Preferential recognition of hepatitis B nucleocapsid antigens by Th1 or Th2 cells is epitope and major histocompatibility complex dependent

Early application of IFNγ mediated the persistence of HBV in an HBV mouse model

The antiviral activity of interferon gamma (IFNγ) against hepatitis B virus (HBV) was demonstrated both in vivo and in vitro in a previous study. IFNγ can suppress HBV replication by accelerating the decay of replication-competent nucleocapsids of HBV. However, in this study, we found that the direct application of the mouse IFNγ (mIFNγ) expression plasmid to the liver of an HBV hydrodynamic injection (HI) mouse model led to the persistence of HBV, as indicated by sustained HBsAg and HBeAg levels in the serum as well as an increased percentage of the HBsAg positive mice, whereas the level of HBV DNA in the serum and the expression of HBcAg in the liver were inhibited at the early stage after HI. Meanwhile, we found that the productions of both HBcAb and HBsAb were suppressed after the application of mIFNγ. In addition, we found that HBV could be effectively inhibited in mice immunized with HBsAg expression plasmid before the application of mIFNγ. Furthermore, mIFNγ showed antiviral effect and promoted the production of HBsAb when the mice subjected to the core-null HBV plasmid. These results indicate that the application of mIFNγ in the HBV HI mouse model, the mice showed defective HBcAg-specific immunity that impeded the production of HBcAb and HBsAb, finally allowing the persistence of the virus. Moreover, IFNγ-induced negative immune regulatory factors also play an important role in virus persistence.

Mechanisms of HBV immune evasion

The concept of immune evasion is a longstanding topic of debate during chronic Hepatitis B Virus infection. The 292 million individuals chronically infected by HBV are clear evidence that the virus avoids elimination by the immune system. The exact mechanisms of immune evasion remain undefined and are distinct, but likely interconnected, between innate and adaptive immunity. There is a significant body of evidence that supports peripheral tolerance and exhaustion of adaptive immunity but our understanding of the role that central tolerance plays is still developing. Innate immunity instructs the adaptive immune response and subversion of its functionality will impact both T and B cell responses. However, literature around the interaction of HBV with innate immunity is inconsistent, with reports suggesting that HBV avoids innate recognition, suppresses innate recognition, or activates innate immunity. This complexity has led to confusion and controversy. This review will discuss the mechanisms of central and peripheral tolerance/exhaustion of adaptive immunity in the context of chronic HBV infection. We also cover the interaction of HBV with cells of the innate immune system and propose concepts for the heterogeneity of responses in chronically infected patients.

A non-human hepadnaviral adjuvant for hepatitis C virus-based genetic vaccines

Human hepatitis B virus (HBV) core antigen (HBcAg) can act as an adjuvant in hepatitis C virus (HCV)-based DNA vaccines. Since two billion people are, or have been, in contact with HBV, one may question the use of human HBV sequences as adjuvant. We herein evaluated non-human stork hepatitis B virus core gene-sequences from stork as DNA vaccine adjuvants. Full-length and fragmented stork HBcAg gene-sequences were added to an HCV non-structural (NS) 3/4A gene (NS3/4A-stork-HBcAg). This resulted in an enhanced priming of HCV-specific IFN-γ and IL-2 responses in both wild-type (wt)- and NS3/4A-transgenic (Tg) mice, the latter with dysfunctional NS3/4A-specific T cells. The NS3/4A-stork-HBcAg vaccine primed NS3/4A-specific T cells in hepatitis B e antigen (HBeAg)-Tg mice with dysfunctional T cells to HBcAg and HBeAg. Repeated immunizations boosted expansion of IFN-γ and IL-2-producing NS3/4A-specific T cells in wt- and NS3/4A-Tg mice. Importantly, NS3/4A-stork-HBcAg-DNA induced in vivo long-term functional memory T cell responses, whose maintenance required CD4(+) T cells. Thus, avian HBcAg gene-sequences from stork can effectively act as a DNA vaccine adjuvant. This technology can most likely be universally expanded to other genetic vaccine antigens, as this completely avoids the use of sequences from a human virus where a pre-existing immunity may interfere with its adjuvant effect.

Functional aspects of intrahepatic hepatitis B virus-specific T cells induced by therapeutic DNA vaccination

Current therapies for the hepatitis B virus (HBV), a major cause of severe liver disease, suppress viral replication but replication rebounds if therapy is withdrawn. It is widely accepted that immune activation is needed to control replication off-therapy. To specifically activate T cells crossreactive between the hepatitis B core and e antigens (HBcAg/HBeAg) in chronically infected patients, we developed a therapeutic vaccine candidate. The vaccine encompass codon-optimized HBcAg and IL-12 expressing plasmids delivered using targeted high-pressure injection combined with in vivo electroporation. One dose of the vaccine primed a B-cell-independent polyfunctional T-cell response, in wild-type, and in HBeAg-transgenic mice with an impaired ability to respond to HBc/eAg. The response peaked at 2 weeks and contracted at week 6 after vaccination. Coadministration of IL-12 improved antibody levels, and T-cell expansion and functionality. The vaccine primed T cells that, 2 weeks after a single dose, cleared hepatocytes transiently expressing HBcAg in vaccinated wild-type and HBeAg-transgenic mice. However, 4 weeks later, these functional responses were lost. Booster doses after 8-12 weeks effectively restored function and expansion of the rapidly contracting T cells. Thus, this vaccine strategy primes functional HBcAg-specific T cells in a host with dysfunctional response to HBV.

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.

Impact of the Immunogen Nature on the Immune Response against the Major HBV Antigens in an HBsAg and HLA-humanized Transgenic Mouse Model

Hepatitis B chronic carriage remains as a major public health problem. Protein and DNA vaccines are now widely used in therapeutic vaccine candidates. Although, the hepatitis B surface antigen (HBsAg) based vaccines have been largely studied, candidates comprising both HBsAg and core (HBcAg) either protein- or DNA-based approaches deserve further immunological characterization.

In the present study, a repeated dose administration schedule for protein or DNA immunogens was conducted in order to characterize the resulting immune response in a humanized and HBsAg-tolerized setting. A novel transgenic (Tg) mice that express the HBsAg, human MHC class I (HLA-A*0201) and MHC class II (HLA-DRB1*01) molecules and devoid of endogenous murine class I and II molecules was used as a model of HBV chronic carrier. Mice were immunized by subcutaneous (protein) or intramuscular (DNA) routes and the humoral and cellular responses were evaluated.

Protein or DNA immunization induced humoral immune responses against both HBsAg and HBcAg. The systematic analysis of epitopes that activate CD4+ and CD8+ T lymphocytes confirmed the accuracy of the model. Cellular immune responses were detected differing in their nature. CD8 T-cell responses were induced mostly after DNA immunization while CD4 T-cell responses were predominant in protein based immunizations. In addition, the intensity of HLA-A2-restricted CD8+ T cell responses was reduced in Tg mice expressing HBsAg when compared to control Tg mice.

In conclusion, our results indicate that cellular immune responses necessary for the development of protective immunity can be achieved by DNA or protein immunization. However, important differences in their nature arise when immunogens are administered several times.

How to cite this article: Mancini-Bourgine M, Guillen G, Michel ML, Aguilar JC. Impact of the Immunogen Nature on the Immune Response against the Major HBV Antigens in an HBsAg and HLA-humanized Transgenic Mouse Model. Euroasian J Hepato-Gastroenterol 2014;4(1):36-44.

A VLP library of C-terminally truncated Hepatitis B core proteins: correlation of RNA encapsidation with a Th1/Th2 switch in the immune responses of mice

An efficient pBR327- and Ptrp-based E. coli expression system was used to generate a large-scale library of virus like particles (VLP) formed by recombinant hepatitis B virus (HBV) core (HBc) protein derivatives. To construct the library, the gene of HBc protein of the genotype D/subtype ayw2 virus was gradually truncated from the 3`-end and twenty-two HBc variants (with truncation up to 139 aa) were expressed at high levels. The proteins were purified by salt precipitation and gel filtration. Background RNA binding was observed for VLPs formed by HBc1-149, which lacked all C-terminal Arg blocks, and the addition of three Arg residues (HBc1-152) only slightly increased RNA binding. The presence of two Arg blocks (proteins HBc1-162 and HBc1-163) resulted in approximately half of the typical level of RNA binding, and the presence of three blocks (protein HBc1-171) led to approximately 85% of the typical level of binding. Only a small increase in the level of RNA binding was found for the HBc1-175 VLPs, which contained all four Arg blocks but lacked the last 8 aa of the full-length HBc protein. VLPs containing high levels of RNA had higher antigenicity according to an ELISA with anti-HBc mAbs than the VLPs formed by HBc variants without C-terminal Arg blocks and lacking RNA. The results indicate that the VLPs were stabilised by nucleic acids. The immunogenicity in BALB/c mice was comparable for VLPs formed by different HBc proteins, but a clear switch from a Th1 response to a Th2 response occurred after the loss of encapsidated RNA. We did not observe significant differences in lymphocyte proliferation in vitro for the tested VLP variants; however, the loss of RNA encapsidation correlated with a decreased level of IFN-γ induction, which is a measure of the potential CTL activity of immunogens.

Hepatitis B core-based virus-like particles to present heterologous epitopes

Since the first effort to recombinantly express the hepatitis B core protein (HBc) in bacteria, the remarkable virion-like structure has fuelled interest in unraveling the structural and antigenic properties of this protein. Initial studies proved HBc virus-like particles to possess strong immunogenic properties, which can be conveyed to linked antigens. More than 35 years later, numerous studies have been performed using HBc as a carrier protein for antigens derived from over a dozen different pathogens and diseases. In this review, the authors highlight the intriguing features of HBc as carrier and antigen, illustrated by some examples and experimental results that underscore the value of HBc as an antigen-presenting platform. Two of these HBc fusions, targeting influenza A and malaria, have even progressed into clinical testing. In the future, the HBc-based virus-like particles platform will probably continue to be used for the display of poorly immunogenic antigens, mainly because virus-like particle formation by HBc capsomers is compatible with nearly any available recombinant gene expression system.

Predominance of precore mutations and clinical significance of basal core promoter mutations in chronic hepatitis B virus infection in Indonesia

Chronic hepatitis B virus (HBV) infection is a major health problem worldwide, with a particularly high prevalence in the Asian-Pacific region. During chronic hepatitis B virus (HBV) infection, mutations commonly occur in the basal core promoter (BCP) and precore (PC) regions of HBV, affecting HBeAg expression, particularly following HBeAg serocon-version. Mutations in the B- and T-cell epitopes of the HBV core have also been observed during disease progression. The clinical significance of HBV genome variability has been demonstrated, however the results are a subject of controversy. Considering the characteristics of the virus associated with geographical location, the profiles of BCP, PC and core mutations and their clinical implications in patients with chronic HBV infection in Surabaya, Indonesia, were investigated. The BCP, PC and core mutations and HBV genotypes were detected by direct sequencing. The HBeAg/anti-HBe status and HBV DNA levels were also assessed. This study enrolled 10 patients with chronic HBV infection (UC) from Dr Soetomo General Hospital and Indonesian Red Cross, Surabaya, East Java, Indonesia, 10 patients with chronic hepatitis B and liver cirrhosis (LC) and 4 patients with chronic hepatitis B and hepatocellular carcinoma (HCC) from Dr Soetomo General Hospital. The PC mutation A1896 was predominant in all the groups (60-100%), together with the PC variant T1858, which was associated with HBV genotype B. The number of detected core mutations (Thr/Ser130) was higher in HCC patients (50%). However, the BCP mutations T1762/A1764 were predominant in LC patients (50-60%). The LC and HCC patients carried HBV isolates with additional mutations, at least at BCP or PC, mainly following HBeAg seroconversion. In the majority of anti-HBe-positive samples, the BCP T1762/A1764 mutations were associated with a high viral load, regardless of the PC 1896 status. In conclusion, the PC mutations were found to be predominant in all the groups. However, the BCP mutations were mainly detected in the LC group and may be considered as a critical indicator of a poor clinical outcome.

DNA immunization with HBsAg-based particles expressing a B cell epitope of amyloid β-peptide attenuates disease progression and prolongs survival in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is an incurable and progressive neurodegenerative senile disorder associated with the brain accumulation of Aβ plaques. Although vaccines that reduce Aβ plaques can control AD, the rationale for their use at the onset of the disease remains debatable. Old humans and mice usually respond poorly to vaccines due to presumably age-related immunological impairments. Here, we report that by modifying vaccines, the poor responsiveness of old mice can be reversed. Unlike the Aβ peptide vaccine, DNA immunizations with the amino-terminal Aβ(1-11) fragment exposed on the surface of HBsAg particles elicit high levels of anti-Aβ antibody both in young and old mice. Importantly, in AD model 3xTgAD mice, the vaccine reduced Aβ plaques, ameliorated cognitive impairments and, surprisingly, significantly increased life span. Hence, we propose that vaccines targeting Aβ(1-11) can efficiently combat AD-induced pathological alterations and provide survival benefit in patients with AD.

HBcAg18-27 epitope fused to HIV-Tat 49-57 adjuvanted with CpG ODN induces immunotherapeutic effects in transgenic mice

Successful immunotherapy of chronic hepatitis B virus (HBV) infection is expected to be characterized by enhanced activation of immune responses. Combining the specificity of hepatitis B core antigen (HBcAg) cytotoxic T lymphocyte (CTL) epitope, the cell-penetrating property of human immunodeficiency virus-1 (HIV)-Tat peptide, and the adjuvanticity of CpG oligodeoxynucleotides (CpG ODNs) may elicit strong immune responses and therapeutic effects in HBV infection. We synthesized a fusion peptide containing HBcAg18-27 CTL epitope and HIV-Tat(49-57) peptide. The fusion peptide was intramuscularly injected to HBV transgenic mice with CpG ODN as adjuvant at 2-week intervals three times. The percentages of CD3(+), CD4(+) and CD8(+) cells in spleen lymphocytes and the levels of circulating interferon (IFN)-gamma and interleukin (IL)-2 were determined for the evaluation of immune responses and the levels of serum HBV DNA and the expression of hepatitis B surface antigen (HBsAg) and HBcAg in liver tissue were determined for the assessment of therapeutic effects. Our results showed that the synthesized fusion peptide adjuvanted with CpG ODN could induce significant increase of the percentages of CD3(+), CD4(+) and CD8(+) cells and the levels of IFN-gamma and IL-2, indicating the strong immune responses, and reduced HBV DNA levels and decreased expression of HBsAg and HBcAg in liver tissue, suggesting the therapeutic effects. Collectively, our study supports that HBcAg18-27 CTL epitope fused to HIV-Tat(49-57) peptide adjuvanted with CpG ODN may be a promising strategy for immunotherapy of chronic HBV infection.

Molecular characteristics and stages of chronic hepatitis B virus infection

Hepatitis B virus (HBV) is a common viral pathogen that causes a substantial health burden worldwide. Remarkable progress has been made in our understanding of the natural stages of chronic HBV infection. A dynamic balance between viral replication and host immune response is pivotal to the pathogenesis of liver disease. Knowledge of the HBV genome organization and replication cycle can unravel HBV genotypes and molecular variants, which contribute to the heterogeneity in outcome of chronic HBV infection. Most HBV infections are spontaneously resolved in immunocompetent adults, whereas they become chronic in most neonates and infants at a great risk of developing complications such as cirrhosis and hepatocellular carcinoma (HCC). Those with chronic HBV infection may present in one of the four phases of infection: immune tolerance, immune clearance [hepatitis B e antigen (HBeAg)-positive chronic hepatitis B (CHB)], inactive carrier state, and reactivation (HBeAg-negative CHB). Understanding the dynamic nature of chronic HBV infection is crucial in the management of HBV carriers. Long-term monitoring and optimal timing of antiviral therapy for chronic HBV infection help to prevent progression of HBV-related liver disease to its later stage, particularly in patients with higher risk markers of HCC, such as serum DNA concentration, HBeAg status, serum aminotransferase, HBV genotypes, and pre-core or core mutants.

Interaction of the hepatitis B core antigen and the innate immune system

Previous studies demonstrated that the primary APCs for the hepatitis B core Ag (HBcAg) were B cells and not dendritic cells (DC). We now report that splenic B1a and B1b cells more efficiently present soluble HBcAg to naive CD4(+) T cells than splenic B2 cells. This was demonstrated by direct HBcAg-biotin-binding studies and by HBcAg-specific T cell activation in vitro in cultures of naive HBcAg-specific T cells and resting B cell subpopulations. The inability of DC to function as APCs for exogenous HBcAg relates to lack of uptake of HBcAg, not to processing or presentation, because HBcAg/anti-HBc immune complexes can be efficiently presented by DC. Furthermore, HBcAg-specific CD4(+) and CD8(+) T cell priming with DNA encoding HBcAg does not require B cell APCs. TLR activation, another innate immune response, was also examined. Full-length (HBcAg(183)), truncated (HBcAg(149)), and the nonparticulate HBeAg were screened for TLR stimulation via NF-kappaB activation in HEK293 cells expressing human TLRs. None of the HBc/HBeAgs activated human TLRs. Therefore, the HBc/HBeAg proteins are not ligands for human TLRs. However, the ssRNA contained within HBcAg(183) does function as a TLR-7 ligand, as demonstrated at the T and B cell levels in TLR-7 knockout mice. Bacterial, yeast, and mammalian ssRNA encapsidated within HBcAg(183) all function as TLR-7 ligands. These studies indicate that innate immune mechanisms bridge to and enhance the adaptive immune response to HBcAg and have important implications for the use of hepadnavirus core proteins as vaccine carrier platforms.

Biodegradable nanoparticle delivery of a Th2-biased peptide for induction of Th1 immune responses

The type of immune response developed against the hepatitis B virus (HBV) is crucial in determining the outcome of the disease. The protective effects of vaccine-induced antibody responses against subsequent exposure to HBV are well-established. After the establishment of chronic HBV infection, cell-mediated immune response is curative while humoral response is detrimental. A therapeutic vaccine that could switch the type of response could lead to disease resolution. Hepatitis B core antigen (HBcAg)(129-140) has been identified as a Th2-biased peptide in H-2(b) mice when it is administered along with complete Freund's adjuvant (CFA). We formulated HBcAg(129-140) along with monophosphoryl lipid A in poly(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles. Naive mice immunized with the nanoparticle formulation developed a strong Th1-type response while mice immunized with the control formulation of CFA and peptide did not. We then primed mice with CFA and peptide to establish a Th2-type immune response before administering the nanoparticle formulation. Mice receiving the nanoparticle formulation being primed with CFA still developed a strong Th1-type response, while mice that received incomplete Freund's adjuvant and peptide instead of nanoparticles did not. The ability of PLGA nanoparticles to alter the type of immune response elicited by a peptide, even in the context of an ongoing immune response, makes PLGA nanoparticles a strong candidate for the formulation of therapeutic vaccines.

Different response requirements for IFNgamma production in ELISPOT assays by CD4+ T cells from mice early and late after immunization

Antigen specific immune responses that occur early after antigen exposure differ from those that are present late in the response. The present study focused on detecting changes in production of IFNgamma by CD4+ T cells over time during chronic antigen exposure. (C3HxCB17)F1 mice were primed with recombinant hepatitis B core antigen (rHBcAg) in incomplete Freund's adjuvant to allow persistent antigen exposure. To assay the CD4+ T cell response to HBcAg, splenocytes from immunized mice were restimulated with rHBcAg for 24 or 48 h in vitro and tested for IFNgamma and IL-5 secreting cells by ELISPOT. Results showed that early after antigen exposure (7 days for primary and 3 days for secondary exposures), the maximal number of IFNgamma secreting cells was detected in the ELISPOT after 24 h of restimulation. However, late after antigen exposure (28 days for primary and 14 days for secondary exposures), the maximum number of IFNgamma secreting cells was not detected until 48 h of restimulation in this assay. This delay in IFNgamma production was related to the availability of IL-2, since addition of IL-2 allowed the delayed cells from late responses to develop peak IFNgamma production in vitro by 24 h, equivalent to that of cells from early responses. This IL-2 dependent delay occurred in Th1-type IFNgamma responses but not in Th2-type IL-5 responses. These observations indicate that, when detecting IFNgamma secreting cells it is important to screen responses at different times of restimulation or in the presence and absence of IL-2 to ensure optimal detection. This approach should prove critical, particularly when evaluating patients with chronic infections and in determining the effectiveness of vaccines since these deal with both early and late responses.

Mutations in hepatitis B virus core regions correlate with hepatocellular injury in Chinese patients with chronic hepatitis B

AIM: To elucidate the relationship between the frequency of core mutations and the clinical activity of hepatitis B virus (HBV)-related liver disease and to characterize the amino acid changes in the core region of HBV.

METHODS: We studied 17 Chinese patients with chronic hepatitis B according to their clinical courses and patterns of the entire core region of HBV.

RESULTS: Amino acid changes often appeared in the HBV core region of the HBV gene in patients with high values of alanine aminotransferase (ALT) or with the seroconversion from HbeAg to anti-HBe. The HBV core region with amino acid changes had high frequency sites that corresponded to HLA I/II restricted recognition epitopes reported by some investigators.

CONCLUSION: The core amino acid changes of this study occur due to influence of host immune system. The presence of mutations in the HBV core region seems to be important for predicting the clinical activity of hepatitis B in Chinese patients.

Identification of HLA-DRB1-bound self-peptides following measles virus infection

We developed a B-lymphocyte cell line derived from a measles seropositive individual who was homozygous for the HLA-DRB1*0301 allele. Peptides associated with the HLA-DRB1*0301 protein were purified from this lymphoblastoid cell line after infection with the Attenuvax measles vaccine virus (Merck Research Laboratories, West Point, PA) and with "sham" infection. More than 40 peptide sequences were obtained by nano-scale reversed phase-high performance liquid chromatography coupled to tandem mass spectrometry (nano-LC/MS/MS). These peptides originated from 21 different source proteins--the majority from membrane-bound proteins. Most of the peptides (>73%) bound to HLA-DRB1*0301 appeared to be in lower abundance on measles-infected cells compared to the "sham-infected" cells. However, 26% of the identified peptides seem to have increased expression after measles infection. Measles vaccine virus infection did not change the level of HLA-DR expression. We demonstrate the power of nano-LC/MS/MS in the rapid determination of changes in the spectrum and expression of HLA-DRB1*0301-bound peptides after infection with measles virus. This provides further knowledge of the changes in peptide expression after viral infection and provides a powerful tool for identifying HLA-presented host and viral epitopes in the context of class II HLA molecules.

HLA class II alleles and measles virus-specific cytokine immune response following two doses of measles vaccine

Measles virus-specific T cells and the production of cytokines play a critical role in the immune response following measles immunization. To understand the genetic factors that influence variation in IFN-gamma and IL-4 responses following measles immunization and to provide insight into the factors influencing both cellular and humoral immunity to measles, we assessed associations between human leukocyte antigen (HLA) class II genes and measles-specific Th1 and Th2-type cytokine responses in peripheral blood lymphocytes from 339 children previously vaccinated with two doses of measles-mumps-rubella vaccine (MMR-II). Median values for measles-specific IFN-gamma and IL-4 secretion levels were 40.73 and 9.71 pg/ml, respectively. The global tests suggested associations between measles-specific IFN-gamma response and alleles of the DRB1 and DQB1 loci (P=0.07 and P=0.02, respectively). Specifically, DRB1*0301, *0901, and *1501 alleles were significantly associated with IFN-gamma secretion. The alleles that suggested evidence of an HLA association with IL-4 secretion were DRB1*0103, *0701, and *1101. Th1 cytokine responses and DQB1 allele associations revealed that the alleles with the strongest association with IFN-gamma secretion were DQB1*0201, *0303, *0402, and *0602. Specific alleles with a suggestive association with low measles-specific Th2 cytokine responses were DQB1*0202 and *0503. In addition, DPB1*0101, *0201, and *0601 alleles provided suggestive evidence of an HLA association with measles-induced IFN-gamma response, while DPB1*0501 was associated with an IL-4 response. These data suggest that IFN-gamma and IL-4 cytokine responses to measles may be genetically restricted in part by HLA class II genes, which in turn can restrict the cellular immune response to measles vaccine.

Contribution of respiratory syncytial virus G antigenicity to vaccine-enhanced illness and the implications for severe disease during primary respiratory syncytial virus infection

BACKGROUND

Immunization of BALB/c mice with vaccinia virus expressing the G glycoprotein (vvG) of respiratory syncytial virus (RSV) or with formalin-inactivated alum-precipitated RSV (FI-RSV) predisposes for severe illness, type 2 cytokine production and pulmonary eosinophilia after challenge with live RSV. This similar disease profile has led to the proposal that the presence of the G glycoprotein in the FI-RSV preparation was the immunologic basis for the vaccine-associated enhancement of disease observed in the failed clinical trials of the 1960s. However, processes of disease pathogenesis observed in FI-RSV- and vvG-immunized mice suggest that FI-RSV and vvG immunizations induce immune responses of different compositions and requirements that converge to produce similar disease outcomes upon live virus challenge.

METHODS

The potential role of RSV G present in FI-RSV preparations in increasing postimmunization disease severity was explored in mice.

RESULTS

The absence of RSV G or its immunodominant epitope during FI-RSV immunization does not reduce disease severity after RSV challenge. Furthermore although depletion of V beta 14+ T cells during RSV challenge modulates disease in G-primed mice, minimal impact on disease in FI-RSV-immunized mice is observed.

CONCLUSION

FI-RSV vaccine-enhanced illness is not attributable to RSV G. Furthermore formulation of a safe and effective RSV vaccine must ensure RSV antigen production, processing and presentation via the endogenous pathways. Thus gene delivery by vector, by DNA or by live attenuated virus are attractive vaccine approaches.

Response of primed human PBMC to synthetic peptides derived from hepatitis B virus envelope proteins: a search for promiscuous epitopes

This investigation was aimed at identifying effective T helper cell epitopes to the hepatitis B virus in humans. A panel of synthetic peptides that represent the hepatitis B virus whole envelope proteins was examined for their capability to stimulate peripheral blood mononuclear cells from human subjects infected with hepatitis B virus naturally. In addition, a large number of subjects were examined and their human leukocyte antigen (HLA) class II allele types were identified to determine whether the helper T cell epitope is specific for a particular HLA allele or 'promiscuous'. The peptides of the amino acid residues 52-67, 110-125, 190-205, and 228-243 appeared to be immunogenic, and particularly, the 52-67 residue was the most promiscuous epitope peptide. These results would contribute to the better understanding of the helper T cell responses to the hepatitis B virus and provide a useful way in designing epitope-based vaccines and future therapeutic strategies.

Priming Th1 immunity to viral core particles is facilitated by trace amounts of RNA bound to its arginine-rich domain

Particulate hepatitis B core Ag (C protein) (HBcAg) and soluble hepatitis B precore Ag (E protein) (HBeAg) of the hepatitis B virus share >70% of their amino acid sequence and most T and B cell-defined epitopes. When injected at low doses into mice, HBcAg particles prime Th1 immunity while HBeAg protein primes Th2 immunity. HBcAg contains 5-20 ng RNA/microg protein while nucleotide binding to HBeAg is not detectable. Deletion of the C-terminal arginine-rich domain of HBcAg generates HBcAg-144 or HBcAg-149 particles (in which >98% of RNA binding is lost) that prime Th2-biased immunity. HBcAg particles, but not truncated HBcAg-144 or -149 particles stimulate IL-12 p70 release by dendritic cells and IFN-gamma release by nonimmune spleen cells. The injection of HBeAg protein or HBcAg-149 particles into mice primes Th1 immunity only when high doses of RNA (i.e., 20-100 microg/mouse) are codelivered with the Ag. Particle-incorporated RNA has thus a 1000-fold higher potency as a Th1-inducing adjuvant than free RNA mixed to a protein Ag. Disrupting the particulate structure of HBcAg releases RNA and abolishes its Th1 immunity inducing potency. Using DNA vaccines delivered intradermally with the gene gun, inoculation of 1 microg HBcAg-encoding pCI/C plasmid DNA primes Th1 immunity while inoculation of 1 microg HBeAg-encoding pCI/E plasmid DNA or HBcAg-149-encoding pCI/C-149 plasmid DNA primes Th2 immunity. Expression data show eukaryotic RNA associated with HBcAg, but not HBeAg, expressed by the DNA vaccine. Hence, codelivery of an efficient, intrinsic adjuvant (i.e., nanogram amounts of prokaryotic or eukaryotic RNA bound to arginine-rich sequences) by HBcAg nucleocapsids facilitates priming of anti-viral Th1 immunity.

Flow cytometric determination of cytokine production and proliferation in hepatitis B core antigen specific murine CD4 cells: lack of correlation between number of cytokine producing cells and cytokine levels in supernatant

Hepatitis B virus (HBV) core antigen (HBcAg) has extraordinary immunostimulatory properties. The majority of studies done so far on HBcAg induced responses have used ELISA or bioassay for cytokine determination and the 3[H]thymidine incorporation assay to measure proliferation. Here multiparameter flow cytometry was used to measure HBcAg induced cytokine production and proliferation of murine T cells. The advantage with this technique was that we could analyse the cytokine phenotype of proliferating cells of a particular cell type. We found that IL-10 expression was strongly induced in CD4+ T cells after HBcAg immunization. Importantly, we found that IL-4 producing HBcAg-specific CD4+ T cells are common after immunization although detection of IL-4 in culture supernatants indicates only low levels of IL-4. In contrast, IFN-gamma producing HBcAg-specific CD4+ T cells were found at lower numbers despite the detection of high levels of IFN-gamma in culture supernatants. Thus, the frequency of these cells is not accurately reflected by the detectability of the respective cytokine in culture supernatants. A low number of specific CD4+ T cells may effectively produce high levels of cytokine. We therefore suggest that different types of cytokine assays are used in order to obtain the most accurate picture of the intrinsic cytokine phenotype of the CD4+ T cells primed by HBcAg.

Type 2 cytokines predominate in the human CD4(+) T-lymphocyte response to Epstein-Barr virus nuclear antigen 1

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that persistently infects 85% of the adult population worldwide. In this report, we examine the proliferative response and cytokine secretion profile of CD4(+) T lymphocytes from a panel of unrelated EBV-positive donors against two EBV latent antigens, EBNA1 and EBNA3C. Substantial proliferative responses by CD4(+) lymphocytes were demonstrated to both antigens in multiple, randomly selected donors. Surprisingly, we observed a striking and consistent difference in cytokine response to EBNA1 and EBNA3C. EBNA1-specific CD4(+) T lymphocytes from multiple unrelated donors preferentially produced type 2-like cytokines in response to antigenic stimulation, while the response to EBNA3C was a characteristic type 1 response. The implications of these findings for EBV persistence and the development of EBV-associated malignancies are discussed.

Glycine-rich cell wall proteins act as specific antigen targets in autoimmune and food allergic disorders

Our objective was to investigate the presence of a B and T cell immune response directed against the glycine-rich cell wall protein (GRP) in patients with different autoimmune disorders and with food allergy. GRP is an ubiquitous food protein that has high homology with cytokeratins and other self proteins [Epstein-Barr virus nuclear antigen-1 (EBNA-I), heterogeneous nuclear ribonucleoprotein, fibrillar collagen] which are common targets in autoimmune disorders. A peptide (GGYGDGGAHGGGYGG) derived from GRP was used to screen human sera in direct and competitive ELISA assay. Anti-GRP-specific IgG were analyzed for their ability to cross-react with autoantigens. The intracellular cytokine profiles of the peptide-specific T cell clones obtained from representative patients have been studied. BALB/c mice were immunized with the peptide coupled to the carrier protein keyhole limpet hemocyanin (KLH). Serum IgG antibodies directed against the GRP peptide were detected in several autoimmune disorders and in food allergic patients, and were able to cross-react with autoantigens including keratin, collagen and EBNA-I. Twenty-five T cell clones showed a specific proliferative response to the GRP peptide and were of the T(h)0 phenotype. Eight of the 10 BALB/c mice immunized with the peptide coupled to KLH developed an autoimmune response. Our data suggest that phylogenetically highly conserved epitopes in plants, viruses and humans may be responsible for an autoimmune response in susceptible individuals. They also indicate that the antigen spreading of a particular sequence among apparently divergent proteins may participate to initiate or amplify an immune response.

Distinct immunomodulation by autoimmunogenic xenobiotics in susceptible and resistant mice

HgCl(2) and diphenylhydantoin (DPH) are prototype chemicals associated with diverse (auto)immune effects in genetically susceptible individuals. Both chemicals activate T cells, and the balance of Th1 versus Th2 activation may influence the clinical outcome of exposure. It is unknown which chemically created neoantigens are responsible for Th activation. We therefore investigated the effect of DPH and HgCl(2) on specific responses to TNP-ovalbumin, in mouse strains with varying sensitivity for the adverse effects. HgCl(2) was found to enhance Th2-driven antibody responses in susceptible B10.s, but protective type 1 responses in resistant B10.d2 mice. This was chemical-specific, as DPH enhanced type 2 responses in both strains. DBA/2 mice were relatively unresponsive to HgCl(2), whereas DPH stimulated type 1 responses in these mice. Interestingly, prior exposure to HgCl(2), but not DPH, facilitated IC deposition in B10.s mice only. Thus, we demonstrate that, depending on MHC-II and background genes, HgCl(2) and DPH preferentially adjuvate type 1 or type 2 responses. In case of HgCl(2), the type of response corresponds with susceptibility to antibody-mediated autoimmunity induced by this chemical. In addition, we demonstrate that, within one strain, different autoimmunogenic chemicals can enhance distinct responses to the same antigen.

Virus-specific lymphokine production differs quantitatively but not qualitatively in acute and chronic hepatitis B infection

Cytokines that are secreted as a response to viral antigen not only have direct antiviral properties but also crucially influence immune reactions determining the outcome of infection. As an advantageous alternative to the study of cytokines present in the supernatants of antigen-specific T cell clones and lines, we have used ELISPOT assays to determine the number of interferon-gamma (IFN-gamma)- and IL4-producing cells generated by peripheral blood mononuclear cells from patients with acute hepatitis B (AHB) and chronic hepatitis B (CHB) infection in response to HBcAg in a short-term culture (48 h). In response to HBcAg IFN-gamma was predominantly produced. In contrast to the results obtained in acute hepatitis B, the typical lymphokine pattern in CHB was characterized by a weak or absent antigen-specific IFN-gamma production. A predominance of IL-4-producing cells was not observed in either AHB or CHB. A significant number of IFN-gamma-producing cells was usually detectable during phases of viral elimination and the quality of the lymphokine response seemed to be epitope independent. Comparison of the results obtained in proliferation assays and ELISPOT assays clearly shows that lymphokine production upon stimulation with viral protein is totally independent of T cell proliferation and more sensitively reflects antiviral reactivity.

Vaccination with different HSV-1 glycoproteins induces different patterns of ocular cytokine responses following HSV-1 challenge of vaccinated mice

We previously reported that vaccination of BALB/c mice with different baculovirus expressed HSV-1 glycoproteins induced varying degrees of protection against HSV-1 ocular challenge, ranging from complete protection to no protection, to exacerbation of eye disease. To correlate specific local immune responses with protection and exacerbation of corneal scarring, we examined immune cell infiltrates in the cornea after ocular HSV-1 challenge of vaccinated mice. Mice were vaccinated with gD, which completely protects against corneal scarring, gG, which produces no protection against corneal scarring, or gK, which exacerbates corneal scarring. Cryostat sections of cornea were taken at different times after challenge and examined for infiltrating cells containing IL-2, IL-4, IFN-gamma, IL-6, or TNF-alpha. No corneal infiltrates were seen before challenge or 1 day after ocular challenge in any groups. By days 3-7, many cells containing IL-4 and IFN-gamma, but few cells containing IL-2, had infiltrated into the corneas of gG or mock vaccinated mice. At the same times, many cells containing IL-2, but few cells containing IL-4 or IFN-gamma, were seen in the corneas of gD vaccinated mice. In contrast, the corneas of mice vaccinated with gK contained large amounts of IL-2, IFN-gamma, and IL-4. Our results suggest that: (1) corneas from gD vaccinated mice had no corneal disease and developed a response highly biased toward IL-2 responses; (2) corneas from gG or mock vaccinated eyes had significant corneal disease and developed a mostly IL-4 and IFN-gamma cytokine response; and (3) corneas from gK vaccinated mice had exacerbated corneal disease and developed strong IL-2, IL-4 and IFN-gamma cytokine responses.

Influence of HLA-DR on the phenotype of CD4+ T lymphocytes specific for an epitope of the 16-kDa alpha-crystallin antigen of Mycobacterium tuberculosis

T helper phenotype may be influenced by cytokine milieu, the differential expression of co-stimulatory molecules, antigen dose, and by differences in affinity at the TCR-peptide-MHC interface. We investigated the latter hypothesis by examining the response of six HLA-DR-restricted CD4+ T cell lines specific for the immunodominant and permissively recognized p91-110 epitope of the 16-kDa alpha-crystallin protein of Mycobacterium tuberculosis. Each line was generated from a sensitized HLA-DR-heterozygous donor and all proliferated when peptide was presented by autologous irradiated peripheral blood mononuclear cells. However, when HLA-DR-matched homozygous Epstein-Barr-virus-transformed B cell lines (L-BCL) were used as peptide-presenting cells there was heterogeneity in the response. The most pronounced proliferative response, and the highest IFN-gamma secretion and cytolytic activity was stimulated by L-BCL expressing molecules (DRB1*0101, *1501 and *0401) with high affinity (IC50 < 10 microM) for the 16p91-110 peptide. By comparison, IL-4 secretion or a lower proliferative response could occur when peptide was presented by alleles of high, or of intermediate (10 microM < IC50 < 100 microM), affinity. These data support the hypothesis that the host MHC can influence CD4+ phenotype and have implications for subunit vaccination against tuberculosis.

Differential regulation of Th1 and Th2 cells by p91-110 and p21-40 peptides of the 16-kD alpha-crystallin antigen of Mycobacterium tuberculosis

Permissively recognized peptides which can activate lymphocytes from subjects with a variety of class II HLA types are interesting diagnostic and vaccine candidates. In this study we generated T helper clones reactive to the permissively recognized p21-40 and p91-110 peptides of the 16-kD heat shock protein of Mycobacterium tuberculosis. All the clones specific for p91-110 secreted interferon-gamma (IFN-gamma) and were of the Th1 phenotype. By contrast, the p21-40 peptide favoured the generation of IL-4-producing clones. Antibody blockade established that the peptide-specific Th clones could either be DR-, DP- or DQ-restricted. Thus, two permissively recognized sequences p21-40 and p91-110 from the same mycobacterial antigen can drive the differentiation of functionally distinct T helper subsets. Attempts to immunize against tuberculosis should bear in mind epitope specificity if a favourable Th subtype response is to be generated.

The role of neutralizing antibody and T-helper subtypes in protection and pathogenesis of vaccinated mice following ocular HSV-1 challenge

In order to determine the possible correlation of specific immune responses with protection against mortality and ocular disease following ocular herpes simplex virus type 1 (HSV-1) challenge, BALB/c mice were vaccinated with different doses and regimens of baculovirus-expressed gD. Neutralizing antibody, virus titres in the eyes, corneal scarring, and survival were measured. In addition, infiltration into the cornea of CD4+ T cells and cells containing the lymphokines interleukin-2 (IL-2), IL-4, IL-6 and tumour necrosis factor-alpha (TNF-alpha) were monitored on days 3, 7, 10, 14 and 21 post-challenge by immunocytochemistry. The vaccination regimens used induced varying degrees of immune responses and protection upon ocular challenge with HSV-1. Our results suggest that neutralizing antibody was the most important immune response in protecting mice against lethal ocular challenge and corneal scarring. TNF-alpha and IL-2 were not crucial in terms of survival and corneal scarring, since gD1 (one vaccination with 1 microg of gD) and gD0.1 (one vaccination with 0.1 microg of gD), both of which provided high levels of protection, showed no TNF-alpha or IL-2 expression. However, TNF-alpha and IL-2 were crucial in terms of virus clearance from the eyes, since gD3 (three vaccinations with 1 microg of gD), which had less virus in their eyes, had high numbers of TNF-alpha and IL-2 infiltrates. Finally, mock-vaccinated mice were not protected from death and corneal disease following HSV-1 challenge. Eyes of mock-vaccinated mice had little or no TNF-alpha or IL-2 responses and the strongest IL-4 and IL-6 responses.

Use of a liposome antigen delivery system to alter immune responses in vivo

It has been reported that a certain peptide encompassing residues 129-140 of the hepatitis B virus core antigen (HBcAg) leads to a Th2-type response in C57BL/10 mice. We postulated that by formulating the peptide in liposomes along with an immune modulator known as MPLA the immune response could be directed toward a Th1-type response. If these liposomes could deliver the peptide along with MPLA to antigen presenting cells, then the immune response generated could be polarized to a Th1 response. The type of immune response initiated after immunization with the peptide HBcAg (126-140) in different formulations was determined by an ex vivo T cell proliferation assay and by analysis of the cytokine profile of the proliferating T cells. A group of C57BL/6 mice immunized with peptide plus MPLA in a liposome formulation displayed a strong T cell proliferative response. The T cell subset was identified as Th1 based on the cytokine profile. The cytokine profiles showed significant production of interferon-gamma (IFN-gamma, a Th1-type cytokine) and extremely low levels of interleukin-4 (IL-4, a Th2-type cytokine). The control group of C57BL/6 mice immunized with peptide plus alum showed a very low level of T cell proliferation, and no increase was seen in IFN-gamma or IL-4 production. These data signify that a Th1-type response occurred in mice treated with peptide in a liposome formulation but not in mice treated with the control formulation.

Evidence for the genetic basis of non-response in mice

In the murine model the immune response to both the hepatitis B envelope and nucleocapsid antigens are linked to the MHC class II haplotype but they are independently restricted. Although in a human outbred population non-response is less likely, the host genetic environment may be important in determining the level of response to vaccine and inclusion of antigens apart from the S antigen may improve protection. The inclusion of HBcAg in vaccine remains controversial since, despite its high immunogenicity, the Th-cell response to this antigen may have a role in the down regulation of the immune response to HBV so promoting persistence.

Schistosoma mansoni: genetic restriction and cytokine profile of the CD4 + T helper cell response to dominant epitope peptide of major egg antigen Sm-p40

Granuloma formation in schistosomiasis is mediated by MHC class II-restricted CD4 + T helper lymphocytes sensitized to egg antigens. We previously reported that C3H mice, which develop large granulomas, display strong CD4 + T helper cell responses to the major egg antigen Sm-p40. Moreover, all members of a panel of egg antigen-specific T cell hybridomas responded to the Sm-p40 antigen. Given the significance of the Sm-p40 molecule in the C3H T cell repertoire against schistosomal egg antigens, the current work was undertaken to map its immunogenic epitopes, using a library of 15 synthetic overlapping 30-mer peptides. The dominant epitope recognized by polyclonal CD4 + Th cells was located in peptide 10 (amino acids 229-258); subdominant epitopes were detected in peptides 8 (amino acids 179-208) and 12 (amino acids 279-308). The anti-Sm-p40 T cell hybridomas variously responded to any one of the same three stimulatory peptides. Furthermore, studies with various mouse strains demonstrated that a strong anti-Sm-p40 response was restricted by H-2(k). Interestingly, the cells responding to peptide 10 and to the Sm-p40 antigen only secreted IL-2 and IFN-gamma, but not IL-4 and IL-10, indicating that they are entirely of the Th-1-type, a subset with demonstrated capacity to mediate egg granuloma formation. The identification of dominant epitopes within key egg antigens offers opportunities for desensitization of the CD4 + Th cells that mediate pathology in schistosomia sis.

Eliminating a region of respiratory syncytial virus attachment protein allows induction of protective immunity without vaccine-enhanced lung eosinophilia

In a murine model of respiratory syncytial virus disease, prior sensitization to the attachment glycoprotein (G) leads to pulmonary eosinophilia and enhanced illness. Three different approaches were taken to dissect the region of G responsible for enhanced disease and protection against challenge. First, mutant viruses, containing frameshifts that altered the COOH terminus of the G protein, were used to challenge mice sensitized by scarification with recombinant vaccinia virus (rVV) expressing wild-type G. Second, cDNA expressing these mutated G proteins were expressed by rVV and used to vaccinate mice before challenge with wild-type respiratory syncytial virus (RSV). These studies identified residues 193-205 to be responsible for G-induced weight loss and lung eosinophilia and showed that this region was not was not necessary for induction of protective immunity. Third, mice were sensitized using an rVV that expressed only amino acids 124-203 of the G protein. Upon RSV challenge, mice sensitized with this rVV developed enhanced weight loss and eosinophilia. This is the first time that a region within RSV (amino acids 193-203) has been shown to be responsible for induction of lung eosinophilia and disease enhancement. Moreover, we now show that it is possible to induce protective immunity with an altered G protein without inducing a pathological response.

The influence of major histocompatibility complex class II genes and T-cell Vbeta repertoire on response to immunization with HBsAg

Nonresponsiveness to HBsAg vaccination is observed in 5-10% of vaccine recipients and is possibly caused by a defect in the T helper cell compartment. The immune response to HBsAg is influenced by genes of the major histocompatibility complex. We have investigated MHC class I and class II antigens in 53 adult responders and 73 nonresponders. Results obtained in this first study were tested in a second study with 56 responders and 62 nonresponders from an infant vaccination trial. In addition, the peripheral Vbeta-chain T-cell receptor repertoire was investigated using monoclonal antibodies and flow-cytometry in 26 adult responders and 38 nonresponders. As previously reported, nonresponsiveness to HBsAg vaccination was associated with DRB1*3 and DRB1*7. In addition, DRB1*13 was significantly increased among vaccine responders (35.2% vs 5.4%;p < 0.0001) suggesting an immune response promoting effect for this allele whereas the closely related allele DRB1*14 was associated with nonresponse in the infant study. There was no evidence for a hole in the T cell receptor Vbeta repertoire. In conclusion, in agreement with results obtained in mice there appears to be a hierarchy of DRB1* genes in the HBsAg immune response. The possible differential association of DRB1*13 and DRB1*14 may allow the identification of differences between responsiveness and nonresponsiveness to a few amino acid differences in the beta1-domain of the class II heterodimer.

Priming with secreted glycoprotein G of respiratory syncytial virus (RSV) augments interleukin-5 production and tissue eosinophilia after RSV challenge

The respiratory syncytial virus (RSV) G glycoprotein promotes differentiation of type 2 CD4+ T lymphocytes and induces an eosinophilic response in lungs of RSV-infected mice. A unique feature of G is that a second initiation codon in the transmembrane region of the glycoprotein results in secretion of soluble protein from infected cells. Recombinant vaccinia viruses that express wild-type G (vvWT G), only secreted G (vvM48), or only membrane-anchored G (vvM48I) were used to define the influence of G priming on immunopathogenesis. Mice immunized with vvM48 had more severe illness following RSV challenge than did mice primed with vvWT G or vvM48I. Coadministration of purified G during priming with the construct expressing membrane-anchored G shifted immune responses following RSV challenge to a more Th2-like response. This was characterized by increased interleukin-5 in lung supernatants and an increase in G-specific immunoglobulin G1 antibodies. Eosinophils were present in the infiltrate of all mice primed with G-containing vectors but were greatest in mice primed with regimens including secreted G. These data suggest the form of G protein available for initial antigen processing and presentation is an important factor in promoting Th2-like immune responses, including the induction of lung eosinophilia. The ability of RSV to secrete G protein may therefore represent a viral strategy for immunomodulation and be a key determinant of disease pathogenesis.

How the MHC selects Th1/Th2 immunity

While the effects of cytokines on T helper 1 (Th1)/Th2 differentiation are well documented, it is less clear why a dichotomy of effector cytokine production would initiate from antigen-specific lymphocytes. Nevertheless, in defined experimental systems, the interaction between T-cell receptor (TCR), peptide and major histocompatibility complex (MHC) can determine Th1/Th2 dominance. Here, Joseph Murray discusses how TCR affinity and ligand density might interface with innate forces in the selection of CD4+ T-cell functions.

Influence of T-helper cell subsets and crossregulation in hepatitis B virus infection

Serological and biochemical studies indicate that acute HBV infection is resolved in the context of an efficient cell-mediated immune (CMI) response, whereas, chronic infection is characterized by weak to undetectable CMI responses and relatively efficient humoral immunity. Because humoral immunity and CMI are regulated by different TH subsets, factors which influence the induction of TH1 vs TH2 cells specific for the HBV nucleocapsid antigens (HBcAg, HBeAg) were examined in a murine model system. The factors which affected the HBc/HBeAg-specific TH1/TH2-cell balance included: (1) the structure of the antigen (i.e. HBcAg vs HBeAg); (2) the host MHC and T-cell site recognized; (3) crossregulation between TH1 and TH2 cells; (4) T-cell tolerance, which is more complete in TH1 than in TH2 cells; (5) secreted HBeAg, which preferentially depletes TH1 cells; (6) the HBV-specific subset response could be skewed towards either TH1 or TH2 predominance by cytokine treatment in vivo. The results suggest that the balance between TH1 and TH2 cells specific for the HBc/HBeAgs may be relevant in acute and chronic HBV infections. Importantly, HBeAg-specific TH2 cells preferentially evade tolerance induction as compared to their TH1-cell counterparts. Because HBeAg may act as a tolerogen during the vertical transmission of chronic HBV infection and preferentially depletes TH1 cells in the circulation, the predominance of HBeAg-specific TH2 cells may influence the initiation or maintenance of the chronic carrier state. In this case, cytokine therapy designed to shift a TH2-like response toward TH1 predominance (i.e. IL-12) may be beneficial in the treatment of chronic HBV infection.

Nucleic acid-based antiviral and gene therapy of chronic hepatitis B infection

Persistent hepatitis B virus (HBV) infection often leads to the development of chronic hepatitis, cirrhosis and hepatocellular carcinoma. There is a need to develop new antiviral approaches for the treatment of this disease. We have explored various nucleic acid-based strategies designed to inhibit HBV replication including: the use of antisense RNA and DNA constructs, DNA-based immunization techniques to stimulate broad-based cellular immune responses with particular emphasis on the generation of cytotoxic lymphocyte (CTL) activity to viral structural proteins, hammerhead ribozymes to cleave HBV pregenomic RNA in vitro and dominant negative HBV core mutant proteins as inhibitors of nucleocapsid formation within cells. In order to optimize these antiviral effects, various novel expression vectors have been developed to deliver such DNA constructs to cells. For example, adenoviral vectors carrying genes that encode for dominant negative proteins have been employed to transfect hepatocytes in vitro and in vivo. In addition, plasmid vectors have been produced to promote expression of HBV structural genes following injection into muscle cells as a means to stimulate the host's cellular and humoral immune response in the context of histocompatibility antigen (HLA) class I and II antigen presentation. These experimental approaches may have important implications for the generation of efficient antiviral effects during chronic HBV infection.

Therapeutic vaccination of woodchucks against chronic woodchuck hepatitis virus infection

BACKGROUND/AIMS

Therapeutic vaccination is a new approach to treat patients with chronic hepatitis B virus infection. We have used the woodchuck model to examine the efficacy and safety of this approach.

METHODS

Seven woodchucks chronically infected with woodchuck hepatitis virus were immunized with surface antigen from this virus, purified from plasma, in conjunction with a peptide named FIS (encompassing amino acids 106-118: FISEAIIHVLHSR from sperm whale myoglobin), which is recognized by T helper lymphocytes. As controls, two woodchucks chronically infected with woodchuck hepatitis virus were immunized: one with FIS only and the other with surface antigen only.

RESULTS

Co-immunization with surface antigen and FIS, but not with FIS or surface antigen alone, induced anti-surface antibodies in 7/7 immunized woodchucks. In the two woodchucks in which the highest titer of anti-surface antibody was elicited, severe liver damage was observed: one died of fulminant hepatitis and the other became seriously ill with hepatic injury and had to be sacrificed.

CONCLUSIONS

Co-immunization of chronically infected woodchucks with surface antigen and a peptide recognized by T helper cells produces a good anti-surface antibody response. However, this strategy needs to be optimized before its implementation in humans. Although our experiments are not strictly comparable to vaccination of chronically hepatitis B virus-infected patients with recombinant or plasma-derived vaccines, we believe that precautions should be taken to avoid the risk of severe liver injury when immunizing hepatitis B virus carriers.

Antibodies to the hepatitis B e antigen (HBeAg) can be induced in HBeAg-transgenic mice by adoptive transfer of a specific T-helper 2 cell clone

Production of antibody to hepatitis B e antigen (HBeAg); i.e., anti-HBe antibody,) in HBeAg-transgenic mice is believed to be mediated by T-helper 2 (Th2) cells. Injection of an HBeAg-specific Th2 clone into HBeAg-transgenic H-2k mice induced anti-HBe antibody production, confirming the function of Th2 cells in this model system.

Characterization of humoral and CD4+ cellular responses after genetic immunization with retroviral vectors expressing different forms of the hepatitis B virus core and e antigens

The humoral and CD4+ cellular immune responses in mice following genetic immunization with three retroviral vectors encoding different forms of hepatitis B virus core antigen (HBcAg) and e antigen (HBeAg) were analyzed. The retroviral vectors induced expression of intracellular HBcAg (HBc[3A4]), secreted HBeAg (HBe[5A2]), or an intracellular HBcAg-neomycin phosphoryltransferase fusion protein (HBc-NEO[6A3]). Specific antibody levels and immunoglobulin G isotype restriction were highly dependent on both the host major histocompatibility complex and the transferred gene. Humoral and CD4+ cellular HBcAg and/or HBeAg (HBc/eAg)-specific immune responses following retroviral vector immunization were of a lower magnitude but followed the same characteristics compared with those after immunization with HBc/eAg in adjuvant. Two factors influenced the humoral responses. First, in vivo depletion of CD8+ cells in HBc-NEO[6A3]-immunized H-2k mice abrogated both HBcAg-specific antibodies and in vitro-detectable cytotoxic T lymphocytes. Second, priming of H-2b mice with an HBc/eAg-derived T-helper (Th) peptide in adjuvant prior to retroviral vector immunization greatly enhanced the HBc/eAg-specific humoral responses to all three vectors, suggesting that insufficient HBc/eAg-specific CD4+ Th-cell priming limits the humoral responses. In conclusion, direct injection of retroviral vectors seems to be effective in priming HBc/eAg-specific CD8+ but comparatively inefficient in priming CD4+ Th cells and subsequently specific antibodies. However, the limited HBc/eAg-specific CD4+ cell priming can effectively be circumvented by prior administration of a recombinant or synthetic form of HBc/eAg in adjuvant.

The hepatitis B virus core and e antigens elicit different Th cell subsets: antigen structure can affect Th cell phenotype

Secretion of the hepatitis B virus (HBV) e antigen (HBeAg) has been conserved throughout the evolution of hepadnaviruses. However, the function of this secreted form of the viral nucleoprotein remains enigmatic. It has been suggested that HBeAg functions as an immunomodulator. We therefore examined the possibility that the two structural forms of the viral nucleoprotein, the particulate HBV core (HBcAg) and the nonparticulate HBeAg, may preferentially elicit different T helper (Th) cell subsets. For this purpose, mice were immunized with recombinant HBcAg and HBeAg in the presence and absence of adjuvants, and the immunoglobulin G (IgG) isotype profiles of anti-HBc and anti-HBe antibodies were determined. Second, in vitro cytokine production by HBcAg- and HBeAg-primed Th cells was measured. The immunogenicity of HBcAg, in contrast to that of HBeAg, did not require the use of adjuvants. Furthermore, HBcAg elicited primarily IgG2a and IgG2b anti-HBc antibodies, with a low level of IgG3, and no IgG1 anti-HBc antibodies. In contrast, the anti-HBe antibody response was dominated by the IgG1 isotype; low levels of IgG2a or IgG2b anti-HBe antibodies and no IgG3 anti-HBe antibodies were produced. Cytokine production by HBcAg- and HBeAg-primed Th cells was consistent with the IgG isotype profiles. HBcAg-primed Th cells efficiently produced interleukin-2 (IL-2) and gamma interferon (IFN-gamma) and low levels of IL-4. Conversely, efficient IL-4 production and lesser amounts of IFN-gamma were elicited by HBeAg immunization. The results indicate that HBcAg preferentially, but not exclusively, elicits Th1-like cells and that HBeAg preferentially, but not exclusively, elicits Th0 or Th2-like cells. Because HBcAg and the HBeAg are cross-reactive in terms of Th cell recognition, these findings demonstrate that Th cells with the same specificity can develop into different Th subsets based on the structural form of the immunogen. These results may have relevance to chronic HBV infection. Circulating HBeAg may downregulate antiviral clearance mechanisms by virtue of eliciting anti-inflammatory Th2-like cytokine production. Last, the influence of antigen structure on Th cell phenotype was not absolute and could be modulated by in vivo cytokine treatment. For example, IFN-alpha treatment inhibited HBeAg-specific Th2-mediated antibody production and altered the IgG anti-HBe isotype profile toward the Th1 phenotype.

Effects of the route of infection on immunoglobulin G subclasses and specificity of the reovirus-specific humoral immune response

Reovirus serotype 1, strain Lang (T1/L), a well characterized enteric virus, elicits humoral and cellular immune responses in mice. Although orally and intradermally induced infections generate comparable reovirus-specific serum antibody titers, little is known about the effects of the route of infection on the systemic immunoglobulin G (IgG) response. To assess whether the route of exposure affects virus-specific humoral immunity, we infected various strains of mice with reovirus T1/L by the oral or intradermal routes. At day 10 following infection, virus-specific serum antibody titers and IgG subclasses were determined by enzyme-linked immunosorbent assay. Serum IgG2a and IgG2b antibodies were detected in all mouse strains independent of the route of infection. Mice of the H-2d haplotype that received an intradermal infection also had high levels of reovirus-specific serum IgG1. This dichotomy of responses was not associated with differences in the types of cytokine produced by draining peripheral lymph nodes. However, peripheral lymph node lymphocytes from C3H mice produced significantly higher levels of gamma interferon than did BALB/c, C57BL/6, and B10.D2 mice. Additionally, peripheral lymph node lymphocytes from all strains of mice produced only low levels of interleukin-5, with no detectable level of interleukin-4 or interleukin-6. Analysis of specific antibody at inductive sites of the immune response showed that orally infected Peyer's patches produced predominantly IgA and intradermally infected peripheral lymph nodes produced predominantly IgG2a. Western blot (immunoblot) analysis showed that virus-specific IgA, IgG1, and IgG2a reacted with reovirus structural proteins. These data suggest that the route of infection affects the isotype and IgG subclasses, but not the antigen specificity, of the local antibody response. In addition, virus-specific IgG1 generated following an intradermally induced infection is linked to the H-2d major histocompatibility complex haplotype.

Interleukin-4 causes delayed virus clearance in influenza virus-infected mice

Two different subsets of T cells, Th1 and Th2 cells, have been demonstrated to secrete different profiles of cytokines and to influence various infections in different ways. Whereas cytokines secreted by Th1 cells, particularly gamma interferon, promote the generation of cell-mediated immunity, Th2 cells and their cytokines (interleukin-4 [IL-4], IL-5, IL-10, and IL-13) have been shown to function in recovery from parasitic infections and in antibody responses. In this study, we analyzed the effects of the dominant Th2 cytokine, IL-4, on immunity to virus infection. We assessed the effects of IL-4 on both secondary immune responses by an adoptive transfer assay and primary immune responses by in vivo treatment of influenza virus-infected mice with IL-4. The results demonstrated that IL-4 can function to inhibit antiviral immunity at both stages. We found that IL-4 treatment of sensitized cells during secondary stimulation in vitro had little effect on their ability to lyse virus-infected target cells in a 51Cr release assay. Nevertheless, the clearance of influenza A/PR/8/34 (H1N1) virus from the lungs of infected BALB/c mice was significantly delayed after the transfer of virus-specific T cells secondarily stimulated in the presence of IL-4 in comparison to virus clearance in recipients of cells stimulated in the absence of IL-4. In contrast to the adoptive transfer results, the treatment of PR8 virus-infected mice with IL-4 during primary infection greatly suppressed the generation of cytotoxic T-cell precursors, as assessed by secondary stimulation in vitro. In addition, culture supernatants of secondarily stimulated spleen cells from IL-4-treated mice contained significantly less gamma interferon and more IL-4 than did spleen cells from controls. More importantly, the treatment of mice with IL-4 resulted in an extremely significant delay in virus clearance. Thus, IL-4 can inhibit both primary and secondary antiviral immune responses.