Differential interferon responses to influenza A and B viruses in primary ferret respiratory epithelial cells

Influenza B viruses (IBV) cocirculate with influenza A viruses (IAV) and cause periodic epidemics of disease, yet antibody and cellular responses following IBV infection are less well understood. Using the ferret model for antisera generation for influenza surveillance purposes, IAV resulted in robust antibody responses following infection, whereas IBV required an additional booster dose, over 85% of the time, to generate equivalent antibody titers. In this study, we utilized primary differentiated ferret nasal epithelial cells (FNECs) which were inoculated with IAV and IBV to study differences in innate immune responses which may result in differences in adaptive immune responses in the host. FNECs were inoculated with IAV (H1N1pdm09 and H3N2 subtypes) or IBV (B/Victoria and B/Yamagata lineages) and assessed for 72 h. Cells were analyzed for gene expression by quantitative real-time PCR, and apical and basolateral supernatants were assessed for virus kinetics and interferon (IFN), respectively. Similar virus kinetics were observed with IAV and IBV in FNECs. A comparison of gene expression and protein secretion profiles demonstrated that IBV-inoculated FNEC expressed delayed type-I/II IFN responses and reduced type-III IFN secretion compared to IAV-inoculated cells. Concurrently, gene expression of Thymic Stromal Lymphopoietin (TSLP), a type-III IFN-induced gene that enhances adaptive immune responses, was significantly downregulated in IBV-inoculated FNECs. Significant differences in other proinflammatory and adaptive genes were suppressed and delayed following IBV inoculation. Following IBV infection, ex vivo cell cultures derived from the ferret upper respiratory tract exhibited reduced and delayed innate responses which may contribute to reduced antibody responses in vivo.IMPORTANCEInfluenza B viruses (IBV) represent nearly one-quarter of all human influenza cases and are responsible for significant clinical and socioeconomic impacts but do not pose the same pandemic risks as influenza A viruses (IAV) and have thus received much less attention. IBV accounts for greater severity and deaths in children, and vaccine efficacy remains low. The ferret can be readily infected with human clinical isolates and demonstrates a similar course of disease and immune responses. IBV, however, generates lower antibodies in ferrets than IAV following the challenge. To determine whether differences in initial innate responses following infection may affect the development of robust adaptive immune responses, ferret respiratory tract cells were isolated, infected with IAV/IBV, and compared. Understanding the differences in the initial innate immune responses to IAV and IBV may be important in the development of more effective vaccines and interventions to generate more robust protective immune responses.

Palmitoylation of the hemagglutinin of influenza B virus by ER-localized DHHC enzymes 1, 2, 4, and 6 is required for efficient virus replication

IMPORTANCE

Influenza viruses are a public health concern since they cause seasonal outbreaks and occasionally pandemics. Our study investigates the importance of a protein modification called "palmitoylation" in the replication of influenza B virus. Palmitoylation involves attaching fatty acids to the viral protein hemagglutinin and has previously been studied for influenza A virus. We found that this modification is important for the influenza B virus to replicate, as mutating the sites where palmitate is attached prevented the virus from generating viable particles. Our experiments also showed that this modification occurs in the endoplasmic reticulum. We identified the specific enzymes responsible for this modification, which are different from those involved in palmitoylation of HA of influenza A virus. Overall, our research illuminates the similarities and differences in fatty acid attachment to HA of influenza A and B viruses and identifies the responsible enzymes, which might be promising targets for anti-viral therapy.

Insights from the comparison of genomic variants from two influenza B viruses grown in the presence of human antibodies in cell culture

Understanding the extent and limitation of viral genome evolution can provide insight about potential drug and vaccine targets. Influenza B Viruses (IBVs) infect humans in a seasonal manner and causes significant morbidity and mortality. IBVs are negative-sense single-stranded RNA viruses with a segmented genome and can be divided into two antigenically distinct lineages. The two lineages have been circulating and further evolving for almost four decades. The immune response to IBV infection can lead to antibodies that target the strain causing the infection. Some antibodies are cross-reactive and are able to bind strains from both lineages but, because of antigenic drift and immunodominance, both lineages continue to evolve and challenge human health. Here we investigate changes in the genomes of an IBVs from each lineage after passage in tissue culture in the presence of human sera containing polyclonal antibodies directed toward antigenically and temporally distinct viruses. Our previous analysis of the fourth segment, which encodes the major surface protein HA, revealed a pattern of change in which signature sequences from one lineage mutated to the signature sequences of the other lineage. Here we analyze genes from the other genomic segments and observe that most of the quasispecies’ heterogeneity occurs at the same loci in each lineage. The nature of the variants at these loci are investigated and possible reasons for this pattern are discussed. This work expands our understanding of the extent and limitations of genomic change in IBV.

Functional growth inhibition of influenza A and B viruses by liquid and powder components of leaves from the subtropical plant Melia azedarach L

We evaluated the anti-influenza-virus effects of Melia components and discuss the utility of these components. The effects of leaf components of Melia azedarach L. on viruses were examined, and plaque inhibition tests were performed. The in vivo efficacy of M. azedarach L. was tested in a mouse model. Leaf components of Melia azedarach L. markedly inhibited the growth of various influenza viruses. In an initial screening, multiplication and haemagglutination (HA) activities of H1N1, H3N2, H5, and B influenza viruses were inactivated by the liquid extract of leaves of M. azedarach L. (MLE). Furthermore, plaque inhibition titres of H1N1, H3N2, and B influenza viruses treated with MLE ranged from 103.7 to 104.2. MLE possessed high plaque-inhibitory activity against pandemic avian H5N1, H7N9, and H9N2 vaccine candidate strains, with a plaque inhibition titre of more than 104.2. Notably, the buoyant density decreased from 1.175 to 1.137 g/cm3, and spikeless particles appeared. We identified four anti-influenza virus substances: pheophorbide b, pheophorbide a, pyropheophorbide a, and pheophytin a. Photomorphogenesis inside the envelope may lead to removal of HA and neuraminidase spikes from viruses. Thus, MLE could efficiently remove floating influenza virus in the air space without toxicity. Consistent with this finding, intranasal administration of MLE in mice significantly decreased the occurrence of pneumonia. Additionally, leaf powder of Melia (MLP) inactivated influenza viruses and viruses in the intestines of chickens. MLE and MLP may have applications as novel, safe biological disinfectants for use in humans and poultry.

Protein disulfide isomerases as potential therapeutic targets for influenza A and B viruses

Seasonal flu as well as potential pandemic flu outbreaks continuously underscores the importance of the preventive and therapeutic measures against influenza viruses. During screening of natural and synthetic small molecules against influenza A and B virus, we identified juniferdin as a highly effective inhibitor against both viruses in cells. Since juniferdin is known to inhibit protein disulfide isomerases (PDIs), multiple PDI inhibitors were tested against these viruses. Among PDI inhibitors, 16F16, PACMA31, isoquercetin, epigallocatechin-3-gallate or nitazoxanide significantly reduced the replication of influenza A and B viruses in MDCK and A549 cells. Furthermore, siRNAs specific to three PDI family members (PDI1, PDIA3 or PDIA4) also significantly reduced the replication of influenza A and B viruses in cells. These results suggest that PDIs may serve as excellent targets for the development of new anti-influenza drugs.

Influenza B virus reverse genetic backbones with improved growth properties in the EB66® cell line as basis for vaccine seed virus generation

Vaccination remains the best available prophylaxis to prevent influenza virus infections, yet current inadequacies in influenza virus vaccine manufacturing often lead to vaccine shortages at times when the vaccine is most needed, as it was the case during the last influenza virus pandemic. Novel influenza virus vaccine production systems will be crucial to improve public health and safety. Here we report the optimization of influenza B virus growth in the proprietary EB66® cell line, currently in use for human vaccine production. To this end, we collected, curated and sequenced 71 influenza B viruses selected for high diversity in date of isolation and lineage. This viral collection was tested for ability to enter and replicate within EB66® cells in a single cycle assay and appears to readily infect these cells. When the collection was tested for viral progeny production in a multi-cycle assay, we found a large variation from strain to strain. The strains with the top growth characteristics from the B/Victoria and B/Yamagata lineages were selected for vaccine backbone generation using a reverse genetics system. We then showed that these backbones maintain their desirable growth within EB66® cells when the HA and NA from poorly growing strains were substituted for the parental segments, indicating that the selected backbones are viable options for vaccine production in EB66®. Finally, we show that compounds previously reported to enhance influenza virus growth in cell culture also increase virus production in the EB66® cell line.

Comparative study of influenza virus replication in MDCK cells and in primary cells derived from adenoids and airway epithelium

Although clinical trials with human subjects are essential for determination of safety, infectivity, and immunogenicity, it is desirable to know in advance the infectiousness of potential candidate live attenuated influenza vaccine strains for human use. We compared the replication kinetics of wild-type and live attenuated influenza viruses, including H1N1, H3N2, H9N2, and B strains, in Madin-Darby canine kidney (MDCK) cells, primary epithelial cells derived from human adenoids, and human bronchial epithelium (NHBE cells). Our data showed that despite the fact that all tissue culture models lack a functional adaptive immune system, differentiated cultures of human epithelium exhibited the greatest restriction for all H1N1, H3N2, and B vaccine viruses studied among three cell types tested and the best correlation with their levels of attenuation seen in clinical trials with humans. In contrast, the data obtained with MDCK cells were the least predictive of restricted viral replication of live attenuated vaccine viruses in humans. We were able to detect a statistically significant difference between the replication abilities of the U.S. (A/Ann Arbor/6/60) and Russian (A/Leningrad/134/17/57) cold-adapted vaccine donor strains in NHBE cultures. Since live attenuated pandemic influenza vaccines may potentially express a hemagglutinin and neuraminidase from a non-human influenza virus, we assessed which of the three cell cultures could be used to optimally evaluate the infectivity and cellular tropism of viruses derived from different hosts. Among the three cell types tested, NHBE cultures most adequately reflected the infectivity and cellular tropism of influenza virus strains with different receptor specificities. NHBE cultures could be considered for use as a screening step for evaluating the restricted replication of influenza vaccine candidates.

Involvement of type I immune responses in swine-origin H1N1 influenza virus infection

Swine-origin H1N1 influenza virus (S-OIV) appeared in 2009 with a higher incidence rate among children. Although fever was the most common symptom, some complicated cases occurred. We evaluated the percentages of effector T cells, B cells, and regulatory T cells in peripheral blood from 5 children infected by S-OIV (1 with acute necrotizing encephalitis, 2 with pneumonia, and 2 without complications), 5 children with seasonal influenza, and 5 healthy children. We found higher percentages of T-bet(+) CD4(+)CD8(+) T cells, monocytes, and B cells, granzyme B(+) and perforin(+) CD4(+), and CD8(+) T cells in affected children with both seasonal and H1N1 influenza than in controls, whereas both groups demonstrated similar percentages of CD4(+)CD25(+)Foxp3(+) regulatory T cells. In infected children with complications we observed high percentages of perforin(+) and interferon-γ(+) CD4(+) and CD8(+) T cells associated with low percentages of T regulatory cells. Our data suggest a dysregulation of antipathogen type I immune responses in complicated S-OIV infections.

Linker and/or transmembrane regions of influenza A/Group-1, A/Group-2, and type B virus hemagglutinins are packed differently within trimers

Influenza virus hemagglutinin is a homotrimeric spike glycoprotein crucial for virions' attachment, membrane fusion, and assembly reactions. X-ray crystallography data are available for hemagglutinin ectodomains of various types/subtypes but not for anchoring segments. To get structural information for the linker and transmembrane regions of hemagglutinin, influenza A (H1-H16 subtypes except H8 and H15) and B viruses were digested with bromelain or subtilisin Carlsberg, either within virions or in non-ionic detergent micelles. Proteolytical fragments were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Within virions, hemagglutinins of most influenza A/Group-1 and type B virus strains were more susceptible to digestion with bromelain and/or subtilisin compared to A/Group-2 hemagglutinins. The cleavage sites were always located in the hemagglutinin linker sequence. In detergent, 1) bromelain cleaved hemagglutinin of every influenza A subtype in the linker region; 2) subtilisin cleaved Group-2 hemagglutinins in the linker region; 3) subtilisin cleaved Group-1 hemagglutinins in the transmembrane region; 4) both enzymes cleaved influenza B virus hemagglutinin in the transmembrane region. We propose that the A/Group-2 hemagglutinin linker and/or transmembrane regions are more tightly associated within trimers than type A/Group-1 and particularly type B ones. This hypothesis is underpinned by spatial trimeric structure modeling performed for transmembrane regions of both Group-1 and Group-2 hemagglutinin representatives. Differential S-acylation of the hemagglutinin C-terminal anchoring segment with palmitate/stearate residues possibly contributes to fine tuning of transmembrane trimer packing and stabilization since decreased stearate amount correlated with deeper digestion of influenza B and some A/Group-1 hemagglutinins.

Overexpression of α-2,6 sialyltransferase stimulates propagation of human influenza viruses in Vero cells

Human influenza viruses are major concern as the leading cause of global pandemics. In infecting cells, they preferentially bind to sialyloligosaccharides containing terminal N-acetyl sialic acid linked to galactose by an α-2,6-linkage (NeuAcα2,6Gal). The amount of NeuAcα2,6Gal in Vero cells, which are predominantly used for production of influenza vaccines over the past 30 years, may not be as high as that in epithelial cells of human respiratory tract, what leads to the suboptimal virus growth in Vero cells. In this study, we stably transfected Vero cells with cDNA of human α-2,6-sialyltransferase (SIAT1), an enzyme catalyzing α-2,6-sialylation of galactose on glycoproteins. Overexpression of SIAT1 in the transfected Vero cells (Vero-SIAT1 cells) was confirmed by Western blot analysis and immunofluorescence microscopy. Vero-SIAT1 cells expressed 7 times higher amounts of NeuAcα2,6Gal, but 3 times lower amounts of NeuAcα2,3Gal as compared to parental Vero cells. Furthermore, the influenza viruses A (H1N1 and H3N2) and B grew in Vero-SIAT1 cells to the higher titers than in Vero cells. Taken together, these results imply that Vero-SIAT1 cells are useful not only for the propagation of human influenza viruses, but also for the preparation of influenza vaccines.

[Influenza virus reproduction in the MDCK cells adapted to growth in serum-free Hybris-2 medium]

Whether the MDCK cell line might adapt to grow in serum-free Hybris-2 medium and influenza viruses might be reproduced in the adapted cells was studied. Seventeen passages using the Hybris-2 medium yielded cells adapted to growth in this medium (MDCK-BS). The reproduction of influenza A (H1N1 and H3N2) and B viruses versus the cells cultured in Eagle's medium was studied. The laboratory strain of influenza A/Aichi/1/68 (H3N2) and the strain B/Ohio/01/05 of influenza B in equal titers were shown to be reproduced in both control cells on Eagle's medium and MDCK-BS cells adapted to growth in the Hybris-2 medium. The reproduction of the strains A/Brisbane/10/07 (H3N2) and A/Solomon Islands/3/06 (H1N1) was less active in the MDCK cells. Each strain of influenza viruses displayed varying infective activities. The developed serum-free Hybris-2 medium may be used for cultivation of monolayer continuous MDCK cells and for their reproduction of influenza A and B viruses.

Screening of a high growth influenza B virus strain in Vero cells

Due to the insufficient supply of embryonated chicken eggs, the preparation of large quantities of inactivated influenza vaccines will require an alternative virus culture system after the emergence or reemergence of a pandemic influenza virus. The Vero cell is one of the ideal options since it was used for producing many kinds of human vaccines. However, most of the influenza viruses can not grow well in Vero cells. To develop a new influenza vaccine with Vero cells as a substrate, the virus needs to adapt to this cell substrate to maintain high growth characteristics. By serial passages in Vero cells, the B/Yunnan/2/2005va (B) strain was successfully adapted to Vero cells, with the hemagglutination titer (HAT) of the virus reaching 1:512. The high growth characteristic of this strain is stable up to 21 passages. The strain was identified by hemagglutination inhibition (HAI) test and sequencing respectively; the HA₁ gene sequence of the virus was cloned and analyzed. The screening and establishment of high growth B virus provides an important tool for influenza vaccine production in Vero cells.

[Comparison study of a real-time reverse transcription polymerase chain reaction assay with an enzyme immunoassay and shell vial culture for influenza A and B virus detection in adult patients]

INTRODUCTION

The age of the patients and the type of sample are major problems in the diagnosis of influenza. Most available diagnostic techniques are highly effective in pediatric patients and in nasopharyngeal aspirates. However, in the adult population and using throat swabs, these techniques are much less reliable.

AIM

We performed a prospective study comparing the efficacy of a commercial real-time reverse transcription PCR assay (RT-PCR) with that of an enzyme immunoassay (EIA) or shell vial culture (SV) in the detection of influenza A and B viruses in 125 throat swabs from adults with clinically suspected influenza during the 2007-2008 flu season.

MATERIAL AND METHODS

Throat swabs were subjected to rapid antigen detection for influenza viruses by means of a commercial dot-blot EIA. For the RT-PCR technique, RNA was extracted from 200 microL of each sample by the automated extraction system, EZ1 virus minikit (version 2.0). Genomic amplification of the extracted viral RNA was carried out using the OneStep RT-PCR FluA+FluB automated system with the SmartCycler amplification system. Each sample was inoculated into 2 SV of the MDCK cell line. Turnaround times were calculated from the time specimens were received in the laboratory to the time the result was reported to clinicians.

RESULTS

The EIA system detected 27 (21.6%) positive samples, RT-PCR 62 (49.6%) positive samples, and SV 56 (44.8%) positive samples. Among the 62 positive samples, EIA detected 27 (43.5%), RT-PCR 62 (100%) and SV 56 (90.3%). With the use of RT-PCR, 38.4% of the adults studied were diagnosed on the same day samples were received. Among the total, 67.2% of diagnostic results were obtained within the first 24 hours; turnaround time was 1.1 days.

CONCLUSION

The real-time RT-PCR method studied displayed high sensitivity and specificity in the detection of influenza virus in adult patients, when compared with the conventional techniques. With real-time RT-PCR, large numbers of samples can be rapidly tested and results provided the same day samples are received.

Stabilizing the glycosylation pattern of influenza B hemagglutinin following adaptation to growth in eggs

The currently circulating influenza B viruses from both antigenic lineages contain an N-linked glycosylation site in the hemagglutinin (HA) protein at positions of 196 or 197. However, egg adaptation caused the loss of the glycosylation site that could impact virus antigenicity and vaccine efficacy. The effect of the 196/197 glycosylation site on influenza B virus growth and antigenicity was systemically evaluated in this study by the molecular approach. Paired recombinant 6:2 reassortant influenza B vaccine strains, with or without the 196/197 glycosylation site, were generated by reverse genetics and the glycosylation site was retained in MDCK cells. In contrast, all the viruses that contained the introduced glycosylation site were unable to grow in eggs and rapidly lost the glycosylation site once adapted to grow in eggs. We showed that glycosylation affected virus binding to the alpha-2,3-linked sialic acid receptor and affected virus antigenicity as tested by postinfected ferret sera. We have further identified that the Arginine residue at amino acid position 141 (141R) can stabilize the 196/197 glycosylation site without affecting virus antigenicity. Thus, the 141R could be introduced into vaccine strains to retain the 196/197 glycosylation site for influenza B vaccines.

Generation of the influenza B viruses with improved growth phenotype by substitution of specific amino acids of hemagglutinin

Variability in growth characteristics of influenza B viruses remains a serious limitation in the manufacture of inactivated influenza vaccines. Currently, serial passage in eggs is the strategy used in most instances for selection of high growth virus variants. In previous studies we found that adaptation of the strain B/Victoria/504/2000 to high growth in eggs was associated with changes only in hemagglutinin (HA). The high growth phenotype was associated with acquisition of either two (R162M and D196Y) or three (G141E, R162M and D196Y) amino acid (AA) substitutions, predicted to be near the receptor-binding domain of HA. In the present study we analyzed, using reverse genetics, the contribution to virus growth of each of these AA substitutions and determined their effect on antigenic properties. We found that G141E and R162M were most favorable for virus growth; however, only R162M could improve virus growth without antigenic alteration. Substitution D196Y had least effect on virus growth but substantially altered antigenic properties. Additional virus variants with AA substitutions at positions 126, 129, 137 and 141 were generated and characterized. The AA changes advantageous for growth of B/Victoria/504/2000 were also tested in the context of the HA of the B/Beijing/184/93, a virus with stable low-growth phenotype. All of the tested AA substitutions improved the replicative capabilities of the corresponding viruses, but only N126D and K129E had no effect on antigenicity. The results of our studies demonstrate that introduction of specific AA substitutions into viral HA can improve viral replicative efficiency while preserving the original antigenic properties.

Yield increases in intact influenza vaccine virus from chicken allantoic fluid through isolation from insoluble allantoic debris

A yield enhancement technology for use in influenza vaccine manufacturing has been developed to maximize the recovery of influenza virus from allantoic fluid of virus-infected chick embryos; the standard raw material for influenza vaccine. Virus associated with amorphous debris in the allantoic fluid can be dissociated from the debris and recovered, thereby increasing viral yield. Dissociation can be achieved by subjecting the virus-debris complex to conditions of increased ionic strength at defined pH. Multifold increases in viral yield per ml of allantoic fluid were observed. The degree of yield enhancement is strain-specific, however, increases were observed in all type A and type B influenza strains tested. The heightened influenza virus recoveries can facilitate rapid vaccine manufacture, with increased numbers of doses produced, and may become essential at a time of influenza pandemic.

Inhibitory effect of cinnamaldehyde, derived from Cinnamomi cortex, on the growth of influenza A/PR/8 virus in vitro and in vivo

We have investigated the inhibitory effect of trans-cinnamaldehyde (CA), one of the principal constituents of essential oil derived from Cinnamomi cortex, on the growth of influenza A/PR/8 virus in vitro and in vivo. When 1-h drug treatment was initiated at various times post-infection (p.i.) in Madin-Darby canine kidney cells using a fixed dose of CA (40 microM), the maximum inhibitory effect (29.7% virus yield of control) was obtained when drug treatment was started at 3h p.i. Under the same treatment schedule, CA inhibited the virus growth in a dose-dependent manner (20-200 microM), and, at 200 microM, the virus yield was reduced to an undetectable level. RT-PCR and SDS-PAGE analyses showed that CA inhibited viral protein synthesis at the post-transcriptional level. In mice infected with the lung-adapted PR-8 virus, inhalation (50mg/cage/day) and nasal inoculation (250 microg/mouse/day) of CA significantly increased survival rates on the 8 days to 100% and 70%, respectively, in contrast to a survival rate of 20% in the untreated control group. Importantly, inhalation of CA caused virus yield reduction by 1 log in bronchoalveolar lavage fluid on day 6 after infection, compared with that of the untreated control group. These findings might provide further support to the empirical indication of Cinnamomi cortex-containing Kampo medicines for acute respiratory infectious diseases.

Impact of influenza treatment with oseltamivir on health, sleep and daily activities of otherwise healthy adults and adolescents

OBJECTIVE

To determine the effect of oseltamivir (75mg twice daily) on time to return to baseline health, sleep and activity in patients with laboratory-confirmed influenza infection.

PATIENTS AND METHODS

Data from 1642 otherwise healthy adults (aged 13-64 years), who had experienced a febrile influenza-like illness (>38 degrees C) of up to 36 hours' duration together with at least one respiratory and one systemic/constitutional symptom, were pooled from four randomised, double-blind, placebo-controlled clinical trials. Patients in these trials had been randomised to receive either oseltamivir or placebo for 5 days and had been allowed unlimited use of symptom-relief medications. The primary analysis examined the effect of oseltamivir treatment on patients' general health status, sleep and normal activities as measured by visual analogue scales. Secondary analyses examined the possible effects of gender, influenza type, smoking, employment status and time to treatment (< or = or >24 hours) on these endpoints.

RESULTS

Oseltamivir significantly reduced the time taken to return to baseline health, sleep and activity across all pooled patients (p < 0.0001) and increased the proportion of patients returning to full activity within the first 7 days following treatment start. Gender, smoking status, time to treatment, influenza subtype and employment status had no appreciable effect on the effectiveness of oseltamivir.

CONCLUSIONS

In otherwise healthy adults, oseltamivir reduces the time to return to pre-illness levels of health, sleep and activity, and may help to decrease the overall burden of influenza on society. This provides an important rationale for the early use of antiviral treatment, such as oseltamivir, for the treatment of influenza in otherwise healthy adults and adolescents.

Synthesis and biological evaluation of dihydrofuran-fused perhydrophenanthrenes as a new anti-influenza agent having novel structural characteristic

Dihydrofuran-fused perhydrophenanthrenes were synthesized by means of o-quinodimethane chemistry with high generality and stereoselectivity, and found to exhibit potent anti-influenza activity. These compounds exerted an inhibitory effect on various strains of influenza virus growth, including influenza A and B, with a concentration dependent manner, and direct cytotoxicity was low. Several biological experiments suggested that these new drugs affected a virus replication process before mRNA synthesis stage. Novel rigid cage-type of structural characteristic of the compounds has not been found in hitherto anti-influenza drugs, and will provide new basis and motif for exploring promising and unprecedented anti-influenza agents.

Characterization of various strains of influenza B virus in a neuroblastoma and a glioblastoma cell line

BACKGROUND AND PURPOSE

Although influenza B virus has been reported to be involved in central nervous system infection, little is known about the infectivity of the virus. We evaluated the ability of several strains of influenza B virus to grow in 2 nerve cell culture systems.

METHODS

Five isolates of influenza B virus were infected into a neuroblastoma cell line, IMR-32 and a human glioblastoma cell line, GBM 8401, respectively. To determine the permissiveness of these virus strains in both cells, the severity of the cytopathic effect (CPE), relative quantitative analysis with hemadsorption and hemagglutination, reverse transcriptase-polymerase chain reaction (RT-PCR) as well as kinetic study of viral protein synthesis were performed.

RESULTS

All tested viruses grew well in IMR-32, but only B/3143/Taiwan/97 replicated well in GBM 8401, according to the results of CPE, hemagglutination, hemadsorption, RT-PCR and viral protein synthesis.

CONCLUSIONS

Besides the binding of viral receptor and hemagglutinin being critical for a permissive infection, the interaction of other virus proteins and the other unknown host factors might also affect the ability of influenza B virus to infect a host cell.

Evaluation of the Quidel QuickVue test for detection of influenza A and B viruses in the pediatric emergency medicine setting by use of three specimen collection methods

The Quidel QuickVue influenza test was compared to viral culture and reverse transcriptase PCR by the use of three different respiratory specimen types. Of 122 pediatric subjects enrolled, 59 had influenza virus infections: 44 were infected with influenza A virus and 15 were infected with influenza B virus. The sensitivity of the QuickVue test was 85% with nasopharyngeal swabs, 78% with nasal swabs, and 69% with nasopharyngeal washes. Specificities were equivalent (97% to 98%) for all three collection methods.

[Genetic stability of cold-adapted influenza viruses]

The stability of cold adaptation, temperature-sensitivity, and marker mutations that are typical of attenuated influenza A and B viruses--master donor strains and their based reassortant vaccine strains was studied. After 5 sequential passages in chick embryos (CE) at resolving temperatures of 32 and 37 degrees C, the master donor strains and vaccine viruses retained their adaptability and temperature sensitive phenotype. Passage at the temperatures maximally permissible for viral reproduction (39 and 38 degrees C for influenza A and B viruses, respectively, aborted infection just during the second passage. After a series of passages at all study temperatures), there was neither loss or nor substitution of the marker mutations typical of the cold-adapted and temperature-sensitive phenotype of attenuated viruses. The study supports the high genetic stability of attenuated cold-adapted influenza A and B viruses during CE passage not only at the optimum, but also at elevated incubation temperatures.

Genetic and phenotypic stability of cold-adapted influenza viruses in a trivalent vaccine administered to children in a day care setting

The genetic and phenotypic stability of viruses isolated from young children following intranasal administration of the trivalent live-attenuated influenza virus vaccine (LAIV, marketed in the United States as FluMist) was evaluated by determination of genomic sequence and assessment of the cold-adapted (ca), temperature-sensitive (ts) and attenuated (att) phenotypes. The complete genomic sequence was determined for 56 independent isolates obtained from children following vaccination (21 type A/H1N1, 12 A/H3N2, 1 A/H3N1 and 22 type B viruses), 20% of which had no nucleotide misincorporations compared with administered vaccine. The remaining isolates had from one to seven changes per genome. None of the observed misincorporations resulted in predicted amino acid codon substitutions at sites previously shown to contribute to the ca, ts or att phenotypes, and all vaccine-derived isolates retained ca and ts phenotypes consistent with the observation that none of the vaccine recipients displayed distinctive symptoms. The results indicate that LAIV strains undergo very limited genetic change following replication in vaccine recipients and that those changes did not affect vaccine attenuation.

Genetic mapping of the cold-adapted phenotype of B/Ann Arbor/1/66, the master donor virus for live attenuated influenza vaccines (FluMist)

Cold adapted (ca) B/Ann Arbor/1/66 is the master donor virus for the influenza B (MDV-B) vaccine component of the live attenuated influenza vaccine (FluMist). The six internal genes contributed by MDV-B confer the characteristic cold-adapted (ca), temperature-sensitive (ts) and attenuated (att) phenotypes to the vaccine strains. Previously, it has been determined that the PA and NP segments of MDV-B control the ts phenotype while the att phenotype requires the M segment in addition to PA and NP. Here, we show that the PA, NP and PB2 segments are responsible for the ca phenotype of MDV-B when examined in chicken cell lines. Five loci in three RNA segments, R630 in PB2, M431 in PA and A114, H410 and T509 in NP, are sufficient to allow efficient virus growth at 25 degrees C. Substitution of these five amino acids with wt (wild type) residues completely reverted the MDV-B ca phenotype. Conversely, introduction of these five ca amino acids into B/Yamanashi/166/98 imparted the ca phenotype to this heterologous wt virus. In addition, we also found that the MDV-B M1 gene affected virus replication in chicken cells at 33 and 37 degrees C. Recombinant viruses containing the two MDV-B M1 residues (Q159, V183) replicated less efficiently than those containing wt M1 residues (H159, M183) at 33 and 37 degrees C, implicating the role of the MDV-B M segment to the att phenotype. The complexity of the multigenic signatures controlling the ca, ts and att phenotypes of MDV-B provides the molecular basis for the observed genetic stability of the FluMist vaccines.

Multiple gene segments control the temperature sensitivity and attenuation phenotypes of ca B/Ann Arbor/1/66

Cold-adapted (ca) B/Ann Arbor/1/66 is the influenza B virus strain master donor virus for FluMist, a live, attenuated, influenza virus vaccine licensed in 2003 in the United States. Each FluMist vaccine strain contains six gene segments of the master donor virus; these master donor gene segments control the vaccine's replication and attenuation. These gene segments also express characteristic biological traits in model systems. Unlike most virulent wild-type (wt) influenza B viruses, ca B/Ann Arbor/1/66 is temperature sensitive (ts) at 37 degrees C and attenuated (att) in the ferret model. In order to define the minimal genetic components of these phenotypes, the amino acid sequences of the internal genes of ca B/Ann Arbor/1/66 were aligned to those of other influenza B viruses. These analyses revealed eight unique amino acids in three proteins: two in the polymerase subunit PA, two in the M1 matrix protein, and four in the nucleoprotein (NP). Using reverse genetics, these eight wt amino acids were engineered into a plasmid-derived recombinant of ca B/Ann Arbor/1/66, and these changes reverted both the ts and the att phenotypes. A detailed mutational analysis revealed that a combination of two sites in NP (A114 and H410) and one in PA (M431) controlled expression of ts, whereas these same changes plus two additional residues in M1 (Q159 and V183) controlled the att phenotype. Transferring this genetic signature to the divergent wt B/Yamanashi/166/98 strain conferred both the ts and the att phenotypes on the recombinant, demonstrating that this small, complex, genetic signature encoded the essential elements for these traits.

Comparative study of influenza virus replication in Vero and MDCK cell lines

The choice of a cell line for the production of influenza vaccines is determined by how well the virus is able to replicate and how easily the cell line can be maintained. Madin-Darby canine kidney (MDCK) cells have long been known to successfully support influenza growth. Vero cells are also another well studied candidate cell line. In this work, we have compared these two cell lines for their ability to propagate type A and type B cold-adapted and wild type influenza viruses. The growth of these viruses has been measured as plaque forming units (via plaque assay) as well as viral particle formation (via a novel quantitative RT-PCR assay) to assess the suitability of these cell lines to support the development of live attenuated influenza vaccines. The novel qRT-PCR assay outlined in this work was demonstrated to be an efficient, sensitive and reproducible method for measuring wild type (wt) and cold-adapted (ca) influenza strains. Replicates of six per sample consistently showed an average variation around +/-10%. In this study we have also found qRT-PCR to be a useful method for differentiating between wt and ca influenza strains based on their differing growth characteristics at varying temperatures. This can subsequently be used to assess reassortants prepared from ca donor strains for the purposes of live viral vaccine development. For type A and B influenza viruses studied in this work, MDCK cells supported a more rapid viral growth (measured in terms of genome copies) compared with Vero cells. For the type A viruses studied here, the genome copies: infectious unit (genome copy, gc:infectious unit, iu) ratio was found to be more favorable for Vero cells compared with MDCK cells. For the type B viruses studied in this work, the gc:iu was equivalent in both cell lines tested. Ultimately, however, the use of any new cell line would need to be approved by regulatory agencies prior to its commercial application.

Mutational pattern of influenza B viruses adapted to high growth replication in embryonated eggs

Improved replication of influenza viruses in embryonated chicken eggs (CE) permits increased vaccine production and availability. We investigated the growth properties of influenza B viruses in relation to specific mutations occurring after serial passage in CE. In serial passage experiments yielding high growth variants of B/Victoria/504/2000, mutations predicted to alter amino acid (AA) composition occurred only near the receptor-binding pocket of the hemagglutinins (HA) and in no other genes. Two B/Victoria/504/2000 high growth variants had the same AA substitutions in HA (R162M and D196Y), but the higher yield variant had a third substitution (G141E), which also altered antigenic characteristics. In a serial passage experiment yielding a high growth variant of B/Hong Kong/330/2001, mutations predicted to alter AA composition occurred only in PB2 and NP in domains predicted to relate to RNP formation and function. Our results indicate that adaptation of influenza B viruses to high-yield replication by serial passage in CE requires few mutations either in internal or external genes. Specific modifications of genes or a combination of genes could be used to optimize or create influenza B viruses for specific growth substrates.

Influenza B virus BM2 protein is a crucial component for incorporation of viral ribonucleoprotein complex into virions during virus assembly

Influenza B virus contains four integral membrane proteins in its envelope. Of these, BM2 has recently been found to have ion channel activity and is considered to be a functional counterpart to influenza A virus M2, but the role of BM2 in the life cycle of influenza B virus remains unclear. In an effort to explore its function, a number of BM2 mutant viruses were generated by using a reverse genetics technique. The BM2DeltaATG mutant virus synthesized BM2 at markedly lower levels but exhibited similar growth to wild-type (wt) virus. In contrast, the BM2 knockout virus, which did not produce BM2, did not grow substantially but was able to grow normally when BM2 was supplemented in trans by host cells expressing BM2. These results indicate that BM2 is a required component for the production of infectious viruses. In the one-step growth cycle, the BM2 knockout virus produced progeny viruses lacking viral ribonucleoprotein complex (vRNP). The inhibited incorporation of vRNP was regained by trans-supplementation of BM2. An immunofluorescence study of virus-infected cells revealed that distribution of hemagglutinin, nucleoprotein, and matrix (M1) protein of the BM2 knockout virus at the apical membrane did not differ from that of wt virus, whereas the sucrose gradient flotation assay revealed that the membrane association of M1 was greatly affected in the absence of BM2, resulting in a decrease of vRNP in membrane fractions. These results strongly suggest that BM2 functions to capture the M1-vRNP complex at the virion budding site during virus assembly.

Association of influenza epidemics with global climate variability

The reasons for the seasonality and annual changes in the impact of influenza epidemics remain poorly understood. We investigated the covariations between a major component of climate, namely the El Niño Southern Oscillation (ENSO), and indicators of the impact of influenza, as measured by morbidity, excess mortality and viral subtypes collected in France during the period 1971-2002. We show that both the circulating subtype and the magnitude of ENSO are associated with the impact of influenza epidemics. Recognition of this association could lead to better understanding of the mechanisms of emergence of influenza epidemics.

Antigenic alteration of influenza B virus associated with loss of a glycosylation site due to host-cell adaptation

Effects of host-cell adaptation of the hemagglutinin (HA) protein were evaluated by the analyses of four pairs of recent influenza B field isolates, each pair consisting of an Madin Darby canine kidney (MDCK)- and an embryonated chicken egg-derived isolates from the same clinical specimen. Among the isolates examined, all of the MDCK-derived isolates retained glycosylation site at amino acid 197 on the HA1 molecule, whereas three egg-derived isolates lost it. Antigenic difference in the HA molecule between an MDCK- and an egg-derived isolates of three of these pairs was demonstrated to be associated with the glycosylation 197. Replication of the MDCK-derived isolates was suppressed in eggs, suggesting that the presence of the glycosylation 197 was disadvantageous to replication in eggs. Virus-binding affinity assay revealed that the loss of carbohydrate chain did not significantly alter the preferential recognition of sialic acid linkage. Immunogenicity and vaccine efficacy of an MDCK- and an egg-derived clones of B/Akita/27/2001, the former retained the glycosylation 197 and the latter lost it, were compared in a hamster model. When formalin-inactivated whole virion vaccines prepared from the paired isolates were administered into hamsters, no significant difference between them was observed in protective ability against challenges by the homologous and heterologous clones. Implication of the egg adaptation of influenza virus to antigenic surveillance of the field isolates as well as the selection of vaccine strains, and possibility of the involvement of the viral protein(s) other than the HA in the egg adaptation were discussed.

New estimates of influenza-related pneumonia and influenza hospitalizations among the elderly

OBJECTIVES

The aim of this study is to present a method to provide accurate estimates of influenza-associated pneumonia and influenza (P&I) hospitalizations and costs for use in tracking the continuing burden of influenza.

METHODS

We estimated influenza-associated P&I hospitalizations among the U.S. elderly population for six influenza seasons, 1990-91 through 1995-96, by applying a Poisson regression model to national influenza virus surveillance information and Medicare administrative data. This model is similar to that recently published by the U.S. National Centers for Disease Control and Prevention (CDC) to estimate influenza-related mortality.

RESULTS

During the six years of the study, 318,666 (9.8%) of P&I hospitalizations were estimated to be associated with influenza: range = 25,819 to 70,068 per year; average annual cost = $372.3 million. Influenza A(H3N2) was associated with 73.9% of influenza-related P&I hospitalizations; influenza B with 21.3% and influenza A(H1N1) with 4.8%.

CONCLUSIONS

Our estimates were consistent with the estimates of influenza-associated P&I mortality reported by CDC. Thus, we suggest that estimates of influenza-associated morbidity and costs based on virus surveillance and administrative data may be used for monitoring the impact of influenza and of intervention strategies.

Influenza virological surveillance in children: the use of the QuickVue rapid diagnostic test

New rapid diagnostic methods are needed to identify influenza infections to improve virological surveillance usually undertaken with conventional time-consuming, complex, and even expensive laboratory methods. Another reason for using a rapid test is to avoid inappropriate therapy, particularly in children, where use of antibiotics inappropriately and high influenza-related rates of hospitalisation are described. During two winter seasons, the performance of the QuickVue Influenza test (QV) was evaluated in children under 14 presenting with influenza like illness, and compared the results with those obtained from sentinel network surveillance using standard protocols for the sample collection and the laboratory analysis by virus culture and reverse transcription-polymerase chain reaction (RT-PCR). During the first influenza season (2000/2001), 22 paediatricians collected one nose- and one throat-swab from each of the 586 children 0-6 years old recruited in the study. The QV test was carried out in the physician's office by primary care staff on the nose swab material. When compared with virus culture of the throat swab, the QV test had a sensitivity of 36.5%. In the following 2001/2002-influenza season, the performance of the QV test as a rapid laboratory screening assay was assessed. 342 children aged 0-14 years were enrolled with only one throat swab collected from each patient and sent to the laboratory where the QV, virus culture, and RT-PCR tests were performed. The results showed a better sensitivity (54.5%) of the test in comparison with virus culture and RT-PCR assays. The data indicate that rapid QV testing in the physician office setting, using these easily obtained samples, may be too insensitive to be useful for surveillance and for immediate clinical management of children presenting with influenza-like illness. Nevertheless, the QV test may be a valuable diagnostic tool if used in laboratory, as a rapid screening test.

Evaluation of R-Mix shell vials for the diagnosis of viral respiratory tract infections

Respiratory viruses cause significant morbidity and mortality. The management of these infections can be improved by a rapid diagnosis and administration of available virus-specific therapy. The goal of this study was to compare R-Mix, an engineered tissue monolayer for rapid shell vial (SV) diagnosis of viral respiratory infections, with conventional tissue culture (TC) and conventional respiratory SV (primary rhesus monkey kidney (RhMK) and Hep2 monolayers). The primary outcome measure was sensitivity for detection of influenza A and B, respiratory syncytial virus, parainfluenza 1-3, and adenovirus. The study was performed in two phases: (1) the three methods were compared using 250 nasal washes from children with lower respiratory tract infections; (2) a modified R-Mix SV harvesting schedule (SV were harvested at 24 and 120 h) was compared with TC and conventional RhMK/Hep2 SV using 311 respiratory specimens. A total of 110 viruses were identified in the first and 55 in the second phase. Diagnostic accuracies of R-Mix harvested at 24, 48, and 120 h were 98%, whereas for TC varied between 99 and 100%, and for RhMK/Hep2 SV between 98 and 99%. Sensitivities of R-Mix harvested at 24, 48, and 120 h were 26, 75, and 47%, respectively, whereas for TC varied between 60 and 94%, and for RhMK/Hep2 SV between 62 and 85%. R-Mix harvested at 48 h represent a valuable substitute for RhMK/Hep2 SV because they have comparable sensitivities and diagnostic accuracies, but R-Mix offers several technical advantages. In contrast, R-Mix harvested at 24h did not seem a very useful diagnostic tool. The utility of R-Mix harvested at 120 h, which accelerated the diagnosis of 16% of positive specimens in study phase 2, needs further investigation.

Synthesis, characterization and antiviral activity against influenza virus of a series of novel manganese-substituted rare earth borotungstates heteropolyoxometalates

A series of novel manganese-substituted mixed-valence rare earth borotungsto-heteropoly blues, Ln2H3[BW9(VI)W2(V)Mn(H2O)O39] x 12H2O (Ln(2), Ln = La, Ce, Pr, Nd, Sm, Eu and Gd), as well as their corresponding heteropoly acids (Ln(0)), have been prepared and characterized by cyclic voltammetry (CV), infrared (IR), ultraviolet (UV), thermal gravimetric (TG) and differential thermal (DTA) analysis, X-ray photoelectron spectroscopy (XPS) and electrochemistry. It's shown that the heteropoly blues anion in Ln(2) still retains the alpha-Keggin structure but with a slight distortion as heteropoly acids do, and Mn and W atoms distribute statistically in the whole molecular. At the same time, the cell toxicity and antiviral activity of these rare earth borotungstateheteropoly blues against influenza virus type A and type B in MDCK cells have been investigated using plaque reduction assay. The results elucidated that these complexes exhibit a significantly inhibitory activity and almost no cytotoxicity comparable with those obtained from virazole, and the anti-virus activity depend on the structure of these complexes.

[Relationship between absolute humidity and influenza prevalence in Odate and Akita cities, Akita Prefecture, in 2001 and 2002]

The dynamics of influenza viruses in relation to one meteorological factor, absolute humidity, was investigated. The number of influenza patients, absolute humidity, and isolation of influenza viruses were compared between Odate City the north and Akita City in central Akita Prefecture from 2001 to 2002. The results were as follows: 1) In both Odate and Akita cities, Influenza A (H1N1 and H3N2) and Influenza B (Victoria and Yamagata) viruses were isolated when absolute humidity ranged between 2.7 and 8.8 g/m3. 2) In Akita City in 2002, the influenza viruses were isolated in May (weeks 20 and 22), and the absolute humidity was below 9 g/m3, suggesting that the influenza season lasted until May in this year. 3) A correlation between absolute humidity and isolation of influenza viruses was observed, and the influenza prevalence may occur below 9 g/m3 of absolute humidity. 4) In Odate and Akita cities, the absolute humidity of 10 g/m3, a level at which 5% of influenza viruses can survive after six hours, was observed from January to June and October to December. 5) Influenza prevalence show differential occurrence by time and place. Therefore, further research is required to clarify the absolute humidity related to influenza prevalence.

Influenza B virus requires BM2 protein for replication

The BM2 protein of influenza B virus functions as an ion channel, which is suggested to be important for virus uncoating in endosomes of virus-infected cells. Because direct support for this function is lacking, whether BM2 plays an essential role in the viral life cycle remains unknown. We therefore attempted to generate BM2 knockout viruses by reverse genetics. Mutant viruses possessing M segments with the mutated initiation codon of BM2 protein at the stop-start pentanucleotide were viable and still expressed BM2. The introduction of multiple stop codons and a one-nucleotide deletion downstream of the stop-start pentanucleotide, in addition to disablement of the BM2 initiation codon, failed to generate viable mutant viruses, but the mutant M segments still expressed proteins that reacted with the BM2 peptide antiserum. To completely abolish BM2 expression, we generated a mutant M gene whose BM2 open reading frame was deleted. Although this mutant was not able to replicate in normal MDCK cells, it did replicate in a cell line that we established which constitutively expresses BM2. Furthermore, a virus possessing the mutant M gene lacking the BM2 open reading frame and a mutant NA gene containing the BM2 open reading frame instead of the NA open reading frame underwent multiple cycles of replication in MDCK cells, with exogenous sialidase used to supplement the deleted viral sialidase activity. These findings demonstrate that the BM2 protein is essential for influenza B virus replication.

The influenza B virus nonstructural NS1 protein is essential for efficient viral growth and antagonizes beta interferon induction

We analyzed the functions of the influenza B virus nonstructural NS1-B protein, both by utilizing a constructed mutant virus (Delta NS1-B) lacking the NS1 gene and by testing the activities of the protein when expressed in cells. The mutant virus replicated to intermediate levels in 6-day-old embryonated chicken eggs that contain an immature interferon (IFN) system, whereas older eggs did not support viral propagation to a significant extent. The Delta NS1-B virus was a substantially stronger inducer of beta IFN (IFN-beta) transcripts in human lung epithelial cells than the wild type, and furthermore, transiently expressed NS1-B protein efficiently inhibited virus-dependent activation of the IFN-beta promoter. Interestingly, replication of the Delta NS1-B knockout virus was attenuated by more than 4 orders of magnitude in tissue culture cells containing or lacking functional IFN-alpha/beta genes. These findings show that the NS1-B protein functions as a viral IFN antagonist and indicate a further requirement of this protein for efficient viral replication that is unrelated to blocking IFN effects.

New point of care test is highly specific but less sensitive for influenza virus A and B in children and adults

The importance of rapid diagnosis of influenza has increased with the availability of neuraminidase inhibitors, which need to be commenced within 48 hr of symptom onset. Furthermore, the recent development of influenza-like clinical syndromes with novel aetiologies (severe acute respiratory syndrome, SARS) has increased the need for rapid and accurate near-patient diagnosis. A new, modified point of care (POC) diagnostic test (ZstatFlu) was assessed on 469 nasopharyngeal aspirates (NPAs) and 260 nose/throat swabs (TS) taken from children and adults. The test was specific (77-98%) for all specimen types for influenza virus A and B, depending upon incubation conditions. However, it was less sensitive, detecting 65-77% of specimens confirmed as positive on culture, direct immunofluorescence or PCR testing. A positive test is useful, for both directing initiation of therapy in the clinician's office, and making a positive diagnosis of influenza in patients with influenza-like clinical syndromes.

Genetic and phenotypic analysis of reassortants of high growth and low growth strains of influenza B virus

The yield of influenza virus in eggs is critical to influenza vaccine production and availability, but the contribution of specific genes to the growth properties of influenza B viruses is not well understood. Influenza B/Beijing/184/93 and B/Shangdong/7/97 were chosen for study because B/Shangdong/7/97 replicated to several fold higher titers in eggs than B/Beijing/184/93 as demonstrated by hemagglutination titers and EID50. A reassortant with the HA, NP and PB2 genes from B/Beijing/184/93 and all other genes from B/Shangdong/7/97 had the high growth phenotype of B/Shangdong/7/97 in eggs, which suggests that NS, M, NA, PB1 or PA, or a combination of these genes derived from B/Shangdong/7/97 were needed for the high growth phenotype of the reassortants. A high degree of homology was found among the genetic sequences of B/Beijing/184/93, B/Shangdong/7/97, and other influenza B viruses. However, differences potentially related to growth characteristics were suggested by analysis of the deduced amino acid (AA) sequences of four genes: NS (NS1, NS2), M (BM2), NA (NA, NB) and PB1. The studies identify multiple genes that may affect growth of influenza B viruses in eggs.

Chimeric influenza A viruses with a functional influenza B virus neuraminidase or hemagglutinin

Reassortment of influenza A and B viruses has never been observed in vivo or in vitro. Using reverse genetics techniques, we generated recombinant influenza A/WSN/33 (WSN) viruses carrying the neuraminidase (NA) of influenza B virus. Chimeric viruses expressing the full-length influenza B/Yamagata/16/88 virus NA grew to titers similar to that of wild-type influenza WSN virus. Recombinant viruses in which the cytoplasmic tail or the cytoplasmic tail and the transmembrane domain of the type B NA were replaced with those of the type A NA were impaired in tissue culture. This finding correlates with reduced NA content in virions. We also generated a recombinant influenza A virus expressing a chimeric hemagglutinin (HA) protein in which the ectodomain is derived from type B/Yamagata/16/88 virus HA, whereas both the cytoplasmic and the transmembrane domains are derived from type A/WSN virus HA. This A/B chimeric HA virus did not grow efficiently in MDCK cells. However, after serial passage we obtained a virus population that grew to titers as high as wild-type influenza A virus in MDCK cells. One amino acid change in position 545 (H545Y) was found to be responsible for the enhanced growth characteristics of the passaged virus. Taken together, we show here that the absence of reassortment between influenza viruses belonging to different A and B types is not due to spike glycoprotein incompatibility at the level of the full-length NA or of the HA ectodomain.

Additional inhibitory effect of tea extract on the growth of influenza A and B viruses in MDCK cells

It has been previously reported that green-tea extract (GTE) inhibits the growth of influenza virus by preventing its adsorption. In this study, we further investigated whether GTE exerts an additional inhibitory effect on the acidification of intracellular compartments such as endosomes and lysosomes (referred to as ELS) and thereby inhibits the growth of influenza A and B viruses in Madin-Darby canine kidney cells. The vital fluorescence microscopic study showed that GTE inhibited acidification of ELS in a concentration-dependent manner. Moreover, the growth of influenza A and B viruses was equally inhibited when the cells were treated with GTE within as early as 5 to 15 min after infection, depending on the virus strains. The fact that (-)epigallocatechin (EGC), one of major catechin molecules in GTE, exerts the inhibitory effects on the acidification of ELS and virus growth in a manner similar to that of GTE strongly suggests that EGC is one of the active components in the extract.

Cryopreserved cell monolayers for rapid detection of herpes simplex virus and influenza virus

Cryopreserved cell monolayers are a new cell culture technology intended to ensure the availability of cells in the laboratory for virus detection. Two cryopreserved cell monolayers, ELVIS for the detection of herpes simplex virus (HSV) and R-Mix for the detection of influenza virus, were evaluated. The results indicated that fresh and cryopreserved cell monolayers are comparable in sensitivity for the detection of HSV and influenza virus. The cells retain the same level of sensitivity for up to 4 months at -80 degrees C.

Rescue of influenza B virus from eight plasmids

Influenza B virus causes a significant amount of morbidity and mortality, yet the systems to produce high yield inactivated vaccines for these viruses have lagged behind the development of those for influenza A virus. We have established a plasmid-only reverse genetics system for the generation of recombinant influenza B virus that facilitates the generation of vaccine viruses without the need for time consuming coinfection and selection procedures currently required to produce reassortants. We cloned the eight viral cDNAs of influenza B/Yamanashi/166/98, which yields relatively high titers in embryonated chicken eggs, between RNA polymerase I and RNA polymerase II transcription units. Virus was detected as early as 3 days after transfection of cocultured COS7 and Madin-Darby canine kidney cells and achieved levels of 10(6)-10(7) plaque-forming units per ml of cell supernatant 6 days after transfection. The full-length sequence of the recombinant virus after passage into embryonated chicken eggs was identical to that of the input plasmids. To improve the utility of the eight-plasmid system for generating 6 + 2 reassortants from recently circulating influenza B strains, we optimized the reverse transcriptase-PCR for cloning of the hemagglutinin (HA) and neuraminidase (NA) segments. The six internal genes of B/Yamanashi/166/98 were used as the backbone to generate 6 + 2 reassortants including the HA and NA gene segments from B/Victoria/504/2000, B/Hong Kong/330/2001, and B/Hawaii/10/2001. Our results demonstrate that the eight-plasmid system can be used for the generation of high yields of influenza B virus vaccines expressing current HA and NA glycoproteins from either of the two lineages of influenza B virus.

R-Mix cells are faster, at least as sensitive and marginally more costly than conventional cell lines for the detection of respiratory viruses

OBJECTIVE

To evaluate shell vials of R-Mix, a combination of mink lung cells and human adenocarcinoma cells (strains Mv1Lu and A549, respectively, Diagnostic Hybrids, Athens, OH) to detect respiratory viruses from prospective clinical respiratory specimens and frozen stocks.

STUDY DESIGN

We compared the performance of R-Mix to conventional culture (CC) using tubes of PMK, Hep-2, and MRC5 to detect respiratory viruses from fresh clinical specimens. For each respiratory specimen submitted to virology, two shell vials of R-Mix were inoculated and examined twice (generally after 24 and 48 h) by an indirect test with a pool of immunofluorescent antisera to influenza A and B, adenovirus, parainfluenza 1-3 and RSV (DAKO, Carpinteria, CA). If positive, testing with monoclonal antisera was done. CCs were incubated for 10 days, examined daily for cytopathological effect, hemadsorbed twice and stained if positive. Cost comparison was done. Lastly, respiratory viruses frozen from previous years were inoculated onto R-Mix.

RESULTS

R-Mix was positive for all 29 frozen virus stocks. In the clinical trial, 396 prospective specimens were inoculated into R-Mix and CC. R-Mix identified 21 specimens as respiratory virus positive; CC identified 19. Turn-around time of R-Mix for positive specimens was 1.4 days; for CC it was 5.2 days. Turn-around time of R-Mix for all specimens (positive and negative) was 2.0 days; for CC it was 9.8 days. The overall cost of R-Mix was approximately 11% more than that of CC.

CONCLUSION

R-Mix enabled rapid identification of all the frozen virus stocks representing the seven major respiratory viral groups. When compared to CC, R-Mix was slightly more sensitive than three cell lines (four tubes) used in CC but it was several days faster.

[Development of a novel influenza vaccine derived from a continuous cell line]

Influenza viruses for production are presently produced in embryonated hen"s eggs. This conventional standard methodology is extremely cumbersome; it requires millions of eggs and an extensive purification to reduce the amount of contaminating egg proteins and to minimise the risk of allergies against egg albumin. The shortage of eggs in a pandemic situation, the selection of egg-adapted variants and the presence of adventitious viruses has emphasised the necessity for production of Influenza vaccines on a well characterised stable cell line. Our established serum and protein free Vero cell technology has been successfully adapted to large scale production of a huge variety of Influenza virus strains. The production in 1200 liter fermenter cultures under serum free conditions gave antigen yields comparable to the conventional embryonated egg technology. The development of a rapid and efficient purification scheme resulted in a safe high purity vaccine which was at least as immunogenic as conventional egg-derived vaccines in a mouse model. Clinical trials in the UK, Poland and Austria demonstrated that the Vero cell derived influenza vaccine is well tolerated, safe and highly immunogenic in humans.

In vitro selection and characterisation of influenza B/Beijing/1/87 isolates with altered susceptibility to zanamivir

We describe the in vitro selection and characterisation of virus derived from B/Beijing/1/87 passaged in the presence of zanamivir. During zanamivir passage, the phenotype of virus isolates was either drug dependent or drug resistant in plaque reduction assays. The susceptibility of the neuraminidase of the drug-dependent isolates was unchanged from that of the wild-type enzyme. The drug-dependent isolates contained two mutations in the viral haemagglutinin: V90A, close to the proposed secondary sialic acid-binding site, and L240Q, close to the primary sialic acid-binding site. Virus isolates that were drug resistant contained the same mutations in the haemagglutinin but also contained the mutation E116G in the neuraminidase. For the drug-dependent viruses, zanamivir susceptibility could not be measured because plaque numbers increased with increasing drug concentration. The in vitro zanamivir susceptibility of drug-resistant viruses was lower than that of the wild-type virus by a factor of 275- to >2532-fold. Neuraminidase containing the E116G mutation has a 33-fold lower affinity for zanamivir than the wild-type enzyme. The finding that the same haemagglutinin mutations are found in both drug-dependent and drug-resistant viruses confirms that the same changes to the receptor binding function can contribute to both phenotypes. This observation demonstrates the interplay between the influenza virus haemagglutinin and neuraminidase in escape from zanamivir inhibition in vitro.

The development of live attenuated cold-adapted influenza virus vaccine for humans

A procedure to attenuate live influenza virus of type A and type B was developed using adaptation of the virus to grow at 25 degrees C (cold adaptation; ca). Through a series of stepwise passages, two stable mutants were obtained and designated as 'Master' strains, one for type A influenza virus (A/Ann Arbor/6/60-H2N2) and one for type B influenza virus (B/Ann Arbor/1/66). These mutants were used in genetic reassortment using either the classical method or more recently described reverse genetics to update the relevant surface antigens of the circulating strains of influenza virus. The derivation is based on the concept of 6/2 where 6 signifies the six internal genes of the master strain and 2 refers to the two genes coding for the two surface glycoproteins HA and NA of the circulating influenza virus. The advantages of this vaccine were demonstrated to be (1) proper level of attenuation, (2) non-transmissibility, (3) genetic stability, (4) presence of the ca and ts markers and (5) immunogenicity involving both local and the cell-mediated immune responses. The clinical trials in infants, children, adults and elderly have provided the necessary data for eventual licensing of this vaccine. The ease of administration (intranasal) safety and high efficacy make this vaccine suitable to prevent influenza virus infection in all age groups.

Influvac: a safe Madin Darby Canine Kidney (MDCK) cell culture-based influenza vaccine

Influenza vaccine production technology based on large scale cell culture technology has been developed. From the characterization of the continuous cell line MDCK as well as drug safety studies we conclude that this cell line and the cell culture system are suitable for biological production. The Down Stream Process (DSP) of the virus-containing harvest fluids guarantees sufficient inactivation of influenza viruses and adequate removal or inactivation of putative adventitious or endogenous viruses, mycoplasma or bacteria. Our data indicate that the tissue culture-based production technology is feasible.

A novel mammalian cell (Vero) derived influenza virus vaccine: development, characterization and industrial scale production

Influenza virus for vaccine production are presently produced in embryonated chicken eggs. This conventional standard methodology is extremely cumbersome; it requires a huge amount of eggs and an extensive purification to reduce the amount of contaminating egg proteins and to minimize the risk of allergies against egg albumin. The shortage of eggs in a pandemic situation, the selection of egg-adapted variants and the presence of adventitious viruses has emphasized the necessity for production of influenza vaccines on a well characterized stable cell line. Our established Vero cell technology has been successfully adapted to large scale production of a variety of influenza virus strains. The production in 1200 litre fermenter cultures under serum-free conditions gave antigen yields comparable to the conventional embryonated egg technology. The development of a rapid and efficient purification scheme resulted in a safe high purity vaccine which was at least as immunogenic as conventional egg-derived vaccines in a mouse model. This vaccine has been shown to be safe and highly immunogenic in chimpanzees and to be capable of protecting ferrets against challenge with live virus. Clinical trials have now been initiated in the UK and Austria.