Induction of cytokine production and proliferation of memory lymphocytes by murine liver dendritic cell progenitors: role of these progenitors as immunogenic resident antigen-presenting cells in the liver

Comprehensive analysis of lncRNA-mediated ceRNA networkfor hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is a high-burden cancer. The molecular mechanism of HCC has not been fully elucidated. Notably, current research has revealed a significant function for long non-coding RNAs (lncRNAs) in the prognosis of patients with HCC. Here, this study aims to construct a regulated lncRNA-mediated ceRNA network and find biological targets for the treatment of HCC.

Methods

Based on the RNA expression patterns from the TCGA, we did an analysis to determine which genes were expressed differently between liver tumor tissues and noncancerous tissues. Then, using bioinformatic tools, we built a lncRNA-miRNA-mRNA ceRNA network and used GO and KEGG functional analyses on the DEmRNAs connected to ceRNA networks. The main lncRNAs in the subnetwork were chosen, and we next looked at the relationships between these lncRNAs and the clinical characteristics of patients with HCC. The prognosis-related genes and immune cells were identified using Kaplan-Meier and Cox proportional hazard analyses, and CIBERSORT was utilized to separate the 22 immune cell types. CCK8 assay was performed to measure cell viability in HCC cells after lncRNA HOTTIP modulation.

Results

Differentially expressed mRNA and lncRNAs in HCC and paracancerous tissues were identified. There are 245 lncRNAs, 126 miRNAs, and 1980 mRNAs that are expressed differently in liver tumour tissues than in noncancerous cells. Function analysis showed that mRNAs in ceRNA network were significantly enriched in G1/S transition of mototiv cell cycle, positive regulation of cell cycle process, hepatocellular carcinoma, and cancer related pathways. CD8 T cells and T follicular helper cells had a favourable link with a 0.65 correlation coefficient. Additionally, there was a strong correlation between Eosinophils, activated NK cells, and B memory cells. Strikingly, depletion of lncRNA HOTTIP inhibited viability of HCC cells. In addition, miR-205 upregulation suppressed viability of HCC cells, while miR-205 downregulation repressed viability of HCC cells. Notably, miR-205 depletion rescued HOTTIP depletion-mediated suppression of cell viability in HCC.

Conclusion

A ceRNA network was created by examining the lncRNA, miRNA, and mRNA expression profiles of liver tumours from the TCGA database. LncRNA HOTTIP promoted cell viability via inhibition of miR-205 in HCC cells.

α-Mannosidase I Protein Expression in Peripheral Blood Mononuclear Cells Is Upregulated During Hepatitis B Virus Infection

Hepatitis B virus (HBV) has been reported to be recognized by dendritic cell-specific ICAM-3-grabbing nonintegrin in the presence of the α-mannosidase I inhibitor kifunensine, whereas native HBV is not. The aim of our study was to determine whether changes in α-mannosidase I expression in peripheral blood mononuclear cells (PBMCs) occur in patients with HBV infection. Peripheral blood was collected from 90 HBV-infected patients (grouped into immune tolerance, chronic hepatitis B, or inactive carrier group based on their clinical states) and 30 healthy donors. Expression of the three α-mannosidase I subtypes, MAN1A1, MAN1A2, and MAN1C1, was measured using western blot analyses. Compared with the healthy controls, significant increases in the MAN1A1, MAN1A2, and MAN1C1 expression levels were observed in the three HBV-infected groups, among whom the immune tolerance group showed the largest increase. For the patients in the immune tolerance phase, the expression levels of both MAN1A1 and MAN1A2 were linearly and positively correlated with the hepatitis B e antigen (HBeAg) titer and HBV DNA level, although a positive correlation was only found between MAN1C1 expression and the HBeAg titer. These results indicate that increased α-mannosidase I expression in PBMCs may play an important role in HBV immune escape and that its expression level is closely related to viral replication activity.

Saikosaponin-d affects the differentiation, maturation and function of monocyte-derived dendritic cells

Saikosaponin-d (Ssd) is a triterpenoid saponin derived from Bupleurum falcatum L., which has been shown to exhibit a variety of pharmacological properties, including anti-inflammatory, antibacterial and antiviral properties. The aim of the present study was to investigate the effect of Ssd on the differentiation, maturation and function of human monocyte-derived dendritic cells (DCs) isolated from condylomata acuminata patients. The results of the present study demonstrated that Ssd reduced the differentiation of DCs, as evidenced by decreased expression levels of cluster of differentiation (CD)1a, CD80 and CD86 molecules and increased CD14 expression. Expression levels of the mannose receptor and CD32 were also significantly elevated, which was associated with enhanced fluorescein isothiocyanate-dextran endocytic activity. Furthermore, Ssd treatment promoted DC maturation by increasing the expression levels of CD40, CD83, CD80 and CD86. In addition, the function of mature DCs, including the secretion of IL-12 and the stimulation of lymphocyte proliferation, was significantly increased following Ssd administration. In conclusion, the present study indicated that Ssd exhibited immunomodulatory effects and may be a novel potent chemopreventive drug candidate for the treatment of condylomata acuminata.

Saikosaponin-d affects the differentiation, maturation and function of monocyte-derived dendritic cells

Saikosaponin-d (Ssd) is a triterpenoid saponin derived from Bupleurum falcatum L., which has been shown to exhibit a variety of pharmacological properties, including anti-inflammatory, antibacterial and antiviral properties. The aim of the present study was to investigate the effect of Ssd on the differentiation, maturation and function of human monocyte-derived dendritic cells (DCs) isolated from condylomata acuminata patients. The results of the present study demonstrated that Ssd reduced the differentiation of DCs, as evidenced by decreased expression levels of cluster of differentiation (CD)1a, CD80 and CD86 molecules and increased CD14 expression. Expression levels of the mannose receptor and CD32 were also significantly elevated, which was associated with enhanced fluorescein isothiocyanate-dextran endocytic activity. Furthermore, Ssd treatment promoted DC maturation by increasing the expression levels of CD40, CD83, CD80 and CD86. In addition, the function of mature DCs, including the secretion of IL-12 and the stimulation of lymphocyte proliferation, was significantly increased following Ssd administration. In conclusion, the present study indicated that Ssd exhibited immunomodulatory effects and may be a novel potent chemopreventive drug candidate for the treatment of condylomata acuminata.

Hepatic stellate cells preferentially induce Foxp3+ regulatory T cells by production of retinoic acid

The liver has long been described as immunosuppressive, although the mechanisms underlying this phenomenon are incompletely understood. Hepatic stellate cells (HSCs), a population of liver nonparenchymal cells, are potent producers of the regulatory T cell (Treg)-polarizing molecules TGF-β1 and all-trans retinoic acid, particularly during states of inflammation. HSCs are activated during hepatitis C virus infection and may therefore play a role in the enrichment of Tregs during infection. We hypothesized that Ag presentation in the context of HSC activation will induce naive T cells to differentiate into Foxp3(+) Tregs. To test this hypothesis, we investigated the molecular interactions between murine HSCs, dendritic cells, and naive CD4(+) T cells. We found that HSCs alone do not present Ag to naive CD4(+) T cells, but in the presence of dendritic cells and TGF-β1, preferentially induce functional Tregs. This Treg induction was associated with retinoid metabolism by HSCs and was dependent on all-trans retinoic acid. Thus, we conclude that HSCs preferentially generate Foxp3(+) Tregs and, therefore, may play a role in the tolerogenic nature of the liver.

Hepatic stellate cells preferentially induce Foxp3+ regulatory T cells by production of retinoic acid

The liver has long been described as immunosuppressive, although the mechanisms underlying this phenomenon are incompletely understood. Hepatic stellate cells (HSCs), a population of liver nonparenchymal cells, are potent producers of the regulatory T cell (Treg)-polarizing molecules TGF-β1 and all-trans retinoic acid, particularly during states of inflammation. HSCs are activated during hepatitis C virus infection and may therefore play a role in the enrichment of Tregs during infection. We hypothesized that Ag presentation in the context of HSC activation will induce naive T cells to differentiate into Foxp3(+) Tregs. To test this hypothesis, we investigated the molecular interactions between murine HSCs, dendritic cells, and naive CD4(+) T cells. We found that HSCs alone do not present Ag to naive CD4(+) T cells, but in the presence of dendritic cells and TGF-β1, preferentially induce functional Tregs. This Treg induction was associated with retinoid metabolism by HSCs and was dependent on all-trans retinoic acid. Thus, we conclude that HSCs preferentially generate Foxp3(+) Tregs and, therefore, may play a role in the tolerogenic nature of the liver.

A pcDNA-Ehcpadh vaccine against Entamoeba histolytica elicits a protective Th1-like response in hamster liver

DNA vaccines are promising tools to fight parasitic diseases, including amoebiasis caused by the protozoan Entamoeba histolytica. Here we studied the immunogenicity and protective efficacy of a DNA vaccine against this parasite composed by the EhCPADH surface complex encoding genes (Ehcp112 and Ehadh112). EhCPADH is formed by an adhesin (EhADH112) and a cysteine proteinase (EhCP112), both involved in the parasite virulence. We evaluated transcription, protein expression, immunological response and protection against hepatic amoebiasis in hamsters intradermally and intramuscularly immunized with a mixture of pcDNA-Ehadh112 and pcDNA-Ehcp112 plasmids. RT-PCR and immunohistochemical assays showed that both antigens were differentially expressed in spleen and liver of immunized animals. No significant antibody immune response was induced by either route. However, intradermally inoculated hamsters presented a robust Th1-like immune response, characterized by high levels of INF-gamma and TNF-alpha cytokines, detected in the liver of animals challenged with virulent trophozoites. Animals showed significant protection against amoebiasis manifested by a higher survival rate and a significant prevention of liver abscess formation. We conclude that a refinement of this DNA vaccine could be a good choice to control hepatic amoebiasis.

Hepatitis C virus and ethanol alter antigen presentation in liver cells

Alcoholic patients have a high incidence of hepatitis C virus (HCV) infection. Alcohol consumption enhances the severity of the HCV disease course and worsens the outcome of chronic hepatitis C. The accumulation of virally infected cells in the liver is related to the HCV-induced inability of the immune system to recognize infected cells and to develop the immune responses. This review covers the effects of HCV proteins and ethanol on major histocompatibility complex (MHC) class I- and class II-restricted antigen presentation. Here, we discuss the liver which functions as an immune privilege organ; factors, which affect cleavage and loading of antigenic peptides onto MHC class I and class II in hepatocytes and dendritic cells, and the modulating effects of ethanol and HCV on antigen presentation by liver cells. Altered antigen presentation in the liver limits the ability of the immune system to clear HCV and infected cells and contributes to disease progression. HCV by itself affects dendritic cell function, switching their cytokine profile to the suppressive phenotype of interleukin-10 (IL-10) and transforming growth factor beta (TGFβ) predominance, preventing cell maturation and allostimulation capacity. The synergistic action of ethanol with HCV results in the suppression of MHC class II-restricted antigen presentation. In addition, ethanol metabolism and HCV proteins reduce proteasome function and interferon signaling, thereby suppressing the generation of peptides for MHC class I-restricted antigen presentation. Collectively, ethanol exposure further impairs antigen presentation in HCV-infected liver cells, which may provide a partial explanation for exacerbations and the poor outcome of HCV infection in alcoholics.

Recruitment of dendritic cells in human liver with metastases

Dendritic cells (DCs) play a key role in the generation of antitumor immune responses as the most potent professional antigen-presenting cells. In this study we examined the distribution of DCs subsets in selected areas of liver metastases and adjacent liver tissue of 74 patients with gastrointestinal cancers (14 gastric, 47 colon, and 13 rectal) using immunohistochemistry for the DCs markers S-100 protein, HLA-DR, CD1a, and CD83. S-100 protein-positive DCs were localized mainly in clusters in metastases and at the tumor border with the surrounding liver tissue, while HLA-DR-positive DCs were significantly more in number (P<0.0001) and were diffusely distributed in metastasis stroma and at the tumor border. S-100 protein-positive DCs with mature phenotype were presented around metastases and in the sinusoidal lumena, whereas S-100 protein-positive DCs with less mature phenotype based on their ultrastructure were scattered in the tumor stroma. CD1a- and CD83-positive DCs were observed predominantly in small groups or as single cells in the tumor stroma and in the invasive margin. The numbers of CD1a-positive DCs (immature) and CD83-positive DCs (mature) were comparable, but significantly lower than that of S-100 protein-positive (P<0.0001) and HLA-DR-positive cells (P<0.0001).We observed more S-100 protein-positive DCs and HLA-DR-expressing cells in the sinusoids and portal tracts of the liver tissue, surrounding metastases, than in control liver tissue. In conclusion, this study provides additional information on the functional subtypes and distribution of DCs infiltrating metastatic tissue and local liver environment in patients with liver metastases from gastrointestinal cancers.

Zinc finger proteins designed to specifically target duck hepatitis B virus covalently closed circular DNA inhibit viral transcription in tissue culture

Duck hepatitis B virus (DHBV) is a model virus for human hepatitis B virus (HBV), which infects approximately 360 million individuals worldwide. Nucleoside analogs can decrease virus production by inhibiting the viral polymerase; however, complete clearance by these drugs is not common because of the persistence of the HBV episome. HBV DNA is present in the nucleus as a covalently closed circular (cccDNA) form, where it drives viral transcription and progeny virus production. cccDNA is not the direct target of antiviral nucleoside analogs and is the source of HBV reemergence when antiviral therapy is stopped. To target cccDNA, six different zinc finger proteins (ZFP) were designed to bind DNA sequences in the DHBV enhancer region. After the binding kinetics were assessed by using electrophoretic mobility shift assays and surface plasmon resonance, two candidates with dissociation constants of 12.3 and 40.2 nM were focused on for further study. The ZFPs were cloned into a eukaryotic expression vector and cotransfected into longhorn male hepatoma cells with the plasmid pDHBV1.3, which replicates the DHBV life cycle. In the presence of each ZFP, viral RNA was significantly reduced, and protein levels were dramatically decreased. As a result, intracellular viral particle production was also significantly decreased. In summary, designed ZFPs are able to bind to the DHBV enhancer and interfere with viral transcription, resulting in decreased production of viral products and progeny virus genomes.

Dendritic cells, the liver, and transplantation

Interstitial liver dendritic cells (DCs) exhibit phenotypic diversity and functional plasticity. They play important roles in both innate and adaptive immunity. Their comparatively low inherent T cell stimulatory ability and the outcome of their interactions with CD4(+) and CD8(+) T cells, as well as with natural killer (NK) T cells and NK cells within the liver, may contribute to regulation of hepatic inflammatory responses and liver allograft outcome. Liver DCs migrate in the steady state and after liver transplantation to secondary lymphoid tissues, where the outcome of their interaction with antigen-specific T cells determines the balance between tolerance and immunity. Systemic and local environmental factors that are modulated by ischemia-reperfusion injury, liver regeneration, microbial infection, and malignancy influence hepatic DC migration, maturation, and function. Current research in DC biology is providing new insights into the role of these important antigen-presenting cells in the complex events that affect liver transplant outcome.

Response to interferon-alpha treatment correlates with recovery of blood plasmacytoid dendritic cells in children with chronic hepatitis B

BACKGROUND/AIMS

To investigate whether dendritic cell changes are associated with the efficacy of interferon-alpha treatment we longitudinally analyzed circulating dendritic cells in children chronically infected with hepatitis B virus (HBV) undergoing interferon-alpha treatment.

METHODS

Thirty-one children with chronic hepatitis B (CHB) received interferon-alpha antiviral treatment for 52 weeks. Myeloid and plasmacytoid dendritic cell (pDCs) frequency and function were analyzed at weeks 0, 2, 12, 24, 36 and 52 in 22 CHB patients.

RESULTS

All patients exhibited an initially rapid decrease of circulating pDC numbers and CpG-induced endogenous interferon-alpha production within 2 weeks of interferon-alpha treatment. Subsequently, all responders displayed a continuous increase of both pDC numbers and function peaking around week 12. These responses were consequently accompanied by viral clearance, hepatitis B e antigen seroconversion, and the improvement of circulating myeloid dendritic cells and type 1T helper cytokine levels. However, non-responders lacked these sequential responses compared with responders.

CONCLUSIONS

pDCs may actively correlate with interferon-alpha therapy-induced viral clearance in pediatric patients with CHB. The recovery of blood pDC number and function may represent a prognostic marker for favourable response to interferon-alpha treatment in chronic hepatitis B.

The role of CD11c(+) hepatic dendritic cells in the induction of innate immune responses

The role of the liver in the initiation and maintenance of tolerance is a critical immune function that involves multiple lineages of immune cells. Included within these populations are liver dendritic cells (DCs). Although there has been significant work on the phenotypic and functional roles of splenic and bone marrow dendritic cells, as well as their subsets, comparable studies in liver have often been difficult. To address this issue we have isolated, from C57BL/6 mice, relatively pure populations of DCs and compared phenotype and function to the data from spleen using flow cytometry, cell sorter assisted purification and culture, morphology by cytospin and May-Giemsa staining, cell cycle progression, antigen uptake, cytokine production and allo-activation potential. natural killer (NK)1.1(-)CD11c(+) liver DC subsets (conventional DCs, T cell receptor (TcR)beta(-)NK1.1(-)CD11c(+)B220(-) and plasmacytoid DCs, TcRbeta(-)NK1.1(-)CD11c(+)B220(+)) efficiently endocytose dextran and produce significant levels of tumour necrosis factor (TNF)-alpha, interleukin (IL)-6 and IL-12 p40 in response to Toll-like receptor (TLR) ligands, with responses higher than splenic DCs. There is also a differential capability of hepatic DCs to respond to innate signals. Indeed, CD11c(+) hepatic DCs have a greater capacity to respond to innate stimulation but are less capable of inducing CpG activated-allogeneic T cells. These data suggest that hepatic dendritic cells function as a critical bridge between innate and adaptive immunity and are capable of inducing stronger innate responses with a lower capacity for allo-stimulation than splenic dendritic cells. These properties of liver dendritic cells contribute to their unique role in the induction of tolerance.

The role of CD11c(+) hepatic dendritic cells in the induction of innate immune responses

The role of the liver in the initiation and maintenance of tolerance is a critical immune function that involves multiple lineages of immune cells. Included within these populations are liver dendritic cells (DCs). Although there has been significant work on the phenotypic and functional roles of splenic and bone marrow dendritic cells, as well as their subsets, comparable studies in liver have often been difficult. To address this issue we have isolated, from C57BL/6 mice, relatively pure populations of DCs and compared phenotype and function to the data from spleen using flow cytometry, cell sorter assisted purification and culture, morphology by cytospin and May-Giemsa staining, cell cycle progression, antigen uptake, cytokine production and allo-activation potential. natural killer (NK)1.1(-)CD11c(+) liver DC subsets (conventional DCs, T cell receptor (TcR)beta(-)NK1.1(-)CD11c(+)B220(-) and plasmacytoid DCs, TcRbeta(-)NK1.1(-)CD11c(+)B220(+)) efficiently endocytose dextran and produce significant levels of tumour necrosis factor (TNF)-alpha, interleukin (IL)-6 and IL-12 p40 in response to Toll-like receptor (TLR) ligands, with responses higher than splenic DCs. There is also a differential capability of hepatic DCs to respond to innate signals. Indeed, CD11c(+) hepatic DCs have a greater capacity to respond to innate stimulation but are less capable of inducing CpG activated-allogeneic T cells. These data suggest that hepatic dendritic cells function as a critical bridge between innate and adaptive immunity and are capable of inducing stronger innate responses with a lower capacity for allo-stimulation than splenic dendritic cells. These properties of liver dendritic cells contribute to their unique role in the induction of tolerance.

Characterization of human liver dendritic cells in liver grafts and perfusates

It is generally accepted that donor myeloid dendritic cells (MDC) are the main instigators of acute rejection after organ transplantation. The aim of the present study was to characterize MDC in human donor livers using liver grafts and perfusates as a source. Perfusates were collected during ex vivo vascular perfusion of liver grafts pretransplantation. MDC, visualized in wedge biopsies by immunohistochemistry with anti-BDCA-1 monoclonal antibody (mAb), were predominantly observed in the portal fields. Liver MDC, isolated from liver wedge biopsies, had an immature phenotype with a low expression of CD80 and CD83. Perfusates were collected from 20 grafts; perfusate mononuclear cells (MNC) contained 1.5% (range, 0.3-6.6%) MDC with a viability of 97 +/- 2%. Perfusates were a rich source of hepatic MDC since 0.9 x 10(6) (range, 0.11-4.5 x 10(6)) MDC detached from donor livers during vascular perfusion pretransplantation. Perfusate MDC were used to further characterize hepatic MDC. Perfusate MDC expressed less DC-LAMP (P = 0.000), CD80 (P = 0.000), CD86 (P = 0.003), and CCR7 (P = 0.014) than mature hepatic lymph node (LN) MDC, and similar CD86 (P = 0.140) and CCR7 (P = 0.262) as and more DC-LAMP (P = 0.007) and CD80 (P = 0.002) than immature blood MDC. Perfusate MDC differed from blood MDC in producing significantly higher amounts of interleukin (IL)-10 in response to lipopolysaccharide (LPS), and in being able to stimulate allogeneic T-cell proliferation. In conclusion, human donor livers contain exclusively immature MDC that detach in high numbers from the liver graft during pretransplantation perfusion. These viable MDC have the capacity to stimulate allogeneic T-cells, and thus may represent a major player in the induction of acute rejection.

Effect of Tinospora cordifolia on the antitumor activity of tumor-associated macrophages-derived dendritic cells

We and others previously have reported that extract prepared from medicinal plant Tinospora cordifolia shows a wide spectrum of immunoaugmentary effects. Tinospora cordifolia was shown to upregulate antitumor activity of tumor-associated macrophages (TAM). In this article we present evidence to show that an alcoholic extract of Tinospora cordifolia (ALTC) enhances the differentiation of TAM to dendritic cells (DC) in response to granulocyte/macrophage-colony-stimulating factor, interleukin-4, and tumor necrosis factor. DC differentiated in vitro from TAM that were harvested from tumor-bearing mice after i.p. administration of ALTC (200 mg/kg body weight) 2 days posttumor transplantation shows an enhanced tumor cytotoxicity and production of tumoricidal soluble molecules like TNF, IL-1, and NO. Adoptive transfer of these TAM-derived DC to Dalton's lymphoma-bearing mice resulted in prolongation of survival of tumor-bearing mice. This is the first report regarding the differentiation and antitumor functions of TAM-derived DC obtained from tumor-bearing host administered with ALTC. The possible mechanisms involved also are discussed.

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Defective antigen-presenting capacity of murine dendritic cells during starvation

Significant impairments of several aspects of immunity have been described in acute and chronic nutritional deficiencies; however, there have been few studies on antigen-presenting cells during starvation. We examined the antigen-presenting capacities of mouse dendritic cells (DCs) from lymphoid organ (spleen DCs) and non-lymphoid tissue (liver DCs) during starvation. The total numbers of spleen DCs and liver DCs were significantly fewer in starved mice than in control mice. Functional analysis showed that the proliferative activities of spleen DCs and liver DCs were significantly impaired in starved mice compared with control mice. In particular, liver DCs from starved mice were unable to induce interferon-gamma. Liver DCs from starved mice were unable to induce proliferation of antigen-specific memory lymphocytes. These data indicated that one major cause of impairment of immunologic responses during starvation may be mediated through DCs.

Immune responses in hepatitis C virus infection: the role of dendritic cells

Cellular immune responses are critical for the clearance of hepatitis C virus. Persistent infection results from a narrow and weak cellular immune response, in direct contrast to the broad, strong response associated with viral clearance in acute infection. The presence of dendritic cells in the liver facilitates presentation of viral antigens to both CD4+ and CD8+ T cell populations. Exploiting the potent antigen presentation capability of dendritic cells for immunotherapy of chronic hepatitis C is attractive; however, infection or transfection of segments or the entire hepatitis C virus genome appears to impair the allostimulation capacity of dendritic cells. If dendritic cell immunotherapy for hepatitis C virus infection is to become a reality, the mechanism behind the defective allostimulatory capacity needs to be deciphered.

DNA-based immunotherapy: potential for treatment of chronic viral hepatitis?

Persistent HBV and HCV infection represent major causes of chronic liver disease with a high risk of progression to liver cirrhosis and hepatocellular carcinoma (HCC). Conventional protein-based vaccines are highly efficacious in preventing HBV infection; whereas in therapeutic settings with chronically infected patients, results have been disappointing. Prophylactic vaccination against HCV infection has not yet been achieved due to many impediments including frequent spontaneous mutations of the virus with escape from immune system control. Using animal models it has been demonstrated that DNA-based immunisation strategies may overcome this problem because of their potential to induce immunity against multiple viral epitopes. DNA-based vaccines mimic the effect of live attenuated viral vaccines, eliciting cell mediated immunity in addition to inducing humoral responses. Efficacy may further be improved by addition of DNA encoding immunomodulatory cytokines and more recently, direct genetic modulation of antigen-presenting cells, such as dendritic cells (DC), has been shown to increase antigen-specific immune responses. This review focuses on immunological aspects of chronic HBV and HCV infection and on the potential of DNA- and DC-based vaccines for the treatment of chronic viral hepatitis.

Role of primary intrahepatic T-cell activation in the 'liver tolerance effect'

There is accumulating evidence suggesting that hepatic permeability to both naive and activated T lymphocytes may be unique among the solid organs. The possibility that the liver may act as a site of primary activation for CD8+ T lymphocytes is supported by experimental data and may contribute to some of the unique immunological properties of this organ, particularly its ability to induce antigen-specific tolerance. This review discusses the nature of the liver APC inducing primary T-cell activation within the liver: Kupffer cells, liver dendritic cells, liver sinusoidal endothelial cells and hepatocytes are favourably located to allow physical contact with circulating T lymphocytes. Here, we examine the capability of each cell type to act as APC for naive CD4+ or CD8+ T cells and to induce tolerance.

Immunobiology of liver dendritic cells

Dendritic cells (DC) are rare, bone marrow-derived antigen-presenting cells that play a critical role in the induction and regulation of immune reactivity. In this article, we review the identification and characterization of liver DC, their ontogenic development, in vivo mobilization and population dynamics. In addition, we discuss the functions of DC isolated from liver tissue or celiac lymph, or propagated in vitro from liver-resident haemopoietic stem/progenitor cells. Evidence concerning the role of DC in viral hepatitis, liver tumours, autoimmune liver diseases, granulomatous inflammation and the outcome of liver transplantation is also discussed.

Peripheral blood T-cell responses to pyruvate dehydrogenase complex in primary biliary cirrhosis: role of antigen-presenting dendritic cells

Patients with primary biliary cirrhosis (PBC) are usually characterized by the presence of antibody to pyruvate dehydrogenase complex (PDC) in the sera and PDC-specific T cells in the liver. However, most of the patients with PBC do not show peripheral blood T cells response to PDC. In this study, we re-evaluated the peripheral blood T cell responses to PDC in PBC using antigen-presenting dendritic cells (DCs). Twenty-four patients with PBC (AMA-positive: 16; AMA-negative: 8) and 13 normal controls were enrolled in the study. Peripheral blood mononuclear cells (PBMC) and highly enriched populations of T cells were stimulated with either only PDC or DCs plus PDC or PDC-pulsed DC plus PDC. Antibodies to different components of PDC were estimated by an immunoblotting technique. PBMC from only one out of ten AMA-positive PBC patients proliferated when cultured with only PDC. However, peripheral blood T cells from ten out of ten AMA-positive PBC patients and three out of ten AMA-negative PBC patients, but none of the five normal controls showed PDC-specific proliferation when cultured with PDC-pulsed DCs. Two of these three AMA-negative PBC patients, although negative for AMA, were positive for antibodies to other components of PDC. PDC-specific T cells are present in the peripheral blood from most of the patients with PBC. This is the first report on the effectiveness of antigen-pulsed DCs for the elucidation of autoantigen-specific immune response in human autoimmune diseases.