Avian Flu to Human Influenza

Modeling cellular co-infection and reassortment of bluetongue virus in Culicoides midges

When related segmented RNA viruses co-infect a single cell, viral reassortment can occur, potentially leading to new strains with pandemic potential. One virus capable of reassortment is bluetongue virus (BTV), which causes substantial health impacts in ruminants and is transmitted via Culicoides midges. Because midges can become co-infected by feeding on multiple different host species and remain infected for their entire life span, there is a high potential for reassortment to occur. Once a midge is co-infected, additional barriers must be crossed for a reassortant virus to emerge, such as cellular co-infection and dissemination of reassortant viruses to the salivary glands. We developed three mathematical models of within-midge BTV dynamics of increasing complexity, allowing us to explore the conditions leading to the emergence of reassortant viruses. In confronting the simplest model with published data, we estimate that the average life span of a bluetongue virion in the midge midgut is about 6 h, a key determinant of establishing a successful infection. Examination of the full model, which permits cellular co-infection and reassortment, shows that small differences in fitness of the two infecting strains can have a large impact on the frequency with which reassortant virions are observed. This is consistent with experimental co-infection studies with BTV strains with different relative fitnesses that did not produce reassortant progeny. Our models also highlight several gaps in existing data that would allow us to elucidate these dynamics in more detail, in particular the times it takes the virus to disseminate to different tissues, and measurements of viral load and reassortant frequency at different temperatures.

Plant-based, adjuvant-free, potent multivalent vaccines for avian influenza virus via Lactococcus surface display

Influenza epidemics frequently and unpredictably break out all over the world, and seriously affect the breeding industry and human activity. Inactivated and live attenuated viruses have been used as protective vaccines but exhibit high risks for biosafety. Subunit vaccines enjoy high biosafety and specificity but have a few weak points compared to inactivated virus or live attenuated virus vaccines, especially in low immunogenicity. In this study, we developed a new subunit vaccine platform for a potent, adjuvant-free, and multivalent vaccination. The ectodomains of hemagglutinins (HAs) of influenza viruses were expressed in plants as trimers (tHAs) to mimic their native forms. tHAs in plant extracts were directly used without purification for binding to inactivated Lactococcus (iLact) to produce iLact-tHAs, an antigen-carrying bacteria-like particle (BLP). tHAs BLP showed strong immune responses in mice and chickens without adjuvants. Moreover, simultaneous injection of two different antigens by two different formulas, tHAH5N6 + H9N2 BLP or a combination of tHAH5N6 BLP and tHAH9N2 BLP, led to strong immune responses to both antigens. Based on these results, we propose combinations of plant-based antigen production and BLP-based delivery as a highly potent and cost-effective platform for multivalent vaccination for subunit vaccines.

Natural Killer Cells Dampen the Pathogenic Features of Recall Responses to Influenza Infection

Despite evidence of augmented Natural Killer (NK) cell responses after influenza vaccination, the role of these cells in vaccine-induced immunity remains unclear. Here, we hypothesized that NK cells might increase viral clearance but possibly at the expense of increased severity of pathology. On the contrary, we found that NK cells serve a homeostatic role during influenza virus infection of vaccinated mice, allowing viral clearance with minimal pathology. Using a diphtheria toxin receptor transgenic mouse model, we were able to specifically deplete NKp46+ NK cells through the administration of diphtheria toxin. Using this model, we assessed the effect of NK cell depletion prior to influenza challenge in vaccinated and unvaccinated mice. NK-depleted, vaccinated animals lost significantly more weight after viral challenge than vaccinated NK intact animals, indicating that NK cells ameliorate disease in vaccinated animals. However, there was also a significant reduction in viral load in NK-depleted, unvaccinated animals indicating that NK cells also constrain viral clearance. Depletion of NK cells after vaccination, but 21 days before infection, did not affect viral clearance or weight loss—indicating that it is the presence of NK cells during the infection itself that promotes homeostasis. Further work is needed to identify the mechanism(s) by which NK cells regulate adaptive immunity in influenza-vaccinated animals to allow efficient and effective virus control whilst simultaneously minimizing inflammation and pathology.

Influenza A(H5N1) Virus Subunit Vaccine Administered with CaPNP Adjuvant Induce High Virus Neutralization Antibody Titers in Mice

The highly pathogenic avian influenza H5N1 virus continues to spread globally in domestic poultry with sporadic transmission to humans. The possibility for its rapid transmission to humans raised global fears for the virus to gain capacity for human-to-human transmission to start a future pandemic. Through direct contact with infected poultry, it caused the largest number of reported cases of severe disease and death in humans of any avian influenza strains. For pandemic preparedness, use of safe and effective vaccine adjuvants and delivery systems to improve vaccine efficacy are considered imperative. We previously demonstrated CaPtivate's proprietary CaP nanoparticles (CaPNP) as a potent vaccine adjuvant/delivery system with ability to induce both humoral and cell-mediated immune responses against many viral or bacterial infections. In this study, we investigated the delivery of insect cell culture-derived recombinant hemagglutinin protein (HA) of A/H5N1/Vietnam/1203/2004 virus using CaPNP. We evaluated the vaccine immunogenicity in mice following two intramuscular doses of 3 μg antigen combined with escalating doses of CaPNP. Our data showed CaPNP-adjuvanted HA(H5N1) vaccines eliciting significantly higher IgG, hemagglutination inhibition, and virus neutralization titers compared to non-adjuvanted vaccine. Among the four adjuvant doses that were tested, CaPNP at 0.24% final concentration elicited the highest IgG and neutralizing antibody titers. We also evaluated the inflammatory response to CaPNP following a single intramuscular injection in guinea pigs and showed that CaPNP does not induce any systemic reaction or adverse effects. Current data further support our earlier studies demonstrating CaPNP as a safe and an effective adjuvant for influenza vaccines.

Anti-Influenza A Viral Butenolide from Streptomyces sp. Smu03 Inhabiting the Intestine of Elephas maximus

Actinobacteria are a phylum of bacteria known for their potential in producing structurally diversified natural products that are always associated with a broad range of biological activities. In this paper, using an H5N1 pseudo-typed virus drug screening system combined with a bioassay guided purification approach, an antiviral butanolide (1) was identified from the culture broth of Streptomyces sp. SMU03, a bacterium isolated from the feces of Elephas maximus in Yunnan province, China. This compound displayed broad and potent activity against a panel of influenza viruses including H1N1 and H3N2 subtypes, as well as influenza B virus and clinical isolates with half maximal inhibitory concentration values (IC₅₀) in the range of 0.29 to 12 µg/mL. In addition, 1 was also active against oseltamivir-resistant influenza virus strain of A/PR/8/34 with NA-H274Y mutation. Studies on the detailed modes of action suggested that 1 functioned by interfering with the fusogenic process of hemagglutinin (HA) of influenza A virus (IAV), thereby blocking the entry of virus into host cells. Furthermore, the anti-IAV activity of 1 was assessed with infected BALB/c mice, of which the appearance, weight, and histopathological changes in the infected lungs were significantly alleviated compared with the no-drug-treated group. Conclusively, these results provide evidence that natural products derived from microbes residing in animal intestines might be a good source for antiviral drug discovery.

Potential Role of MicroRNAs in the Regulation of Antiviral Responses to Influenza Infection

Influenza is a major health burden worldwide and is caused by influenza viruses that are enveloped and negative stranded RNA viruses. Little progress has been achieved in targeted intervention, either at a population level or at an individual level (to treat the cause), due to the toxicity of drugs and ineffective vaccines against influenza viruses. MicroRNAs (miRNAs) are small non-coding RNAs that play critical roles in gene expression, cell differentiation, and tissue development and have been shown to silence viral replication in a sequence-specific manner. Investigation of these small endogenous nucleotides may lead to new therapeutics against influenza virus infection. Here, we describe our current understanding of the role of miRNAs in host defense response against influenza virus, as well as their potential and limitation as new therapeutic approaches.

Development and Bench Validation of Real-Time Reverse Transcription Polymerase Chain Reaction Protocols for Rapid Detection of the Subtypes H6, H9, and H11 of Avian Influenza Viruses in Experimental Samples

Real-time reverse transcription polymerase chain reaction (RRT-PCR) is commonly used for the rapid detection, as well as to determine the subtype, of avian influenza viruses (AIVs). There are 16 known serologically distinct hemagglutinin (HA) subtypes of AIV described. Currently, determination of the subtypes of AIVs by RRT-PCR tests has been limited to the H5 and H7 subtypes. In this study, RRT-PCR assays were developed in simplex formats for rapid detection of AIV subtypes H6, H9, and H11. The primers and probes for RRT-PCR were designed from nucleotide sequences of the HA genes, which were either downloaded from GenBank (for H6 and H9) or sequenced for this study. The specificity and sensitivity of the RRT-PCR assays were determined based on the detection of the virus from a proficiency panel consisting of 15 different HA subtypes of AIVs and from serial dilutions of target viral RNA. The subtype-specific RRT-PCR assays were used to detect the virus in cloacal and oropharyngeal swabs of experimental chickens inoculated with H6, H9, and H11 AIVs, and the test results were compared with validated RRT-PCR assays based on the amplification of AI matrix (MA) gene. A high correlation of the matrix test and the specific H6, H9, and H11 by the RRT-PCR assays was observed; kappa coefficients for the agreement of test results in cloacal and oropharyngeal swabs combined were 0.927, 0.962, and 0.981, respectively.

Economic evaluation of pediatric influenza immunization program compared with other pediatric immunization programs: A systematic review

This study compared the economic value of pediatric immunisation programmes for influenza to those for rotavirus (RV), meningococcal disease (MD), pneumococcal disease (PD), human papillomavirus (HPV), hepatitis B (Hep B), and varicella reported in recent (2000 onwards) cost-effectiveness (CE) studies identified in a systematic review of PubMed, health technology, and vaccination databases. The systematic review yielded 51 economic evaluation studies of pediatric immunisation - 10 (20%) for influenza and 41 (80%) for the other selected diseases. The quality of the eligible articles was assessed using Drummond's checklist. Although inherent challenges and limitations exist when comparing economic evaluations of immunisation programmes, an overall comparison of the included studies demonstrated cost-effectiveness/cost saving for influenza from a European-Union-Five (EU5) and United States (US) perspective; point estimates for cost/quality-adjusted life-years (QALY) from dominance (cost-saving with more effect) to ≤45,444 were reported. The economic value of influenza programmes was comparable to the other vaccines of interest, with cost/QALY in general considerably lower than RV, Hep B, MD and PD. Independent of the perspective and type of analysis, the economic impact of a pediatric influenza immunisation program was influenced by vaccine efficacy, immunisation coverage, costs, and most significantly by herd immunity. This review suggests that pediatric influenza immunisation may offer a cost effective strategy when compared with HPV and varicella and possibly more value compared with other childhood vaccines (RV, Hep B, MD and PD).

The significance of naturally occurring neuraminidase quasispecies of H5N1 avian influenza virus on resistance to oseltamivir: a point of concern

Viral adaptability and survival arise due to the presence of quasispecies populations that are able to escape the immune response or produce drug-resistant variants. However, the presence of H5N1 virus with natural mutations acquired without any drug selection pressure poses a great threat. Cloacal samples collected from the 2004-2005 epidemics in Thailand from Asian open-billed storks revealed one major and several minor quasispecies populations with mutations on the oseltamivir (OTV)-binding site of the neuraminidase gene (NA) without prior exposure to a drug. Therefore, this study investigated the binding between the NA-containing novel mutations and OTV drug using molecular dynamic simulations and plaque inhibition assay. The results revealed that the mutant populations, S236F mutant, S236F/C278Y mutant, A250V/V266A/P271H/G285S mutant and C278Y mutant, had a lower binding affinity with OTV as compared with the WT virus due to rearrangement of amino acid residues and increased flexibility in the 150-loop. This result was further emphasized through the IC50 values obtained for the major population and WT virus, 104.74 nM and 18.30 nM, respectively. Taken together, these data suggest that H5N1 viruses isolated from wild birds have already acquired OTV-resistant point mutations without any exposure to a drug.

Emerging Infections of CNS: Avian Influenza A Virus, Rift Valley Fever Virus and Human Parechovirus

History is replete with emergent pandemic infections that have decimated the human population. Given the shear mass of humans that now crowd the earth, there is every reason to suspect history will repeat itself. We describe three RNA viruses that have recently emerged in the human population to mediate severe neurological disease. These new diseases are results of new mutations in the infectious agents or new exposure pathways to the agents or both. To appreciate their pathogenesis, we summarize the essential virology and immune response to each agent. Infection is described in the context of known host defenses. Once the viruses evade immune defenses and enter central nervous system (CNS) cells, they rapidly co-opt host RNA processing to a cataclysmic extent. It is not clear why the brain is particularly susceptible to RNA viruses; but perhaps because of its tremendous dependence on RNA processing for physiological functioning, classical mechanisms of host defense (eg, interferon disruption of viral replication) are diminished or not available. Effectiveness of immunity, immunization and pharmacological therapies is reviewed to contextualize the scope of the public health challenge. Unfortunately, vaccines that confer protection from systemic disease do not necessarily confer protection for the brain after exposure through unconventional routes.

Oseltamivir hydroxamate and acyl sulfonamide derivatives as influenza neuraminidase inhibitors

Tamiflu, the ethyl ester form of oseltamivir carboxylic acid (OC), is the first orally available anti-influenza drug for the front-line therapeutic option. In this study, the OC-hydroxamates, OC-sulfonamides and their guanidino congeners (GOC) were synthesized. Among them, an OC-hydroxamate 7d bearing an O-(2-indolyl)propyl substituent showed potent NA inhibition (IC50 = 6.4 nM) and good anti-influenza activity (EC50 = 60.1 nM) against the wild-type H1N1 virus. Two GOC-hydroxamates (9b and 9d) and one GOC-sulfonamide (12a) were active to the tamiflu-resistant H275Y virus (EC50 = 2.3-6.9 μM).

Study of oseltamivir and zanamivir resistance-related mutations in influenza viruses isolated from wild mallards in Sweden

Resistance to neuraminidase inhibitors (NAIs) is a growing problem in battle against influenza A virus. However, little is known about the resistance of viruses isolated from dabbling ducks, the natural reservoir of the influenza virus. To our knowledge, no low-pathogenic avian influenza (LPAI) virus resistant to NAIs has been detected. The aim of this study was to investigate mallard isolates of influenza A virus previously identified to carry oseltamivir carboxylate (OC) or zanamivir (ZA) resistance-related mutations. In this work, 21 viruses belonging to the N1, N3, N6 and N9 subtypes were analyzed using a colorimetric NA inhibition assay. The results of assay showed no NAIs-resistant phenotype for any of the viruses. The R118K mutation was the most recurrent, as it was observed in all subtypes except for N6. IC₅₀ values confirmed the differences in sensitivity to OC or ZA observed in the N1 and N2 groups of NAs. Furthermore, both wild types (WTs) in the N6 and one WT in the N9 subtype were less sensitive to ZA than were genotypically related mutants with R152K and R118K change in the respective subtypes. This may indicate that these and probably even other NAIs resistance-related mutations found in our virus collection were not induced by NAIs residuals in the environment and that the impact of such mutations in an avian influenza could be dependent on subtype, strain and host species.

Role of Fat-Soluble Vitamins A and D in the Pathogenesis of Influenza: A New Perspective

Reduced exposure to solar radiation, leading to a deficiency of vitamin D and hence impaired innate immunity, has been suggested as a trigger for influenza viral replication and as an explanation of seasonal influenza. Although this hypothesis accounts for many unexplained facts about the epidemiology of influenza, gaps remain in understanding the pathogenesis and manifestations of the disease. Several observations suggest a role for vitamin A compounds (retinoids) in the disease. This paper presents a new model of the etiopathogenesis of influenza, suggesting that host resistance and susceptibility depend importantly on the ratio of vitamin D to vitamin A activity. Retinoid concentrations within normal physiological limits appear to inhibit influenza pathogenesis whereas higher background concentrations (i.e., very low vitamin D : A ratios) increase the risk of severe complications of the disease. There is also evidence that influenza-induced or preexisting liver disease, diabetes, and obesity worsen the severity of infection, possibly via liver dysfunction and alterations in retinoid metabolism. The model could be tested by determining the presence of retinoids in the secretions of patients with influenza and by studies of retinoid profiles in patients and controls. Potential strategies for prevention and treatment are discussed.

Innate immunity to influenza in chronic airways diseases

Influenza presents a unique human infectious disease that has a substantial impact on the public health, in general, and especially for those with chronic airways diseases. People with asthma and chronic obstructive pulmonary disease (COPD) are particularly vulnerable to influenza infection and experience more severe symptoms with the worsening of their pre-existing conditions. Recent advances in reverse genetics and innate immunity has revealed several influenza virulence factors and host factors involved in influenza pathogenesis and the immune responses to infection. Early innate immunity plays a critical role of limiting viral infection and spread; however, the underlying mechanisms that lead to enhanced susceptibility to influenza infection and severe symptoms in those with asthma and COPD to infection remain un-investigated. This review will explore the importance of early innate antiviral responses to influenza infection and how these responses are altered by influenza virus and in those with chronic airways diseases.

A multi-scale analysis of influenza A virus fitness trade-offs due to temperature-dependent virus persistence

Successful replication within an infected host and successful transmission between hosts are key to the continued spread of most pathogens. Competing selection pressures exerted at these different scales can lead to evolutionary trade-offs between the determinants of fitness within and between hosts. Here, we examine such a trade-off in the context of influenza A viruses and the differential pressures exerted by temperature-dependent virus persistence. For a panel of avian influenza A virus strains, we find evidence for a trade-off between the persistence at high versus low temperatures. Combining a within-host model of influenza infection dynamics with a between-host transmission model, we study how such a trade-off affects virus fitness on the host population level. We show that conclusions regarding overall fitness are affected by the type of link assumed between the within- and between-host levels and the main route of transmission (direct or environmental). The relative importance of virulence and immune response mediated virus clearance are also found to influence the fitness impacts of virus persistence at low versus high temperatures. Based on our results, we predict that if transmission occurs mainly directly and scales linearly with virus load, and virulence or immune responses are negligible, the evolutionary pressure for influenza viruses to evolve toward good persistence at high within-host temperatures dominates. For all other scenarios, influenza viruses with good environmental persistence at low temperatures seem to be favored.

It has recently been suggested that for avian influenza viruses, prolonged persistence in the environment plays an important role in the transmission between birds. In such situations, influenza virus strains may face a trade-off: they need to persist well in the environment at low temperatures, but they also need to do well inside an infected bird at higher temperatures. Here, we analyze how potential trade-offs on these two scales interact to determine overall fitness of the virus. We find that the link between infection dynamics within a host and virus shedding and transmission is crucial in determining the relative advantage of good low-temperature versus high-temperature persistence. We also find that the role of virus-induced mortality, the immune response and the route of transmission affect the balance between optimal low-temperature and high-temperature persistence.

An Influenza Virus M2 Protein Specific Chimeric Antigen Receptor Modulates Influenza A/WSN/33 H1N1 Infection In Vivo

A potential target for the development of universal vaccine strategies against Influenza A is the M2 protein – a membrane protein with a highly conserved extracellular domain. In this study we developed engineered T-cell receptors, by fusing M2-specific antibody sequences with T-cell receptor transmembrane and signaling domains to target influenza infected cells. When expressed on T-cells, these novel T-cell receptors (chimeric antigen receptors - CARs) are able to recognize specific antigens on the surface of target cells via an MHC-independent mechanism. Using an existing monoclonal antibody (14C2) specific for the M2 ectodomain (M2e), we generated an M2-specific CAR. We tested the specificity of this M2 CAR in vitro by measuring the activation of T-cells in response to M2-specific peptides or M2-expressing cell lines. Both Jurkat T-cells and peripheral blood mononuclear cells expressing the M2-specific CAR responded to specific antigen stimulation by upregulating NFAT and producing γ-interferon. To test whether the M2-specific CAR are effective at recognizing influenza infected cells in vivo we used an established BALB/c murine infection model. At day 4 post-infection, when M2 CAR expressing splenocytes could be detected in the lung, the Influenza A/WSN/33 virus titre was around 50% of that in control mice. Although the lung virus titre later increased in the treated group, virus was cleared in both groups of mice by day 8. The results provide support for the development of M2e as a target for cell mediated immunotherapy.

Cross-allele cytotoxic T lymphocyte responses against 2009 pandemic H1N1 influenza A virus among HLA-A24 and HLA-A3 supertype-positive individuals

Lack of a universal vaccine against all serotypes of influenza A viruses and recent progress on T cell-related vaccines against influenza A virus illuminate the important role of human leukocyte antigen (HLA)-restricted cytotoxic T lymphocytes (CTLs) in anti-influenza virus immunity. However, the diverse HLA alleles among humans complicate virus-specific cellular immunity research, and elucidation of cross-HLA allele T cell responses to influenza virus specificity requires further detailed work. An ideal CTL epitope-based vaccine would cover a broad spectrum of epitope antigens presented by most, if not all, of the HLAs. Here, we evaluated the 2009 pandemic influenza A (H1N1) virus-specific T cell responses among the HLA-A24(+) population using a rationally designed peptide pool during the 2009 pandemic. Unexpectedly, cross-HLA allele T cell responses against the influenza A virus peptides were detected among both HLA-A11(+) and HLA-A24(+) donors. Furthermore, we found cross-responses in the entire HLA-A3 supertype population (including HLA-A11, -A31, -A33, and -A30). The cross-allele antigenic peptides within the peptide pool were identified and characterized, and the crystal structures of the major histocompatibility complex (MHC)-peptide complexes were determined. The subsequent HLA-A24-defined cross-allele peptides recognized by the HLA-A11(+) population were shown to mildly bind to the HLA-A*1101 molecule. Together with the structural models, these results partially explain the cross-allele responses. Our findings elucidate the promiscuity of the cross-allele T cell responses against influenza A viruses and are beneficial for the development of a T cell epitope-based vaccine applied in a broader population.

Altered lymphocyte counts in a pediatric patient with H5N1 infection

Flow cytometry was used to analyze the changes in lymphocyte subsets in the youngest child with avian influenza in China. During the early stage, the absolute CD3 count was 62.9% (lower limit of normal), the CD8 count was 32.5% (slightly higher than normal), and the CD4 count was 28.6% (lower than normal). The CD4/CD8 ratio was also decreased (0.88). The natural killer (CD3CD1656) cell count was 4.9% (lower than normal). During the convalescent stage, the CD4 count and the CD4/CD8 ratio returned to normal. The CD3CD1656 count increased from its value at the early stage of the disease.

Emergency rabies control in a community of two high-density hosts

Background

Rabies is a fatal viral disease that potentially can affect all mammals. Terrestrial rabies is not present in the United Kingdom and has been eliminated from Western Europe. Nevertheless the possibility remains that rabies could be introduced to England, where it would find two potentially suitable hosts, red foxes and badgers. With the aim to analyse the spread and emergency control of rabies in this two species host community, a simulation model was constructed. Different control strategies involving anti-rabies vaccination and population culling were developed, considering control application rates, spatial extent and timing. These strategies were evaluated for efficacy and feasibility to control rabies in hypothetical rural areas in the South of England immediately after a disease outbreak.

Results

The model confirmed that both fox and badger populations, separately, were competent hosts for the spread of rabies. Realistic vaccination levels were not sufficient to control rabies in high-density badger populations. The combined species community was a very strong rabies host. However, disease spread within species appeared to be more important than cross-species infection. Thus, the drivers of epidemiology depend on the potential of separate host species to sustain the disease. To control a rabies outbreak in the two species, both species had to be targeted. Realistic and robust control strategies involved vaccination of foxes and badgers, but also required badger culling. Although fox and badger populations in the UK are exceptionally dense, an outbreak of rabies can be controlled with a higher than 90% chance, if control response is quick and follows a strict regime. This requires surveillance and forceful and repeated control campaigns. In contrast, an uncontrolled rabies outbreak in the South of England would quickly develop into a strong epizootic involving tens of thousands of rabid foxes and badgers.

Conclusions

If populations of both host species are sufficiently large, epizootics are driven by within-species transmission, while cross-species-infection appears to be of minor importance. Thus, the disease control strategy has to target both host populations.

Cationic liposome-DNA complexes (CLDC) adjuvant enhances the immunogenicity and cross-protective efficacy of a pre-pandemic influenza A H5N1 vaccine in mice

The development of pre-pandemic influenza A H5N1 vaccines that confer both antigen-sparing and cross-clade protection are a high priority given the limited worldwide capacity for influenza vaccine production, and the antigenic and genetic heterogeneity of circulating H5N1 viruses. The inclusion of potent adjuvants in vaccine formulations may achieve both of these aims. Here we show that the addition of JVRS-100, an adjuvant consisting of cationic liposome-DNA complexes (CLDC) to a clade 1-derived H5N1 split vaccine induced significantly higher virus-specific antibody than unadjuvanted formulations, with a >30-fold dose-sparing effect and induction of increased antigen-specific CD4(+) T-cell responses in mice. All mice that received one dose of adjuvanted vaccine and subsequent H5N1 viral challenges exhibited mild illness, lower lung viral titers, undetectable spleen and brain viral titers, and 100% survival after either homologous clade 1 or heterologous clade 2 H5N1 viral challenges, whereas unadjuvanted vaccine recipients showed significantly increased weight loss, viral titers, and mortality. The protective immunity induced by JVRS-100 adjuvanted H5N1 vaccine was shown to last for over one year without significant waning. Thus, JVRS-100 adjuvanted H5N1 vaccine elicited enhanced humoral and T-cell responses, dose-sparing, and cross-clade protection in mice. CLDC holds promise as an adjuvant for human pre-pandemic inactivated H5N1 vaccines.

Evaluation of immune responses to seasonal influenza vaccination in healthy volunteers in South Apulia, Italy: a pilot study

BACKGROUND

The aim of our pilot study is to investigate different components of the immune response to influenza vaccination in a group of healthy volunteers. We evaluated the cellular immune response (CD4(+) T lymphocytes) by flow cytometry. The humoral immune response was assessed by measuring the serum haemagglutination inhibition antibody response.

METHODS

Healthy adult donors (n = 18), were vaccinated with a commercially influenza virus vaccine (FLUARIX® GlaxoSmithKline S.p.a. Verona, Italy), peripheral blood was drawn the same day as influenza virus vaccination and one month later in order to enumerate the antigen-specific CD4(+) T lymphocytes. Hemagglutination inhibition assay was performed to enumerate the titer of neutralizing antibodies. Samples of nasal-pharyngeal secretions were taken by swabbing, from ILI (Influenza like Illness) subjects among the studied group, in order to verify influenza infections and eventually identify viruses using Real Time PCR.

RESULTS AND CONCLUSIONS

Parenteral influenza vaccination results in significant increase in the CD4(+) Th cell population after vaccination. The number of pre-vaccination CD4(+) T cells was 0.018 [the results are presented as number of percent fluorescent cells per 10 000 lymphocytes (fixed cells)], while there was a significantly higher number of CD4(+) Th cells one month after vaccination (statistical significance was set at the level of α = 0.01). Twenty-two percent of patients demonstrated protective antibody levels to influenza A H1/N1 serotype. None was diagnosed with influenza type A or B.

KEYWORDS

T cells; Flow cytometry; Influenza virus; Influenza vaccine.

Discovery of dihydro-alkyloxy-benzyl-oxopyrimidines as promising anti-influenza virus agents

A series of novel dihydro-alkyloxy-benzyl-oxopyrimidine derivatives were synthesized and evaluated for their activity against influenza virus in Madin-Darby canine kidney cells. Four dihydro-alkyloxy-benzyl-oxopyrimidine derivatives (4a1, 4a2, 4a3, and 4d1) showed potent activity against influenza virus. Among them, compound 4a3 was the most promising lead with broad activity against influenza A (antiviral EC(50) values of 9 and 18 μm for the A/H1N1 and A/H3N2 subtype, respectively) and influenza B viruses (EC(50) : 33 μm). The antiviral mechanism of action of these dihydro-alkyloxy-benzyl-oxopyrimidine derivatives must be quite different from that of the currently approved anti-influenza virus drugs that target the viral M2 or neuraminidase proteins. The dihydro-alkyloxy-benzyl-oxopyrimidine derivatives represent a new avenue for further optimization and development of novel anti-influenza virus agents.

Inhibition of influenza A virus replication by RNA interference targeted against the PB1 subunit of the RNA polymerase gene

Influenza (flu) pandemics have posed a great threat to human health in the last century. However, current vaccination strategies and antiviral drugs provide limited protection. RNA interference (RNAi) is an effective means of suppressing influenza virus replication. PB1 is the critical protein subunit of the influenza virus RNA polymerase. The gene encoding this protein, PB1, is highly conserved among different subtypes of IAV and was therefore chosen as the target in this study. The oligonucleotide, PB1-shRNA, contains a 21-bp siRNA corresponding to nucleotides 1,632 to 1,652 of PB1 linear vRNA with BamHI or EcoRI restriction enzyme sites incorporated at the ends. The PB1-shRNA oligonucleotide was directionally cloned into the RNAi-ready pSIREN-shuttle vector. The correct structure of the resulting pSIREN/PB1 plasmid was confirmed by restriction endonuclease digestion. Madin-Darby canine kidney (MDCK) cells were transfected with pSIREN/PB1 and subsequently infected with IAV at an MOI of 0.1 (A/PR/8/34, H1N1). The virus titer in cell culture supernatants was determined 48 hours later, and it was found that virus growth was inhibited by more than 50-fold relative to controls. Furthermore, embryonated eggs and mice were inoculated with liposome-encapsulated pSIREN/PB1 and then challenged with the A/PR/8/34 virus. The results showed at least a 100-fold inhibition in virus replication in egg allantoic fluid and a survival rate of between 50% and 100% in experimental mice. This study demonstrates that PB1-shRNA expressed by the recombinant plasmid pSIREN/PB1 inhibits influenza A virus replication both in vitro and in vivo. These observations provide a foundation for the development of a new and efficient treatment of influenza infections.

Type 1 responses of human Vγ9Vδ2 T cells to influenza A viruses

γδ T cells are essential constituents of antimicrobial and antitumor defenses. We have recently reported that phosphoantigen isopentenyl pyrophosphate (IPP)-expanded human Vγ9Vδ2 T cells participated in anti-influenza virus immunity by efficiently killing both human and avian influenza virus-infected monocyte-derived macrophages (MDMs) in vitro. However, little is known about the noncytolytic responses and trafficking program of γδ T cells to influenza virus. In this study, we found that Vγ9Vδ2 T cells expressed both type 1 cytokines and chemokine receptors during influenza virus infection, and IPP-expanded cells had a higher capacity to produce gamma interferon (IFN-γ). Besides their potent cytolytic activity against pandemic H1N1 virus-infected cells, IPP-activated γδ T cells also had noncytolytic inhibitory effects on seasonal and pandemic H1N1 viruses via IFN-γ but had no such effects on avian H5N1 or H9N2 virus. Avian H5N1 and H9N2 viruses induced significantly higher CCL3, CCL4, and CCL5 production in Vγ9Vδ2 T cells than human seasonal H1N1 virus. CCR5 mediated the migration of Vγ9Vδ2 T cells toward influenza virus-infected cells. Our findings suggest a novel therapeutic strategy of using phosphoantigens to boost the antiviral activities of human Vγ9Vδ2 T cells against influenza virus infection.

Role for proteases and HLA-G in the pathogenicity of influenza A viruses

Influenza is one of the most common infectious diseases in humans occurring as seasonal epidemic and sporadic pandemic outbreaks. The ongoing infections of humans with avian H5N1 influenza A viruses (IAV) and the past 2009 pandemic caused by the quadruple human/avian/swine reassortant (H1N1) virus highlights the permanent threat caused by these viruses. This review aims to describe the interaction between the virus and the host, with a particular focus on the role of proteases and HLA-G in the pathogenicity of influenza viruses.

2009 H1N1 influenza and experience in three critical care units

AIM

We describe futures of ICU admission, demographic characteristics, treatment and outcome for critically ill patients with laboratory-confirmed and suspected infection with the H1N1 virus admitted to the three different critical care departments in Turkey.

METHODS

Retrospective study of critically ill patients with 2009 influenza A(H1N1) at ICU. Demographic data, symptoms, comorbid conditions, and clinical outcomes were collected using a case report form.

RESULTS

Critical illness occurred in 61 patients admitted to an ICU with confirmed (n=45) or probable and suspected 2009 influenza A(H1N1). Patients were young (mean, 41.5 years), were female (54%). Fifty-six patients, required mechanical ventilation (14 invasive, 27 noninvasive, 15 both) during the course of ICU. On admission, mean APACHE II score was 18.7±6.3 and median PaO(2)/FIO(2) was 127.9±70.4. 31 patients (50.8%) was die. There were no significant differences in baseline PaO(2)/FIO(2 )and ventilation strategies between survivors and nonsurvivors. Patients who survived were more likely to have NIMV use at the time of admission to the ICU.

CONCLUSION

Critical illness from 2009 influenza A(H1N1) in ICU predominantly affects young patients with little major comorbidity and had a high case-fatality rate. NIMV could be used in 2009 influenza A (H1N1) infection-related hypoxemic respiratory failure.

Structure and binding analysis of Polyporus squamosus lectin in complex with the Neu5Ac{alpha}2-6Gal{beta}1-4GlcNAc human-type influenza receptor

Glycan chains that terminate in sialic acid (Neu5Ac) are frequently the receptors targeted by pathogens for initial adhesion. Carbohydrate-binding proteins (lectins) with specificity for Neu5Ac are particularly useful in the detection and isolation of sialylated glycoconjugates, such as those associated with pathogen adhesion as well as those characteristic of several diseases including cancer. Structural studies of lectins are essential in order to understand the origin of their specificity, which is particularly important when employing such reagents as diagnostic tools. Here, we report a crystallographic and molecular dynamics (MD) analysis of a lectin from Polyporus squamosus (PSL) that is specific for glycans terminating with the sequence Neu5Acα2-6Galβ. Because of its importance as a histological reagent, the PSL structure was solved (to 1.7 Å) in complex with a trisaccharide, whose sequence (Neu5Acα2-6Galβ1-4GlcNAc) is exploited by influenza A hemagglutinin for viral adhesion to human tissue. The structural data illuminate the origin of the high specificity of PSL for the Neu5Acα2-6Gal sequence. Theoretical binding free energies derived from the MD data confirm the key interactions identified crystallographically and provide additional insight into the relative contributions from each amino acid, as well as estimates of the importance of entropic and enthalpic contributions to binding.

Multistrain influenza protection induced by a nanoparticulate mucosal immunotherapeutic

All commercial influenza vaccines elicit antibody responses that protect against seasonal infection, but this approach is limited by the need for annual vaccine reformulation that precludes efficient responses against epidemic and pandemic disease. In this study we describe a novel vaccination approach in which a nanoparticulate, liposome-based agent containing short, highly conserved influenza-derived peptides is delivered to the respiratory tract to elicit potent innate and selective T cell-based adaptive immune responses. Prepared without virus-specific peptides, mucosal immunostimulatory therapeutic (MIT) provided robust, but short-lived, protection against multiple, highly lethal strains of influenza in mice of diverse genetic backgrounds. MIT prepared with three highly conserved epitopes that elicited virus-specific memory T-cell responses but not neutralizing antibodies, termed MITpep, provided equivalent, but more durable, protection relative to MIT. Alveolar macrophages were more important than dendritic cells in determining the protective efficacy of MIT, which induced both canonical and non-canonical antiviral immune pathways. Through activation of airway mucosal innate and highly specific T-cell responses, MIT and MITpep represent novel approaches to antiviral protection that offer the possibility of universal protection against epidemic and pandemic influenza.

Proteotyping to establish the lineage of type A H1N1 and type B human influenza virus

The ability to establish the lineage of type A H1N1 and type B human influenza virus strains using a new proteotyping approach is demonstrated. Lineage-specific signature peptides have been determined for the hemagglutinin antigen of type A H1N1 and type B influenza viruses. The detection of these peptides alone within the high resolution mass spectra of whole antigen digests enables the lineage of the strain to be rapidly and unequivocally assigned. This proteotyping approach complements conventional PCR approaches and should aid in the monitoring of the evolution of the influenza virus in both humans and animals.

Cationic lipid/DNA complex-adjuvanted influenza A virus vaccination induces robust cross-protective immunity

Influenza A virus is a negative-strand segmented RNA virus in which antigenically distinct viral subtypes are defined by the hemagglutinin (HA) and neuraminidase (NA) major viral surface proteins. An ideal inactivated vaccine for influenza A virus would induce not only highly robust strain-specific humoral and T-cell immune responses but also cross-protective immunity in which an immune response to antigens from a particular viral subtype (e.g., H3N2) would protect against other viral subtypes (e.g., H1N1). Cross-protective immunity would help limit outbreaks from newly emerging antigenically novel strains. Here, we show in mice that the addition of cationic lipid/noncoding DNA complexes (CLDC) as adjuvant to whole inactivated influenza A virus vaccine induces significantly more robust adaptive immune responses both in quantity and quality than aluminum hydroxide (alum), which is currently the most widely used adjuvant in clinical human vaccination. CLDC-adjuvanted vaccine induced higher total influenza virus-specific IgG, particularly for the IgG2a/c subclass. Higher levels of multicytokine-producing influenza virus-specific CD4 and CD8 T cells were induced by CLDC-adjuvanted vaccine than with alum-adjuvanted vaccine. Importantly, CLDC-adjuvanted vaccine provided significant cross-protection from either a sublethal or lethal influenza A viral challenge with a different subtype than that used for vaccination. This superior cross-protection afforded by the CLDC adjuvant required CD8 T-cell recognition of viral peptides presented by classical major histocompatibility complex class I proteins. Together, these results suggest that CLDC has particular promise for vaccine strategies in which T cells play an important role and may offer new opportunities for more effective control of human influenza epidemics and pandemics by inactivated influenza virus vaccine.

Analyses of the specificity of CD4 T cells during the primary immune response to influenza virus reveals dramatic MHC-linked asymmetries in reactivity to individual viral proteins

Influenza is a contagious, acute respiratory disease that is a major cause of morbidity and mortality throughout the world. CD4 T cells play an important role in the immune response to this pathogen through the secretion of antiviral cytokines, and by providing help to CD8 T cells and B cells to promote the development of immunological memory and neutralizing antibody responses. Despite these well-defined roles in the anti-influenza response, our understanding of CD4 T-cell diversity and specificity remains limited. In the study reported here, overlapping peptides representing 5 different influenza viral proteins were used in EliSpot assays to enumerate and identify the specificity of anti-influenza CD4 T cells directly ex vivo following infection of mice with influenza virus, using two strains that express unrelated MHC class II molecules. These experiments evaluated whether the reactivity of CD4 T cells generally tracked with particular influenza proteins, or whether MHC preferences were the predominant factor dictating anti-CD4 T-cell specificity in the primary immune response. We made the unexpected discovery that the distribution of CD4 T-cell specificities for different influenza proteins varied significantly depending on the single class II molecule expressed in vivo. In SJL mice, the majority of epitopes were specific for the HA protein, while the NP protein dominated the response in C57BL/10 mice. Given the diversity of human MHC class II molecules, these findings have important implications for the ability to rationally design a vaccine that will generate a specific CD4 T-cell immune response that is effective across diverse human populations.

Development of avian influenza virus H5 DNA vaccine and MDP-1 gene of Mycobacterium bovis as genetic adjuvant

Background

Studies have shown that DNA vaccines can induce protective immunity, which demonstrated the high potential of DNA vaccines as an alternative to inactivated vaccines. Vaccines are frequently formulated with adjuvants to improve their release, delivery and presentation to the host immune system.

Methods

The H5 gene of H5N1 virus (A/Ck/Malaysia/5858/04) was cloned separately into pcDNA3.1 + vector. The immunogenicity of the cloned H5 DNA vaccine was tested on SPF chickens using two different approaches. First approach was using H5 DNA vaccine (pcDNA3.1/H5) and the second was using H5 DNA vaccine in addition to the pcDNA3.1/MDP1 vaccine. Ten days old chickens inoculated three times with two weeks intervals. The spleen and muscle samples from chickens immunized with H5 (pcDNA3.1/H5) and H5 + MDP1 (pcDNA3.1/H5 + pcDNA3.1/MDP1) vaccines were collected after sacrificing the chickens and successfully expressed H5 and MDP1 RNA transcripts. The sera of immunized chickens were collected prior to first immunization and every week after immunization; and analyzed using enzyme-linked immunosorbent assay (ELISA) and hemagglutination inhibition (HI) test.

Results

Results of competitive ELISA showed successful antibody responses two weeks post immunization. The HI test showed an increased in antibody titers during the course of experiment in group immunized with H5 and H5 + MDP1 vaccines. The result showed that the constructed DNA vaccines were able to produce detectable antibody titer in which the group immunized with H5 + MDP1 vaccine produced higher antibody comparing to H5 vaccine alone.

Conclusions

This study shows for the first time the usefulness of MDP1 as a genetic adjuvant for H5 DNA vaccine.

Inhibition of human natural killer cell activity by influenza virions and hemagglutinin

Natural killer (NK) cells keep viral infections under control at the early phase by directly killing infected cells. Influenza is an acute contagious respiratory viral disease transmitted from host-to-host in the first few days of infection. The evasion of host innate immune defenses including NK cells is important for its success as a viral pathogen of humans and animals. NK cells encounter influenza virus within the microenvironment of infected cells. It therefore is important to investigate the direct effects of influenza virus on NK cell activity. Recently we demonstrated that influenza virus directly infects human NK cells and induces cell apoptosis to counter their function (H. Mao, W. Tu, G. Qin, H. K. W. Law, S. F. Sia, P.-L. Chan, Y. Liu, K.-T. Lam, J. Zheng, M. Peiris, and Y.-L. Lau, J. Virol. 83:9215-9222, 2009). Here, we further demonstrated that both the intact influenza virion and free hemagglutinin protein inhibited the cytotoxicity of fresh and interleukin-2 (IL-2)-activated primary human NK cells. Hemagglutinin bound and internalized into NK cells via the sialic acids. This interaction did not decrease NKp46 expression but caused the downregulation of the zeta chain through the lysosomal pathway, which caused the decrease of NK cell cytotoxicity mediated by NKp46 and NKp30. The underlying dysregulation of the signaling pathway involved zeta chain downregulation, leading to decreased Syk and ERK activation and granule exocytosis upon target cell stimulation, finally causing reduced cytotoxicity. These findings suggest that influenza virus developed a novel strategy to evade NK cell innate immune defense that is likely to facilitate viral transmission and also contribute to virus pathogenesis.

Using 3 TLR ligands as a combination adjuvant induces qualitative changes in T cell responses needed for antiviral protection in mice

TLR ligands are promising candidates for the development of novel vaccine adjuvants that can elicit protective immunity against emerging infectious diseases. Adjuvants have been used most frequently to increase the quantity of an immune response. However, the quality of a T cell response can be more important than its quantity. Stimulating certain pairs of TLRs induces a synergistic response in terms of activating dendritic cells and eliciting/enhancing T cell responses through clonal expansion, which increases the number of responding T cells. Here, we have found that utilizing ligands for 3 TLRs (TLR2/6, TLR3, and TLR9) greatly increased the protective efficacy of vaccination with an HIV envelope peptide in mice when compared with using ligands for only any 2 of these TLRs; surprisingly, increased protection was induced without a marked increase in the number of peptide-specific T cells. Rather, the combination of these 3 TLR ligands augmented the quality of the T cell responses primarily by amplifying their functional avidity for the antigen, which was necessary for clearance of virus. The triple combination increased production of DC IL-15 along with its receptor, IL-15Ralpha, which contributed to high avidity, and decreased expression of programmed death-ligand 1 and induction of Tregs. Therefore, selective TLR ligand combinations can increase protective efficacy by increasing the quality rather than the quantity of T cell responses.

Enhancement of the influenza A hemagglutinin (HA)-mediated cell-cell fusion and virus entry by the viral neuraminidase (NA)

Background

The major role of the neuraminidase (NA) protein of influenza A virus is related to its sialidase activity, which disrupts the interaction between the envelope hemagglutin (HA) protein and the sialic acid receptors expressed at the surface of infected cells. This enzymatic activity is known to promote the release and spread of progeny viral particles following their production by infected cells, but a potential role of NA in earlier steps of the viral life cycle has never been clearly demonstrated. In this study we have examined the impact of NA expression on influenza HA-mediated viral membrane fusion and virion infectivity.

Methodology/Principal Findings

The role of NA in the early stages of influenza virus replication was examined using a cell-cell fusion assay that mimics HA-mediated membrane fusion, and a virion infectivity assay using HIV-based pseudoparticles expressing influenza HA and/or NA proteins. In the cell-cell fusion assay, which bypasses the endocytocytosis step that is characteristic of influenza virus entry, we found that in proper HA maturation conditions, NA clearly enhanced fusion in a dose-dependent manner. Similarly, expression of NA at the surface of pseudoparticles significantly enhanced virion infectivity. Further experiments using exogeneous soluble NA revealed that the most likely mechanism for enhancement of fusion and infectivity by NA was related to desialylation of virion-expressed HA.

Conclusion/Significance

The NA protein of influenza A virus is not only required for virion release and spread but also plays a critical role in virion infectivity and HA-mediated membrane fusion.

Pandemic influenza planning by videoconference

Collaboration between nations and sectors is crucial to improve regional preparedness against pandemic influenza. In 2008, a Virtual Symposium was organized in the Asia-Pacific region by the Asia-Pacific Economic Cooperation Emerging Infections Network (APEC EINet) to discuss pandemic preparedness. The multipoint videoconference lasted approximately 4.5 hours and was attended by 16 APEC members who shared best practices in public-private partnerships for pandemic influenza preparedness planning. Twelve of the 16 APEC members who participated responded to a post-event survey. The overall experience of the event was rated highly. Partnering public health, technology and business communities to discuss best practices in preparedness using videoconferencing may be an effective way to improve regional preparedness. Utilization of videoconferencing on a routine basis should be considered to improve preparedness among APEC members and enhance its usability during a pandemic.

Phosphoantigen-expanded human gammadelta T cells display potent cytotoxicity against monocyte-derived macrophages infected with human and avian influenza viruses

BackgroundInfluenza virus is a cause of substantial annual morbidity and mortality worldwide. The potential emergence of a new pandemic strain (eg, avian influenza virus) is a major concern. Currently available vaccines and anti-influenza drugs have limited effectiveness for influenza virus infections, especially for new pandemic strains. Therefore, there is an acute need to develop alternative strategies for influenza therapy. γδ T cells have potent antiviral activities against different viruses, but no data are available concerning their antiviral activity against influenza viruses

MethodsIn this study, we used virus-infected primary human monocyte-derived macrophages (MDMs) to examine the antiviral activity of phosphoantigen isopentenyl pyrophosphate (IPP)–expanded human Vγ9Vδ2 T cells against influenza viruses

ResultsVγ9Vδ2 T cells were selectively activated and expanded by IPP from peripheral blood mononuclear cells. IPP-expanded Vγ9Vδ2 T cells efficiently killed MDMs infected with human (H1N1) or avian (H9N2 or H5N1) influenza virus and significantly inhibited viral replication. The cytotoxicity of Vγ9Vδ2 T cells against influenza virus–infected MDMs was dependent on NKG2D activation and was mediated by Fas–Fas ligand and perforin–granzyme B pathways

ConclusionOur findings suggest a potentially novel therapeutic approach to seasonal, zoonotic avian, and pandemic influenza—the use of phosphoantigens to activate γδ T cells against influenza virus infections

CAPIH: a Web interface for comparative analyses and visualization of host-HIV protein-protein interactions

Background

The Human Immunodeficiency Virus type one (HIV-1) is the major causing pathogen of the Acquired Immune Deficiency Syndrome (AIDS). A large number of HIV-1-related studies are based on three non-human model animals: chimpanzee, rhesus macaque, and mouse. However, the differences in host-HIV-1 interactions between human and these model organisms have remained unexplored.

Description

Here we present CAPIH (Comparative Analysis of Protein Interactions for HIV-1), the first web-based interface to provide comparative information between human and the three model organisms in the context of host-HIV-1 protein interactions. CAPIH identifies genetic changes that occur in HIV-1-interacting host proteins. In a total of 1,370 orthologous protein sets, CAPIH identifies ~86,000 amino acid substitutions, ~21,000 insertions/deletions, and ~33,000 potential post-translational modifications that occur only in one of the four compared species. CAPIH also provides an interactive interface to display the host-HIV-1 protein interaction networks, the presence/absence of orthologous proteins in the model organisms in the networks, the genetic changes that occur in the protein nodes, and the functional domains and potential protein interaction hot sites that may be affected by the genetic changes. The CAPIH interface is freely accessible at http://bioinfo-dbb.nhri.org.tw/capih.

Conclusion

CAPIH exemplifies that large divergences exist in disease-associated proteins between human and the model animals. Since all of the newly developed medications must be tested in model animals before entering clinical trials, it is advisable that comparative analyses be performed to ensure proper translations of animal-based studies. In the case of AIDS, the host-HIV-1 protein interactions apparently have differed to a great extent among the compared species. An integrated protein network comparison among the four species will probably shed new lights on AIDS studies.

Replication and pathogenesis associated with H5N1, H5N2, and H5N3 low-pathogenic avian influenza virus infection in chickens and ducks

A comparative study examining replication and disease pathogenesis associated with low-pathogenic H5N1, H5N2, or H5N3 avian influenza virus (AIV) infection of chickens and ducks was performed. The replication and pathogenesis of highly pathogenic AIV (HPAIV) has received substantial attention; however, the behavior of low-pathogenic AIVs, which serve as precursors to HPAIVs, has received less attention. Thus, chickens or ducks were inoculated with an isolate from a wild bird [A/Mute Swan/MI/451072/06 (H5N1)] or isolates from chickens [A/Ck/PA/13609/93 (H5N2), A/Ck/TX/167280-4/02 (H5N3)], and virus replication, induction of a serological response, and disease pathogenesis were investigated, and the hemagglutinin and neuraminidase (NA) gene sequences of the isolates were determined. Virus isolated from tracheal and cloacal swabs showed that H5N1 replicated better in ducks, whereas H5N2 and H5N3 replicated better in chickens. Comparison of the NA gene sequences showed that chicken-adapted H5N2 and H5N3 isolates both have a deletion of 20 amino acids in the NA stalk region, which was absent in the H5N1 isolate. Histopathological examination of numerous organs showed that H5N2 and H5N3 isolates caused lesions in chickens in a variety of organs, but to a greater extent in the respiratory and intestinal tracts, whereas H5N1 lesions in ducks were observed mainly in the respiratory tract. This study suggests that the H5N1, H5N2, and H5N3 infections occurred at distinct sites in chicken and ducks, and that comparative studies in different model species are needed to better understand the factors influencing the evolution of these viruses.

Avian influenza H5N1: an update on molecular pathogenesis

Avian influenza A virus constitutes a large threat to human health. Recent outbreaks of highly pathogenic avian influenza H5N1 virus in poultry and in humans have raised concerns that an influenza pandemic will occur in the near future. Transmission from avian species to humans remains sporadic, but the mortality associated with human infection is very high (about 62%). To date, there are no effective therapeutic drugs or a prophylactic vaccines available, which means that there is still a long way to go before we can eradicate or cure avian influenza. This review focuses on the molecular pathogenesis of avian influenza H5N1 virus infection. An understanding of the viral pathogenesis may facilitate the development of novel treatments or effective eradication of this fatal disease.

H5N1 strain-specific hemagglutinin CD4+ T cell epitopes restricted by HLA DR4

CD4+ T cells play a pivotal role in the viral immunity, and as such identification of unique strain-specific HLA class II restricted epitopes is essential for monitoring cellular strain-specific viral immunity. Using Tetramer-Guided Epitope Mapping technique, we identified HLA-DR0401 restricted HA epitopes that are strain-specific to H5N1 virion. Two immunodominant epitopes H5HA(441-460) and H5HA(57-76) were identified from in vitro stimulated human PBMC. Both epitopes elicit strong cellular immune responses when HLA-DR0401 transgenic mice are immunized with H5N1 subvirion indicating in vivo naturally processed immunodominant epitopes. The H5HA(57-76) epitope is unique for the H5N1 strain but conserved among all H5N1 clades recommended for vaccine development by World Health Organization. The unique H5HA(57-76) response was uncommon in unexposed individuals and only observed in the naïve T cell subset. Thus, H5N1 strain-specific H5HA(57-76) immunogenic epitope represents a unique marker for monitoring the efficacy of vaccination or as a candidate vaccine peptide.

Infection of HLA-DR1 transgenic mice with a human isolate of influenza a virus (H1N1) primes a diverse CD4 T-cell repertoire that includes CD4 T cells with heterosubtypic cross-reactivity to avian (H5N1) influenza virus

The specificity of the CD4 T-cell immune response to influenza virus is influenced by the genetic complexity of the virus and periodic encounters with variant subtypes and strains. In order to understand what controls CD4 T-cell reactivity to influenza virus proteins and how the influenza virus-specific memory compartment is shaped over time, it is first necessary to understand the diversity of the primary CD4 T-cell response. In the study reported here, we have used an unbiased approach to evaluate the peptide specificity of CD4 T cells elicited after live influenza virus infection. We have focused on four viral proteins that have distinct intracellular distributions in infected cells, hemagglutinin (HA), neuraminidase (NA), nucleoprotein, and the NS1 protein, which is expressed in infected cells but excluded from virion particles. Our studies revealed an extensive diversity of influenza virus-specific CD4 T cells that includes T cells for each viral protein and for the unexpected immunogenicity of the NS1 protein. Due to the recent concern about pandemic avian influenza virus and because CD4 T cells specific for HA and NA may be particularly useful for promoting the production of neutralizing antibody to influenza virus, we have also evaluated the ability of HA- and NA-specific CD4 T cells elicited by a circulating H1N1 strain to cross-react with related sequences found in an avian H5N1 virus and find substantial cross-reactivity, suggesting that seasonal vaccines may help promote protection against avian influenza virus.