological evaluation. Peripheral lymphocytes were subjected to monoclonal antibodies to CD56 antigen, KIRs and NKG2D antigens. Cells were assayed by flow cytometry for the ratio of positive cells and mean fluorescence intensity (MFI). Results were evaluated regarding the presence of liver steatosis. Significantly higher mean AST activity as well as higher AST-to-platelets ratio index (APRI) was observed in a group of children with coexisting liver steatosis. These children had significantly higher MFI for CD158e and lower MFI for NKG2D. All CHC patients had significantly higher MFI for NKG2D than the controls. The proportion of cells with expression of CD158i, KIR2D and APRI was found independent predictors of liver steatosis in univariate analysis and body mass index in logistic regression. The expression of NK cell receptors is altered in coexisting steatosis that may influence long-term prognosis in CHC.

Individualization of chronic hepatitis C treatment according to the host characteristics

Hepatitis C virus (HCV) infection is a global health problem that affects more than 170 million people worldwide. It is a major cause of cirrhosis and hepatocellular carcinoma, making the virus the most common cause of liver failure and transplantation. The standard-of-care treatment for chronic hepatitis C (CHC) has been changed during the last decade and direct acting antiviral drugs have already been used. Besides, understanding of the pathogenesis of CHC has evolved rapidly during the last years and now several host factors are known to affect the natural history and response to treatment. Recent genome-wide association studies have shown the important role of interleukin-28B and inosine triphosphatase in HCV infection. The present review article attempts to summarize the current knowledge on the role of host factors towards individualization of HCV treatment.

TCRγδ(+)CD4(-)CD8(-) T cells suppress the CD8(+) T-cell response to hepatitis B virus peptides, and are associated with viral control in chronic hepatitis B

The immune mechanisms underlying failure to achieve hepatitis B e antigen (HBeAg) seroconversion associated with viral control in chronic hepatitis B (CHB) remain unclear. Here we investigated the role of CD4(-)CD8(-) T (double-negative T; DNT) cells including TCRαβ(+) DNT (αβ DNT) and TCRγδ(+) DNT (γδ DNT) cells. Frequencies of circulating DNT cell subsets were measured by flow cytometry in a retrospective cohort of 51 telbivudine-treated HBeAg-positive CHB patients, 25 immune tolerant carriers (IT), 33 inactive carriers (IC), and 37 healthy controls (HC). We found that γδ DNT cell frequencies did not significantly change during treatment, being lower at baseline (P = 0.019) in patients with HBeAg seroconversion after 52 weeks of antiviral therapy (n = 20) than in those without (n = 31), and higher in the total CHB and IT than IC and HC groups (P<0.001). αβ DNT cell frequencies were similar for all groups. In vitro, γδ DNT cells suppressed HBV core peptide-stimulated interferon-γ and tumor necrosis factor-α production in TCRαβ(+)CD8(+) T cells, which may require cell-cell contact, and could be partially reversed by anti-NKG2A. These findings suggest that γδ DNT cells limit CD8(+) T cell response to HBV, and may impede HBeAg seroconversion in CHB.

The natural killer cell response to HCV infection

In the last few years major progress has been made in better understanding the role of natural killer (NK) cells in hepatitis C virus (HCV) infection. This includes multiple pathways by which HCV impairs or limits NK cells activation. Based on current genetic and functional data, a picture is emerging where only a rapid and strong NK cell response early on during infection which results in strong T cell responses and possible subsequent clearance, whereas chronic HCV infection is associated with dysfunctional or biased NK cells phenotypes. The hallmark of this NK cell dysfunction is persistent activation promoting ongoing hepatitis and hepatocyte damage, while being unable to clear HCV due to impaired IFN-γ responses. Furthermore, some data suggests certain chronically activated subsets that are NKp46^high may be particularly active against hepatic stellate cells, a key player in hepatic fibrogenesis. Finally, the role of NK cells during HCV therapy, HCV recurrence after liver transplant and hepatocellular carcinoma are discussed.

Compromised function of natural killer cells in acute and chronic viral hepatitis

BACKGROUND

 Natural killer (NK) cells are an integral part of the innate immune system. They have been suggested to play an important role in both defense against viral hepatitis and the pathogenesis of other liver diseases.

METHODS

 NK cells from 134 individuals including patients with acute hepatitis B and C as well as chronic hepatitis B, C, and delta (D) patients were studied.

RESULTS

 Infection with viral hepatitis was associated with increased frequencies of NK cells in the peripheral blood; that NK cells showed a less activated phenotype and were compromised in cytolotytic function and cytokine production in all viral hepatitis infections: Hepatitis virus infections did not alter NK cell differentiation, and the activity and severity of liver disease were reflected by alterations of NK cell surface receptors as demonstrated by principal component analysis.

CONCLUSION

 NK cell phenotypic and functional alterations can equally be observed in HBV, HCV, and HDV infections. Instead, patterns of NK cell alterations differ in acute and chronic infections. Thus, our data suggest a common mechanism in the alteration of NK cell phenotype and function with unique variations that depend on disease activity rather than virus-specific factors.

Synergistic inhibition of natural killer cells by the nonsignaling molecule CD94

Peptide selectivity is a feature of inhibitory receptors for MHC class I expressed by natural killer (NK) cells. CD94-NKG2A operates in tandem with the polymorphic killer cell Ig-like receptors (KIR) and Ly49 systems to inhibit NK cells. However, the benefits of having two distinct inhibitory receptor-ligand systems are not clear. We show that noninhibitory peptides presented by HLA-E can augment the inhibition of NKG2A(+) NK cells mediated by MHC class I signal peptides through the engagement of CD94 without a signaling partner. Thus, CD94 is a peptide-selective NK cell receptor, and NK cells can be regulated by nonsignaling interactions. We also show that KIR(+) and NKG2A(+) NK cells respond with differing stoichiometries to MHC class I down-regulation. MHC-I-bound peptide functions as a molecular rheostat controlling NK cell function. Selected peptides which in isolation do not inhibit NK cells can have different effects on KIR and NKG2A receptors. Thus, these two inhibitory systems may complement each other by having distinct responses to bound peptide and surface levels of MHC class I.

Emerging concepts in immunity to hepatitis C virus infection

Since the discovery of hepatitis C virus (HCV) by molecular cloning almost a quarter of a century ago, unprecedented at the time because the virus had never been grown in cell culture or detected serologically, there have been impressive strides in many facets of our understanding of the natural history of the disease, the viral life cycle, the pathogenesis, and antiviral therapy. It is apparent that the virus has developed multiple strategies to evade immune surveillance and eradication. This Review covers what we currently understand of the temporal and spatial immunological changes within the human innate and adaptive host immune responses that ultimately determine the outcomes of HCV infection.

Pathogenesis of chronic viral hepatitis: differential roles of T cells and NK cells

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections account for 57% of cases of liver cirrhosis and 78% of cases of primary liver cancer worldwide and cause a million deaths per year. Although HBV and HCV differ in their genome structures, replication strategies and life cycles, they have common features, including their noncytopathic nature and their capacity to induce chronic liver disease, which is thought to be immune mediated. However, the rate of disease progression from chronic hepatitis to cirrhosis varies greatly among infected individuals, and the factors that regulate it are largely unknown. This review summarizes our current understanding of the roles of antigen-specific and nonspecific immune cells in the pathogenesis of chronic hepatitis B and C and discusses recent findings that identify natural killer cells as regulators of T cell function and liver inflammation.

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?

Interferon- α -Induced Changes to Natural Killer Cells Are Associated with the Treatment Outcomes in Patients with HCV Infections

Aim. We analyzed the pretreatment natural killer (NK) cell functions with the aim of predicting the sustained virological response (SVR) or the interleukin (IL) 28B polymorphism that is strongly associated with the treatment response. Methods. The peripheral NK cells from chronic hepatitis patients with HCV genotype 1 and high virus titers were activated using a Toll-like receptor (TLR) 4 ligand and IFN-α. The cell surface markers were evaluated using a flow cytometric analysis, and IFN-γ production was evaluated using an enzyme-linked immunosorbent assay (ELISA). The genotyping of the polymorphisms in the IL28B gene region (rs8099917) on chromosome 19 was performed on the DNA collected from each patient. Results. The production of IFN-γ was significantly higher in the SVR patients compared with the no-response (NR) patients, whereas the cell surface markers were similar between the SVR and the NR patients. There were no significant differences found in the IL28B genotype distribution associated with the production of IFN-γ. Conclusion. Differences in the NK cell functions were observed between the SVR patients and the NR patients, suggesting that NK cells play a potential role in the treatment response independent of the IL28B genotype.

Natural killer cell dynamic profile is associated with treatment outcome in patients with chronic HCV infection

BACKGROUND & AIMS

A substantial proportion of patients with chronic hepatitis C virus infection treated with pegylated interferon α/ribavirin fail to achieve sustained virological response (SVR). Since growing evidence suggests that innate immunity may influence treatment responses, we examined natural killer (NK) cell phenotypic and functional changes during standard antiviral therapy.

METHODS

Expression of several NK-cell regulatory molecules was evaluated by flow cytometry in 37 consecutive patients with chronic HCV infection at baseline and at different time points during and after discontinuation of treatment. Cytokine production was evaluated by intracellular staining. Cytolytic potential was assessed as degranulation and as antibody-dependent cytotoxicity.

RESULTS

Baseline frequencies of CD56(dim) NK cells and perforin content were significantly higher, whereas CD16 expression was lower in SVR vs. non-responder subjects. Analysis by linear regression for repeated measures during the first 12 weeks showed significantly increased frequencies of activated (CD69(+)) NK cells in rapid virological responders (RVR) and identified a typical NK cell profile associated with SVR, featuring higher NK perforin content, lower CD16 expression, and higher proportion of CD56(dim)/CD16(-) cells. Moreover, SVR patients displayed higher natural and antibody-dependent NK cell cytotoxicity. IL28B rs12979860 CC homozygosis was significantly associated with SVR, independently of NK-cell phenotype and function.

CONCLUSIONS

Different NK-cell phenotypic and functional features, in patients with chronic hepatitis C treated with standard therapy, were observed between non-responder vs. SVR patients, suggesting a potential role of NK cells in the response to treatment.

HLA-E variants are associated with sustained virological response in HIV/hepatitis C virus-coinfected patients on hepatitis C virus therapy

OBJECTIVES

To analyze whether human leukocyte antigen (HLA)-E allelic variants are associated with and may predict response to peg-interferon (IFN) alpha and ribavirin treatment in HIV/hepatitis C virus (HCV)-coinfected patients.

DESIGN

Retrospective follow-up study.

METHODS

We studied 321 naive patients who started HCV treatment. HLA-E genotyping was performed by restriction fragment length polymorphism. A sustained virological response (SVR) was defined as undetectable plasma HCV-RNA up through 24 weeks after the end of HCV treatment.

RESULTS

The HLA-E*0101 allele increased the odds of achieving SVR for all patients [adjusted odds ratio (aOR) = 2.03 (95% confidence interval, 95% CI = 1.35-3.06); P = 0.001], for HCV genotype (GT) 1/4 patients (aOR = 1.62 (95% CI = 1.03-2.54), P = 0.035), and for GT2/3 patients [aOR = 9.87 (95% CI = 2.47-31.89), P = 0.001]. For decision tree analysis, the SVR rate increased from 0 to 82.6% and then to 92.5% in GT2/3 patients when the count of HLA-E*0101 alleles increased. In GT1/4 patients with rs8099917 TT genotype, the SVR rate increased from 33.3 to 54.8% and then to 61.8% when the count of HLA-E*0101 alleles increased. In GT1/4 patients with rs8099917 GT/GG genotype, the SVR rate increased from 15.4 to 22% and then to 44% when the count of HLA-E*0101 alleles increased. The overall percentage of patients correctly classified was 73.2% and the area under the receiver operating characteristic curve (AUROC) was 0.803 ± 0.024.

CONCLUSION

The HLA-E*0101 allele was associated with increased odds of HCV clearance and could help to predict SVR among HIV/HCV-coinfected patients on HCV therapy. This would be helpful to avoid treatment in those less likely to respond to pegylated-interferon-alpha and ribavirin treatment.

Phenotypic characteristics of natural killer cells in acute hepatitis

Natural killer (NK) cells are the principal effector cell population in innate immune defense against many types of infections. These cells are enriched in the liver, where they comprise approximately 40% to 60% of the intrahepatic lymphocyte pool compared to the peripheral blood compartment. In chronic HBV and HCV infection, NK cells were reported to be partially dysfunctional due to impaired IFN-Γ secretion. Few studies have examined phenotypic features of NK cells in acute hepatitis. We identified NK (CD56+CD3-) cell populations in patients with acute hepatitis by examining the expressions of phenotypic NK cell markers (CD16, NKG2A, and NKG2D). Peripheral blood mononuclear cells were isolated from patients with acute hepatitis A (7) and patients with non-viral acute toxic hepatitis (6) during the symptomatic and convalescent phases. Expressions of NK (CD56+CD3-) cell markers, CD16, NKG2A, and NKG2D, were measured by flow cytometry. Symptomatic acute hepatitis including non-viral hepatitis and HAV infection showed significant increases of NKG2A expression compared to healthy controls. Interestingly, there was a direct correlation between the proportion of NK cell populations and liver function parameters (AST, ALT) in HAV infection. The strong correlation was also observed between the expression of NKG2A+NK cells and ALT, which suggests that most of NK cells in severe phase of disease express high level of NKG2A on their surface. In addition, decreased number of NK cells (CD56+CD3-) in symptomatic phase began to increase in the convalescent phase of acute hepatitis A. However, the expression of NKG2A tended to be reduced, which indicates that NKG2A, the inhibitory receptor on NK cells, can be a severity parameter in acute hepatitis.

Natural killer KIR3DS1 is closely associated with HCV viral clearance and sustained virological response in HIV/HCV patients

Aim

To evaluate the influence of the presence of the killer cell immunoglobulin-like receptor (KIR) 3DS1 on HCV treatment response in HIV/HCV genotype 1 co-infected patients

Methods

HIV/HCV co-infected patients were included. KIR3DS1, their specific HLA-B ligands and IL28B gene were genotyped. Reductions of plasma HCV RNA levels between baseline and week 1, week 2 and week 4 were analyzed for IL28B genotype and KIR3DS1 (HLA Bw4 or Bw6). Rapid and sustained virological response (RVR and SVR) rates were also analyzed.

Results

Sixty HIV/HCV genotype 1 co-infected patients were included. Patients with KIR3DS1 and Bw4 had higher rates of HCV viral decline than those who were not carriers of KIR3DS1 (week1: p = 0.01; week2: p = 0.038; week 4: p = 0.03). Patients carrying KIR3DS1/Bw4 had higher rates of RVR and SVR than those who did not carry KIR3DS1 (RVR: 46.15% versus 17.02%, p = 0.012; SVR: 63.6% versus 13 26.5%, p = 0.031). With respect to patients carrying the IL28B-CC genotype, those with KIR3DS1/Bw4 had greater rates of HCV viral clearance (week1: p<0.001; week2: p = 0.01; week 4: p = 0.02), RVR (p = 0.015) and SVR (p = 0.029) than those not carrying KIR3DS1.

Conclusion

Our results show that the KIR3DS1 genotype has a positive effect on HCV viral clearance during the first weeks of Peg-IFN/RBV treatment in HCV/HCV co-infected patients bearing genotype 1, and higher RVR and SVR rates.

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.

Natural killer cell functional dichotomy: a feature of chronic viral hepatitis?

Natural killer (NK) cells are involved in innate immune responses to viral infections either via direct cytotoxicity which destroys virus-infected cells or production of immunoregulatory cytokines which modulate adaptive immunity and directly inhibit virus replication. These functions are mediated by different NK subpopulations, with cytotoxicity being generally performed by CD56(dim) NK cells, whereas CD56(bright) NK cells are mainly involved in cytokine secretion. NK functional defects are usually combined so that impaired degranulation is often associated with deficient cytokine production. Innate immunity is thought to be relevant in the control of hepatitis virus infections such as hepatitis B virus (HBV) and hepatitis C virus (HCV), and recent findings reproducibly indicate that NK cells in chronic viral hepatitis are characterized by a functional dichotomy, featuring a conserved or enhanced cytotoxicity and a reduced production of interferon (IFN)-γ and tumor necrosis factor-α. In chronic HCV infection this appears to be caused by altered IFN-α signaling resulting from increased signal transducer and activator of transcription 1 (STAT1) phosphorylation, which polarizes NK cells toward cytotoxicity, and a concomitantly reduced IFN-α induced STAT4 phosphorylation yielding reduced IFN-γ mRNA levels. These previously unappreciated findings are compatible on the one hand with the inability to clear HCV and HBV from the liver and on the other they may contribute to understand why these patients are often resistant to IFN-α-based therapies.

Genomics and HCV infection: progression of fibrosis and treatment response

HCV infection is a global health problem that affects 170 million people worldwide. The severity of the disease varies from asymptomatic chronic infection to cirrhosis and hepatocellular carcinoma (HCC). Recently, the standard of care for genotype 1 patients has greatly improved with the addition of protease inhibitors (telaprevir or boceprevir) to pegylated interferon (PegIFN) and ribavirin (RBV). The prediction of fibrosis progression and the response to antiviral treatment are two major issues in the management of patients with chronic hepatitis C. Differential expression of mRNAs was first analyzed for both progression of fibrosis and treatment response. Specific polymorphisms, associated with either fibrosis or viral response, were identified thanks to major improvements in genome scanning technologies. Since 2009, several independent genome wide association studies (GWAS) have reported an association between genetic polymorphisms within the IL-28B promoter and both natural and treatment-induced clearance in genotype 1 infected patients. These different studies showed the strong association and the importance of IL-28B polymorphisms in the treatment response. Combining the different genetic factors could improve their predictive value and help identify patients at a high risk of progression of fibrosis as well as those with a lower chance of responding to treatment. The aim of this review was to discuss the genomic factors (mRNAs, miRNAs, and SNPs) and HCV infection with clinical implications for either progression of fibrosis or treatment response. Recent findings on the IL-28B polymorphism and its application in clinical practice will also be discussed.

Complete definition of immunological correlates of protection and clearance of hepatitis C virus infection: a relevant pending task for vaccine development

Hepatitis C virus (HCV) infects approximately 3% of global population. This pathogen is one of the main causes of chronic viral hepatitis, cirrhosis, and liver cancer, as well as the principal reason for liver transplant in Western countries. Therapy against HCV infection is effective in only half of treated patients. There is no vaccine available against HCV. Some vaccine candidates have reached the clinical trials but several factors, including the incomplete definition of immunological correlates of protection and treatment-related clearance have slowed down vaccine development. Precisely, the present review discusses the state of the art in the establishment of parameters related with immunity against HCV. Validity and limitations of the information accumulated from chimpanzees and other animal models, analysis of studies in humans infected with HCV, and relevance of aspects like type, strength, duration, and specificity of immune response related to successful outcome are evaluated in detail. Moreover, the immune responses induced in some clinical trials with vaccine candidates resemble the theoretical immunological correlates, raising questions about the validity of those correlates. When all facts are taken together, complete definition of immunological correlates for protection or treatment-related clearance is an urgent priority. A limited or wrong criterion with respect to this relevant matter might cause incorrect vaccine design and selection of immunization strategies or erroneous clinical evaluation.