NLRX1 can counteract innate immune response induced by an external stimulus favoring HBV infection by competitive inhibition of MAVS-RLRs signaling in HepG2-NTCP cells

INTRODUCTION

This study is aimed at the determination of the effect of the immune-regulatory factor NLRX1 on the antiviral activity of hepatocytes against an external stimuli favoring hepatitis B virus infection, and to explore its mechanism of action.

METHODS

A HepG2-NTCP model was established using the LV003 lentivirus. Cells were transfected using an overexpression vector and NLRX1 siRNA to achieve overexpression and interference of NLRX1 expression (OV-NLRX1, si-NLRX1). Levels of HBsAg and HBcAg were determined using Western blotting analysis and immunohistochemical analysis. The levels of hepatitis B virus DNA and hepatitis B virus cccDNA were determined by real-time quantitative polymerase chain reaction. The expression and transcriptional activity of IFN-α, IFN-β, and IL-6 were measured using real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and promoter-luciferase reporter plasmids. Co-immunoprecipitation was used to determine the effect of NLRX1 on the interaction between MAVS and RIG-1. Western blotting was used to obtain the phosphorylation of essential proteins in the MAVS-RLRs signaling pathways.

RESULTS

NLRX1 promoted HepG2-NTCP cell hepatitis B virus infection. Compared to the control group, the levels of HBsAg, HBcAg, hepatitis B virus cccDNA, and hepatitis B virus DNA increased in the OV-NLRX1 group and decreased in the si-NLRX1. Co-immunoprecipitation results showed that NLRX1 competitively inhibited the interaction between MAVS and RIG-1, and inhibited the phosphorylation of p65, IRF3, and IRF7. Additionally, NLRX1 reduced the transcription activity and expression levels of the final products: IFN-α, IFN-β, and IL-6.

CONCLUSIONS

NLRX1 can counteract innate immune response induced by an external stimuli favoring hepatitis B virus infection by competitive inhibition of MAVS-RLRs signaling in HepG2-NTCP cells. Inhibition of the MAVS-RLR-mediated signaling pathways leads to a decline in the expression levels of I-IFN and IL-6.

Silica nanoparticles as the adjuvant for the immunisation of mice using hepatitis B core virus-like particles

Advances in nanotechnology and nanomaterials have facilitated the development of silicon dioxide, or Silica, particles as a promising immunological adjuvant for the generation of novel prophylactic and therapeutic vaccines. In the present study, we have compared the adjuvanting potential of commercially available Silica nanoparticles (initial particles size of 10–20 nm) with that of aluminium hydroxide, or Alum, as well as that of complete and incomplete Freund's adjuvants for the immunisation of BALB/c mice with virus-like particles (VLPs) formed by recombinant full-length Hepatitis B virus core (HBc) protein. The induction of B-cell and T-cell responses was studied after immunisation. Silica nanoparticles were able to adsorb maximally 40% of the added HBc, whereas the adsorption capacity of Alum exceeded 90% at the same VLPs/adjuvant ratio. Both Silica and Alum formed large complexes with HBc VLPs that sedimented rapidly after formulation, as detected by dynamic light scattering, spectrophotometry, and electron microscopy. Both Silica and Alum augmented the humoral response against HBc VLPs to the high anti-HBc level in the case of intraperitoneal immunisation, whereas in subcutaneous immunisation, the Silica-adjuvanted anti-HBc level even exceeded the level adjuvanted by Alum. The adjuvanting of HBc VLPs by Silica resulted in the same typical IgG2a/IgG1 ratios as in the case of the adjuvanting by Alum. The combination of Silica with monophosphoryl lipid A (MPL) led to the same enhancement of the HBc-specific T-cell induction as in the case of the Alum and MPL combination. These findings demonstrate that Silica is not a weaker putative adjuvant than Alum for induction of B-cell and T-cell responses against recombinant HBc VLPs. This finding may have an essential impact on the development of the set of Silica-adjuvanted vaccines based on a long list of HBc-derived virus-like particles as the biological component.

[Human plasmacytoid dendritic cells from patients with chronic hepatitis B induce the generation of CD4+CD25+Treg in vitro]

OBJECTIVE

To compare the ability of plasmacytoid dendritic cells (pDCs) from chronic HBV patients and healthy controls to induce the the generation of CD4+CD25+Treg cells.

METHODS

The pDCs were isolated from PBMCs of 46 chronic HBV patients, 10 resolved HBV patients and 25 healthy controls by magnetic cell sorting. Purified CD4+CD45RA+ naive T cells were incubated with allogeneic pDCs from chronic HBV infected patients, resolved HBV patients or healthy controls. The cells were stimulated with HBcAg or tetanus toxin. The proportion of CD4+CD25+Treg in CD4+ T cells primed by pDCs was determined by flow cytometry, the expression of Fox p3 mRNA was detected by RT-PCR, IL-10 and TGFb1 expression was quantified using ELISA kits.

RESULTS

Compared with pDC isolated from healthy controls and the resolved HBV patients, pDC from chronic HBV patients was more effective in suppression of CD4+ T cells proliferation and interferon production when CD25-depleted PBMCs were stimulated with HBcAg, (7999.36+/-374.74 vs 11 282.56+/-1174.46; 7999.36+/-374.74 vs 12 304.58+/-1462.81, P less than 0.05 ). Depletion of CD4+CD25+ Treg from CD4+ T cells primed by pDC led to the lose of capability to suppress HBV-specific T-cell responses. When CD25- depleted PBMCs were stimulated with purified tetanus toxin, there was no significantly difference in proliferation between CD25-depleted PBMC co-cultured with pDC-primed CD4+ T cells and CD25-depleted PBMC cultured without pDC-primed CD4+ T cells. A higher percentage of CD4+CD25+ Treg was detected within the population of CD4+ T cells primed by pDC from chronic HBV patients compared with healthy controls and resolved HBV patients (5.99%+/-1.85% vs 3.04%+/-0.79%; 5.99%+/-1.85% vs 3.01%+/-1.53%, P less than 0.05). Accordingly, CD25+Treg from pDC-primed CD4+ T cells displayed a higher Fox P3 mRNA level. The IL-10 and TGFb1 could be also detectable in the supernatants of pDC-primed CD4+ T cells.

CONCLUSION

pDCs from chronic hepatitis B induce the generation of a higher proportion of CD4+CD25+ Treg compared with pDCs from healthy controls.

Coimmunization with IL-15 plasmid enhances the longevity of CD8 T cells induced by DNA encoding hepatitis B virus core antigen

AIM: To test the feasibility of delivering a plasmid encoding IL-15 as a DNA vaccine adjuvant for improving the immune responses induced by hepatitis B virus core gene DNA vaccine.

METHODS: We used RT-PCR based strategies to develop IL-15 expression constructs. We first confirmed that the gene could be expressed in Escherichia coli due to the poor expression of IL-15. Then the bioactivity of IL-15 plasmid expression product was identified by CTLL-2 proliferation assay. One hundred micrograms of DNA from each of the IL-15 eukaryotic expressed plasmid and the recombinant plasmid harboring DNA encoding the 144 amino acids of the N-terminus of HBV core gene (abbreviated pHBc144) was used to co-immunize C57 BL/6 mice. The titer of anti-HBcIgG was detected by ELISA and the antigen-specific CD8⁺ T cells (CD8⁺IFN-γ⁺ T cells) were detected by intracellular cytokine staining at different time points.

RESULTS: After co-immunization by pIL-15 and pHBc144 DNA vaccine the antigen-specific CD8⁺ cells of mice increased gradually, the first peak of immune response appeared 14 d later, then the number of antigen-specific CD8⁺ Ts cells decreased gradually and maintained at a steady level in 3 mo. After boosting, the number of antigen-specific CD8⁺ T cells reached the second peak 10 d later with a double of the 1st peak, then the number of antigen-specific CD8⁺ T cells decreased slowly. IL-15 as a gene adjuvant had no significant effect on humoral immune responses induced by hepatitis B virus core gene DNA vaccine, but increased the memory antigen-specific CD8⁺ T cells induced by hepatitis B virus core gene DNA vaccine.

CONCLUSION: DNA vaccine constructed by HBc Ag 1-144 amino acid induces effective cell immunity, and cytokine plasmid-delivered IL-15 enhances the longevity of CD8⁺ T cells.

Cytokine Induction by the Hepatitis B Virus Capsid in Macrophages Is Facilitated by Membrane Heparan Sulfate and Involves TLR2

The hepatitis B virus (HBV) core Ag (HBcAg) serves as the structural subunit of the highly immunogenic capsid shell. HBcAg harbors a unique arginine-rich C terminus that was implicated in immune responses induced by the capsid. In this study, we examined the capacity of the HBV capsid to induce proinflammatory and regulatory cytokines in human THP-1 macrophages and the possible underlying mechanism. Full-length HBc capsids, but not HBc-144 capsids lacking the arginine-rich domain of HBcAg, efficiently bound differentiated THP-1 macrophages and strongly induced TNF-alpha, IL-6, and IL-12p40. Capsid binding to macrophages and cytokine induction were independent of the RNA associated with the arginine-rich domain. Soluble heparin and heparan sulfate but not chondroitin sulfates greatly diminished cytokine induction through inhibition of capsid binding to THP-1 macrophages. Furthermore, serine phosphorylation in the arginine-rich domain modulates capsid binding to macrophages and the cytokine response. Induction of cytokines by the capsid involved activation of NF-kappaB, ERK-1/2, and p38 MAPK and did not require endosomal acidification. Finally, NF-kappaB activation by the capsid in HEK 293 cells specifically required expression of TLR2 and was compromised by soluble heparin. Thus, cytokine induction by the HBV capsid in macrophages is facilitated by interaction of its arginine-rich domain with membrane heparan sulfate and involves signaling through TLR2.

Interferon-gamma (IFN-gamma) response to different hepatitis B virus antigens in hepatitis B virus infection

The IFN-gamma levels in serum and cultured supernatant of peripheral blood mononuclear cells (PBMCs) were compared after stimulation by HBsAg ad, HBsAg ay and HBcAg among 3 groups of subjects i.e. patients with acute HBV infection, patients with chronic HBV infection and subjects recovered from HBV infection. Uninfected vaccinated group was taken as control. Serum and PBMCs were obtained from 38 individuals between 18-50 years of age. PBMCs were separated from heparinised blood by Ficoll-Hypaque density gradient centrifugation technique and cultured in CO2 incubator after stimulation by HBV surface and core antigens. IFN-gamma concentration was measured in serum and culture supernatant of PBMCs by an in-house ELISA technique. The mean serum IFN-gamma levels in acute, chronic, recovered and control groups were 88 pg/ml, 96.6 pg/ml, 155 pg/ml and 205 pg/ml respectively. On stimulation by HBsAg ad, IFN-gamma levels in cultured PBMCs of the above mentioned groups were 282.50 pg/ml, 307.45 pg/ml, 915.62 pg/ml and 511.67 pg/ml respectively, while in the same group on HBsAg ay stimulation, IFN-gamma levels were 246.25 pg/ml, 374.70 pg/ml, 1040 pg/ml and 465.83 pg/ml respectively. On stimulation by HBcAg, the IFN-gamma levels were 875 pg/ml, 128.50 pg/ml, 905 pg/ml and 235.33 pg/ml respectively in the acute, chronic, recovered and control groups. When compared with serum, significantly higher levels of IFN-gamma in cultured supernatant of PBMCs were observed after stimulation by HBsAg ad and HBsAg ay subtype in cases of chronic (p<0.05) and recovered groups (p<0.01 and p<0.001 respectively). However, no statistically significant difference of IFN-gamma level was observed between serum and PBMCs amongst the acute and control groups when stimulated by either of the HBsAg subtypes or HBcAg. In the recovered group, IFN-gamma levels produced by PBMCs after stimulation by HBcAg were significantly higher than that of serum (p<0.01). The study concludes that on subsequent exposure, PBMCs of the recovered group produces higher levels of IFN-gamma in response to different hepatitis B antigens. This response perhaps is able to protect individuals who are unable to develop anti-HBs.

Therapeutic polypeptides based on HBcAg18-27 CTL epitope can induce antigen-specific CD8+ CTL-mediated cytotoxicity in HLA-A2 transgenic mice

AIM: To explore how to trigger an HLAI-restricted CD8⁺ T cell response to exogenously synthesized polypeptides in vivo.

METHODS: Three mimetic therapeutic polypeptides based on the immunodominant CTL epitope of HBcAg, the B- epitope of HBV PreS₂ region and a common T helper sequence of tetanus toxoid were designed and synthesized with Merrifield’s solid-phase peptide synthesis method. Their immunological properties of inducing T_H1 polarization, CD8⁺ HBV-specific CTL expansion and CD8⁺ T cell mediated cytotoxicity were investigated in HLA-A2 transgenic mice.

RESULTS: Results demonstrated that the mimetic polypeptides comprised of the immunodominant CTL, B-, and T helper epitopes could trigger specifically and effectively vigorous CD8⁺ HBV-specific CTL-mediated cytotoxicity and T_H1 polarization of T cells in HLA-A2 transgenic mice.

CONCLUSION: A designed universal T helper plus B-epitopes with short and flexible linkers could dramatically improve the immunogenicity of CTL epitopes in vivo. And that the mimetic therapeutic peptides based on the reasonable match of the above CTL, B- and T helper epitopes could be a promising therapeutic peptide vaccine candidate against HBV infection.

A study on interferon-gamma (IFN-gamma) response by T cells stimulated by hepatitis B virus core antigen

Cell-mediated immune response by lymphocyte induced through recognition of HBV core antigen during acute HBV infection, chronic HBV infection and in subjects recovered from HBV infection was investigated in the present study by assessing the competence of IFN-gamma secretion by cultured PBMCs on stimulation by HBV nucleocapsid antigen (HBcAg). Fresh blood was collected in heparin from acute, chronic and recovered groups of HBV infected patients and uninfected vaccinated healthy controls aged between 18-50 years. PBMCs were separated by Ficoll-Hypaque density gradient centrifugation technique and were stimulated with hepatitis B virus core antigen (HBcAg) and mitogen (lectin). Stimulated PBMCs were cultured in CO2 and IFN-gamma levels were measured from the culture supernatant by an in-house ELISA technique. The mean+/-SE levels of IFN-gamma in HBcAg stimulated PBMCs in acute, chronic, recovered and controls groups were 875 pg/ml+/-297.56, 128.50 pg/ml+/-33.66, 905 pg/ml+/-172.51 and 235.33 pg/ml+/-111.28 respectively. IFN-gamma levels produced by HBcAg stimulated PBMCs of acute and recovered groups were significantly higher than that of chronic and control group (p<0.001). All groups responded strongly to lectin stimulation. Thus, it may be concluded that patients with acute HBV infection and those who had recovered from HBV infection show vigorous response to HBcAg stimulation in contrast to patients with chronic HBV infection.

[Effect of IL-18 on peripheral blood monocytes from chronic hepatitis B patients]

OBJECTIVES

To explore the effect of IL-18 on peripheral blood monocytes (PBMCs) from chronic hepatitis B (CHB) patients and HBV DNA released by HepG2.2.15 cells, which were transfected with the gene of HBV.

METHODS

PBMCs were isolated from 25 healthy persons and 25 CHB patients, which were co-cultured with HBcAg and IL-18 at different concentrations for 72 hours. The level of IFN-gamma in the culture supernatant of PBMCs was determined by ELISA. One patient' PBMCs were co-cultured for 96 hours with various concentrations of IL-18 and HepG2.2.15 cells which had been cultured for 24 hours, the supernatant was collected to detect HBV DNA level by PCR.

RESULTS

When PBMCs were stimulated by HBcAg and IL-18 at various concentrations, the levels of supernatant IFN-gamma in the CHB group were much higher than those in the normal control group (at 0.2ng/ml: t=11.7, P<0.01; at 1.0ng/ml: t=16.19, P<0.01; at 5.0ng/ml: t=20.12, P<0.01), especially when the PBMCs were stimulated by HBcAg, IL-18 and IL-12 (1313.20pg/ml+-187.76pg/ml vs. 390.75pg/ml+-43.23pg/ml, t=23.94, P<0.01). The IFN-gamma level in the patients who were stimulated by HBcAg alone was much lower than the levels in the patients who were stimulated by HBcAg and IL-18 at various concentrations, and which were lower than those in the patients stimulated by HBcAg, IL-12 and IL-18 at the same concentrations (light: t=2.2, P<0.05; moderate: t=2.97, P<0.05). The HBV DNA content in the supernatant of co-cultivation with HepG2.2.15 cells and PBMCs was much higher than that of the two kinds of cells stimulated by HBcAg and IL-18 at various concentrations or HBcAg, IL-18 and IL-12/IFN-a1b.

CONCLUSION

IL-18 can improve the PBMCs from CHB patients to produce a great deal of IFN-gamma, so it has a good application prospect in two aspects: immunoregulatory effects and increasing the ability to kill the cells infected with virus.

Reduced virus specific T helper cell induction by autologous dendritic cells in patients with chronic hepatitis B - restoration by exogenous interleukin-12

Insufficient stimulatory capacities of autologous dendritic cells (DC) may contribute in part to impaired T cell stimulation and therefore viral persistence in patients with chronic hepatitis B virus (HBV) infection. In order to characterize the antigen presenting functions of DC from chronic HBV carriers and controls antigen specific T cell responses were analysed. CD34+ peripheral blood progenitor cells were differentiated to immature DC in the presence of GM-CSF, IL-6/IL-6R fusion protein and stem cell factor. Proliferative CD4+ T cell responses and specific cytokine release were analysed in co-cultures of DC pulsed with HBV surface and core antigens or tetanus toxoid and autologous CD4+ T cells. Cultured under identical conditions DC from chronic HBV carriers, individuals with acute resolved hepatitis B and healthy controls expressed similar phenotypical markers but chronic HBV carriers showed less frequent and weaker HBV antigen specific proliferative T helper cell responses and secreted less interferon-gamma while responses to the tetanus toxoid control antigen was not affected. Preincubation with recombinant IL-12 enhanced the HBV specific immune reactivities in chronic HBV patients and controls. In conclusion, the weak antiviral immune responses observed in chronic hepatitis B may result in part from insufficient T cell stimulating capacities of DC. Immunostimulation by IL-12 restored the HBV antigen specific T cell responses and could have some therapeutical benefit to overcome viral persistence.

Inhibition of hepatitis B virus assembly with synthetic peptides derived from the viral surface and core antigens

The long surface antigen (L-HBsAg) of hepatitis B virus (HBV) plays a central role in the production of infectious virions. During HBV morphogenesis, both the PreS and S domains of L-HBsAg form docking sites for the viral nucleocapsids. Thus, a compound that disrupts the interaction between the L-HBsAg and nucleocapsids could serve as a therapeutic agent against the virus based upon inhibition of morphogenesis. Synthetic peptides correspond to the binding sites in L-HBsAg inhibited the association of L-HBsAg with core antigen (HBcAg). A synthetic peptide carrying the epitope for a monoclonal antibody to the PreS1 domain competed weakly with L-HBsAg for HBcAg, but peptides corresponding to a linear sequence at the tip of the nucleocapsid spike did not, showing that the competing peptide does not resemble the tip of the spike.

[Interleukin 10(IL-10) levels in serums and in culture supernatants of peripheral blood mononuclear cells from patients with chronic hepatitis B]

OBJECTIVE

To understand the impacts of interleukin 10(IL-10) in serums and in culture supernatants of peripheral blood mononuclear cells (PBMCs) from patients with chronic hepatitis B (CHB) on the persistent infection of hepatitis B virus (HBV).

METHODS

The levels of IL-10 in serums and in culture supernatants of PBMCs from 15 patients with CHB and 6 normal controls were measured by ELISA method. PBMCs were cultured with or without Staphylococcus aureus enterotoxin B(SEB; 0.2 microgram/ml) or recombinant HBcAg(rHBcAg; 1.0 microgram/ml) for 48 hours in vitro.

RESULTS

The levels of IL-10 in serums was greater in patients with CHB (123.11 +/- 13.89 ng/L) than in controls (95.97 +/- 11.68 ng/L, P < 0.01). Spontaneous, SEB-induced and rHBcAg-induced IL-10 production by PBMCs after culturing in vitro for 48 hours was also higher in patients with CHB (280.82 +/- 50.56 ng/L, 321.69 +/- 37.04 ng/L and 369.58 +/- 30.52 ng/L) than in controls (100.2 +/- 8.54 ng/L, 203.41 +/- 12.02 ng/L and 202.38 +/- 15.79 ng/L; P < 0.01). In addition, IL-10 production by rHBcAg-stimulated PBMCs was significantly greater than by SEB-stimulated PBMCs in patients with CHB. Patients with seropositive for HBV DNA had higher levels of IL-10 in serums and in culture supernatants of PBMCs than patients with seronegative for HBV DNA. But the levels of IL-10 were lower in patients with chronic heavy and severe hepatitis B than in patients with chronic mild and moderate hepatitis B.

CONCLUSION

IL-10 may have an important role in persistent infection of HBV in patient with CHB.

Cytokine release of peripheral blood mononuclear cells in children with chronic hepatitis B virus infection

BACKGROUND

Immune response to hepatitis B virus (HBV) antigens or mitogens in Asian children with chronic HBV infection who are mainly perinatally infected has not been studied in connection with the production of various cytokines, although these patients are considered to be less responsive to antiviral therapy.

METHODS

The production of the cytokines interferon (IFN)-gamma, lymphotoxin, interleukin (IL)-4, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-1beta by peripheral blood mononuclear cells (PBMCs) was studied in 17 hepatitis B surface antigen (HBsAg) carrier children with raised alanine transferase levels (group 1), 17 HBsAg carrier children with normal alanine transferase levels (group 2), and 20 healthy noncarrier control subjects (group 3).

RESULTS

Hepatitis B core antigen (HBcAg)-stimulated IFN-gamma production was significantly higher in group 1 than in groups 2 and 3, serum HBeAg cleared within 1 year in five of eight children in group 1 with stimulation indexes higher than 3, and HBcAg-induced IL-4 secretion was minimal in all groups. Interferon-gamma produced by PBMCs stimulated by purified HBsAg did not differ among the three groups. Higher lymphotoxin production by PBMCs stimulated by HBcAg was also noted in groups 1 and 2 than in group 3. Lipopolysaccharide (LPS)-stimulated TNF-alpha production by PBMCs was significantly higher in group 1 than in group 2. There was no association between HBeAg-anti-HBe status and production of various cytokines. No differences were seen in the profile of cytokines induced by HBV antigens or LPS in children of carrier mothers compared with children of HBsAg-negative mothers.

CONCLUSION

Increased IFN-gamma production resulting from HBcAg-specific T-helper lymphocyte type 1 response, and increased TNF-alpha production may contribute to cell-mediated antiviral immune response in children with chronic hepatitis B. In HBV carrier children, the ability to produce the studied cytokines is related to whether an endogenous immune attempt to eliminate HBV infection emerges in the patients but is not related to the different modes of acquisition of HBV infection.

HBV-specific lymphoproliferative and cytokine responses in patients with chronic hepatitis B

BACKGROUND/AIMS

Hepatitis B virus specific T cell responses are crucial for viral elimination but their nature is not fully understood.

METHODS

We studied the regulation of proliferation and cytokine production after antigenic stimulation in peripheral blood mononuclear cells from chronically HBV-infected patients and subjects with natural immunity after recovery from an acute infection. Proliferation and production of interferon-gamma, IL-10 and tumor necrosis factor-alpha were determined after stimulation with HBcAg, HBeAg or HBsAg in the absence or presence of IL-12 or neutralizing antibodies to IL-12, interferon-gamma, IL-4, IL-10 or tumor necrosis factor-alpha.

RESULTS

Upon stimulation with HBcAg or HBeAg, peripheral blood mononuclear cells from chronic hepatitis B virus patients displayed a clear class-II restricted proliferative response (SI greater than 2.5). Both interferon-gamma (less than 50 IU/ml) and IL-10 levels up to 600 pg/ml were detected. Proliferative or cytokine responses to HBsAg were very weak or absent. Addition of IL-12 to HBeAg-stimulated cultures increased the production of interferon-gamma to more than 200 IU/ml in all patients and slightly increased the production of IL-10. Neutralization of IL-10 increased the HBeAg-induced interferon-gamma production but had no effect on tumor necrosis factor-alpha production. Addition of anti-IL-4 or anti-tumor necrosis factor-alpha had no significant influence on proliferation or cytokine release. Importantly, in both chronic hepatitis B virus patients and naturally immune subjects, IL-12 induced proliferative and interferon-gamma responses in peripheral blood mononuclear cells stimulated with HBsAg.

CONCLUSIONS

Our data indicate that peripheral blood mononuclear cells from chronic hepatitis B virus patients proliferate and produce interferon-gamma and IL-10 upon HBeAg but not upon HBsAg stimulation. IL-12 augments the HBeAg-induced responses and, additionally, provokes proliferation and interferon-gamma production in HBsAg-stimulated cultures.

HLA-A31- and HLA-Aw68-restricted cytotoxic T cell responses to a single hepatitis B virus nucleocapsid epitope during acute viral hepatitis

We have recently developed the technology to identify and characterize the human histocompatibility leukocyte antigen (HLA) class I-restricted, CD8+ cytotoxic T lymphocyte (CTL) response to hepatitis B virus (HBV)-encoded antigens in patients with acute viral hepatitis. CTL are expanded in vitro by stimulation with HBV-derived synthetic peptides and selected by restimulation with a panel of HLA-matched stable transfectants that express the corresponding HBV protein. We have recently reported the existence of an HLA-A2-restricted, CD8+ CTL response to an epitope located between residues 18 and 27 of the HBV nucleocapsid core antigen (HBcAg). We now report the discovery of a CTL epitope located between HBcAg residues 141 and 151 that completely overlaps a critical domain in the viral nucleocapsid protein that is essential for its nuclear localization and genome packaging functions as well as processing of the precore protein. The CTL response to this epitope is dually restricted by the HLA-A31 and HLA-Aw68 alleles, which, unexpectedly, appear to use a common binding motif based on the results of alanine substitution and competition analysis, and the binding properties of these two alleles predicted from their known primary sequence, and from the three-dimensional structure of HLA-Aw68. We have also demonstrated that the HBV-specific CTL response to this epitope is polyclonal during acute viral hepatitis, since these two restriction elements can present the HBcAg 141-151 epitope to independent CTL clones derived from a single patient; and that the CTL response is multispecific, since HLA-A2-restricted and HLA-Aw68-restricted CTL responses to HBcAg 18-27 and HBcAg 141-151, respectively, have been identified to coexist in another patient. The foregoing argue against the emergence of CTL escape mutants as a significant problem during HBV infection, especially at this locus, where mutations might be incompatible with viral replication. Finally, our data suggest an association between the HBV-specific CTL response and viral clearance, and they have implications for the design of immunotherapeutic strategies to terminate HBV infection in chronically infected patients.

HBcAg induced T-cell independent anti-HBc production in chronic HBsAg carriers

The capacity of the nucleocapsid protein of HBV to function as a T-cell independent antigen in man was studied. When T-cell depleted B-cell cultures were challenged with E coli-derived HBcAg, anti-HBc production was registered in culture supernatants from the majority of chronic HBsAg carriers in a quiescent stage of disease. In contrast, similarly prepared and stimulated cultures from donors with natural acquired immunity to hepatitis B or HB-susceptible controls were non-responsive. Addition of autologous T-cells effectively restored anti-HBc responsiveness in T-cell depleted B-cell cultures from HB-immune donors, demonstrating the T-cell dependency for anti-HBc induction in natural HBV-infection.

Identification of the hepatitis B virus factor that inhibits expression of the beta interferon gene

The identity of the trans-acting factor encoded by the 1,828-bp BamHI DNA fragment of hepatitis B virus (HBV) that suppresses the transcription of the human beta interferon gene was investigated. Each complete and partial open reading frame (ORF) present within the 1,828-bp BamHI HBV DNA fragment was cloned into a simian virus 40 expression vector, and the resulting gene products were assayed for their ability to inhibit the activity of the regulatory DNA region that governs the expression of the beta interferon gene. Only the proteins encoded by the C ORF inhibited the activity of the beta interferon regulatory DNA region; putative proteins encoded by the partial X, P, and S ORFs present in the 1,828-bp BamHI HBV DNA fragment had no effect. A plasmid encoding only the native HBV core antigen, but not one coding for a truncated core antigen, possessed this inhibitory activity. The inhibition by the core antigen was specific for the regulatory elements of the beta interferon gene; none of a variety of viral transcriptional elements was inhibited.