NK cells in self‐limited HCV infection exhibit a more extensively differentiated,but not memory‐like,repertoire

Natural killer (NK) cells have long been thought of as a purely innate immune cell population, but increasing reports have described developmental and functional qualities of NK cells that are commonly associated with cells of the adaptive immune system. Of these features, the ability of NK cells to acquire functional qualities associated with immunological memory and continuous differentiation resulting in the formation of specific NK cell repertoires has recently been highlighted in viral infection settings. By making use of a unique cohort of monitored, at‐risk intravenous drug users in this study, we were able to dissect the phenotypic and functional parameters associated with NK cell differentiation and NK cell memory in patients 3 years after acute HCV infection and either the subsequent self‐clearance or progression to chronicity. We observed increased expression of cytolytic mediators and markers CD56^bright and NKp46⁺ of NK cells in patients with chronic, but not self‐limited HCV infection. Patients with a self‐limited infection expressed higher levels of differentiation‐associated markers CD57 and KIRs, and lower levels of NKG2A. A more extensively differentiated NK cell phenotype is associated with self‐clearance in HCV patients, while the NK cells of chronic patients exhibited more naïve and effector NK cell phenotypic and functional characteristics. The identification of these distinct NK cell repertoires may shed light on the role NK cells play in determining the outcome of acute HCV infections, and the underlying immunological defects that lead to chronicity.     

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

Aim: Previous studies have revealed that functional impairment of innate immune cells, including natural killer (NK) and natural killer T (NKT) cells, might be associated with the persistence of hepatitis C virus (HCV) infection. However, the involvement of innate immune cells, which predominate in the liver, in therapeutic HCV clearance is still unclear. Methods: To clarify the role of intrahepatic innate immune cells in the clinical outcome of patients with chronic hepatitis C (CHC) treated with interferon-alpha plus ribavirin (IFN/RBV), we prospectively investigated the status of NK and NKT cells in paired liver biopsy and peripheral blood (PB) samples obtained from 21 CHC patients before and immediately after IFN/RBV treatment by flow cytometry. Normal liver and PB samples were obtained from 10 healthy donors for living donor liver transplantation. Results: Before treatment, intrahepatic NK and NKT cells constituted a significantly lower proportion in CHC patients than in healthy individuals (P < 0.05). After IFN/RBV treatment, the proportions and absolute numbers of CD3(-)CD161(+) NK and CD3(+)CD56(+) NKT cells in the liver, but not in PB, were significantly increased in sustained responders (SR) as compared with poor responders (P < 0.05). The proportion of CD3(+)CD161(+) NKT cells was also increased in the liver of SR after the treatment. Moreover, there was a striking increase of activated CD152(+) cells among CD3(+)CD56(+) NKT cells in the liver of SR (P = 0.041). Conclusion: These findings demonstrate that sustained response to IFN/RBV treatment for patients with CHC is closely associated with increased dynamism of NK and NKT cells in the liver.     

Surface expression and cytolytic function of natural killer cell receptors is altered in chronic hepatitis C

INTRODUCTION: Impaired activity of natural killer (NK) cells has been proposed as a mechanism contributing to viral persistence in hepatitis C virus (HCV) infection. As the function of NK cells is primarily regulated by NK cell receptors (NKR), we analysed whether decreased NK cell function in hepatitis C may be related to dysregulated NKR expression. PATIENTS AND METHODS: Expression of NK cell was analysed by flow cytometry on lymphocytes from HCV(+) subjects (n = 30), patients who became HCV(-) after antiviral therapy (n = 10), healthy individuals (n = 10), and hepatitis B virus (HBV) infected patients (n = 9). Cytolytic function of lymphocytes was studied in a redirected lysis assay and in a standard 51chromium release cytotoxicity assay, respectively. RESULTS: In patients with chronic hepatitis C, we found a significantly reduced proportion of NKp46 and NKp30 expressing NK cells compared with healthy and HBV infected subjects. Low expression of natural cytotoxicity receptor (NCR) was also confirmed in in vitro activated NK cell populations derived from HCV patients compared with uninfected donors. In contrast, patients who cleared HCV under antiviral therapy showed normal expression of NKp44, NKp30, and NKp46. Reduced NCR expression in chronic hepatitis C was associated with a parallel decrease in NCR mediated target cell killing. Furthermore, we found a significantly increased proportion of NKG2A expressing NK cells and CD8+ T cells in HCV positive patients, resulting in a reduced cytolytic activity against cells incubated with the HLA-E stabilising peptide HCV core35-44. CONCLUSION: The present study indicates that defective expression of NKR represents a novel mechanism contributing to impaired function of NK cells and CD8+ T cells in chronic hepatitis C.     

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

Aim:  Previous studies have revealed that functional impairment of innate immune cells, including natural killer (NK) and natural killer T (NKT) cells, might be associated with the persistence of hepatitis C virus (HCV) infection. However, the involvement of innate immune cells, which predominate in the liver, in therapeutic HCV clearance is still unclear.
Methods:  To clarify the role of intrahepatic innate immune cells in the clinical outcome of patients with chronic hepatitis C (CHC) treated with interferon-α plus ribavirin (IFN/RBV), we prospectively investigated the status of NK and NKT cells in paired liver biopsy and peripheral blood (PB) samples obtained from 21 CHC patients before and immediately after IFN/RBV treatment by flow cytometry. Normal liver and PB samples were obtained from 10 healthy donors for living donor liver transplantation.
Results:  Before treatment, intrahepatic NK and NKT cells constituted a significantly lower proportion in CHC patients than in healthy individuals ( P  < 0.05). After IFN/RBV treatment, the proportions and absolute numbers of CD3^-CD161⁺ NK and CD3⁺CD56⁺ NKT cells in the liver, but not in PB, were significantly increased in sustained responders (SR) as compared with poor responders ( P  < 0.05). The proportion of CD3⁺CD161⁺ NKT cells was also increased in the liver of SR after the treatment. Moreover, there was a striking increase of activated CD152⁺ cells among CD3⁺CD56⁺ NKT cells in the liver of SR ( P  = 0.041).
Conclusion:  These findings demonstrate that sustained response to IFN/RBV treatment for patients with CHC is closely associated with increased dynamism of NK and NKT cells in the liver.     

Immunological changes in different patient populations with chronic hepatitis C virus infection

AIM: To investigate killer inhibitory and activating receptor expression by natural killer(NK), natural killer T-like(NKT-like) and CD8+ T lymphocytes in patients with chronic hepatitis C virus(HCV) infection with elevated and with persistently normal alanine aminotransferase(PNALT).METHODS: The percentage of peripheral blood Treg cells, KIR2DL3, ILT-2, KIR3DL1, CD160, NKG2 D, NKG2 C expressing NK, T and NKT-like cells, cytokine production and NK cytotoxicity were determined by flow cytometry. Twenty-one patients with chronic HCV infection with elevated alanine aminotransferase, 11 HCV carriers with persistently normal alanine aminotransferase and 15 healthy volunteers were enrolled. RESULTS: No significant differences were observed in the percentage of total T, NK or NKT-like cells between study groups. Comparing the activating and inhibitoryreceptor expression by NK cells obtained from HCV carriers with PNALT and chronic HCV hepatitis patients with elevated alanine aminotransferase, NKG2 D activating receptor expression was the only receptor showing a significant difference. NKG2 D expression of NK cells was significantly lower in patients with elevated alanine aminotransferase. The expression of CD160, NKG2 D and NKG2 C activating receptor by CD8+ T cells were significantly lower in patients with chronic HCV hepatitis than in healthy controls and in HCV carriers with PNALT. Plasma TGF-β1 levels inversely correlated with NKG2 D expression by NK cells. In vitro TGF-β1 treatment inhibited NK cells cytotoxic activity and downregulated NKG2 D expression. CD8+ T cells from HCV carriers with PNALT showed significantly elevated expression of CD160, NKG2 D and NKG2 C activating receptors compared to chronic HCV patients with elevated alanine aminotransferase. Enhanced expression of inhibitory KIR2DL3 receptor, and decreased ILT-2 expression on NK cells were also found in chronic hepatitis C patients compared to healthy controls.CONCLUSION: Our study demonstrated a complex dysregulation of activating and inhibitory receptor expression, such as decreased NKG2 D and CD160 activating receptor expression and increased KIR2DL3 inhibitory receptor expression by NK and cytotoxic T cells and may provide further mechanism contributing to defective cellular immune functions in chronic hepatitis C. Increased NKG2 D receptor expression in HCV patients with persistently normal ALT suggests an important pathway for sustaining NK and CD8 T cell function and a protective role against disease progression.     

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.     

Decrease in hepatic CD56(+) T cells and V alpha 24(+) natural killer T cells in chronic hepatitis C viral infection

BACKGROUND/AIMS: The intrahepatic immune system is likely to play a key role in determining the outcome of hepatitis C virus (HCV) infection. The hepatic lymphocyte repertoire is characterised by high CD8/CD4 T cell ratios and large numbers of gamma delta T cells, natural killer (NK) cells, NK T cells and NK receptor-positive T cells. It is not known which of these populations contribute to immunity against HCV or immune pathology. METHODS: To explore the relative contributions of lymphocyte subpopulations, we have compared the intrahepatic lymphocyte repertoires and cytokine expression in 13 patients with mild chronic hepatitis C infection, 14 with end-stage hepatitis C cirrhosis and five histologically normal livers by flow cytometry and immunohistochemistry. RESULTS: CD4(+) T cells bearing alpha beta T cell receptors (TCR) were significantly expanded in livers with chronic HCV infection while CD56(+) alpha beta T cells and V alpha 24 TCR-positive T cells were significantly depleted. Expanded CD4(+)T cells were predominantly Th1 cells, producing interferon-gamma but not interleukin-4. CONCLUSIONS: Failure to resolve HCV infection may be due to deficient innate and/or memory immune responses, while Th1 cells may mediate immune pathology.     

Scavenger receptor class B type I is a key host factor for hepatitis C virus infection required for an entry step closely linked to CD81

Hepatitis C virus (HCV) is a major cause of chronic hepatitis worldwide. Scavenger receptor class B type I (SR-BI) has been shown to bind HCV envelope glycoprotein E2, participate in entry of HCV pseudotype particles, and modulate HCV infection. However, the functional role of SR-BI for productive HCV infection remains unclear. In this study, we investigated the role of SR-BI as an entry factor for infection of human hepatoma cells using cell culture-derived HCV (HCVcc). Anti-SR-BI antibodies directed against epitopes of the human SR-BI extracellular loop specifically inhibited HCVcc infection in a dose-dependent manner. Down-regulation of SR-BI expression by SR-BI-specific short interfering RNAs (siRNAs) markedly reduced the susceptibility of human hepatoma cells to HCVcc infection. Kinetic studies demonstrated that SR-BI acts predominately after binding of HCV at an entry step occurring at a similar time point as CD81-HCV interaction. Although the addition of high-density lipoprotein (HDL) enhanced the efficiency of HCVcc infection, anti-SR-BI antibodies and SR-BI-specific siRNA efficiently inhibited HCV infection independent of lipoprotein. Conclusion: Our data suggest that SR-BI (i) represents a key host factor for HCV entry, (ii) is implicated in the same HCV entry pathway as CD81, and (iii) targets an entry step closely linked to HCV-CD81 interaction.     

Intrahepatic natural killer cell NKp46 expression drives HCV-associated liver inflammation and viral resistance to treatment with interferon alpha

BackgroundThere is evidence that natural killer (NK) cells help control persistent viral infections including hepatitis C virus (HCV). HCV infection is treated with interferon (IFN) alpha, which stimulates the immune system, and is successful in 40–80% of patients. Detailed comparison of the phenotype and function of blood and intrahepatic NK cells in chronic HCV infection and in response to treatment with IFN alpha has not been elucidated.MethodsWe performed a comparison of NK cells derived from blood and intrahepatic compartments in multiple paired samples from 24 HCV infected patients pretreatment and 22 patients with non-viral chronic liver disease (CLD). NK phenotype (CD16, NKp30, NKp46, NKG2D, and NKG2A) and functional profile (CD107a, IFNγ, and granzyme B) were assessed with flow cytometry. In a separate cohort of 17 patients with HCV, who had completed treatment, rate of viral clearance was calculated and pretreatment peripheral blood NK phenotype and CD107a expression (degranulation) in response to increasing stimulation was measured.FindingsNK cells in the liver demonstrate a distinct phenotype compared with blood, manifested as downregulation of the NK cell activation receptors CD16, NKG2D, and NKp30. By contrast, NKp46 expression was not downregulated. Intrahepatic NK cells appeared to be more activated with increased spontaneous degranulation (reduced granzyme B, p<0·001 and increased CD107a, p=0·006) and production of IFNγ (p=0·05). NKp46 expression correlated with NK-cell activation, and correlated closely with the severity of liver inflammation (p=0·035). The rate of viral clearance during treatment with IFN alpha inversely correlated with NKp46 expression at baseline (p=0·01). However, the ability to increase cytotoxic NK function in response to increasing stimulation ex vivo correlated with viral clearance (p=0·029) and inversely with NKp46 (p=0·005).InterpretationThese findings indicate that NKp46 marks out pathologically activated NK cells in HCV, which are unlikely to be involved in viral control in IFN alpha-treated individuals.FundingWelsh Assembly.     

Hepatitis C virus induces interferon-λ and interferon-stimulated genes in primary liver cultures

Hepatitis C virus (HCV) replication in primary liver cells is less robust than that in hepatoma cell lines, suggesting that innate antiviral mechanisms in primary cells may limit HCV replication or spread. Here we analyzed the expression of 47 genes associated with interferon (IFN) induction and signaling following HCV infection of primary human fetal liver cell (HFLC) cultures from 18 different donors. We report that cell culture-produced HCV (HCVcc) induced expression of Type III (λ) IFNs and of IFN-stimulated genes (ISGs). Little expression of Type I IFNs was detected. Levels of IFNλ and ISG induction varied among donors and, often, between adapted and nonadapted HCV chimeric constructs. Higher levels of viral replication were associated with greater induction of ISGs and of λ IFNs. Gene induction was dependent on HCV replication, as ultraviolet light-inactivated virus was not stimulatory and an antiviral drug, 2'-C-methyladenosine, reduced induction of λ IFNs and ISGs. The level of IFNλ protein induced was sufficient to inhibit HCVcc infection of na?ve cultures. Conclusion: Together, these results indicate that despite its reported abilities to blunt the induction of an IFN response, HCV infection is capable of inducing antiviral cytokines and pathways in primary liver cell cultures. Induction of ISGs and λ IFNs may limit the growth and spread of HCV in primary cell cultures and in the infected liver. HCV infection of HFLC may provide a useful model for the study of gene induction by HCV in vivo.     

Skewed B cells in chronic hepatitis C virus infection maintain their ability to respond to virus‐induced activation

Chronic hepatitis C virus (HCV) infection is characterized by persistent B‐cell activation, with enhanced differentiation and reduced proliferative ability. To assess the possible role of HCV in altering B‐cell subset distribution, we examined ex vivo frequencies and B‐cell inhibitory receptor expression in 37 chronic HCV‐infected patients and 25 healthy donors (HD). In addition, we determined whether short‐term exposure to culture‐derived HCV (HCVcc) resulted in B‐cell subset skewing and/or activation. There was a statistically significant increase in the frequencies of immature transitional, activated memory and tissue‐like memory (TLM) B cells in HCV‐infected patients compared with HD. We also found that the frequency of memory B cells correlated with serum HCV RNA levels. The proportion of B cells expressing the marker of exhaustion Fc receptor‐like 4 (FcRL4) was generally low even though significantly higher in the patients' memory B‐cell compartment compared with HD, and a positive correlation was found between the frequencies of the patients' TLM FcRL4+ B cells and serum alanine aminotransferase and histological activity index at liver biopsy. Exposure to cell‐free HCVcc in vitro did not result in B‐cell skewing but induced significant activation of naïve, TLM and resting memory B cells in HCV‐infected patients but not in HD, in whom cell‐associated virus was an absolute requirement for activation of memory B cells. These findings provide corroborative evidence in favour of significant B‐cell subset skewing in chronic HCV infection and in addition show that expression of exhaustion markers in selected B‐cell subsets does not impair virus‐induced B‐cell activation.     

Difference in cytotoxicity against hepatocellular carcinoma between liver and periphery natural killer cells in humans

In rodents, liver natural killer (NK) cells have been shown to mediate higher cytotoxic activity against tumor cells than do peripheral blood (PB) NK cells. However, such differences between liver and PB NK cells have not been extensively investigated in humans. The phenotypical and functional properties of NK cells extracted from liver perfusates at the time of living donor liver transplantation were investigated. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a critical molecule for NK cell-mediated anti-tumor cell killing, was not expressed by freshly isolated PB NK cells or by liver NK cells. Stimulation with interleukin (IL)-2, significantly up-regulated the expression of TRAIL on liver NK cells, but this effect was barely observed on PB NK cells. Donor liver NK cells showed the most vigorous cytotoxicity against HepG2, a hepatocellular carcinoma (HCC) cell line, after IL-2 stimulation (90.5% +/- 2.2% at E: T = 10:1), compared with donor and recipient PB NK cells and recipient liver NK cells (64.8% +/- 8.2%, 56.1% +/- 8.9%, and 34.6% +/- 7.5%, respectively). IL-2 stimulation resulted in an increased expression of killing inhibitory receptors on liver NK cells in parallel with TRAIL expression. Consistently, the cytotoxicities of IL-2-stimulated donor liver NK cells against self and recipient lymphoblasts were negligible. In conclusion, adoptive transfer of IL-2-stimulated NK cells extracted from donor liver graft perfusate could mount an anti-tumor response without causing toxicity against 1-haplotype identical recipient intact tissues. These findings present a concept to prevent recurrence of HCC after liver transplantation.     

Innate immune genes synergize to predict increased risk of chronic disease in hepatitis C virus infection

Hepatitis C is a common infection with significant morbidity and mortality, and only a minority of patients successfully clear the infection. Identification of factors that influence disease progression in HCV infection is difficult owing to the lack of well-defined patient cohorts. However, recent evidence supports a role for the innate immune system in virus clearance. In this study, we investigated innate immune genes for their contribution to disease progression in a unique cohort of well-controlled HCV-infected patients. The Irish cohort of HCV patients is uniquely homogenous; patients were infected with a single genotype of HCV from contaminated anti-D Ig. We genotyped 543 infected patients, including 247 patients who spontaneously resolved infection, for natural killer (NK) cell-associated killer cell Ig-like receptors (KIR) genes and the recently reported IL28B (IFNλ3) SNP. The NK cell gene KIR2DS3 was significantly increased in patients with chronic infection [odds ratio (OR) 1.90, 95% confidence interval (CI) 1.25-2.90, P < 0.002]. The IL28B "T" allele was also significantly increased in chronically infected patients (OR 7.38, 95% CI 4.93-11.07, P < 10(-8)). The presence of both markers synergized to significantly increase the risk of chronic infection over either factor alone (OR 20.11, 95% CI 9.05-44.68, P < 10(-7)). In functional experiments, we found that IL28A significantly inhibited IFN-γ production by NK cells. Thus, we demonstrate a functional link between NK cells and type 3 IFN. Our findings may contribute to the development of a prognostic test for HCV and identify therapeutic strategies for the clinical management of HCV-infected patients.     

High frequencies of CD158b+ NK cells are associated with persistent hepatitis C virus infections

Background. During the early phases of a hepatitis C virus (HCV) infection, NK cell activation appears to be critical to the induction of adaptive immune responses that have the potential of clearing the infection. This study aimed to investigate the phenotype and function of NK cells in chronic HCV (CHC) patients, particularly patients who cleared HCV infections spontaneously (SR-HCV).Material and methods. Peripheral blood NK cells were compared between 36 CHC patients, 12 SR-HCV patients, and 14 healthy controls (HC). The phenotype and function of NK cells were characterized by flow cytometry. In addition, the potential associations between the frequency of NK cell subsets and ALT, AST and HCV viral loads were also analyzed.Results. Our data revealed that the population of CD3-CD56⁺ NK cells was significantly decreased in CHC and SR-HCV patients compared to levels in HC (P = 0.031, P = 0.014). Interestingly, we found that the levels of the CD158b inhibitory receptor were higher in CHC patients compared to levels observed in HC and SR-HCV subjects (P = 0.018, P = 0.036). In addition, the percentages of the activation receptors NKp30 and NKp46 were significantly decreased in CHC and SR-HCV patients compared to their expression levels in HC (P < 0.05). Moreover, the frequencies of inducible CD107a (but not IFN-γ-secreting) NK cells from both CHC and SR-HCV patients were significantly lower than frequencies observed in controls (P = 0.018, P = 0.027).Conclusion. Our data indicated that the higher frequency of inhibitory NK cells combined with fewer activated NK cells may be associated with HCV-related chronic inflammation involved in CHC pathogenesis.     

Decrease in CD3-negative-CD8dim(+) and Vdelta2/Vgamma9 TcR+ peripheral blood lymphocyte counts,low perforin expression and the impairment of natural killer cell activity is associated with chronic hepatitis C virus infection

BACKGROUND/AIMS: As chronic hepatitis C virus (HCV) infection is associated with impaired natural killer (NK) cell cytotoxicity, we examined the phenotypes and perforin expression of peripheral blood lymphocytes, as well as the effect of interferon-alpha2b (IFN-alpha2b) therapy. METHODS: Thirty-three patients had chronic hepatitis C, and of them 12 had been on IFN-alpha2b treatment. Eleven individuals had been treated earlier with IFN-alpha2b and completely cured, and eight were HCV carriers with persistently normal serum alanine aminotransferase. Three-colour flow cytometry was used to measure the percentage of CD3(+/-)CD8+, CD3+CD4+, gammadeltaTcR+, Vdelta2 TcR+, Vgamma9 TcR+, Vdelta1 TcR+, CD3-CD16+, CD3-CD56+, CD19+ and perforin-positive cells. NK cell activity was assessed by single cell cytotoxic and flow cytometric assay. RESULTS: Patients with chronic hepatitis C showed an impaired NK cytotoxicity, decreased percentage of CD3-negative-CD8dim-positive (NK subtype) and Vgamma9/Vdelta2 TcR+ as well as perforin-positive T lymphocytes, compared to controls and to those who were cured from HCV infection. IFN-alpha2b increased NK cell cytotoxicity and the percentage of perforin-positive lymphocytes. CONCLUSIONS: Our findings suggest that in chronic HCV infection a decreased percentage of CD3(-)CD8+, Vgamma9/Vdelta2 TcR+ and perforin-positive T cells and simultaneous decreased peripheral NK activity may contribute to the impaired cellular immune response and the chronicity of the disease.     

Cell culture-produced hepatitis C virus impairs plasmacytoid dendritic cell function

Previous studies suggested a functional impairment of dendritic cells (DCs) in patients with chronic hepatitis C. To investigate whether this effect was mediated by a direct interaction of hepatitis C virus (HCV) with DCs, we studied the effects of infectious cell culture-produced hepatitis C virus (HCVcc) on peripheral blood mononuclear cells (PBMCs), ex vivo isolated plasmacytoid, and myeloid DCs and in vitro generated monocyte-derived DCs of healthy blood donors. HCVcc inhibited toll-like receptor (TLR)-9 (CpG and herpes simples virus)-mediated interferon alpha (IFN-alpha) production by peripheral blood mononuclear cells (PBMC) and plasmacytoid DCs. This inhibitory effect was also observed in response to ultraviolet (UV)-inactivated, noninfectious HCVcc, and it was not abrogated by neutralizing antibodies, and thus did not appear to require DC infection. Influenza A virus restored maturation and TLR9-mediated IFN-alpha production. In contrast to its effect on plasmacytoid DCs, HCVcc did not inhibit TLR3-mediated and TLR4-mediated maturation and interleukin (IL)-12, IL-6, IL-10, interferon gamma (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha) production by myeloid DCs and monocyte-derived DCs. Likewise, HCVcc did neither alter the capacity of myeloid DCs nor monocyte-derived DCs to induce CD4 T cell proliferation. Whereas phagocytosis of apoptotic hepatoma cells resulted in DC maturation, this effect was independent of whether the phagocytosed Huh7.5.1 cells were infected with HCVcc. In contrast to HCVcc, vaccinia virus inhibited maturation and TNF-alpha expression of myeloid DC as well as maturation and IL-6 and IL-10 production of monocyte-derived DC. CONCLUSION: HCVcc inhibited plasmacytoid DCs but not myeloid-derived and monocytoid-derived DCs via a direct interaction that did not require infection. The response of plasmacytoid DCs to influenza A virus infection was not impaired.     

Enhanced natural killer cell activity is found in exposed uninfected recipients of hepatitis C‐contaminated blood

A minority of injecting drug users, termed exposed uninfected, are resistant to hepatitis C (HCV) infection despite repeated low‐dose exposures. We identify for the first time a cohort of blood recipients who remained uninfected despite large‐dose exposure to HCV‐contaminated blood and characterize immune factors that may confer protection. Of 1340 blood recipients from the English Look Back database who were transfused HCV‐contaminated blood, we identified 8 who remained uninfected. In these 8 exposed uninfecteds, we characterized their natural killer (NK) cell populations and HCV‐specific T‐cell responses. Findings were compared with 10 spontaneous resolvers of HCV infection, 10 patients with chronic HCV infection and 10 healthy controls. Exposed uninfecteds had significantly greater numbers of NK cells with the activating receptor NKp30+ on CD56^bright and CD56^dim subsets compared with other groups (P < .05). Following interleukin‐2 activation, NK cells of exposed uninfecteds had enhanced cytotoxicity that positively correlated with NKp30 expression (P = .02). Differences in NKp80 and KIR2DL3 expression were also observed. HCV‐specific T‐cell responses were observed in some exposed uninfecteds but of low amplitude. Exposure without infection following transfusion of HCV‐contaminated blood is a very rare phenomenon and suggests a high level of resistance to infection. Enhanced NK cell activation and killing, with weak HCV‐specific T‐cell responses, were observed many years after exposure in uninfected recipients and may contribute to protection from HCV acquisition, although additional protective factors are being sought in this important cohort.