Immunology and the liver

Intrahepatic expression of pro-inflammatory cytokine mRNAs and interferon efficacy in chronic hepatitis C

To investigate the relationship between intrahepatic cytokine expression and interferon (IFN) response in chronic hepatitis C [CH(C)], interleukin (IL)-1 beta, -2, -4, -6, -8, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and TNF-beta mRNAs were investigated semiquantitatively by reverse transcription polymerase chain reaction using serial liver biopsies taken before and after IFN-alpha treatment from 24 patients with CH(C), including 12 responders and 12 non-responders. Before IFN treatment, IL-2, TNF-beta, IFN-gamma and IL-8 mRNA were associated with severe hepatitis activity whereas IL-4 mRNA was associated with weak hepatitis activity, regardless of IFN response. IL-2, TNF-beta and IFN-gamma mRNAs were significantly greater in IFN non-responders. After IFN treatment a complete response to IFN was significantly associated with the disappearance of these pro-inflammatory cytokines, whereas non-responders retained the expression of cytokine mRNA as before IFN treatment. Our results indicated that IFN-alpha treatment may modulate the intrahepatic cytokine network, and this may be one mechanism of IFN-alpha that reduces hepatitis activity, aside from an anti-viral effect. A difference in cytokine network may be involved in IFN response in CH(C).

Assessment of natural and interleukin-2-induced production of interferon-gamma in patients with liver diseases

AIM: To determine whether the production of lower interferon gamma (IFNl) by lymphocytes in patients with liver diseases is due to defects of the lymphocytes themselves or to other cofactors, such as interleukin-2 (IL-2).

METHODS: Peripheral blood mononuclear cells (PBMCs) from patients with various liver diseases were cultured with or without phytohemagglutinin (PHA) and IL-2. The cells were harvested and counted, and the supernatants were tested for IFNl by a sensitive and quantitative ABC-enzyme-linked immunosorbent assay (ELISA).

RESULTS: IFNl was not found in serum samples from patients or normal individuals. However, IFNl was detectable in supernatants of non-induced and induced PBMCs by ABC-ELISA. In non-induced PBMCs (group 1), the content of IFNl in supernatants from control, chronic active hepatitis (CAH), chronic persistent hepatitis (CPH), and hepatocellular carcinoma (HCC) was 8.72/L, 5.03/L, 6.02/L, and 4.91/L, respectively. The production of IFNl in liver disease was significantly decreased compared to control. In PBMCs stimulated with PHA (group 2), the content of IFNl was 22.71/L, 17.12/L, 14.54/L, and 17.63/L, respectively. In PBMCs induced by IL-2 (group 3), the amount of IFNl in supernatant from control (60.67/L) was much larger than those from CAH (21.70/L), CPH (24.00/L), and HCC (19.15/L) (p < 0.01). When comparing the amount of IFNl in group 3 with that in group 1, we found that IFNl production was enhanced by nearly 4-folds in liver diseases and by over 7-fold in control. In contrast, the number of PBMCs, whether from liver diseases or from control, was increased by only approximately 3-fold.

CONCLUSION: The decreased production of IFNl in liver diseases, including HCC, is mainly due to endogenous defects of lymphocytes but may also involve a decrease in stimulating cofactors, such as IL-2.

Immunology taught by viruses

The survival of viruses depends on the survival of susceptible hosts. The vertebrate immune system and viruses have therefore coevolved complementary facets. Evidence from various balanced virus-host relationships illustrates that immunological specificity and memory may best be defined biologically and that the mature immune system does not discriminate between "self" and "nonself." Rather, B cells distinguish antigen patterns, whereas T cell responses depend on localization, transport, and kinetics of antigen within lymphatic organs.

Therapy for chronic hepatitis B infection

Interferon-alpha is currently the only therapy approved for treatment of chronic HBV in the United States and Europe. Interferon-alpha therapy causes loss of HBeAg and HBV DNA in approximately a third of treated patients, and the loss of these markers of active viral replication is associated with improvements in hepatic histology and ALT levels. However, the long-term effects of interferon-alpha on morbidity and mortality, and especially on the incidence of the complications of chronic HBV infection, remain to be defined. The currently available treatment for chronic HBV is far from perfect. Interferon therapy is usually associated with significant side effects and requires subcutaneous administration. Additionally, there are a large number of patients who either fail to meet criteria for treatment, or who, with therapy, fail to respond (at least 60% of all patients). Moreover, interferon treatment is expensive (approximately $5,000 for a 16 week course of 5MU daily). Hence the search continues for effective, orally-available and cost-efficacious therapy. Of the agents available, the nucleoside analogues appear to have the greatest promise. The availability of cell culture systems and animal models for studying potential anti-HBV drugs will aid in the future development of these agents. Therapeutic vaccines, and combination therapies (given either concurrently or sequentially) may also play a future role in the management of chronic HBV infection. While prevention of disease must be a primary goal in the war against this common infection, a continued focus must be maintained on the treatment of the approximately 300 million individuals world-wide with established chronic HBV infection.

Proliferative response of CD4+ T cells and hepatitis B virus clearance in chronic hepatitis with or without hepatitis B e-minus hepatitis B virus mutants

To assess the significance of cell-mediated immunity, T cells were derived from the peripheral blood and liver tissue of hepatitis B virus (HBV)-infected patients and controls. The analysis of the 3H-thymidine-uptake in response to a panel of recombinant HBV antigens revealed that peripheral blood mononuclear cells (PBMC) of the 25 viremic patients with inflammatory active, chronic hepatitis B, 16 with wild-type and nine with HBe-minus HBV mutant infection, showed stronger proliferative responses to HBc and HBe antigens than 16 asymptomatic nonviremic HBsAg carriers with normal aminotransferase levels (HBc: SI 19.3 +/- 3.9 vs. 13.0 +/- 3.2 vs. 8.0 +/- 1.2; P < .01 and HBe: SI 16.6 +/- 4.0 vs. 10.7 +/- 3.5 vs. 6.9 +/- 1.5; P < .05). In 15 patients with acute self-limited hepatitis B, however, significantly stronger HBc antigen-specific T-cell responses were observed during HBV clearance and HBe/anti-HBe seroconversion, whereas in nine completely HBV-immunized patients only minor proliferative responses to HBV antigens were observed. Six HBe/HBcAg- and two HBeAg-specific CD4+ T-cell lines could be expanded from liver tissue and peripheral blood of six viremic patients with chronic hepatitis B. Irrespectively of HBV mutations the HBV-specific activation of the T-cell lines was restricted by the presence of HLA-DR molecules and resulted in the release of Th1-like cytokine patterns. Follow-up of interferon (IFN) recipients showed simultaneous short-term increase of HBc/HBe-specific T-cell reactivities in responder patients during HBV clearance and HBe/anti-HBe seroconversion, whereas in nonresponders high virus load and HBV-specific immune responses were in imbalance.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleotide sequence of hepatitis B virus isolated from subjects without serum anti-hepatitis B core antibody

The nucleotide sequences of the precore/core and X open reading frames (ORFs) of hepatitis B virus (HBV) were studied in four subjects who were serologically negative for anti-hepatitis B core antibody. These subjects were positive for serum hepatitis B surface antigen and were considered to be asymptomatic HBV carriers. Sequencing of the precore/core ORF revealed precore wild type and 3 to 8 nucleotide substitutions (replacing 0 to 2 amino acids) in the core region compared with the sequence of subtype adr. These substitutions were not considered to have changed the epitope of the core antigen, resulting in the absence of anti-HBc as determined by a conventional diagnostic kit. The X ORF showed 1 to 5 nucleotide substitutions (replacing 1 to 3 amino acids) and the structure of the X protein and the core promoter/enhancer II complex appeared to be conserved. These findings strongly suggest that the absence of serum anti-HBc is not due to mutation of the HBV DNA but to an aberrant immune reaction of the host to HBV.

The expression of IL-2, IL-4 and interferon-gamma (IFN-gamma) mRNA using liver biopsies at different phases of acute exacerbation of chronic hepatitis B

To investigate the hypothesis that Th1 phenotype cytokines are associated with the increasing activity of hepatitis and Th2 phenotype cytokines with decreasing activity in the liver of chronic viral hepatitis, expressions of the mRNA of the cytokines IL-2, IFN-gamma and IL-4 in the liver of 23 patients with chronic hepatitis B were investigated by reverse transcription polymerase chain reaction. Patients were divided into three groups according to the phase of acute exacerbation of hepatitis as increasing (n = 9), decreasing (n = 8), and stable phase (n = 6). Both IL-2 and IFN-gamma mRNA were preferentially expressed in increasing phase than in decreasing phase (P < 0.01, P < 0.05, respectively) and associated with the high serum alanine aminotransferase (ALT) level. On the other hand, IL-4 mRNA was detected in decreasing phase with significant frequency compared with increasing phase (P < 0.05). However, expression of IL-4 mRNA was not associated with serum ALT level. Our results suggest that Th1 phenotype cytokines up-regulate and Th2 phenotype cytokines down-regulate the liver inflammation of chronic viral hepatitis.

Antibody-directed complement-mediated cytotoxicity to hepatocytes from patients with chronic hepatitis B

The susceptibility of hepatocytes from patients with chronic hepatitis B to complement-dependent cytotoxicity mediated by heterologous antibodies to hepatitis B virus core (anti-HBc) and surface (anti-HBs) antigens and to hepatic asialoglycoprotein receptor was examined using a microcytotoxicity assay. The anti-HBc-induced cytotoxicity was found to be markedly enhanced against hepatocytes isolated from patients with chronic active hepatitis (72.6 +/- 9.5% (mean +/- s.e.m.); n = 6) over that against hepatocytes from individuals with chronic persistent hepatitis or inactive liver cirrhosis (40.6 +/- 18.6%; n = 4) (P = 0.019). Overall, values of the anti-HBc-directed cytotoxicity were higher in patients positive for HBcAg in hepatocytes and seropositive for hepatitis B virus e antigen (HBeAg). Hepatocytotoxicity was also exerted by anti-HBs and anti-asialoglycoprotein receptor antibodies in the presence of complement, but it was not seemingly related to disease activity. These results indicate that hepatitis B virus core and surface antigens and asialoglycoprotein receptor at the hepatocyte surface can be recognized by antibodies, and raise the possibility that complement-dependent cytolysis may contribute to the injury of hepatitis B virus-infected hepatocytes. The data also suggest that liver cells of patients with severe chronic hepatitis might be more susceptible to anti-HBc antibody-directed complement-mediated cytotoxicity than those with inactive liver histology.

Viruses, virulence and pathogenicity

Pathogenicity is a complex process with stringent requirements of both the host cell and the infecting virion. Among these requirements are a port of entry into host cells, a means of replication for the virus, and a means by which infection damages host cells. Damage to the host can result from multiple mechanisms including transformation, suppression of cellular metabolism, apoptosis, autoimmune responses directed against infected or uninfected tissues, or by molecular mimicry. In the attempt to identify new associations between viral infection and disease, investigators should be mindful that variable host factors as well as viral infection may be required for pathogenesis. Efforts to associate specific viral infections with specific diseases may be obscured by final common pathways through which multiple agents damage host cells in similar ways.

Bile acids in the diagnosis, pathology, and therapy of hepatobiliary diseases

Bile acids are normally confined in the enterohepatic circulation in which they play an important role in bile formation, biliary lipid excretion, and intestinal lipid absorption. In hepatobiliary diseases, bile acids escape the confinement of the enterohepatic circulation, allowing the measurement of the serum total bile acid concentration as a diagnostic indicator. Accumulation of certain bile acids within the hepatocyte, amplified as a consequence of cholestatic hepatobiliary disease, probably enhances cytotoxicity and leads to secondary pathology. Ursodeoxycholate, a bile acid with atypical physiological effects, may be useful in the treatment of various long-term cholestatic hepatobiliary diseases. Presently, most of the information on the toxicity and therapeutic usefulness of bile acids are based on studies in humans and experimental animals. Further studies, both basic and clinical, are needed to determine the pathologic as well as the therapeutic effects of bile acids in domestic animals.

Immunosuppression by a noncytolytic virus via T cell mediated immunopathology. Implication for AIDS

HIV is basically a non- or poorly cytocidal virus. Therefore, HIV infections in humans represent an apparent perversity in the balance between the host immune system and infectious agent: This noncytopathic virus infects macrophages, antigen presenting cells, helper T cells and other host cells which are then destroyed by the CD8+ T cell immune response. Thus, HIV infects some of the key cells involved in immune reactions and therefore induces the immune system to destroy itself and thereby enables the virus to persist. Accordingly, immunosuppression is not a cause of HIV cytopathogenicity but a consequence of conventional T cell mediated immunopathology that destroys macrophages antigen presenting cells, T helper cells and facilitates infection by trivial intracellular parasites which eventually cause fatal disease. This immunopathological view of AIDS is testable and, if correct, impinges on rationales for AIDS prevention and treatment.

Increased intrahepatic messenger RNA expression of interleukins 2, 6, and 8 in human cirrhosis

BACKGROUND/AIMS

The role of cytokines in the pathogenesis of chronic liver disease is unclear. The aim of this study was to identify intrahepatic cytokines at the messenger RNA (mRNA) level in end-stage human cirrhosis.

METHODS

Cytokine mRNA expression for interleukin (IL) 1 beta, IL-2, IL-6, IL-8, transforming growth factor beta, interferon gamma, and tumor necrosis factor alpha was examined by semiquantitative polymerase chain reaction in 25 human cirrhotic livers and 13 controls. Cellular localization of IL-8 was performed by immunohistochemistry.

RESULTS

The results show that IL-2 (P < 0.0001), IL-6 (P < 0.0001), IL-8 (P < 0.0001), transforming growth factor beta (P < 0.001), and interferon gamma (P < 0.04) were upregulated in human cirrhosis compared with controls. IL-1 beta and interferon gamma mRNA showed increased expression in cirrhotics with autoimmune chronic active hepatitis compared with those with primary biliary cirrhosis. Immunohistochemistry showed that IL-8 protein was expressed by infiltrating cells in portal tracts and fibrotic septae and within hepatic lobules.

CONCLUSIONS

It is concluded that there is significant activation of cytokines at the mRNA level in end-stage cirrhosis. This suggests continued immune activation even at the late stages of cirrhosis and may indicate the importance of cytokines in the pathogenesis and progression of chronic liver disease.

Demographics of anti-asialoglycoprotein receptor autoantibodies in autoimmune hepatitis

BACKGROUND/AIMS

The asialoglycoprotein receptor (ASGPR) is an established, liver-specific autoantigen. This multicenter study investigated the specificity of anti-ASGPR autoantibodies for autoimmune hepatitis (AIH) in different ethnic groups.

METHODS

Nine hundred fourteen sera from European, Japanese, and North American (U.S.) patients with chronic inflammatory liver disorders were tested. An enzyme-immunoassay using human ASGPR and a radioimmunoassay against rabbit ASGPR, performed independently on coded sera, were compared.

RESULTS

The highest frequency (76%) of anti-human ASGPR was found in AIH patients (11/24 U.S.; 21/25 European; 28/30 Japanese), particularly in those with active disease before treatment (53/62, 85%), and decreased in titer with response to immunosuppressive therapy. These antibodies were found at low titers in 43 (11%) of 385 patients with viral hepatitis and in 25 (7.6%) of 328 patients with other chronic inflammatory liver disorders (P < 0.0005 compared with all AIH patients). Twenty of 37 sera tested by enzyme-immunoassay and radioimmunoassay were positive, and nine were negative for anti-ASGPR by both assays (78% concordance); six sera were exclusively positive on human substrate.

CONCLUSIONS

Circulating anti-ASGPR autoantibodies are closely associated with autoimmune hepatitis independent of geographic or ethnic criteria. Two anti-ASGPR assays currently in use show high reliability.

HLA expression in hepatocellular carcinoma cell lines

The present study undertook to investigate the biological significance of human leucocyte antigen expression in hepatocellular carcinoma and to elucidate the role of potential modulating agents on human leucocyte antigen expression. These studies used several hepatic tumour-derived cell lines as in vitro model systems. The cell lines included PLC/PRF/5 (Alexander cell line), Hep3B, HepG2, TONG PHC, HA22T/VGH, HA59T/VGH and Mahlavu. The cell lines K562 and Raji were used as negative and positive controls, respectively. K562, a B lymphoid-derived cell line, was shown to express negligible amounts of human leucocyte antigens, while Raji, an erythromyeloid-derived cell line, expressed both class I and class II human leucocyte antigens as well as their respective invariant chains, beta 2-microglobulin and Ii. Using an ELISA, experiments performed on these cell lines confirmed the natural expression of class I and class II antigens by the HA22T/VGH and HA59T/VGH cell lines, whereas PLC/PRF/5 displayed class II surface antigens only. The effects of modulating agents such as interferon-gamma sodium butyrate and clofazimine on human leucocyte antigen expression were investigated using the HA22T/VGH, HA59T/VGH and TONG PHC cell lines. These agents increased class II and class II human leucocyte antigen expression on HA22T/VGH and TONG PHC cells, but had no effect on the HA59T/VGH cell line. The results suggest a potential use for these agents as modulators of human leucocyte antigen expression by human heptocellular cell lines.

T-cell-mediated immunopathology versus direct cytolysis by virus: implications for HIV and AIDS

It has been much debated as to whether CD4+ T-cell depletion and the pathogenesis of AIDS is the result of direct cytolytic effects of human immunodeficiency virus (HIV), T-cell apoptosis by nonspecific activation, dysregulation of cytokine production, or autoimmunity. In this context, Rolf Zinkernagel and Hans Hengartner discuss data from model infections with non-cytopathic viruses. They suggest that HIV may cause immunosuppression, not by direct cytolytic effects, but rather by a conventional virus-specific cytotoxic T-cell-mediated immunopathology.

Immunogenetics of chronic liver diseases

The genetic background of autoimmune diseases becomes more and more evident. Immunogenetics comprises the analysis of genes and their products located at the region 6p21 on the short arm of chromosome 6, which is also known as the major histocompatibility complex (MHC). MHC class I and II genes are highly polymorphic. The complement genes C2, C4A, C4B, and BF, which are also polymorphic, became known as MHC class III genes. In autoimmune hepatitis type 1, there is a dual association for white persons with either HLA-A1-B8-DR3 or HLA-DR4. In patients from Japan, autoimmune hepatitis type 1 is predominantly associated with HLA-DR4. This dual association is confirmed at the DNA level. Whereas only limited data are available for autoimmune hepatitis type 2, the association of primary biliary cirrhosis with HLA-DR8 is based on several studies. Primary sclerosing cholangitis is associated with HLA-B8-DR3 and -DR52a. This association was confirmed at the DNA level because of a significant increase of the DRB3*0101 allele. For DRB3*0101-negative individuals, a second association with DRB5*0101 (= DR2) was described. Further analysis of the hypervariable region of the HLA class II molecule indicates that lysine at position 71 is crucial for autoimmune hepatitis type 1 in white persons, whereas position 13 is important for people from Japan. In contrast, leucine at position 35 is important for patients with primary biliary cirrhosis, whereas leucine at position 38 is an important risk factor for primary sclerosing cholangitis. The MHC class III allele C4A-QO is significantly increased in autoimmune hepatitis type 1 and 2 and in primary biliary cirrhosis. Advances in immunogenetics will certainly increase our knowledge of the etiology and pathogenesis of immune-mediated liver diseases, which hopefully will lead to more specific therapeutic interventions.

"Occult" hepatitis B virus as source of infection in liver transplant recipients

Hepatitis B virus (HBV) infection almost always recurs after liver transplantation in patients who were surface antigen (HBsAg) positive before surgery but apparent de novo acquisition of infection in a transplant setting has not previously been reported. We have used sensitive techniques to elucidate the origin of such infections in patients in a California transplantation programme. We tested post-transplant serum from 207 patients who had been HBsAg negative and found 20 to be HBsAg positive. The origin of infection was identified in 7 patients, being occult pre-transplant infection in 5 and occult infection in the donor in 2. No pre-transplant patient nor donor with demonstrable HBV DNA had serological markers of hepatitis B. Post-transplant HBV DNA was present in serum from 19 patients. Analysis of the variable pre-S region of HBV demonstrated 100% sequence homology between recipient liver and post-transplant serum (2 patients) and between donor serum and recipient post-transplant serum (2). There was only 84% homology between the 2 different patients infected with subtype adw. 19 patients are alive, 9 without histological evidence of hepatitis (mean follow-up 33 months), and survival was significantly greater than that of a group with recurrent HBV infection. Apparent acquisition of HBV infection with liver transplantation is not rare, and may be due to occult pre-transplant infection or occult infection in the donor. The post-transplant outcome of this infection tends to be benign but our findings do underscore the clinical relevance of HBV infection in the absence of serological markers.

Fine needle aspirative biopsy of the liver in HBsAG-positive patients with end-stage renal failure

HBsAg-positive patients with end-stage renal failure have a high prevalence of asymptomatic chronic hepatitis. In order to determine the usefulness of hepatic cytology in the diagnosis of liver disease, the findings of hepatic needle core biopsy (NCB) and fine needle aspirative biopsy (FNAB) were compared in 15 HBsAg-positive uremic patients. The patients, aged 42 +/- 12 years, 14 males, were on hemodialysis for periods ranging from 13 to 105 months. The NCB was processed by standard histologic and immunohistochemical techniques and FNAB by the conventional technique, using the total corrected increment score (TCI). Plasma samples were collected for evaluation of hepatic function and for viral serologic tests. In 15 patients a diagnosis was made by NCB: normal, 7 cases; chronic persistent hepatitis, 4 cases; and chronic active hepatitis, 4 cases. When the patients were allocated into two groups according to the severity of the liver histologic findings [group I--minor changes (normal+chronic persistent hepatitis), 11 patients; group II--major changes (chronic active hepatitis), 4 patients], statistically higher values were found in the major changes group for alanine aminotransferase (49 +/- 33 vs. 24 +/- 11, p = 0.04), gamma-glutamyl transpeptidase [148 +/- 53 vs. 38 +/- 28, p < (minor) 0.02] and TCI (3.7 +/- 1.2 vs. 2.5 +/- 0.8, p = 0.04). In conclusion, liver FNAB can be useful as a screening procedure for the identification of liver histologic changes (minor or major) in uremic HBsAG-positive patients.

Etiology and pathogenesis in primary sclerosing cholangitis

The etiology and pathogenesis of the inflammatory and fibrotic bile duct lesions characteristic of primary sclerosing cholangitis (PSC) is unknown, but several lines of evidence support the contention that genetic and immunologic factors are involved. There is an association with human leukocyte antigens (HLA) with an increased frequency of DR3, DR6, and DR2 positive haplotypes. DRB3*0101(DR52a) is the most strongly associated allele in some studies, but the HLA gene conferring the primary HLA associated susceptibility to PSC remains to be established. There is an aberrant expression of HLA class II antigens (DR and DP) on bile duct epithelial cells, with the potential to present antigens to the surrounding T-lymphocytes. A defective suppressor T-cell function has been suggested in some studies. The patients may have elevated levels of circulating immune complexes, immunoglobulins, and non-organ-specific autoantibodies. Antibodies to perinuclear antigens (pANCA) are present in about 80% of cases. Increased metabolism of complement C3, reduced clearance of immune complexes, and increased concentration of biliary immune complexes have been found. The strong association between PSC and ulcerative colitis (UC) has not been explained. The detection of circulating IgG antibodies against a specific epitope shared by epithelial cells in the bile ducts and colon in about two-thirds of PSC patients may be of importance. Portal bacteremia secondary to a diseased bowel may possibly contribute to development of liver disease in UC. Viral infections and toxic and ischemic factors have also been implicated in the pathogenesis of PSC. In conclusion, PSC seems to occur in genetically predisposed individuals, mediated by immunologic mechanisms. The primary event triggering the disease development is, however, unknown.

Hepatitis C virus (HCV)-specific cytotoxic T lymphocytes recognize epitopes in the core and envelope proteins of HCV

Hepatitis C virus (HCV) is a major cause of posttransfusion and community-acquired hepatitis, and a majority of individuals infected with this virus will subsequently develop chronic hepatitis. Characterization of the host immune response to this infection is an important first step that should facilitate the development of immunomodulatory agents and vaccines. Cellular immune responses, especially those mediated by cytotoxic T lymphocytes (CTL), are important in the control of many viral diseases. In this study, liver-infiltrating lymphocytes from persons with chronic HCV hepatitis were examined for evidence of HCV-specific CTL by using target cells infected with recombinant vaccinia viruses expressing the HCV core, E1, E2, and part of the NS2 proteins. Bulk expansion of liver-derived CD8+ lymphocytes resulted in the detection of HCV-specific CTL activity, whereas activity could not be found in CD8+ lymphocytes expanded from peripheral blood. Epitopes recognized by these CTL were defined by using CTL clones obtained by limiting dilution and target cells sensitized with synthetic HCV peptides. Four distinct HLA class I-restricted epitopes were identified, including two epitopes in the amino-terminal portion of the core protein. These studies provide evidence that the highly conserved core protein is a target for HCV-specific CTL and identify CTL epitopes within the more highly variable E2 envelope protein. Our studies also suggest that HCV-specific CTL are localized at the site of tissue injury in infected persons with chronic hepatitis. Identification of the epitopes recognized by HCV-specific CTL will facilitate exploration of their role in disease pathogenesis and may provide information useful in development of therapeutic interventions or vaccines.

Lysis of infected cells in vivo by antiviral cytolytic T cells demonstrated by release of cell internal viral proteins

Immunocompetent adult mice infected with lymphocytic choriomeningitis virus (LCMV) generate a strong antiviral cytotoxic T cell response that clears virus from all organs. Although there is good evidence that immune cytotoxic T lymphocytes (CTL) kill target cells in vitro, in vivo it is debated whether antiviral activity of CD8+ T cells is mediated via direct target cell lysis or via soluble mediators. To demonstrate CD8+ T cell-mediated destruction of infected cells in vivo a specific cell-internal releasable marker was used as label, i.e. the nucleoprotein (NP) of LCMV. Since LCMV is non-cytopathic the viral NP will only be released in substantial amounts because of destruction of infected host cells by immune CTL. It is shown here that the amount of NP released from infected and 51Cr-labeled target cells in vitro correlated well with the amount of radioactivity released. Viral NP released in vivo by CTL is bound and masked by the anti-NP antibodies that are produced very early and efficiently. However, NP could readily be detected in sera of LCMV-infected CD8+ competent mice that could not generate antibodies specific for the NP because they were treated with a depleting anti-CD4 antibody. NP was also detected in the cerebrospinal fluid of mice suffering from CD8+ T cell-mediated lymphocytic choriomeningitis after intracerebral infection. NP titers in sera of anti-CD4-treated LCMV-infected mice exhibited a peak around day 7-8 when CTL activity was highest. When mice were CD8 T cell-depleted with anti-CD8 monoclonal antibody or in LCMV-carrier mice, no NP was detected in the serum. Highly activated LCMV-specific CTL adoptively transfused to LCMV-infected irradiated recipient mice also caused a time-dependent release of NP into serum. This confirms that the CD8+ population is responsible for the release of NP from infected host cells. These results represent an in vivo correlate of CTL-mediated cytolysis and evidence that antiviral cytotoxic T cells are cytolytic in vivo. They also suggest that antibody responses to internal antigens of non-cytopathic viruses may signal CD8+ T cell-mediated destruction of infected host cells.

Identifying strategies for immune intervention

In recent years the molecular basis of antigen recognition by T cells has been unraveled and the various pathways that control T cell activation and functional specialization have been defined. Consequently, it is now possible to delineate various strategies for intervention with the immune system to design protective vaccines, to induce an effective response to tumor antigens, and to control graft rejection and autoimmune diseases.

Virus persistence in acutely infected immunocompetent mice by exhaustion of antiviral cytotoxic effector T cells

Viruses that are non- or poorly cytopathic have developed various strategies to avoid elimination by the immune system and to persist in the host. Acute infection of adult mice with the noncytopathic lymphocytic choriomeningitis virus (LCMV) normally induces a protective cytotoxic T-cell response that also causes immunopathology. But some LCMV strains (such as DOCILE (LCMV-D) or Cl-13 Armstrong (Cl-13)) derived from virus carrier mice tend to persist after acute infection of adult mice without causing lethal immunopathological disease. Tendency to persist correlates with tropism, rapidity of virus spread and virus mutations. We report here that these LCMV isolates may persist because they induce most of the specific antiviral CD8+ cytotoxic T cells so completely that they all disappear within a few days and therefore neither eliminate the virus nor cause lethal immunopathology. The results illustrate that partially and sequentially induced (protective) immunity or complete exhaustion of T-cell immunity (high zone tolerance) are quantitatively different points on the scale of immunity; some viruses exploit the latter possibility to persist in an immunocompetent host.

Interferon in the management of chronic hepatitis B

Many drugs have been used in the treatment of chronic hepatitis B, but with the exception of interferon, none have proved to be effective. Several studies have found that a sustained loss of viral replication occurs in approximately 40% of patients who started with a 16-week course of recombinant interferon alfa-2b given in a dose of 5 million units daily or 10 million units three times weekly. Moreover, disappearance of hepatitis B surface antigen in serum has been observed in 10-15% of treated patients. Based on these results, the Food and Drug Administration approved the use of this form of interferon in chronic hepatitis B in July 1992. This article reviews the importance of chronic hepatitis B as a health problem as well as the mechanisms of action, benefits, and adverse effects associated with interferon. Particular emphasis is given to the safety and efficacy data for recombinant interferon alfa-2b.