Immunopathology of hepatitis C

Modeling T cell responses to antigenic challenge

T cell responses are a crucial part of the adaptive immune system in the fight against infections. This article discusses the use of mathematical models for understanding the dynamics of cytotoxic T lymphocyte (CTL) responses against viral infections. Complementing experimental research, mathematical models have been very useful for exploring new hypotheses, interpreting experimental data, and for defining what needs to be measured to improve understanding. This review will start with minimally parameterized models of CTL responses, which have generated some valuable insights into basic dynamics and correlates of control. Subsequently, more biological complexity is incorporated into this modeling framework, examining different mechanisms of CTL expansion, different effector activities, and the influence of T cell help. Models and results are discussed in the context of data from specific infections.

Alanine aminotransferase elevation during peginterferon alpha-2a or alpha-2b plus ribavirin treatment

Alanine aminotransferase (ALT) elevation was occassionally observed during the treatment with combination peginterferon alpha plus ribavirin. Two forms of peginterferon are currently available as a standard of care with or without direct-acting antivirals against hepatitis C virus (HCV). Until the appearance of interferon-sparing regimen, peginterferon alpha plus ribavirin will play a central role in the eradication of HCV. In the present study, we compared ALT elevations in response to peginterferon alpha-2a plus ribavirin or peginterferon alpha-2b plus ribavirin in HCV genotype-1-infected patients. There were no significant differences in ALT elevations between treatments with the two peginterferons, but in a comparison of the proportions of patients with transient ALT elevation from baseline between the two groups, transient ALT elevation was observed more in sustained virological response (SVR) patients treated with peginterferon alpha-2a than with peginterferon alpha-2b. However, no patients discontinued treatment due to ALT elevation. Patients with transient ALT elevation from baseline during the treatment had less favorable IL28B rs8099917 genotype in the peginterferon alpha-2b group. Patients achieving SVR tended to have lower ALT levels, although some had persistent ALT elevation during treatment. In conclusion, clinicians should pay attention to possible ALT elevation during the treatment of chronic hepatitis C patients.

Rapid reduction of hepatitis C virus-Core protein in the peripheral blood improve the immunological response in chronic hepatitis C patients

AIM

  The extracellular hepatitis C virus (HCV)-antigen, including HCV-Core protein, can suppress immune cells. Recently, the efficacy of double filtration plasmapheresis (DFPP) for chronic hepatitis C (CHC) was reported. However, the mechanism of efficacy of DFPP might not be only the reduction of HCV but also the effect of immune cells via direct and/or indirect mechanisms. The aim of this study is to analyze the virological and immunological parameters of difficult-to-treat HCV patients treated with DFPP combined with Peg-interferon and RBV (DFPP/Peg-IFN/RBV) therapy.

METHODS

  Twelve CHC patients were enrolled and treated with DFPP/Peg-IFN/RBV therapy. The immunological, virological and genetic parameters were studied.

RESULTS

  All patients (4/4) treated with the major IL28B allele (T/T) could achieve complete early virological response (EVR). The amounts of HCV-Core antigen in the peripheral blood of EVR patients treated with DFPP/Peg-IFN/RBV rapidly declined in comparison to those of late virological response (LVR) patients treated with DFPP/Peg-IFN/RBV and EVR patients treated with Peg-IFN and RBV (Peg-IFN/RBV). The amount of IFN-γ produced from peripheral blood gradually increased. On the other hand, the amount of IL10 gradually decreased in the EVR patients. The frequencies of HCV-Core binding on CD3+ T cells rapidly declined in EVR patients treated with DFPP/Peg-IFN/RBV therapy. Moreover, the distributions of activated CD4(+) and CD8(+) T cells and CD16-CD56 high natural killer cells were significantly changed between before and after DFPP.

CONCLUSIONS

  The rapid reduction of HCV-Core antigens and changes in the distribution of lymphoid cells could contribute to the favorable immunological response during DFPP/Peg-IFN/RBV therapy.

Dysfunction of Immune Systems and Host Genetic Factors in Hepatitis C Virus Infection with Persistent Normal ALT

Patients with chronic hepatitis C (CHC) virus infection who have persistently normal alanine aminotransferase levels (PNALT) have mild inflammation and fibrosis in comparison to those with elevated ALT levels. The cellular immune responses to HCV are mainly responsible for viral clearance and the disease pathogenesis during infection. However, since the innate and adaptive immune systems are suppressed by various kinds of mechanisms in CHC patients, the immunopathogenesis of CHC patients with PNALT is still unclear. In this review, we summarize the representative reports about the immune suppression in CHC to better understand the immunopathogenesis of PNALT. Then, we summarize and speculate on the immunological aspects of PNALT including innate and adaptive immune systems and genetic polymorphisms of HLA and cytokines.

Lymphotropic HCV strain can infect human primary naïve CD4+ cells and affect their proliferation and IFN-γ secretion activity

BACKGROUND

Lymphotropic hepatitis C virus (HCV) infection of B and T cells might play an important role in the pathogenesis of hepatitis C. Recently, we showed that a lymphotropic HCV (SB strain) could infect established T-cell lines and B-cell lines. However, whether HCV replication interferes with cell proliferation and function in primary T lymphocytes is still unclear.

AIM

The aim of this study was to analyze whether HCV replication in primary T lymphocytes affected their development, proliferation, and Th1 commitment.

METHODS

SB strain cell culture supernatant (2 × 10(4) copies/ml HCV) was used to infect several kinds of primary lymphocyte subsets. Mock, UV-irradiated SB-HCV, JFH-1 strain, and JFH-1 NS5B mutant, which could not replicate in T cells, were included as negative controls. Carboxyfluorescein succinimidyl ester (CFSE) and CD45RA double staining was used to evaluate the proliferative activity of CD4(+)CD45RA(+)CD45RO(-) naïve CD4(+) cells. Interferon (IFN)-γ and interleukin (IL)-10 secretion assays magnetic cell sorting (MACS) were carried out.

RESULTS

Negative strand HCV RNA was detected in CD4(+), CD14(+), and CD19(+) cells. Among CD4(+) cells, CD4(+)CD45RA(+)RO(-) cells (naïve CD4(+) cells) were most susceptible to replication of the SB strain. The levels of CFSE and CD45RA expression gradually declined during cell division in uninfected cells, while HCV-infected naïve CD4(+) cells expressed higher levels of CFSE and CD45RA than Mock or UV-SB infected naïve CD4(+) cells. Moreover, the production of IFN-γ was significantly suppressed in SB-infected naïve CD4(+) cells.

CONCLUSIONS

Lymphotropic HCV replication suppressed proliferation and development, including that towards Th1 commitment, in human primary naïve CD4(+) cells.

Soluble inflammatory markers as predictors of liver histological changes in patients with chronic hepatitis C virus infection

Host immune response seems to be mainly responsible for the progression of liver disease among patients with hepatitis C virus (HCV) infection. Immune activation involves the release of cytokines and their receptors that can be measured in plasma samples. The study aimed to evaluate the association between plasma levels of chemokines and soluble tumor necrosis factor receptors (sTNFR) and liver histological changes among patients with chronic HCV infection. Seventy-one treatment-naive patients were included. Plasma levels of CCL2, CCL3, CCL11, CCL24, CXCL9, CXCL10, sTNFR1, and sTNFR2 were measured and liver histological findings were reviewed. Plasma levels of CXCL9, sTNFR1, and sTNFR2 were significantly associated with liver fibrosis, with higher median levels found among patients with moderate/severe fibrosis (F >or= 2) if compared to those with no or mild fibrosis (p = 0.014; p = 0.012; p = 0.009, respectively). Plasma sTNFR2 levels were significantly associated with necroinflammatory activity, with higher median levels among patients with moderate/severe activity (A >or= 2) if compared to those with no or mild activity (2.34 ng/mL vs. 1.99 ng/mL; p = 0.019). In conclusion, plasma levels of CXCL9, sTNFR1, and sTNFR2 were independently associated with liver histological changes, suggesting a role of TNF activation and Th1-type cell-mediated immune response in the pathogenesis of HCV infection.

The entire core protein of HCV JFH1 is required for efficient formation of infectious JFH1 pseudoparticles

The vast majority of hepatitis C virus (HCV) strains cannot be grown in cell culture. Therefore, tests for neutralizing antibodies have relied heavily on retrovirus pseudoparticles displaying the envelope glycoproteins of HCV on their surface (HCVpp). Unfortunately, the envelope proteins of some strains, especially of JFH1, did not efficiently form functional HCVpp. We have manipulated the length and composition of the HCV core gene in the HCVpp expression vectors for three strains of HCV in an attempt to obtain more efficient production of pseudoparticles. The results demonstrated that the truncated core region included in the HCV expression plasmids of the classic pseudoparticle system was optimal for formation of strain H77pp, suboptimal for strain J6pp, and insufficient for strain JFH1pp. Efficiency of JFH1pp formation increased 20-fold when the truncated core gene was replaced with the entire core gene. The full core from J6 and HK had modest effect on the production of infectious J6 and HKpp. The data suggested that pairs of HCV glycoproteins differ inherently in their ability to associate into functional heterodimers and that the core protein, provided in cis as the beginning of the polyprotein product, can in some cases facilitate this process, possibly by increasing the rate of proper folding of the glycoproteins.

Immunomodulation by hepatitis C virus-derived proteins: targeting human dendritic cells by multiple mechanisms

Hepatitis C virus (HCV) has the ability to persist in the majority of infected people. Strong, multispecific and sustained T-cell response is correlated with viral clearance. The mechanisms of chronicity by HCV are unclear. HCV could restrain the immune system and establish chronic infection by modulating dendritic cell (DC) function, T-cell function or both. DC dysfunction has been postulated to be either due to direct HCV infection or by the presence of HCV proteins. In this report, for the first time, we have examined whether soluble HCV proteins can impair DC function or directly inhibit T-cell responses in the cells obtained from healthy uninfected people. Our studies revealed that different HCV proteins used distinct mechanisms to down-regulate DC functions. Individual HCV proteins, Core, NS3, NS4, NS5 as well as fused Polyprotein (Core-NS3-NS4) were found to impair functions of both immature DCs and mature DCs by regulating the expression of co-stimulatory and antigen presentation molecules, strikingly reducing IL-12 secretion, inducing the expression of FasL to mediate apoptosis, interfering with allo-stimulatory capacity, inhibiting toll-like receptor signaling and inhibiting nuclear translocation of NFkappaB in DCs. Interestingly, HCV proteins did not directly inhibit T-cell proliferation. Our findings clearly demonstrate that HCV proteins impair T-cell responses indirectly by inhibiting DCs that could result in a sub-optimal cellular immune response allowing for persistent HCV infections. These studies delineate important mechanisms by which initial DC dysfunction can establish contributing to chronicity. Our data are in agreement with earlier observations that DCs are impaired in HCV infected people.

Hepatitis C virus infection of T cells inhibits proliferation and enhances fas-mediated apoptosis by down-regulating the expression of CD44 splicing variant 6

BACKGROUND

A lymphotropic hepatitis C virus strain (HCV, SB strain, hereafter "SB-HCV") has been shown to infect established T cell lines (Molt-4 and Jurkat) and primary human naive CD4(+) T cells. During T cell development and activation, transient expression of CD44 splicing variant 6 (CD44v6) plays a significant role.

METHODS

SB-HCV was used to infect Molt-4 cells, and their cellular proliferation and CD44 expression was examined.

RESULTS

SB-HCV-infected Molt-4 cells expressed a significantly lower level of the CD44v6 isoform. The infected cells could be divided into 2 carboxyfluorescein succinimidyl ester (CFSE) groups, CFSE-high (indicating low proliferation activity; 34.2% of the cells) and CFSE-low (indicating high proliferation activity; 62.5% of the cells), whereas uninfected cells consisted of only a CFSE-low population. Of the CFSE-high cells, 82.4% were positive for the HCV protein NS5A, whereas only 1.2% of the CFSE-low cells were positive for this protein. Among the HCV proteins, NS5A alone caused the down-regulation of CD44v6 expression. After cells were stimulated with phorbol myristate acetate, the amount of phosphorylated mitogen-activated protein (MAP) kinase was significantly reduced in CFSE-high, SB-HCV-infected Molt-4 cells. After Fas ligand stimulation, SB-HCV-infected Molt-4 cells had increased cleavage of caspase 8 and 3 and enhanced apoptosis, compared with the rates of cleavage and apoptosis in control groups, indicating that SB-HCV infection increased Fas-mediated apoptosis.

CONCLUSION

HCV replication in T cells suppresses cellular proliferation and enhances susceptibility to Fas signaling by inhibiting CD44v6 signaling and expression.

Analysis of CD8+ T-cell-mediated inhibition of hepatitis C virus replication using a novel immunological model

BACKGROUND & AIMS

Virus-specific CD8+ T cells are required for the control of hepatitis C virus (HCV) infection. We investigated the extent to which different effector functions of CD8+ T cells contribute to the inhibition of viral replication.

METHODS

We developed a novel immunologic model by stably transducing the HLA-A2 gene into the replicon system, matching the epitope sequence of the replicon to the sequence targeted by an HCV-specific CD8+ T-cell clone. Luciferase activity was then measured to quantitate HCV RNA replication.

RESULTS

HCV-specific CD8+ T cells strongly inhibited viral replication, through cytolytic and noncytolytic mechanisms, in a dose-dependent manner. HCV replication was almost completely inhibited at an effector-to-target ratio of 1:1 with significant cytotoxicity; however, >95% viral inhibition occurred at ratios as low as 1:100. Importantly, no cytotoxicity was observed at low effector-to-target ratios, indicating a dominant effect of noncytolytic effector functions that was confirmed by Transwell experiments. Neutralization experiments revealed that interferon gamma mediates the noncytolytic inhibition.

CONCLUSIONS

Only a very few HCV-specific CD8+ T cells are required to inhibit HCV replication; inhibition occurs primarily by noncytolytic effector functions.

Molecular and contextual markers of hepatitis C virus and drug abuse

The spread of hepatitis C virus (HCV) infection involves a complex interplay of social risks, and molecular factors of both virus and host. Injection drug abuse is the most powerful risk factor for HCV infection, followed by sexual transmission and additional non-injection drug abuse factors such as co-infection with other viruses and barriers to treatment. It is clearly important to understand the wider context in which the factors related to HCV infection occur. This understanding is required for a comprehensive approach leading to the successful prevention, diagnosis, and treatment of HCV. An additional consideration is that current treatments and advanced molecular methods are generally unavailable to socially disadvantaged patients. Thus, the recognition of behavioral/social, viral, and host factors as components of an integrated approach to HCV is important to help this vulnerable group. Equally important, this approach is key to the development of personalized patient treatment - a significant goal in global healthcare. In this review, we discuss recent findings concerning the impact of drug abuse, epidemiology, social behavior, virology, immunopathology, and genetics on HCV infection and the course of disease.

HLA-class II alleles in Egyptian patients with hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is linked to environmental, dietary, and life style factors. Its incidence and distribution vary widely among ethnic groups, sex, and geographic regions. HBV and HCV Infection, liver cirrhosis, male gender, and old age are important risk factors of HCC. Variability in outcome following exposure, and the clustering of HCC within families raise the possibility that genetic factors are also involved in susceptibility to HCC. The Major Histocompatibility Complex (MHC) plays a key role in anti-virus and tumor defense. HLA polymorphism is implicated in conferring genetic susceptibility to a large number of immune-mediated diseases, including some cancers. The association between HLA class II antigen and HCC in different ethnic populations that has been reported is controversial. Therefore, the aim of this work was to study the association between HLA class II-DRB1 and DQB1 polymorphism and HCC in Egyptian patients and to investigate their role as risk factors for the development of HCC.

METHODS

HLA-class II (DRB1 and DQB1) typing was done by SSP for 100 subjects; 50 patients suffering from HCC (45 males and 5 females) with age range 40-64 years (51.16 years (y) +/- 6.16); and 50 normal healthy control subjects.

RESULTS

1. A significantly increased frequency of DRB1*04, and DQB1 *02 in HCC patients versus control group (p = 0.016, and 0.032, respectively) was found; 2. A significantly decreased frequency of DQB1*06 (p = 0.032) was found; 3. A significantly increased frequency of DRB1*07 (odds ratio (OR) = 4.929) was found; and 4. A significantly decreased frequency of DRB1*15 (OR = 0.316) was seen. In conclusion, while some alleles are significantly associated with HCC (DRB1*04, DQB1*02) and others are not associated (DQB1*06); therefore, it can be concluded that the DRB1*04 and DQB1*02 alleles might be risk factors for the occurrence of HCC (OR = 4.373 and 3.807, respectively), and DQB1*06 may be a protective allele (OR = 0.259).

Peripheral blood lymphocyte populations in end-stage liver diseases

GOALS/BACKGROUND

The aim of this study was to decipher whether end-stage liver failure modifies peripheral blood lymphocytes (PBL) in a homogeneous manner, independently of the base pathology, or, if on the contrary, PBL subsets show a different profile in each hepatic disease.

METHODS

We studied PBL subsets in 71 patients with end-stage liver disease, before liver transplant, and 74 healthy controls by flow cytometry. The results were statistically compared between patients and controls, and cohorts of patients classified according to their base pathology.

RESULTS

We observed lower absolute numbers in all lymphocyte populations in patients compared with controls. We found an increment of CD3+ activated cells (P<10) and CD45RO+CD4+ (P<10) in chronic hepatitis C virus versus controls; hepatitis B virus showed high TCRgammadelta+ and CD8+ T cells with respect to controls (P=0.008 and P=0.029, respectively); alcoholic cirrhotic patients showed low CD8+, mainly CD45RA+CD8+ (P=0.007) and high CD45RO+CD4+ (P<10) compared with the normal population; autoimmune diseases showed lower CD3+ and TCRalphabeta+ (P=0.002 and P=0.0001) than controls.

CONCLUSIONS

Regardless of the base pathology, patients with end-stage liver disease show a low absolute number of lymphocyte populations compared with controls. However, PBL profiles are different, characteristic, and specific of every disease causing chronic liver failure.

Cytokine--chemokine and apoptotic signatures in patients with hepatitis C

Cytokines and chemokines are proteins that play a critical role in the regulation of immunity and inflammation in patients with chronic Hepatitis C. The aim of our study was to correlate serum cytokines, chemokines and apoptosis in non-treated chronic hepatitis C patients with various degrees of inflammation and fibrosis. We studied 778 patients: 59 had low Knodell fibrosis score and low Knodell histological activity index; 372 had mild fibrosis and low histological activity index; 270 had moderate fibrosis and moderate histological activity index; and, 77 had high fibrosis and high histological activity index on their biopsy. Serum cytokines, chemokines and apoptosis were measured by enzyme-linked-immunosorbent-assay. Multivariate analysis was employed for statistical purposes. A positive correlation was seen between the degree of inflammation and tumor necrosis factor-alpha (TNF-alpha) levels (r = 0.92) in non-cirrhotic patients and between interleukin 2 in all patients (r = 0.85). Interleukin-8 increased significantly at higher histological activity indices and continued to increase in patients with cirrhosis. Transforming growth factor-beta (TGF-beta) levels increased significantly with the severity of fibrosis, but decreased in cirrhotics. In conclusion, cytokines, chemokines and apoptosis levels reflect the progression of inflammation and fibrosis in hepatitis C infected patients, but their signatures differ.

Hepatitis C virus infects T cells and affects interferon-gamma signaling in T cell lines

It has been reported that hepatitis C virus (HCV) may infect and replicate in human T cells, particularly in perihepatic lymph nodes, but the extent and consequence of T-cell infection in patients is unclear. This study is conducted to characterize the parameters and functional consequences of HCV infection in T lymphocytes. By using a lymphotropic HCV strain, we showed that HCV could infect T cell lines (Molt-4 and Jurkat cells) in vitro. Both positive- and negative-strand HCV RNA were detected for several weeks after infection. Viral proteins could also be detected by immunofluorescence studies. Moreover, infectious HCV particles were produced from Molt-4 cell cultures, and could be used to infect naïve T cell lines. HCV could also infect human primary CD4+ T cells, particularly naïve (CD45RA+CD45RO-) CD4+ cells, in culture. The amounts of STAT-1 and phosphorylated STAT-1 proteins in the infected Molt-4 cells were significantly less than those in uninfected cultures, suggesting the possibility of defect in interferon-gamma signaling. Indeed, T-bet and STAT-1 mRNA levels after interferon-gamma stimulation in infected Molt-4 were suppressed. In conclusion, HCV could infect and transiently replicate in T cells and that HCV replication suppressed the IFN-gamma/STAT-1/T-bet signaling due to the reduction of STAT-1 and inhibition of its activation (phosphorylation).

Cytotoxic CD4 T cells in viral hepatitis

CD4+ T cells are thought to contribute to antiviral immune responses by secretion of cytokines thereby providing help to CD8+ T and B cells. However, perforin-positive cytotoxic CD4+ T cells have been described in human immunodeficiency virus-positive patients suggesting a role not only of CD8+ but also of CD4+ T cells for killing virus-infected cells. We investigated 76 patients with viral hepatitis [15 hepatitis B virus (HBV), 22 HBV/hepatitis D virus and 17 hepatitis C virus (HCV)] for cytotoxic CD4+ T cells. The frequency of perforin-positive CD4+ T cells in viral hepatitis was highly variable ranging from < 1% to more than 25%. Perforin-positive CD4+ T cells displayed the phenotype of terminally differentiated effector cells (CD28-, CD27-). The highest frequencies of CD4+ cytotoxic T lymphocytes (CTLs) were found in patients with delta hepatitis (P = 0.04 vs HBV and HCV patients), and the presence of CD4+ CTLs was associated with elevated aspartate aminotransferase levels (P = 0.01) and decreased platelet counts (P = 0.03). Perforin-positive CD4+ T cells decreased in two individuals during spontaneous clearance of acute hepatitis C. Significant associations were found between the frequency of perforin-expressing CD4+ cells and age (P = 0.04), perforin-positive CD8+ cells (P < 0.001) and perforin-positive CD4-/CD8- lymphoid cells (P = 0.002). Differentiated CD27- effector CD4+ CTLs can be detected in patients with viral hepatitis. In particular in patients with more advanced liver disease, the accumulation of perforin-positive T cells with age could be one correlate for the more severe course of viral hepatitis in elderly individuals.

Identification of hepatitis C virus (HCV) 2a-derived epitope peptides having the capacity to induce cytotoxic T lymphocytes in human leukocyte antigen-A24+ and HCV2a-infected patients

Since virus-specific cytotoxic T lymphocytes (CTLs) play a critical role in preventing the spread of hepatitis C virus (HCV), vaccine-based HCV-specific CTL induction could be a promising strategy to treat HCV-infected patients. In this study, we tried to identify HCV2a-derived epitopes, which can induce human leukocyte antigen (HLA)-A24-restricted and peptide-specific CTLs. Peripheral blood mononuclear cells of HCV2a-infected patients or healthy donors were stimulated in vitro with HCV2a-derived peptides, which were prepared based on the HLA-A24 binding motif. As a result, three peptides (HCV2a 576-584, HCV2a 627-635, and HCV2a 1085-1094) efficiently induced peptide-specific CTLs from HLA-A24(+) HCV2a-infected patients as well as healthy donors. The cytotoxicity was exhibited by peptide-specific CD8(+) T cells in an HLA-A24-restricted manner. In addition, the HCV2a 627-635 peptide was frequently recognized by immunoglobulin G of HCV2a-infected patients. These results indicate that the identified three HCV2a peptides might be applicable to peptide-based immunotherapy for HLA-A24(+) HCV2a-infected patients.

Accumulation of dysfunctional effector CD8+ T cells in the liver of patients with chronic HCV infection

BACKGROUND/AIMS

Hepatitis C virus (HCV) causes a chronic infection that can lead to fibrosis and carcinoma. Immune responses mediated by cytotoxic T lymphocytes (CTLs) could be involved in viral clearance or persistence, and therefore in determining the course of the disease.

METHODS

Intrahepatic and peripheral blood CD8+T cells were obtained from 32 HCV-chronically infected patients and analysed by flow-cytometry for surface markers of differentiation, IFNgamma and TNFalpha production, degranulation capacity and perforin content, after CD3 triggering. Results were compared with those obtained from 13 patients with a non-viral liver disease.

RESULTS

Intrahepatic CD8+T cells of HCV-infected patients, despite their phenotype of pre-terminally and terminally differentiated effectors (CCR7-CD45RA-/+), are poorly responsive to T cell receptor (TCR)-mediated stimulation compared with those obtained from uninfected subjects. This defect correlates with the severity of fibrosis, is more pronounced in patients with ALT<1.5xN than with ALT>1.5xNU/ml, and is not evident after mitogen stimulation.

CONCLUSIONS

The present study describes the accumulation of hypo-responsive CD8+T cells in the liver of patients with chronic HCV infection. Understanding the mechanisms underlying this impairment may be helpful in the design of innovative strategies for HCV treatment.

Rescue of in vivo FAS-induced apoptosis of hepatocytes by corticosteroids either associated with alcohol consumption by mice or provided exogenously

The pathogenic effects of many hepatic viral infections are mediated, at least in part, by the immune response to the infected hepatocyte. The immune response in the infected liver involves the interaction of cytotoxic T cells (CTL) with the hepatocytes through the interaction of FAS-ligand on the CTL and FAS on the hepatocyte. The initial hypothesis for this study was that alcohol consumption by mice would sensitize the liver to apoptosis induced by ligation of FAS. C57Bl/6 mice fed ethanol in a liquid diet did show an increased percentage of apoptotic cells 2 h after injection with anti-FAS as compared with the percentage in the control mice. However, 4 and 6 h after anti-FAS injection, control mice showed high percentages of apoptotic cells (20% to 41%) compared with 5% and 4% apoptotic cells in the ethanol-fed mice. The decreased apoptosis of ethanol-fed mice correlated closely with corticosterone levels in the sera. This was confirmed by the finding that adrenalectomized (ADX) mice provided a high level of corticosterone in drinking water were protected against FAS-induced hepatocyte apoptosis. Ethanol-fed mice showed a significant elevation of serum alanine aminotransferase (ALT) levels indicating the development of hepatitis in spite of the relatively low proportion of apoptotic cells in the liver. In conclusion, high levels of corticosterone protect hepatocytes from FAS-mediated apoptosis, but do not prevent the ultimate development of liver damage. In experiments where mice were provided ethanol chronically in drinking water, where stress is minimal, higher levels of ALT were noted in animals in the ethanol group as compared with animals in the control group. These data support the suggestion that ethanol increases hepatocyte sensitivity to FAS-mediated damage.

Gene expression profile of T-cell-specific chemokines in human hepatocyte-derived cells: evidence for a synergistic inducer effect of cytokines and hepatitis C virus proteins

Increased levels of chemokines (CK) in chronic hepatitis C virus (HCV) infection have been found. Given that NS5A and core can function as transcriptional transactivators, we aimed to determine whether these HCV proteins might induce CK gene expression in human hepatocyte-derived cells. We assessed (i) regulated upon activation, normal T cells expressed and activated (RANTES), interferon gamma-inducible protein-10 (IP-10), and monokine induced by interferon-gamma (MIG) mRNA levels in NS5A and core stably transfected Chang liver (CHL) cells, stimulated or not with a cytokine mixture (CM), by reverse transcriptase-polymerase chain reaction (RT-PCR) and (ii) quantitative enzyme-linked immunosorbent assay (ELISA) measurements of these CK in the supernatants of CHL cells. Induction of RANTES transcripts in resting HCV-transfected cells was clearly observed, being augmented fourfold in resting NS5A-transfected cells and threefold in resting core-transfected cells over that in resting mock-transfected (control) cells, as well as to a similar extent in CM-stimulated NS5A- and core-transfected cells. Increased RANTES secretion followed the same pattern observed for mRNA expression. Both IP-10 and MIG, such as mRNA and protein levels, were undetectable in resting HCV-transfected and -untransfected cells, whereas IP-10 and MIG mRNA expression was increased by seven- and fivefold in CM-stimulated NS5A-transfected cells and by 10- and 3.5-fold in CM-stimulated core-transfected cells, respectively, above that in CM-stimulated control cells. IP-10 and MIG secretion was enhanced by 2.6- and threefold in CM-stimulated NS5A-transfected cells and by 3.6-fold and 3.7-fold in CM-stimulated core-transfected cells, respectively over that in CM-stimulated control cells. These results demonstrate that NS5A and core proteins, alone or by the synergistic effect of cytokines, are capable of upregulating RANTES, IP-10 and MIG gene expression in cultured human hepatocyte-derived cells.

Different procarcinogenic potentials of lymphocyte subsets in a transgenic mouse model of chronic hepatitis B

The immune response to hepatitis viruses is believed to be involved in the development of chronic hepatitis; however, its pathogenetic potential has not been clearly defined. The current study, using a transgenic mouse model of chronic hepatitis B, was designed to determine the relative contributions of the immune cell subsets to the progression of liver disease that induces hepatocellular carcinogenesis. Hepatitis B virus transgenic mice were adoptively transferred with CD4+ and CD8+ T cell-enriched or -depleted and B cell-depleted splenocytes obtained from hepatitis B surface antigen-primed, syngeneic nontransgenic donors. The resultant liver disease, hepatocyte apoptosis, regeneration, and tumor development were assessed and compared with the manifestations in mice that had received unfractionated spleen cells. Transfer of CD8(+)-enriched splenocytes caused prolonged disease kinetics, and a marked increase in the extent of hepatocyte apoptosis and regeneration. In 12 of 14 mice the transfer resulted in multiple hepatocellular carcinomas (HCCs) comparable with the manifestations seen in the mice transferred with total splenocytes. In contrast, mice that had received CD4(+)-enriched cells demonstrated lower levels of liver disease and developed fewer incidences of HCC (4 of 17). The experiment also revealed that all of the groups of mice complicated with HCC developed comparable mean numbers and sizes of tumors. B-cell depletion had no effect on disease kinetics in this model. Taken together, these results demonstrate that the pathogenetic events induced by CD8+ T-cell subset are primarily responsible for the induction of chronic liver disease that increases tumor incidence, suggesting their potential in triggering the process of hepatocarcinogenesis.

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Increased circulating and intrahepatic T-cell-specific chemokines in chronic hepatitis C: relationship with the type of virological response to peginterferon plus ribavirin combination therapy

AIMS

To determine the serum and intrahepatic levels of T-helper-1-associated chemokines in patients with chronic hepatitis C before, during and after peginterferon plus ribavirin combination therapy and to search for correlations with baseline characteristics of hepatitis C virus-related chronic liver disease and type of therapeutic response.

METHODS

Serum chemokine levels were determined by enzyme-linked immunosorbent assays and intrahepatic chemokine messenger RNA and protein levels were tested by ribonuclease protection assay and immunohistochemistry.

RESULTS

Serum and intrahepatic chemokine levels were elevated in all patients with chronic hepatitis C and showed a marked decrease in patients who obtained a virological response vs. non-responders. Increased serum interferon-gamma-inducible protein-10 levels at baseline in genotype 1-infected patients were significantly associated with greater degrees of intrahepatic inflammation and fibrosis (P = 0.0046 and P = 0.02, respectively) and with virological non-response (P = 0.01). In patients with genotype 1, basal serum interferon-gamma-inducible protein-10 levels greater than 299 pg/mL identified 80% of non-responders and lower than 299 pg/mL identified 63% of responders.

CONCLUSIONS

Circulating and intrahepatic T-helper-1-associated chemokines are abnormally elevated in patients with chronic hepatitis C. Increased baseline serum interferon-gamma-inducible protein-10 levels in genotype 1-infected patients are associated with virological non-response to peginterferon plus ribavirin combination therapy.

T cell dynamics in HIV-1 infection

In the absence of antiretroviral treatment, HIV-1 establishes a chronic, progressive infection of the human immune system that invariably, over the course of years, leads to its destruction and fatal immunodeficiency. Paradoxically, while viral replication is extensive throughout the course of infection, deterioration of conventional measures of immunity is slow, including the characteristic loss of CD4(+) T cells that is thought to play a key role in the development of immunodeficiency. This conundrum suggests that CD4(+) T cell-directed viral cytopathicity alone cannot explain the course of disease. Indeed, recent advances now indicate that HIV-1 pathogenesis is likely to result from a complex interplay between the virus and the immune system, particularly the mechanisms responsible for T cell homeostasis and regeneration. We review these data and present a model of HIV-1 pathogenesis in which the protracted loss of CD4(+) T cells results from early viral destruction of selected memory T cell populations, followed by a combination of profound increases in overall memory T cell turnover, damage to the thymus and other lymphoid tissues, and physiological limitations in peripheral CD4(+) T cell renewal.

Hepatitis C virus dynamics and pathology: the role of CTL and antibody responses

This paper investigates the role of CTL and antibody responses in hepatitis C virus (HCV) dynamics and pathology. Mathematical models suggest that a strong CTL response is required for resolution of HCV infection and that a weak CTL response can result in persistent infection. According to the model, establishment of persistent infection is accompanied mainly by an ongoing antibody response, while CTLs are not maintained at high levels. In the model, this outcome correlates with absence of pathology. Persistent infection in the face of an ongoing antibody response can result in evolution of antigenic escape. According to the model, evolution towards escape from antibodies can shift the balance of immune responses so that the weak CTL levels become increasingly more dominant relative to antibodies. This shift results in onset of liver pathology as the virus evolves towards increased levels of antigenic escape. Therefore, the relative balance of the immune response can be a decisive factor that determines whether patients are asymptomatic or whether pathology is observed. Virus evolution can shift this balance towards pathology over time. Theoretical results are discussed in the context of published data.

Evaluation of hepatitis B and hepatitis C virus-infected renal allograft recipients with liver biopsy and noninvasive parameters

BACKGROUND

Patients with end-stage renal disease are at high risk for hepatitis B (HBV) or hepatitis C virus (HCV) infection. Because therapy indication for viral hepatitis depends on virologic, biochemical, and histologic criteria, liver biopsy usually is necessary. Recently, a panel of serum fibrosis markers has been postulated to allow quantification of liver fibrosis by noninvasive means.

METHODS

A cross-sectional study of all hepatitis B surface antigen (HBsAg)- and anti-HCV-positive renal allograft recipients among 900 renal allograft recipients regularly controlled in the authors' outpatient nephrology service was performed. The correlation between histologic, biochemical, and virologic parameters was assessed with an emphasis on the fibrosis marker hyaluronate in this immunosuppressed population.

RESULTS

Twenty-two HBsAg- and 62 anti-HCV-positive patients were analyzed. Based on polymerase chain reaction results, 86% of anti-HCV-positive and 95% of HBsAg-positive patients had actively replicating infection. In 41 of 67 (61%) patients with replicating disease, liver biopsy was performed, and the association of various biochemical parameters with the histologic scores for necroinflammation and fibrosis was investigated. Less than 10% of these patients had advanced fibrosis, although the mean time of infection was more than 15 years. We found no correlation of any of the serum parameters (including hyaluronate) with histologic activity of liver disease except for the peak glutamate-oxalacetate transaminase value recorded during the entire posttransplant period.

CONCLUSION

Liver biopsy remains the gold standard for evaluation of liver disease and therapy decision in immunosuppressed renal allograft recipients.

Analysis of the CD8-positive T cell response in Japanese patients with chronic hepatitis C using HLA-A*2402 peptide tetramers

Hepatitis C virus (HCV)-specific CD8+ cytotoxic T lymphocytes (CTL) contribute to viral clearance in acute, self-limited hepatitis C as well as to liver cell injury in the more frequent cases with chronic hepatitis C. Although HLA class I-peptide tetramers have been used to detect circulating HCV epitope-specific CTL with a high sensitivity and specificity, this technique has been targeted exclusively to the most frequent HLA haplotypes in the Caucasian population and the large number of HCV-infected Asian patients, most of whom are HLA-A24 positive, have not been studied. The current study determines the frequency, phenotype, and clinical significance of HCV-specific CD8(+) T lymphocytes with five different HLA-A*2402 tetramers in 43 HCV infected Japanese patients and 32 controls. Overall, tetramer(+) cells were detected in the blood of 33 of 43 patients at frequencies of 0.064-0.75% CD8(+)CD4(-)CD14(-)CD19(-) T lymphocytes. Interestingly, although the T cell response was always targeted multispecifically against epitopes in different HCV proteins, the relative frequency of cells stained with individual tetramers differed between patients. Furthermore, tetramer(+)CD8(+) T lymphocytes were highly activated, but the phenotypes of different tetramer(+) cells varied in each patient. In conclusion, HLA-A24 restricted, HCV-specific CD8(+) T lymphocytes are found at similar frequencies in Asian patients as HLA-A2 restricted, HCV-specific CD8(+) T lymphocytes in Caucasian patients. Differences in the frequency and activation status of individual tetramer(+) cell populations suggest that CD8(+) T lymphocytes with different HCV epitope specificity may mediate differential pathogenetic effects in chronic hepatitis C.

Frequency and phenotype of circulating Valpha24/Vbeta11 double-positive natural killer T cells during hepatitis C virus infection

Natural killer T (NKT) cells are thought to be involved in innate responses against infection. We investigated one specific type of NKT cell, Valpha24/Vbeta11 double positive, in hepatitis C virus (HCV) infection. Lower frequencies of this population were detected in the blood of HCV PCR-positive patients than in controls. Unlike Valpha24/Vbeta11 NKT cells found in blood, those in the liver appeared to be recently activated.

Simultaneous evaluation of lymphocyte subpopulations in the liver and in peripheral blood mononuclear cells of HCV-infected patients: relationship with histological lesions

ABBREVIATIONS

Intrahepatic lymphocytes are believed to be involved in the immunopathogenesis of hepatitis C virus (HCV) infection and the evolution of HCV-induced hepatitis. In the present study, we examined the three main intrahepatic lymphocyte subsets, namely CD3+CD56- conventional T lymphocytes, CD3+CD56+ natural T (NT) lymphocytes and CD3-CD56+ natural killer (NK) lymphocytes in HCV-infected patients. The proportion of each lymphocyte subset was evaluated both in liver biopsies and in samples of peripheral blood lymphocytes (PBL) by flow cytometry in 21 patients with histologically proven chronic hepatitis C. Simultaneously, alanine aminotransferase (ALT) levels, viral load and histological lesions were assessed. Neither NT nor NK populations correlated with any biochemical, viral or histological parameters. Furthermore, Valpha24+ NT lymphocytes showed no preferential enrichment in the liver of HCV-infected patients. Regarding conventional T lymphocytes, a highly significant linear correlation was found between intrahepatic CD3+CD56- T lymphocytes and the Knodell score, a numerical score for assessing histological activity and fibrosis (r = 0.715, P < 0.0001) and more specifically with the periportal necrosis parameter, which is the main lesion of chronic hepatitis C. In addition, analysis of the peripheral compartment revealed a high correlation between values of CD3+CD56- lymphocytes and both Knodell score (r = 0.624, P = 0.003) and serum ALT levels and again with periportal necrosis. The strong correlation between the proportion of peripheral CD3+CD56- conventional T lymphocytes and the severity of hepatic lesions leads us to propose that evaluation of this accessible peripheral population could be used as an indicator test for the severity of histological lesions in chronic hepatitis C.

Increased expression of T cell chemokines and their receptors in chronic hepatitis C: relationship with the histological activity of liver disease

OBJECTIVES

Although chemokines seem to be important in certain inflammatory disorders, little is known about the role of these proteins in chronic hepatitis C.

METHODS

Expression of selected CXC and CC chemokines and their receptors was assessed by immunohistochemistry and flow cytometry in chronic hepatitis C. Tissue samples from normal liver and that of sustained responders were also evaluated. A comparative analysis between the histological grading and the intrahepatic expression level of chemokines was performed.

RESULTS

The majority of liver-derived T lymphocytes expressed CXCR3 and CCR5 chemokine receptors, representing high enrichment over levels of CXCR3 + and CCR5 + T cells in blood from chronic hepatitis C. An intense intrahepatic expression of their respective ligands, the CXC chemokine Mig, and RANTES, was detected in the same patients studied, being restricted to the sinusoidal endothelium and to hepatocytes, respectively. A statistically significant association between the intrahepatic chemokine expression level and the inflammatory activity of chronic hepatitis C was found. Of note was the marked expression of both CXCR3 and its ligand Mig on endothelial cells from portal neovessels in chronic hepatitis C.

CONCLUSIONS

Intrahepatic chemokine signaling could play a key role regulating significant pathological events during chronic hepatitis C, opening new avenues for therapeutic interventions based on chemokine activities.

Role of activated CD8+ T cells in the initiation and continuation of hepatic damage

The cause of alcoholic liver disease (ALD) is multifactorial and poorly understood. It is clear that alcohol alone is not responsible for most of the changes associated with ALD and that cofactors are involved in initiation and production of ALD. One cofactor that has received a great deal of attention recently is the concomitant infection with hepatitis C virus (HCV) and alcohol abuse. The interactive effects of HCV and alcohol abuse are still unclear, but apparently they are the result of an inability of the immune system to control the viral infection and exaggerated hepatocyte damage mediated by either the cells of the inflammatory response or factors produced by the inflammatory cells. This review will focus on one aspect of the possible pathogenic effects associated with alcohol abuse and HCV infection: the possible role of the immune system, notably the cytotoxic T lymphocyte (CTL) response. It is clear that the development of a CTL response is critical for the control of HCV infections, and it is also likely that this response is involved in liver damage. In this review, the evidence that shows the importance of the CD8(+) CTL in viral clearance and the role for pathogenesis will be presented. Findings obtained from animal studies that support the suggestion that activated CD8(+) CTLs can induce liver damage will be presented, as will results of recent studies from my laboratory that provide evidence for an effect of alcohol to enhance the liver damage mediated by activated CD8(+) T cells.

Sustained high frequencies of specific CD4 T cells restricted to a single persistent virus

Replication of cytomegalovirus (CMV) is largely controlled by the cellular arm of the immune response. In this study the CMV-specific CD4 T-cell response was characterized in a cohort of apparently healthy individuals. In 11% of all individuals, extremely high frequencies, between 10 and 40%, were found. High-level frequencies of CMV-specific CD4 T cells persisted over several months and were not the result of an acute infection. Specific T cells were oligoclonal and were phenotypically and functionally characterized as mature effector cells, with both cytokine-secreting and proliferative potential. These high-level frequencies do not seem to compromise the immune response towards heterologous infections, and no signs of immunopathology were observed. Whereas a large temporary expansion of virus-specific T cells is well known to occur during acute infection, we now show that extremely high frequencies of virus-specific T cells may continuously exist in chronic CMV infection without overtly compromising the remaining protective immunity.

Single nucleotide insertion in the 5'-untranslated region of hepatitis C virus with clearance of the viral RNA in a liver transplant recipient during acute hepatitis B virus superinfection

Hepatitis C virus (HCV) infection is an important etiology in patients undergoing orthotopic liver transplantation (OLT) world-wide. Antiviral therapy-related clearance of HCV RNA may occur both in patients with chronic HCV infection and in transplanted patients for HCV-related liver cirrhosis, but the role of the 5'-untranslated region (UTR) of HCV containing the internal ribosome entry site (IRES), which directs the translation of the viral open reading frame has not hitherto been evaluated. We studied the 5'-UTR in an HCV-infected recipient of a liver graft that showed spontaneous clearance of HCV RNA during an acute hepatitis B virus (HBV) superinfection. Sequencing of the 5'-UTR of HCV showed a nucleotide A insertion at position 193 of the IRES.

Immunopathogenesis of hepatitis C virus infection

Hepatitis C virus, a recently identified member of the family Flaviviridae, is an important cause of chronic viral hepatitis and cirrhosis. There are similarities in the nature of the immune response to this pathogen with immunity in other flavivirus and hepatotropic virus infections, such as hepatitis B. However, the high rate of viral persistence after primary hepatitis C infection, and the observation that neutralizing antibodies are not protective, would suggest that there are a number of important differences between hepatitis C, other flaviviruses, and hepatitis B. The phenomenon of quasispecies evolution and other viral factors have been proposed to contribute to immune evasion by hepatitis C virus. In the face of established persistent infection, virus-specific cytotoxic T lymphocytes may exert some control over viral replication. However, these same effectors may also be responsible for the progressive liver damage characteristic of chronic hepatitis C infection. The nature of protective immunity, including the role of innate immune responses early after hepatitis C exposure, remains to be defined.

Determinants of viral clearance and persistence during acute hepatitis C virus infection

The virological and immunological features of hepatitis C virus (HCV) infection were studied weekly for 6 months after accidental needlestick exposure in five health care workers, four of whom developed acute hepatitis that progressed to chronicity while one subject cleared the virus. In all subjects, viremia was first detectable within 1-2 weeks of inoculation, 1 month or more before the appearance of virus-specific T cells. The subject who cleared the virus experienced a prolonged episode of acute hepatitis that coincided with a CD38+ IFN-gamma- CD8+ T cell response to HCV and a small reduction in viremia. Subsequently, a strong CD4+ T cell response emerged and the CD8+ T cells became CD38- and started producing IFN-gamma in response to HCV, coinciding with a rapid 100,000-fold decrease in viremia that occurred without a corresponding surge of disease activity. Chronic infection developed in two subjects who failed to produce a significant T cell response and in two other subjects who initially mounted strong CD4+ T cell responses that ultimately waned. In all subjects, viremia was higher at the peak of acute hepatitis than it was when the disease began, and the disease improved during the viremia. These results provide the first insight into the host-virus relationship in humans during the incubation phase of acute HCV infection, and they provide the only insight to date into the virological and immunological characteristics of clinically asymptomatic acute HCV infection, the commonest manifestation of this disease. In addition, the results suggest that the vigor and quality of the antiviral T cell response determines the outcome of acute HCV infection, that the ability of HCV to outpace the T cell response may contribute to its tendency to persist; that the onset of hepatitis coincides with the onset of the CD8+ T cell response, that disease pathogenesis and viral clearance are mediated by different CD8+ T cell populations that control HCV by both cytolytic and noncytolytic mechanisms, and that there are different pathways to viral persistence in asymptomatic and symptomatic acute HCV infection.

Monocyte-dependent cell death of T lymphocyte subsets in chronic hepatitis C

A high incidence of viral persistence and progression to chronic hepatitis are characteristic features of hepatitis C virus (HCV) infection. Since T lymphocytes play a critical role in virus clearance, their abnormalities in undergoing apoptosis may cause the insufficient antiviral immune responses leading to persistent viral infection. Recent reports have suggested that monocyte-dependent cell death (MDCD) is a mechanism of T lymphocyte apoptosis in chronic viral infection. The current study was designed to monitor apoptosis of CD4+ and CD8+ T lymphocyte subsets in co-culture with CD14+ monocytes under the apoptotic stimuli in patients with chronic hepatitis C. Cell mortalities of CD4+ and CD8+ T lymphocyte subsets from patients exhibiting various degrees of chronic hepatitis C were increased to a greater extent when incubated with CD14+ monocyte subset in medium containing phorbol 12-myristate 13-acetate. The current observations demonstrate that MDCD of CD4+ and CD8+ T lymphocyte subsets may provide a cellular basis for immune dysfunction which results in insufficient viral clearance and progression of liver disease in chronic HCV infection.

Direct functional analysis of epitope-specific CD8+ T cells in peripheral blood

The functional status of virus-specific CD8+ T cells is important for the outcome and the immunopathogenesis of viral infections. We have developed an assay for the direct functional analysis of antigen-specific CD8+ T cells, which does not require prolonged in vitro cultivation and amplification of T cells. Whole blood samples were incubated with peptide antigens for <5 h, followed by staining with peptide-MHC tetramers to identify epitope-specific T cells. The cells were also stained for the activation marker CD69 or for the production of cytokines such as interferon-gamma (IFNgamma) or tumor necrosis factor-alpha (TNFalpha). With the combined staining with tetramer and antibodies to CD69 or cytokines the number of antigen-specific CD8+ T cells as well as the functional response of each individual cell to the cognate antigen can be determined in a single experiment. Virus-specific CD8+ T cells that are nonfunctional, as well as those that are functional under the same stimulating conditions can be simultaneously detected with this assay, which is not possible by using other T-cell functional assays including cytotoxicity assay, intracellular cytokine staining, and enzyme-linked immunospot (ELISPOT) assay.

The role of different immunosuppression in the long-term histological outcome of HCV reinfection after liver transplantation for HCV cirrhosis

BACKGROUND

The effect of the type of immunosuppression on the course of posttransplant hepatitis C virus (HCV) infection is unclear. The aim of this study was to evaluate the histological outcome of posttransplant HCV infection with respect to initial immunosuppressive therapy in a cohort of 59 of 65 HCV positive transplant patients who survived at least 12 months.

METHODS

Initial immunosuppressive therapy was triple (cyclosporine or tacrolimus and azathioprine and prednisolone) in 41, double (cyclosporine and prednisolone) in 5, and single (cyclosporine or tacrolimus) in 13 patients. There was blinded histological evaluation, based on necroinflammatory activity (grading score:0-18) and fibrosis (staging score: 0-6). The median histological follow-up was 36 (12-72) months.

RESULTS

In the last liver biopsy, high necroinflammatory activity indicating chronic hepatitis (grading score > or =4) was found in 42 (71%) and severe fibrosis or cirrhosis (staging score > or =4) in 18 (30.5%) patients. High necroinflammatory activity was associated significantly with absence of pretransplant alcohol abuse (P=0.01) and relatively with occurrence of posttransplant acute lobular hepatitis C (P=0.055). Development of severe fibrosis or cirrhosis was significantly associated only with the type of initial immunosuppressive therapy. In particular, severe fibrosis or cirrhosis developed significantly more frequently in patients treated with triple or double (17/46 or 37%) than with single initial immunosuppressive therapy (1/13 or 7.7%) (adjusted for biopsy time: P=0.045).

CONCLUSIONS

Severe fibrosis or cirrhosis appears to develop in 30% of HCV transplant patients in a median of 3 years and to be associated with heavier initial immunosuppression.

A novel cytotoxic T-cell epitope presented by HLA-A24 molecule in hepatitis C virus infection

BACKGROUND/AIMS

It has been suggested that cytotoxic T lymphocytes (CTL) have crucial roles for the hepatocellular damage in hepatitis C virus (HCV) infection. A series of CTL epitopes located in the HCV protein have been identified. However, no CTL epitopes restricted by HLA-A24, a common HLA allele in humans, has been identified.

METHODS

Peripheral blood and liver infiltrating mononuclear cells from the patients with hepatitis C virus infection and healthy controls were stimulated with a series of peptides containing HLA-A24 binding motifs located in HCV protein.

RESULTS

An immunodominant HLA-A24 restricted CTL epitope (A24-4; AYSQQTRGL, amino acids 1031-1039) presented by HLA-A24 molecule was identified using a series of synthetic peptides containing the HLA-A24 binding motifs. The CTL activity against this peptide was induced both in peripheral blood and liver infiltrating mononuclear cells from HLA-A24-positive chronic hepatitis C patients, not from HLA-A24-negative patients and HLA-A24-positive healthy controls. CTL activity was blocked by anti-HLA-A24 and anti-CD8 antibodies, not by anti-CD4 antibody. Furthermore, the A24-4-specific CTL recognized the HCV gene transfected target cells.

CONCLUSIONS

Because this peptide is presented by a common HLA class I molecule, it might be useful for protection against hepatocellular damage and vaccine development in large population of the HCV-infected patients.

Involvement of CD1 in peripheral deletion of T lymphocytes is independent of NK T cells

During peripheral T cell deletion, lymphocytes accumulate in nonlymphoid organs including the liver, a tissue that expresses the nonclassical, MHC-like molecule, CD1. Injection of anti-CD3 Ab results in T cell activation, which in normal mice is followed by peripheral T cell deletion. However, in CD1-deficient mice, the deletion of the activated T cells from the lymph nodes was impaired. This defect in peripheral T cell deletion was accompanied by attenuated accumulation of CD8(+) T cells in the liver. In tetra-parental bone marrow chimeras, expression of CD1 on the T cells themselves was not required for T cell deletion, suggesting a role for CD1 on other cells with which the T cells interact. We tested whether this role was dependent on the Ag receptor-invariant, CD1-reactive subset of NK T cells using two other mutant mouse lines that lack most NK T cells, due to deletion of the genes encoding either beta(2)-microglobulin or the TCR element J alpha 281. However, these mice had no abnormality of peripheral T cell deletion. These findings indicate a novel role for CD1 in T cell deletion, and show that CD1 functions in this process through mechanisms that does not involve the major, TCR-invariant set of NK T cells.

Transcriptional activation of the interleukin-2 promoter by hepatitis C virus core protein

Most patients infected with hepatitis C virus (HCV) become chronic carriers. Viruses that efficiently establish persistent infections must have effective ways of evading host defenses. In the case of HCV, little is known about how chronic infections are established or maintained. Besides hepatocytes, several reports suggest that HCV can infect T and B lymphocytes. Since T cells are essential for viral clearance, direct or indirect effects of HCV on T-cell function could influence the outcome of infection. Given that T-cell growth and differentiation require the cytokine interleukin 2 (IL-2), we asked whether HCV might modulate synthesis of IL-2. Portions of the HCV polyprotein were expressed in Jurkat cells under a variety of conditions. We found that the highly conserved HCV core protein, in combination with other stimuli, was able to dramatically activate transcription from the IL-2 promoter. The carboxy-terminal hydrophobic portion of the core protein was required for this activity. Activation was dependent on nuclear factor of activated T cells (NFAT), occurred in cells deficient in the tyrosine kinase p56(lck), and could be blocked by addition of cyclosporin A and by depletion of calcium. These results suggest that the HCV core protein can activate transcription of the IL-2 promoter through the NFAT pathway. This novel activity may have consequences for T-cell development and establishment of persistent infections.

Effects of immunosuppression and organ transplantation on the natural history and immunopathogenesis of hepatitis C virus infection

The hepatitis C virus (HCV) is recognized as the leading cause for parenterally transmitted hepatitis. It is characterized by a high propensity to chronicity. Several efforts have been directed towards understanding the natural history of chronic HCV infection and the immunopathogenic pathways involved in mediating liver injury in the non-immunosuppressed and immunosuppressed states. In the non-immunosuppressed setting, liver damage seems to be largely immune mediated. In contrast, in the non-immunosuppressed state, there are several other factors that may modify the natural course of the infection and play a role in mediating liver injury. In this review we will address the natural history, virological and immunological aspects of HCV infection. Also, the role played by immunosuppression and organ transplantation in modifying the course of the infection and the pathogenesis of liver injury will be discussed.

Interaction between complement receptor gC1qR and hepatitis C virus core protein inhibits T-lymphocyte proliferation

Hepatitis C virus (HCV) is an important human pathogen that is remarkably efficient at establishing persistent infection. The HCV core protein is the first protein expressed during the early phase of HCV infection. Our previous work demonstrated that the HCV core protein suppresses host immune responses, including anti-viral cytotoxic T-lymphocyte responses in a murine model. To investigate the mechanism of HCV core-mediated immunosuppression, we searched for host proteins capable of associating with the core protein using a yeast two-hybrid system. Using the core protein as bait, we screened a human T cell-enriched expression library and identified a gene encoding the gC1q receptor (gC1qR). C1q is a ligand of gC1qR and is involved in the early host defense against infection. Like C1q, HCV core can inhibit T-cell proliferative responses in vitro. This core-induced anti-T-cell proliferation is reversed by addition of anti-gC1qR Ab in a T-cell proliferation assay. Furthermore, biochemical analysis of the interaction between core and gC1qR indicates that HCV core binds the region spanning amino acids 188 to 259 of gC1qR, a site distinct from the binding region of C1q. The inhibition of T-cell responsiveness by HCV core may have important implications for HCV persistence in humans.

The HCV core protein acts as a positive regulator of fas-mediated apoptosis in a human lymphoblastoid T cell line

Hepatitis C virus (HCV) is a major human pathogen causing mild to severe liver disease worldwide and is remarkably efficient at establishing persistent infections. Previously, we have shown that the core protein has an immunomodulatory function including the suppression of T lymphocyte responses to viral infection. To investigate the underlying mechanism for the role of core protein in immune modulation, we examined the effect of core on the sensitivity of the human T cell line, Jurkat, to Fas-mediated apoptosis. The transient and stable expression of core protein in Jurkat cells increased the sensitivity of cells to Fas-mediated apoptosis when compared to control cells expressing vector DNA alone. In addition, we demonstrated that the core protein binds to the cytoplasmic domain of Fas which may enhance the downstream signaling event of Fas-mediated apoptosis. The expression of core protein did not alter the cell surface expression of Fas, indicating that the increased sensitivity of core-expressing cells to Fas ligand was not due to upregulation of Fas. Furthermore, we observed the augmentation of caspase-3 activity in core-expressing cells. These results suggest that the core protein may promote the apoptosis of immune cells during HCV infection via the Fas signaling pathway, thus facilitating HCV persistence.

HLA association with hepatitis C virus infection

Hepatitis is one of the most important infectious diseases in Thailand. The knowledge of host factors that influence the course of the disease is still limited. In this study, the HLA class I and class II phenotypes were analyzed in the 2 groups of HCV-infected Thai populations. The first group included 43 individuals with transient HCV infection (HCV antibody positive, HCV RNA PCR negative), and the second included 57 individuals with persistent chronic HCV infection (HCV antibody positive, PCR positive). HLA class I typing was performed by 2-stage microlymphocytotoxicity test, and HLA class II typing, by PCR-SSO. No significant difference in the frequencies of HLA-A and -B antigens was observed between the 2 groups of HCV-infected individuals. The frequency of DRB1*0301 and DQB1*0201 was significantly higher in the persistent-infection group than in the transient-infection group (Pc = 0.03, Pc = 0.04, respectively). In addition, DRB1*0701 and DQA1*0201 were significantly decreased in all the HCV-infected patients compared with levels in the normal controls (Pc = 0.003, Pc = 0.001, respectively). This study demonstrated that DRB1*0301 and DQB1*0201 are associated with persistent HCV infection, whereas DRB1*0701 and DQA*0201 are associated with protection against HCV infection.

Leptin-deficient (ob/ob) mice are protected from T cell-mediated hepatotoxicity: role of tumor necrosis factor alpha and IL-18

The role of leptin was investigated in two models of T cell-mediated hepatitis: the administration of Con A or of Pseudomonas aeruginosa exotoxin A (PEA). In both models, leptin-deficient (ob/ob) mice were protected from liver damage and showed lower induction of tumor necrosis factor (TNF) alpha and IL-18 compared with their lean littermates. Neutralization of TNF-alpha reduced induction of IL-18 by either Con A (70% reduction) or PEA (40% reduction). Pretreatment of lean mice with either soluble TNF receptors or with an anti-IL-18 antiserum significantly reduced Con A- and PEA-induced liver damage. The simultaneous neutralization of TNF-alpha and IL-18 fully protected the mice against liver toxicity. However, neutralization of either IL-18 or TNF-alpha did not inhibit Con A-induced production of IFN-gamma. Thymus atrophy and alterations in the number of circulating lymphocytes and monocytes were observed in ob/ob mice. Exogenous leptin replacement restored the responsiveness of ob/ob mice to Con A and normalized their lymphocyte and monocyte populations. These results demonstrate that leptin deficiency leads to reduced production of TNF-alpha and IL-18 associated with reduced T cell-mediated hepatotoxicity. In addition, both TNF-alpha and IL-18 appear to be essential mediators of T cell-mediated liver injury.

Mediastinal fibrosis is associated with human leukocyte antigen-A2

OBJECTIVE

To determine the association between mediastinal fibrosis and human leukocyte antigen (HLA) genes.

DESIGN

Case-control study.

SETTING

Vanderbilt University Medical Center.

SUBJECTS

Nineteen consecutive patients with mediastinal fibrosis who presented to the pulmonary clinic at Vanderbilt University Medical Center from 1987 to 1996. The control subjects were 21,086 whites who were cadaveric kidney donors from October 1987 through December 1993.

MEASUREMENTS

HLA testing was performed on blood samples from all 19 cases. Information on HLA typing for the control subjects was obtained from the United Network for Organ Sharing. Frequency of HLA class I and II antigens found in the cases was compared with the frequency in the control subjects.

RESULTS

The relative risk of mediastinal fibrosis among subjects with the HLA-A2 antigen was 3.32 times that of those who lacked this antigen (95% confidence interval, 1.19 to 9. 2).

CONCLUSION

HLA-A2 was strongly associated with mediastinal fibrosis, suggesting that an abnormal immune response is important in the pathogenesis of this disease. Key words: Histoplasma capsulatum; human leukocyte antigen-A2; mediastinal fibrosis