Impaired TRAIL-dependent cytotoxicity of CD1c-positive dendritic cells in chronic hepatitis C virus infection

Dendritic cells (DCs) play a central role in antiviral immunity. Conflicting data on DC function have been reported for hepatitis C virus (HCV) infection. In addition to antigen presentation and cytokine secretion, a subset of human DCs displays direct cytotoxic activity. It has been suggested that measles virus and human immunodeficiency virus (HIV) may enhance cytotoxicity of DCs potentially leading to apoptosis of activated T cells and subsequent down-regulation of antiviral immune responses. We demonstrate that CD1c-positive myeloid DCs, but not BDCA-4-positive plasmacytoid DCs, are able to kill different target cells mainly via tumour necrosis factor-related apoptosis-inducing ligand. The ability of CD1c+ DCs to lyze target cells was found to be completely impaired in patients with chronic hepatitis C (10 chronic HCV patients vs 10 healthy controls; P < 0.001) but not in patients with primary biliary cirrhosis. Successful antiviral therapy of chronic hepatitis C rescued the cytotoxicity of DCs. Myeloid DCs of HCV patients and healthy controls had a similar phenotype and endocytotic activity, however, the frequency of mDCs in the peripheral blood was lower (P = 0.004) and the allostimulatory function was weaker (P < 0.001) in chronic hepatitis C. Thus, in contrast to HIV and measles virus studies on monocyte-derived DCs, freshly isolated myeloid DCs of patients with hepatitis C do not show an increased but a completely abolished cytotoxic activity. The impaired DC cytotoxicity could represent a novel mechanism for the increased prevalence of autoimmunity in HCV infection.     

Normal functional capacity in circulating myeloid and plasmacytoid dendritic cells in patients with chronic hepatitis C

Initial reports analyzing dendritic cell (DC) function in patients with hepatitis C virus (HCV) infection have been controversial. Here, we enumerate and characterize the function of circulating myeloid and plasmacytoid DCs. The results show lower percentages of myeloid DCs (0.62 vs. 0.83; P = .05) and plasmacytoid DCs (0.11 vs. 0.34; P = .004) in patients with chronic HCV infection than in healthy, non-HCV-infected individuals. Despite the lower numbers of circulating myeloid DCs present, no phenotypic or functional defects were identified. The lower percentage of plasmacytoid DCs resulted in decreased absolute interferon (IFN)-alpha production; however, when analyzed on a per-cell basis, plasmacytoid DCs from HCV-infected patients generated levels of IFN-alpha equivalent to those generated by DCs from healthy, non-HCV-infected individuals. Contrary to data from previous models (which attributed HCV pathogenesis to defects in the DC compartment), our data reveal functional DC subsets in patients with chronic HCV infection. These results are encouraging for DC-based HCV immunotherapy trials.     

慢性丙型肝炎患者抗病毒治疗前后外周血树突状细胞表面共刺激分子的变化及初步分析

目的了解慢性丙型肝炎病毒(HCV)感染者外周血树突状细胞(DC)中髓样DC(mDC)和淋巴样DC(pDC)的表型频数,分析标准抗病毒治疗后获得完全早期病毒学应答(cEVR)患者DC表面共刺激分子(CD80、CD83、CD86)表达变化,探讨不同类型DC的活化在慢性HCV感染发病机制中的作用。方法选取我院住院的20例慢性HCV感染者,在接受初始聚乙二醇化干扰素-α(PEG-IFNα)联合利巴韦林抗病毒治疗达cEVR前后,分离外周血单个核细胞(PBMC),应用流式细胞仪检测mDC和pDC的频数及其表面CD80、CD83、CD86的表达水平。结果与健康对照组相比,慢性HCV感染者mDC、pDC频数均降低,其表面CD80的表达水平降低,CD86的表达水平升高,CD83的表达水平无明显差异。与治疗前相比,经干扰素和利巴韦林治疗达cEVR后,mDC上的CD80表达水平升高,CD83、CD86的表达水平降低;pDC上的CD80、CD83、CD86的表达水平均上升。结论慢性HCV感染者的外周血mDC、pDC频数降低,共刺激分子表达部分受损,干扰素抗病毒治疗可以恢复DC共刺激分子表达。提示DC数量和功能障碍可能是慢性HCV持续感染的重要机制之一。     

Infection and dysfunction of circulating blood dendritic cells and their subsets in chronic hepatitis C virus infection

Background To understand interactions between dendritic cells (DCs) and viruses, in vitro-cultured monocyte-derived DCs are usually used for functional analyses. However, several recent studies indicate that circulating blood DCs are different from monocyte-derived DCs, both phenotypically and functionally. Indeed, circulating DCs act as functional antigen-presenting cells in vivo. This study was conducted to evaluate the function of circulating blood DCs in patients with chronic hepatitis C and to examine whether circulating DCs from these patients were infected by hepatitis C virus (HCV).Methods The phenotypes and biological functions of circulating DCs from patients with chronic hepatitis C (n = 27), patients with non-HCV chronic liver disease (n = 7), and normal volunteers (n = 13) were analyzed. The presence of the HCV genome sequence in circulating blood DCs and in subsets of circulating DCs (myeloid DCs and plasmacytoid DCs) in patients with chronic hepatitis C was assessed.Results The stimulatory capacity of circulating DCs was significantly reduced in patients with chronic hepatitis C compared to patients with non-HCV chronic liver diseases and normal controls (P < 0.01). HCV RNA was identified in the overall population of circulating DCs, and in myeloid DCs and plasmacytoid DCs. Nucleotide sequences of the 5 non-coding region of HCV RNA showed marked differences between paired samples of circulating DCs and sera from the same patients.Conclusions Our results indicate the dysfunction and infection of circulatory blood DCs in chronic HCV infection. This may compromise the capacity of patients with hepatitis C to induce an effective antiviral immune response.     

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 T cell responses against hepatitis C virus by ex vivo targeting of adenoviral particles to dendritic cells

Injection of dendritic cells (DCs) presenting viral proteins constitutes a promising approach to stimulate T cell immunity against hepatitis C virus (HCV). Here we describe a strategy to enhance antigen loading and immunostimulatory functions of DCs useful in the preparation of therapeutic vaccines. Incubation of murine DCs with CFm40L, an adapter molecule containing the coxsackie-adenovirus receptor fused to the ecto-domain of murine CD40L-induced DC maturation, produced high amounts of interleukin-12 and up-regulation of molecules associated with T helper 1 responses. Accordingly, targeting of an adenovirus encoding HCV NS3 protein (AdNS3) to DCs with CFm40L strongly enhanced NS3 presentation in vitro, activating interferon-γ-producing T cells. Moreover, immunization of mice with these DCs promoted strong CD4 and CD8 T cell responses against HCV NS3. CFh40L, a similar adapter molecule containing human CD40L, enhanced transduction and maturation of human monocyte-derived DCs. Comparison of DCs transduced with AdNS3 and CFh40L from patients with chronic HCV infection and healthy donors revealed similar maturation levels. More importantly, DCs from the patients induced NS3-specific responses when transduced with AdNS3 and CFh40L but not with AdNS3 alone. CONCLUSION: DCs transduced with AdNS3 and the adapter molecule CFm/h40L exhibit enhanced immunostimulatory functions, induce robust anti-HCV NS3 immunity in animals, and can induce antiviral immune responses in subjects with chronic HCV infection. This strategy may serve as therapeutic vaccination for patients with chronic hepatitis C.     

Increased frequency of interferon-gamma-producing peripheral blood CD4+ T cells in chronic hepatitis C virus infection

OBJECTIVES: To determine the profile of cytokine secretion by CD4+ T helper (Th) cells in chronic hepatitis C virus (HCV) infection, we used flow cytometry to determine the percentage of interferon (IFN)-gamma and interleukin (IL)-4 producing cells from CD4+ T lymphocytes in peripheral blood obtained from patients chronically infected with HCV. METHODS: Peripheral blood mononuclear cells isolated from 89 HCV infected subjects (22 asymptomatic carriers, 56 patients with chronic hepatitis, and 11 patients with liver cirrhosis) and 24 healthy controls were stained with surface CD4 and intracellular IFN-gamma and IL-4. Serum soluble IL-2 receptor (sIL-2R) levels were analyzed by ELISA. RESULTS: The frequency of IFN-gamma producing CD4+ cells in asymptomatic HCV carriers, patients with chronic hepatitis, and patients with liver cirrhosis were significantly higher than those of healthy controls (p<0.01, respectively). In contrast, the percentages of IL-4-producing CD4+ cells were very low, and there were no significant correlations with disease progression. A significant elevation in serum sIL-2R levels was found in chronic HCV infection compared to healthy controls, and serum sIL-2R levels significantly correlated with the frequency of IFN-gamma-producing cells. CONCLUSIONS: In HCV infected subjects, both serum sIL-2R and IFN-gamma are increased in chronic HCV infection no matter the stage of disease, meaning they are no different in asymptomatic carriers, patients with chronic hepatitis, and patients with liver cirrhosis, and that Th1 cytokine or Th1 cells may participate in the pathogenesis of liver damage in chronic HCV infection.     

Hepatitis C virus E2 and CD81 interaction may be associated with altered trafficking of dendritic cells in chronic hepatitis C

Dendritic cells (DC) are crucially involved in the induction of immune responses; however, reports on DC functions in chronic hepatitis C are controversial. Function of DC includes proper cell trafficking between sites of infection and lympho-cellular compartments. Thus, we analyzed DC compartmentalization and changes in DC migration in hepatitis C virus (HCV)-infected patients. We found significantly lower numbers of circulating BDCA1+ and BDCA2+ DC in HCV(+) patients (n = 20) than in healthy controls (n = 12) (P < .05). Analyzing liver samples from HCV(+) patients (n = 15), HCV(-) controls (n = 15), and disease controls (n = 10), we demonstrated chronic hepatitis C to be associated with intrahepatic DC enrichment (P < .05). In vitro studies indicated that HCV E2-induced secretion of RANTES efficiently attracts CCR5(+) immature DC. Incubation of DC with sera derived from HCV(+) patients made DC unresponsive to CCL21, the chemokine recruiting DC to lymphoid tissues for T cell priming. Unlike attraction of CCR5+ DCs via RANTES, direct inhibition of DC migration in response to CCL21 was specific for patients with chronic hepatitis C and could be attributed to interaction of HCV E2 with CD81 on DC. In conclusion, migration of DC is markedly affected by interaction of HCV E2 with CD81. Failure of DC to recirculate to lymphoid tissue may be critically involved in impaired T cell priming during HCV infection.     

Presence of functional dendritic cells in patients chronically infected with hepatitis C virus

The absence of expanded numbers of hepatitis C virus (HCV)-reactive CD8(+) T lymphocytes (CTLs) in patients chronically infected with HCV has led to the investigation of dendritic cell (DC) function in this population as a potential cause for this defect. Several studies have shown evidence for impaired monocyte-derived DCs in chronically infected patients. As it is difficult to reconcile these data with the fact that patients with chronic HCV are immune competent, we re-evaluated this finding, carefully assessing phenotypic markers and functional activity of patient DCs as compared with noninfected controls. In contrast to these prior studies, DCs from 13 of 13 chronic HCV patients expressed typical maturation markers. These mature DCs were capable of priming allogeneic T lymphocytes, as well as stimulating influenza-specific memory T cells. This finding is consistent with clinical and immunologic data that the deficit in the patient's immune repertoire is HCV-specific and suggests that refined models are required for understanding the role of DCs in HCV pathogenesis.     

Monocyte-derived dendritic cells from chronic HCV patients are not infected but show an immature phenotype and aberrant cytokine profile.

BACKGROUND: Chronic hepatitis C virus (HCV) infection is characterized by an insufficient immune response, possibly owing to impaired function of antigen-presenting cells such as myeloid dendritic cells (DCs). Therapeutic vaccination with in vitro generated DCs may enhance the immune response. Subsets of DCs can originate from monocytes, but the presence of HCV in monocytes that develop into DCs in vitro may impair DC function. Therefore, we studied the presence of HCV RNA in monocytes and monocyte-derived DCs from chronic HCV patients. METHODS: Monocytes were cultured with granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4) for 6 days, and then with GM-CSF, IL-4, tumour necrosis factor-alpha (TNF-alpha), prostaglandin E2, IL-1beta and IL-6 for 2 days to generate mature DCs. HCV RNA was assessed by polymerase chain reaction. Surface molecules were assessed by flow cytometry. Cytokine production was assessed by cytokine bead array. RESULTS: HCV RNA was present in monocytes in 11 of 13 patients, but undetectable in mature DCs in 13 of 13 patients. The morphology of patient DCs was comparable with DCs from healthy controls, but the percentage of cells expressing surface molecules CD83 (P=0.001), CD86 (P=0.023) and human leucocyte antigen-DR (P=0.028) was lower in HCV patients. Compared with control DCs, patient DCs produced enhanced levels of IL-10 (P=0.0079) and IL-8 (P=0.0079), and lower levels of TNF-alpha (P=0.032), IL-6 (P=NS) and IL-1beta (P=0.0079). Patient and control DCs did not produce IL-12. CONCLUSIONS: Monocyte-derived DCs from chronic HCV patients are not infected but show an immature phenotype and aberrant cytokine profile.     

Comparable functions of plasmacytoid and monocyte-derived dendritic cells in chronic hepatitis C patients and healthy donors

BACKGROUND/AIMS: Dendritic cells (DCs) play a key role in immune responses through antigen presentation and cytokine secretion. Hepatitis C virus (HCV) is able to escape elimination by the immune system and often establishes a chronic infection. To investigate whether DC dysfunction is involved in this process, we have studied monoycte-derived DCs (Mo-DCs) and plasmacytoid DCs (pDCs), which produce large amounts of IFN-alpha, from chronic HCV patients and healthy donors. METHODS: We have assessed TNF-alpha and IFN-alpha production by pDCs using intracellular staining after total PBMCs stimulation with unmethylated CG dinucleotides (CpGs). The induction of allogeneic T cell proliferation by immature Mo-DCs was measured using the MLR assay. The up-regulation of maturation markers and the production of TNF-alpha in response to LPS were analyzed using flow cytometry and ELISA, respectively. RESULTS: We have detected comparable frequencies of pDCs producing TNF-alpha and IFN-alpha in both chronic HCV patients and healthy donors and we have found that immature Mo-DCs from both patients and donors similarly induce allogeneic T cell proliferation and mature and secrete TNF-alpha in response to LPS. CONCLUSIONS: Our results demonstrate that both pDC and Mo-DCs are not impaired in HCV infected patients.     

Reduced expression and functional impairment of Toll-like receptor 2 on dendritic cells in chronic hepatitis C virus infection.

BACKGROUND: Dendritic cells (DCs) utilize Toll-like receptors (TLRs) to sense virus and initiate immune responses. We aimed at elucidating the roles of TLRs on DCs in hepatitis C virus (HCV) infection. METHODS: Monocyte-derived DCs were obtained from 32 healthy volunteers (HV) and 30 chronically HCV-infected patients (CH). TLR2, TLR3 and TLR4 expressions on immature DCs were quantified by real-time quantitative RT-PCR. We stimulated DCs with specific TLR ligands and examined DC maturation, cytokine production and ability to stimulate allogeneic CD4(+) T cells. RESULTS: TLR2 expression on immature DCs was lower in the CH group, whereas those of TLR3 or TLR4 were not different between the groups. Each TLR ligand induced DC maturation and stimulated them to release comparable levels of IL-12p70, IL-6, IL-10, TNF-alpha and IFN-beta between the groups. TLR2 and TLR4 ligands enhanced DC ability to stimulate T cell proliferation, with the degree due to the TLR2 ligand being lower in the CH group. CONCLUSIONS: In HCV infection, the TLR2 expression on DCs is reduced and TLR2-stimulated DCs show lesser ability to proliferate T cells than healthy counterparts, suggesting that the TLR2 system is involved in HCV-induced immunopathogenesis.     

Direct enumeration and functional assessment of circulating dendritic cells in patients with liver disease

Chronic liver disease has been shown to be associated with diminished humoral and cellular immune function. Although antigen-presenting cells (APC) that initiate immune responses include various cells (B cells, endothelial cells, macrophages, etc.), the dendritic cell (DC) is a professional APC that activates naive T cells most efficiently. To examine the frequency and function of DCs in chronic liver disease, we studied circulating DCs from a cohort of 112 subjects (23 normal subjects, 29 subjects who had spontaneously recovered from hepatitis C virus [HCV] infection, 30 chronically infected HCV patients, and 30 patients with liver disease unrelated to HCV infection). Our analyses revealed significant reduction in both circulating myeloid (mDC) and plasmacytoid dendritic cells (pDC) in patients with liver disease. In contrast, examination of subjects with spontaneously resolved HCV infection revealed no significant difference in either circulating mDCs or pDCs. We found an inverse correlation with serum alanine aminotransferase (ALT) levels and both mDCs and pDCs frequency. In a subset of patients for whom intrahepatic cells were available, paired analysis revealed enrichment for DCs within the intrahepatic compartment. Interferon alfa (IFN-alpha) production in response to influenza A and poly (I:C) correlated with the frequency of circulating DCs, although IFN-alpha production was comparable on a per-DC basis in patients with liver disease. In conclusion, patients with liver disease exhibit a reduction in circulating DCs. Considering that DCs are essential for initiation and regulation of innate and adaptive immunity, these findings have implications for both viral persistence and liver disease.     

Hepatitis C is associated with perturbation of intrahepatic myeloid and plasmacytoid dendritic cell function

BACKGROUND/AIMS: In most cases infection with hepatitis C results in chronic infection as a consequence of viral subversion and failed anti-viral immune responses. The suggestion that dendritic cells are defective in chronic HCV infection led us to investigate the phenotype and function of liver-derived myeloid (mDC) and plasmacytoid (pDC) dendritic cells in patients with chronic HCV infection. METHODS: Liver DCs were isolated without expansion in cytokines from human liver allowing us to study unmanipulated tissue-resident DCs ex vivo. RESULTS: Compared with mDCs isolated from non-infected inflamed liver mDCs from HCV-infected liver (a) demonstrated higher expression of MHC class II, CD86 and CD123, (b) were more efficient stimulators of allogeneic T-cells and (c) secreted less IL-10. Reduced IL-10 secretion may be a factor in the enhanced functional properties of mDCs from HCV infected liver because antibody depletion of IL-10 enhanced the ability of mDCs from non-infected liver to stimulate T-cells. In contrast, pDCs were present at lower frequencies in HCV-infected liver and expressed higher levels of the regulatory receptor BDCA-2. CONCLUSIONS: In HCV-infected liver the combination of enhanced mDC function and a reduced number of pDCs may contribute to viral persistence in the face of persistent inflammation.     

Hepatitis C virus NS4 protein impairs the Th1 polarization of immature dendritic cells

Summary. Dendritic cells (DCs) in chronic hepatitis C patients display impaired function, although the details remain unclear. To investigate the hepatitis C virus (HCV) protein that has the most impact on DC function, we compared five recombinant proteins and seven HCV protein genes in modulating DC phenotype and function. Immature DCs (iDCs) were established from healthy donor peripheral blood monocytes with granulocyte–macrophage colony stimulating factor (GM‐CSF) and IL‐4. Lipopolysaccharide was used to establish mature DCs (mDCs). Cells were then pulsed with HCV recombinant proteins or transfected with HCV plasmids and subsequently assayed for cell surface marker expression by flow cytometry. For cytokine and proliferative T‐cell response analysis, DCs were cultured with autologous CD4 T cells and tuberculin purified protein derivative (PPD). Mean fluorescent intensity of CD86 was reduced in HCV protein‐pulsed iDCs. Proliferative T‐cell responses and Th1 cytokine concentrations were reduced with HCV nonstructural proteins (NS), particularly with HCV NS4. HCV nonstructural proteins, particularly NS4, change the iDC phenotype and reduce antigen‐specific T‐cell stimulatory function with Th1 cytokine reductions.     

Novel role of plasmacytoid dendritic cells in humans: Induction of interleukin‐10–producing treg cells by plasmacytoid dendritic cells in patients with rheumatoid arthritis responding to therapy

Objective

Reestablishing immune tolerance and long‐term suppression of disease represent major therapeutic goals in rheumatoid arthritis (RA). Dendritic cells (DCs) likely play a central role in such regulation via the expansion and/or induction of Treg cells. The present study was undertaken to explore the contribution of DCs to the development of Treg cells in a human autoimmune disease setting.

Methods

DC subsets were characterized by flow cytometry in the peripheral blood and synovial fluid of patients with RA. Proliferation of and cytokine release by naive CD4+CD25− T cells were measured in cocultures of these cells with DCs from patients with RA and healthy controls. The suppressive capacity of DC‐polarized T cells was explored in vitro by a standard suppression assay.

Results

Only very low numbers of both plasmacytoid DCs (CD303+) and myeloid DCs (CD1c+) were present in the peripheral blood of patients with active RA. In contrast, patients with therapy‐induced remission of RA exhibited higher numbers of circulating plasmacytoid DCs. Mature plasmacytoid DCs from RA patients with low disease activity, but not those from healthy controls, expressed high levels of indoleamine 2,3‐dioxygenase and promoted the differentiation of allogeneic naive CD4+CD25− T cells into interleukin‐10–secreting Treg cells, or Tr1 cells, that showed poor proliferation in vitro. Importantly, these plasmacytoid DC–primed Treg cells potently suppressed the proliferation of autologous naive CD4+ T cells, in a dose‐dependent manner.

Conclusion

These results demonstrate, for the first time, that human plasmacytoid DCs may be educated within the rheumatoid microenvironment to acquire a tolerogenic phenotype. Modulation of the immune response by plasmacytoid DCs might provide novel immune‐based therapies in autoimmunity and transplantation.

     

Association of enhanced activity of indoleamine 2,3-dioxygenase in dendritic cells with the induction of regulatory T cells in chronic hepatitis C infection

Background

Altered functions of dendritic cells (DCs) and/or increases of regulatory T cells (Tregs) are involved in the pathogenesis of chronic hepatitis C virus (HCV) infection. A tryptophan-catabolizing enzyme, indoleamine 2,3-dioxygenase (IDO), is reported to be an inducer of immune tolerance. Our aim was to clarify whether or not IDO is activated in chronic hepatitis C patients and its role in immune responses.

Methods

This study enrolled 176 patients with chronic HCV infection and 37 healthy volunteers. Serum kynurenine concentration was evaluated by high-performance liquid chromatography, and its correlation with clinical parameters was examined. Monocyte-derived DCs were prepared from the subjects and subsequently stimulated with a combination of lipopolysaccharide and interferon-gamma to induce functional IDO (defined as IDO-DCs). The phenotypes, kynurenine or cytokine production, and T-cell responses with IDO-DCs were compared between the patients and healthy volunteers.

Results

The serum kynurenine level in the patients was significantly higher than that in the healthy volunteers, and the level of serum kynurenine was positively correlated with the histological activity or fibrosis score. IDO activity in IDO-DCs from the patients was significantly higher than that in IDO-DCs from the volunteers. Furthermore, IDO-DCs from the patients induced more Tregs in vitro compared with those from the volunteers, and the frequency of induced Tregs by IDO-DCs was decreased with an IDO-specific inhibitor.

Conclusions

Systemic IDO activity is enhanced in chronic hepatitis C patients in correlation with the degree of liver inflammation and fibrosis. In response to inflammatory stimuli, DCs from the patients tend to induce Tregs, with some of this action being dependent on IDO.     

Functional impairment of myeloid and plasmacytoid dendritic cells of patients with chronic hepatitis B

Dendritic cells (DC) play an important role in the induction of T-cell responses. We hypothesize that the hampered antiviral T-cell response in chronic hepatitis B patients is a result of impaired dendritic cell function. In this study, we compared the number, phenotype and functionality of two important blood precursor DC, myeloid DC (mDC) and plasmacytoid DC (pDC), of chronic hepatitis B patients with healthy volunteers. No differences in percentages of mDC and pDC in peripheral blood mononuclear cells were observed between chronic hepatitis B patients and healthy controls. The allostimulatory capacity of isolated and in vitro matured mDC, but not of pDC, was significantly decreased in patients compared to controls. Accordingly, a decreased percentage of mDC expressing CD80 and CD86 was observed after maturation, compared to controls. In addition, mDC of patients showed a reduced capacity to produce tumor necrosis factor alpha after a stimulus with synthetic double-stranded RNA and interferon gamma. Purified pDC from patients produced less interferon alpha, an important antiviral cytokine, in response to stimulation with Staphylococcus aureus Cowan strain I than pDC isolated from controls. In conclusion, mDC and pDC are functionally impaired in patients with chronic hepatitis B. This might be an important way by which hepatitis B virus evades an adequate immune response, leading to viral persistence and disease chronicity.     

Impaired dendritic cell maturation in patients with chronic, but not resolved, hepatitis C virus infection

Dendritic cells (DCs) are important for the initiation of immune responses to foreign antigens. Their antigen uptake and presentation capacities enable them to prime and activate T cells. Immature DCs capture antigens; however, they must be activated to mature before serving as efficient antigen-presenting cells. The antigen-presenting capacity of DCs can be diminished during viral infection and as a consequence of tumor formation. Chronic infection with hepatitis C virus (HCV) has been shown to affect the allostimulatory function of DCs. In this study, it is demonstrated that monocyte-derived DCs from patients with chronic HCV infection do not respond to maturation stimuli. Instead, they maintain their immature phenotype, reflected by the pattern of cell surface markers and by their continued capacity to uptake antigen. Moreover, their allostimulatory abilities are impaired compared with those of mature DCs derived from healthy donors. To investigate a possible correlation between viral clearance and this DC maturation defect, patients with resolved HCV infection after a course of antiviral therapy were studied. Results demonstrate that DCs from patients who cleared HCV behaved like DCs from healthy donors: in response to maturation stimuli, they decrease antigen uptake, up-regulate expression of appropriate surface markers, and are potent stimulators of allogeneic T cells. (Blood. 2001;97:3171-3176)