Type I interferon signaling regulates Ly6C(hi) monocytes and neutrophils during acute viral pneumonia in mice

Type I interferon (IFN-I) plays a critical role in the homeostasis of hematopoietic stem cells and influences neutrophil influx to the site of inflammation. IFN-I receptor knockout (Ifnar1^−/−) mice develop significant defects in the infiltration of Ly6C^hi monocytes in the lung after influenza infection (A/PR/8/34, H1N1). Ly6C^hi monocytes of wild-type (WT) mice are the main producers of MCP-1 while the alternatively generated Ly6C^int monocytes of Ifnar1^−/− mice mainly produce KC for neutrophil influx. As a consequence, Ifnar1^−/− mice recruit more neutrophils after influenza infection than do WT mice. Treatment of IFNAR1 blocking antibody on the WT bone marrow (BM) cells in vitro failed to differentiate into Ly6C^hi monocytes. By using BM chimeric mice (WT BM into Ifnar1^−/− and vice versa), we confirmed that IFN-I signaling in hematopoietic cells is required for the generation of Ly6C^hi monocytes. Of note, WT BM reconstituted Ifnar1^−/− chimeric mice with increased numbers of Ly6C^hi monocytes survived longer than influenza-infected Ifnar1^−/− mice. In contrast, WT mice that received Ifnar1^−/− BM cells with alternative Ly6C^int monocytes and increased numbers of neutrophils exhibited higher mortality rates than WT mice given WT BM cells. Collectively, these data suggest that IFN-I contributes to resistance of influenza infection by control of monocytes and neutrophils in the lung.

Type I interferon (IFN-I) was originally reported as a molecule that interferes with influenza virus replication. Various IFN-I inducible antiviral proteins contribute to dampening virus replication and dissemination. Thus, loss of IFN-I signaling attenuates antiviral response and aggravates disease. Recent studies suggest the possible role of IFN-I in hematopoiesis, which subsequently might have an effect on the immune cell response at the site of infection. Indeed, IFN-I signaling-defective mice have been shown to develop aberrant cell populations. The aim of this current study was to clarify the mechanisms of IFN-I signaling in the regulation of monocytes and neutrophils. We show that IFN-I is directly involved in monocyte differentiation and that loss of IFN-I signaling allows mice to generate monocytes whose gene profile is significantly different. We found that monocytes are an important source of chemokines for further monocyte recruitment, but IFN-I-defective monocytes produce chemokines for neutrophil recruitment. As a result, mice lacking IFN-I signaling recruit more neutrophils and a reduced number of alternatively generated monocytes. Thus, our findings indicate that authentic monocyte differentiation, which requires IFN-I signaling, is critical in controlling neutrophils and protecting mice against influenza virus infection.

Escherichia coli formylmethionine tRNA: mutations in GGGCCC sequence conserved in anticodon stem of initiator tRNAs affect initiation of protein synthesis and conformation of anticodon loop

We have generated mutants of Escherichia coli formylmethionine initiator tRNA in which one, two, and all three G X C base pairs in the GGGCCC sequence in the anticodon stem are changed to those found in E. coli elongator methionine tRNA. Overproduction of the mutant tRNAs using M13 recombinants as an expression vector and development of a one-step purification scheme allowed us to purify, characterize, and analyze the function of the mutant tRNAs. After aminoacylation and formylation, the function of mutant formylmethionyl tRNAs was analyzed in an MS2 RNA-directed in vitro protein-synthesizing system, in AUG-dependent ribosomal P site binding, and in initiation factor binding. The mutant tRNAs show progressive loss of activity in initiation, the mutant with all three G X C base pairs substituted being the least active. The mutations affect binding to the ribosomal P site. None of the mutations affects binding to initiation factor 2. We also show that there is a progressive increase in accessibility of phosphodiester bonds in the anticodon loop of the three mutants to S1 nuclease, such that the cleavage pattern of the mutant with all three G X C base-pair changes resembles that of elongator tRNAs. These results are consistent with the notion that the contiguous G X C base pairs in the anticodon stem of initiator tRNAs impart on the anticodon loop a unique conformation, which may be important in targeting the initiator tRNA to the ribosomal P site during initiation of protein synthesis.

A new method for reconstituting influenza polymerase and RNA in vitro: a study of the promoter elements for cRNA and vRNA synthesis in vitro and viral rescue in vivo

The influenza RNA polymerase is known to catalyse three distinct copying activities: (i) transcription of minus-sense virion RNA (vRNA) into mRNA, (ii) transcription of vRNA into full-length complementary RNA (cRNA), and (iii) transcription of cRNA to vRNA. Ever since the discovery of the conserved 13 and 12 long sequences at each end of all the influenza RNA segments, these have been good candidates for promoters of transcription. By devising a new, simple method for preparing influenza polymerase complex capable of transcribing in vitro added short model RNA templates without interference from endogenous viral RNA, we have now tested the promoter hypothesis. We conclude that the 13 long and the 12 long 3' conserved sequences of cRNA and vRNA of influenza A virus are by themselves sufficient to promote vRNA and cRNA synthesis in vitro. Using our new method, we also show that chloramphenicol acetyl transferase (CAT) activity can be detected in MDBK (bovine kidney) cells, after transfection of influenza polymerase assembled with a negatively stranded CAT RNA, even in the absence of helper virus. As in a previously described method (Luytjes et al., 1989), CAT activity is amplified by helper virus and can be rescued in infectious recombinant virus.

Photochemical cross-linking of influenza A polymerase to its virion RNA promoter defines a polymerase binding site at residues 9 to 12 of the promoter

A previous study of the 12 nucleotide-long influenza A virion RNA promoter has shown that three nucleotides, residues 9 to 11, were crucial for transcription in vitro, although other nucleotides play a significant but less important role. A model for polymerase-promoter recognition was proposed, according to which there were two sites: a binding site at residues 9 to 11 and a regulatory site at or near the site of initiation at residue 1. By studying the effect of point mutations in the promoter on the binding efficiency of the polymerase using a photochemical cross-linking assay, we now show that residues 9 to 12 are crucial for binding. In addition residues 4 to 8, though not as important, are involved in binding, possibly by stabilizing the polymerase-promoter complex. Both PB1 and PB2 apparently play an important role during virion RNA promoter recognition and binding.

Prophylactic and therapeutic efficacy of avian antibodies against influenza virus H5N1 and H1N1 in mice

BACKGROUND

Pandemic influenza poses a serious threat to global health and the world economy. While vaccines are currently under development, passive immunization could offer an alternative strategy to prevent and treat influenza virus infection. Attempts to develop monoclonal antibodies (mAbs) have been made. However, passive immunization based on mAbs may require a cocktail of mAbs with broader specificity in order to provide full protection since mAbs are generally specific for single epitopes. Chicken immunoglobulins (IgY) found in egg yolk have been used mainly for treatment of infectious diseases of the gastrointestinal tract. Because the recent epidemic of highly pathogenic avian influenza virus (HPAIV) strain H5N1 has resulted in serious economic losses to the poultry industry, many countries including Vietnam have introduced mass vaccination of poultry with H5N1 virus vaccines. We reasoned that IgY from consumable eggs available in supermarkets in Vietnam could provide protection against infections with HPAIV H5N1.

METHODS AND FINDINGS

We found that H5N1-specific IgY that are prepared from eggs available in supermarkets in Vietnam by a rapid and simple water dilution method cross-protect against infections with HPAIV H5N1 and related H5N2 strains in mice. When administered intranasally before or after lethal infection, the IgY prevent the infection or significantly reduce viral replication resulting in complete recovery from the disease, respectively. We further generated H1N1 virus-specific IgY by immunization of hens with inactivated H1N1 A/PR/8/34 as a model virus for the current pandemic H1N1/09 and found that such H1N1-specific IgY protect mice from lethal influenza virus infection.

CONCLUSIONS

The findings suggest that readily available H5N1-specific IgY offer an enormous source of valuable biological material to combat a potential H5N1 pandemic. In addition, our study provides a proof-of-concept for the approach using virus-specific IgY as affordable, safe, and effective alternative for the control of influenza outbreaks, including the current H1N1 pandemic.

Mutants of Escherichia coli formylmethionine tRNA: a single base change enables initiator tRNA to act as an elongator in vitro

We show that the absence of a Watson-Crick base pair at the end of the amino acid acceptor stem, which is a hallmark of all prokaryotic initiator tRNAs, is one of the key features that prevents them from acting as an elongator in protein synthesis. We generated mutants of Escherichia coli formylmethionine tRNA that have a base pair at the end of the acceptor stem. The mutants generated were C1----T1, which had a U.A base pair, A72----G72, which had a C.G base pair, and the C1A72----T1G72 double mutant, which lacked the base pair. After aminoacylation, the activity of these and other mutant initiator methionyl-tRNAs (Met-tRNAs) in elongation were assayed in a MS2 RNA-directed E. coli protein-synthesizing system and in binding to the elongation factor Tu (EF-Tu). Unlike wild-type initiator tRNA or the T1G72 double mutant, the T1 and G72 mutant Met-tRNAs were active in elongation, the G72 mutant being more active than the T1 mutant. The T1 and G72 mutant Met-tRNAs also formed a ternary complex with elongation factor EF-Tu.GTP, and their relative affinities for EF-Tu.GTP paralleled their activities in elongation. Combination of the T1 or G72 mutation with mutations in the GGG.CCC sequence conserved in the anticodon stem of initiator tRNAs led to a further increase in the activities of these mutant tRNAs in elongation such that one of these mutants was now almost as good an elongator as E. coli elongator methionine tRNA.

Recombinant enterokinase light chain with affinity tag: expression from Saccharomyces cerevisiae and its utilities in fusion protein technology

Enterokinase and recombinant enterokinase light chain (rEK(L)) have been used widely to cleave fusion proteins with the target sequence of (Asp)(4)-Lys. In this work, we show that their utility as a site-specific cleavage agent is compromised by sporadic cleavage at other sites, albeit at low levels. Further degradation of the fusion protein in cleavage reaction is due to an intrinsic broad specificity of the enzyme rather than to the presence of contaminating proteases. To offer facilitated purification from fermentation broth and efficient removal of rEK(L) after cleavage reaction, thus minimizing unwanted cleavage of target protein, histidine affinity tag was introduced into rEK(L). Utilizing the secretion enhancer peptide derived from the human interleukin 1 beta, the recombinant EK(L) was expressed in Saccharomyces cerevisiae and efficiently secreted into culture medium. The C-terminal His-tagged EK(L) was purified in a single-step procedure on nickel affinity chromatography. It retained full enzymatic activity similar to that of EK(L), whereas the N-terminal His-tagged EK(L) was neither efficiently purified nor had any enzymatic activity. After cleavage reaction of fusion protein, the C-terminal His-tagged EK(L) was efficiently removed from the reaction mixture by a single passage through nickel-NTA spin column. The simple affinity tag renders rEK(L) extremely useful for purification, post-cleavage removal, recovery, and recycling and will broaden the utility and the versatility of the enterokinase for the production of recombinant proteins.

Solubility, Stability, and Avidity of Recombinant Antibody Fragments Expressed in Microorganisms

Solubility of recombinant proteins (i.e., the extent of soluble versus insoluble expression in heterogeneous hosts) is the first checkpoint criterion for determining recombinant protein quality. However, even soluble proteins often fail to represent functional activity because of the involvement of non-functional, misfolded, soluble aggregates, which compromise recombinant protein quality. Therefore, screening of solubility and folding competence is crucial for improving the quality of recombinant proteins, especially for therapeutic applications. The issue is often highlighted especially in bacterial recombinant hosts, since bacterial cytoplasm does not provide an optimal environment for the folding of target proteins of mammalian origin. Antibody fragments, such as single-chain variable fragment (scFv), single-chain antibody (scAb), and fragment antigen binding (Fab), have been utilized for numerous applications such as diagnostics, research reagents, or therapeutics. Antibody fragments can be efficiently expressed in microorganisms so that they offer several advantages for diagnostic applications such as low cost and high yield. However, scFv and scAb fragments have generally lower stability to thermal stress than full-length antibodies, necessitating a judicious combination of designer antibodies, and bacterial hosts harnessed with robust chaperone function. In this review, we discuss efforts on not only the production of antibodies or antibody fragments in microorganisms but also scFv stabilization via (i) directed evolution of variants with increased stability using display systems, (ii) stabilization of the interface between variable regions of heavy (V_H) and light (V_L) chains through the introduction of a non-native covalent bond between the two chains, (iii) rational engineering of V_H-V_L pair, based on the structure, and (iv) computational approaches. We also review recent advances in stability design, increase in avidity by multimerization, and maintaining the functional competence of chimeric proteins prompted by various types of chaperones.

Mutational analysis of the RNA-fork model of the influenza A virus vRNA promoter in vivo

The genome of influenza A virus consists of eight negative-stranded RNA segments which have partially complementary non-coding terminal sequences. Previous transcription studies of the virion RNA promoter in vitro have shown that the 5' terminus forms an integral part of the promoter and an 'RNA-fork' model has been proposed for the initiation of transcription. According to this model part of the promoter is formed by an RNA-duplex which involves complementary residues 10 to 1 2 of the 3' end and residues 11' to 13' of the 5' end. With a reverse genetics system, based on the chloramphenicol acetyltransferase (CAT) gene, we have now tested this part of the promoter in vivo. Single mutations of the conserved residues at positions 11 and 12 of the 3' terminus and at positions 12' and 13' of the 5' terminus abolished promoter activity. The introduction of complementary mutations into both termini partially restored activity. On the other hand, mutations at positions 10 of the 3' terminus and 11' of the 5' terminus inhibited activity independently of whether a base-pair was formed or not. Thus, at these positions, the nature of the residues is apparently more important than their ability to form base-pairs. These results extend our previous virion 'RNA-fork' model and are consistent with in vitro findings that the 5' terminus is involved in the initiation of transcription.

Biological evaluation of anti-influenza viral activity of semi-synthetic catechin derivatives

Catechin derivatives with different alkyl chain length and aromatic ring substitutions at the 3-hydroxyl group were synthesized from epigallocatechin (EGC) and (+)-catechin (C) and their anti-influenza viral activity were evaluated in vitro and in ovo. Pronounced antiviral activity was observed for derivatives carrying moderate chain length (7-9 carbons) as compared to those with aromatic rings, whereas the 5'-hydroxyl group of the trihydroxy benzyl moiety did not significantly contribute to antiviral activity. The derivatives exerted inhibitory effects for all six influenza subtypes tested including three major types of currently circulating human influenza viruses (A/H1N1, A/H3N2 and B type), H2N2 and H9N2 avian influenza virus. The compounds strongly inhibited adsorption of the viruses on red blood cell (RBC). They also restricted the growth of avian influenza virus in ovo with minimum inhibition concentration (MIC) of 5-10 microM far exceeding the neuraminidase (NA) inhibitor oseltamivir or M2 proton channel inhibitor amantadine. The antiviral activity appears to be mediated by interaction with hemagglutinin (HA)/viral membrane rendering HA less fusogenic at the initial stage of infection. The broad spectrum activity against various subtypes of influenza viruses may complement the limitations of current antivirals and contribute for managing potentially emerging influenza pandemic. The structure-activity data of catechin derivatives may usefully guideline future research endeavors for applying green tea catechins as alternative anti-viral agents.

IL-6 induces long-term protective immunity against a lethal challenge of influenza virus

The coadministration of cytokines can modulate immunity in DNA based viral vaccines. In order to determine the effects of various cytokines on long-term protection against the influenza virus, mice were intramuscularly coinoculated with plasmids that encoded either the granulocyte-macrophage colony-stimulating factor (GMCSF), interleukin-4 (IL-4), interleukin-12 (IL-12), or the interleukin-6 (IL-6) gene, in the presence of two plasmids that encoded the nucleoprotein (NP) and the hemagglutinin (HA) gene of the influenza A virus. The coadministration of IL-4, IL-6 and IL-12 transiently enhanced antibody responses against influenza virus in early time points (4 to 7 week post immunization) after post inoculation. The expression of GMCSF gene resulted in the sustained elevation of antibody responses for at least 20 weeks post inoculation. However, NP-specific CTL responses decreased in these animals. Mice that received either the IL-12 or the IL-6 gene had enhanced NP-specific CTL responses. Remarkably, the coadministration of the IL-6 gene completely protected mice from a lethal challenge with influenza virus. Conversely, mice that received the IL-4 gene appeared to be more susceptible to lethal challenge than mice that were inoculated with the NP and the HA genes alone. These results demonstrate that the use of cytokines as molecular adjuvants when coadministered in influenza DNA vaccination must be specific. Our data also demonstrates that the coadministration of IL-6 should be considered to enhance the efficacy of influenza DNA vaccines.

Exploiting virus-like particles as innovative vaccines against emerging viral infections

Emerging viruses pose a major threat to humans and livestock with global public health and economic burdens. Vaccination remains an effective tool to reduce this threat, and yet, the conventional cell culture often fails to produce sufficient vaccine dose. As an alternative to cell-culture based vaccine, virus-like particles (VLPs) are considered as a highpriority vaccine strategy against emerging viruses. VLPs represent highly ordered repetitive structures via macromolecular assemblies of viral proteins. The particulate nature allows efficient uptake into antigen presenting cells stimulating both innate and adaptive immune responses towards enhanced vaccine efficacy. Increasing research activity and translation opportunity necessitate the advances in the design of VLPs and new bioprocessing modalities for efficient and cost-effective production. Herein, we describe major achievements and challenges in this endeavor, with respect to designing strategies to harnessing the immunogenic potential, production platforms, downstream processes, and some exemplary cases in developing VLP-based vaccines.

The Quest for a Truly Universal Influenza Vaccine

There is an unmet public health need for a universal influenza vaccine (UIV) to provide broad and durable protection from influenza virus infections. The identification of broadly protective antibodies and cross-reactive T cells directed to influenza viral targets present a promising prospect for the development of a UIV. Multiple targets for cross-protection have been identified in the stalk and head of hemagglutinin (HA) to develop a UIV. Recently, neuraminidase (NA) has received significant attention as a critical component for increasing the breadth of protection. The HA stalk-based approaches have shown promising results of broader protection in animal studies, and their feasibility in humans are being evaluated in clinical trials. Mucosal immune responses and cross-reactive T cell immunity across influenza A and B viruses intrinsic to live attenuated influenza vaccine (LAIV) have emerged as essential features to be incorporated into a UIV. Complementing the weakness of the stand-alone approaches, prime-boost vaccination combining HA stalk, and LAIV is under clinical evaluation, with the aim to increase the efficacy and broaden the spectrum of protection. Preexisting immunity in humans established by prior exposure to influenza viruses may affect the hierarchy and magnitude of immune responses elicited by an influenza vaccine, limiting the interpretation of preclinical data based on naive animals, necessitating human challenge studies. A consensus is yet to be achieved on the spectrum of protection, efficacy, target population, and duration of protection to define a “universal” vaccine. This review discusses the recent advancements in the development of UIVs, rationales behind cross-protection and vaccine designs, and challenges faced in obtaining balanced protection potency, a wide spectrum of protection, and safety relevant to UIVs.

Tea catechins as a potential alternative anti-infectious agent

Besides well-known health benefits, green tea catechins exert antimicrobial and antiviral activities against a variety of infectious agents. Although the detailed mechanism of the antimicrobial activity of tea catechins remains to be explored, the broad-spectrum activity of catechins may involve common target(s), such as the cell membrane, in addition to specific targets for each pathogen. This extends to antiviral activities, where many pronounced activities were reported for enveloped viruses. Yet, the effectiveness of tea catechins as antimicrobials is compromised by relative chemical instability and poor bioavailability. Whether tea catechins will emerge as a viable option as alternative medicine or as a synergistic combination therapy with pre-existing antivirals or antibiotics must therefore depend on a method of delivery that ensures its stability and bioavailability. However, green tea may provide an option for mitigating the health and economic burdens associated with emerging and re-emerging infectious diseases, especially considering the paucity of effective control measures. Considering the zoonotic nature of newly arising infectious diseases, the dual use of green tea components in both humans and livestock may reduce animal-human transmission, which would complement the current management of infectious diseases.

Options and obstacles for designing a universal influenza vaccine

Since the discovery of antibodies specific to a highly conserved stalk region of the influenza virus hemagglutinin (HA), eliciting such antibodies has been considered the key to developing a universal influenza vaccine that confers broad-spectrum protection against various influenza subtypes. To achieve this goal, a prime/boost immunization strategy has been heralded to redirect host immune responses from the variable globular head domain to the conserved stalk domain of HA. While this approach has been successful in eliciting cross-reactive antibodies against the HA stalk domain, protective efficacy remains relatively poor due to the low immunogenicity of the domain, and the cross-reactivity was only within the same group, rather than among different groups. Additionally, concerns are raised on the possibility of vaccine-associated enhancement of viral infection and whether multiple boost immunization protocols would be considered practical from a clinical standpoint. Live attenuated vaccine hitherto remains unexplored, but is expected to serve as an alternative approach, considering its superior cross-reactivity. This review summarizes recent advancements in the HA stalk-based universal influenza vaccines, discusses the pros and cons of these approaches with respect to the potentially beneficial and harmful effects of neutralizing and non-neutralizing antibodies, and suggests future guidelines towards the design of a truly protective universal influenza vaccine.

Nucleotides 9 to 11 of the influenza A virion RNA promoter are crucial for activity in vitro

The 12 nucleotide conserved sequence at the 3' end of influenza A virion RNA is sufficient to function as a promoter in vitro. By introducing point mutations in all 12 positions of this promoter in model RNA templates and studying the efficiency of RNA synthesis in vitro, we show that only three nucleotides, residues 9, 10 and 11, are crucial for activity, although other nucleotides play a significant but less important role. Additions or deletions within the promoter are tolerated, resulting in either an increase or a decrease in promoter activity, depending on the mutation introduced; in some cases premature termination is caused. Taking these observations into account, a model for RNA polymerase binding and copying of the promoter is discussed.

In vitro transcription and polymerase binding studies of the termini of influenza A virus cRNA: evidence for a cRNA panhandle

An in vitro transcription assay was used to study transcription from synthetic RNA corresponding to the 3' terminus of influenza A virus cRNA. Micrococcal nuclease-treated influenza virus ribonucleoprotein was used as a source of active polymerase complex. Mutations at two regions of the 13 nucleotide-long conserved cRNA 3' terminus were shown to reduce transcription templated by the short added model RNAs. The first region, at positions 1 and 2 from the 3' terminus, was shown to be affected by the exact nature of the dinucleotide primer used in the in vitro transcription reactions and may not be relevant in vivo. The second region, centred on positions 11 and 12, may be involved in base pairing with conserved nucleotides at the 5' terminus of the cRNA. Evidence for this comes from the finding that RNA corresponding to 5' conserved sequences, but mutated to restore the postulated base pairing with the mutated 3' ends, could partly restore transcription. Binding of the influenza virus polymerase complex to a set of 5'-mutated RNAs was investigated using a photochemical cross-linking assay. Specific binding to two regions of the cRNA 5' terminus was demonstrated, at positions 1 to 3 and positions 8 to 10. Together, these observations suggest that a panhandle forms from the termini of the cRNA molecule and that this structure may play a role in transcription to produce virion RNA.

Anti-influenza virus activity of green tea by-products in vitro and efficacy against influenza virus infection in chickens

Polyphenolic compounds present in green tea, particularly catechins, are known to have strong anti-influenza activity. The goal of this study was to determine whether green tea by-products could function as an alternative to common antivirals in animals compared to original green tea. Inhibition of viral cytopathic effects ascertained by neutral red dye uptake was examined with 50% effective (virus-inhibitory) concentrations (EC₅₀)determined. Against the H1N1 virus A/NWS/33, we found the anti-influenza activity of green tea by-products (EC₅₀ = 6.36 µg/mL) to be equivalent to that of original green tea (EC₅₀= 6.72 µg/mL). The anti-influenza activity of green tea by-products was further examined in mouse and chicken influenza infection models. In mice, oral administration of green tea by-products reduced viral titers in the lungs in the early phase of infection, but they could not protect these animals from disease and death. In contrast, therapeutic administration of green tea by-products via feed or water supplement resulted in a dose-dependent significant antiviral effect in chickens, with a dose of 10 g/kg of feed being the most effective (P < 0.001). We also demonstrated that unidentified hexane-soluble fractions of green tea by-products possessed strong anti-influenza activity, in addition to ethyl acetate-soluble fractions, including catechins. This study revealed green tea by-product extracts to be a promising novel antiviral resource for animals.

Mucosal immunity induced by adenovirus-based H5N1 HPAI vaccine confers protection against a lethal H5N2 avian influenza virus challenge

Development of effective vaccines against highly pathogenic avian influenza (HPAI) H5N1 viruses is a global public health priority. Considering the difficulty in predicting HPAI H5N1 pandemic strains, one strategy used in their design includes the development of formulations with the capacity of eliciting broad cross-protective immunity against multiple viral antigens. To this end we constructed a replication-defective recombinant adenovirus-based avian influenza virus vaccine (rAdv-AI) expressing the codon-optimized M2eX-HA-hCD40L and the M1-M2 fusion genes from HPAI H5N1 human isolate. Although there were no significant differences in the systemic immune responses observed between the intramuscular prime-intramuscular boost regimen (IM/IM) and the intranasal prime-intramuscular boost regimen (IN/IM), IN/IM induced more potent CD8(+) T cell and antibody responses at mucosal sites than the IM/IM vaccination, resulting in more effective protection against lethal H5N2 avian influenza (AI) virus challenge. These findings suggest that the strategies used to induce multi-antigen-targeted mucosal immunity, such as IN/IM delivery of rAdv-AI, may be a promising approach for developing broad protective vaccines that may be more effective against the new HPAI pandemic strains.

Virucidal nano-perforator of viral membrane trapping viral RNAs in the endosome

Membrane-disrupting agents that selectively target virus versus host membranes could potentially inhibit a broad-spectrum of enveloped viruses, but currently such antivirals are lacking. Here, we develop a nanodisc incorporated with a decoy virus receptor that inhibits virus infection. Mechanistically, nanodiscs carrying the viral receptor sialic acid bind to influenza virions and are co-endocytosed into host cells. At low pH in the endosome, the nanodiscs rupture the viral envelope, trapping viral RNAs inside the endolysosome for enzymatic decomposition. In contrast, liposomes containing a decoy receptor show weak antiviral activity due to the lack of membrane disruption. The nanodiscs inhibit influenza virus infection and reduce morbidity and mortality in a mouse model. Our results suggest a new class of antivirals applicable to other enveloped viruses that cause irreversible physical damage specifically to virus envelope by viruses' own fusion machine. In conclusion, the lipid nanostructure provides another dimension for antiviral activity of decoy molecules.

The position 4 nucleotide at the 3' end of the influenza virus neuraminidase vRNA is involved in temporal regulation of transcription and replication of neuraminidase RNAs and affects the repertoire of influenza virus surface antigens

Within the sequence motif conserved at the extreme ends of the influenza virus vRNAs, a unique natural variation, U or C, is observed at position 4 of the 3' end. To test the role of this nucleotide, two isogenic A/WSN/33 viruses, carrying either C4 or U4 nucleotide at the 3' end of the neuraminidase (NA) gene, were generated. Compared with the C4 virus, the U4 virus exhibited delayed synthesis of vRNA and stimulation of mRNA synthesis with prolonged accumulation in influenza virus-infected cells. The mRNA/ vRNA ratio was increased up to 20-fold by the C4 --> U4 substitution suggesting that the U4 nucleotide greatly stimulated transcription of the vRNA template. In isolated virion, the U4 virus had higher NA activity than the C4 virus. In MDBK cells, the U4 virus grew to lower haemagglutination (HA) titres but with higher infectivity than the C4 virus, with a corresponding increase in the ratio of p.f.u./HA units of about 10- to 40-fold. Western blot analysis of isolated virion showed that the ratio of two surface proteins, HA/NA, was greatly decreased in the U4 virus. This suggests that the position 4 nucleotide is a genetic determinant for the repertoire of surface antigens and their ratio could be changed without detrimental effects on virus growth. Results could be used to design genetically engineered influenza virus for vaccination. The observed down-regulation of transcription by C4 nucleotide is consistent with its potential role in segment-specific regulation of influenza virus gene expression, especially PB1, PB2 and PA proteins, during virus infection.

Evaluation of green tea extract as a safe personal hygiene against viral infections

Background

Viral infections often pose tremendous public health concerns as well as economic burdens. Despite the availability of vaccines or antiviral drugs, personal hygiene is considered as effective means as the first-hand measure against viral infections. The green tea catechins, in particular, epigallocatechin-3-gallate (EGCG), are known to exert potent antiviral activity. In this study, we evaluated the green tea extract as a safe personal hygiene against viral infections.

Results

Using the influenza virus A/Puerto Rico/8/34 (H1N1) as a model, we examined the duration of the viral inactivating activity of green tea extract (GTE) under prolonged storage at various temperature conditions. Even after the storage for 56 days at different temperatures, 0.1% GTE completely inactivated 10⁶ PFU of the virus (6 log₁₀ reduction), and 0.01% and 0.05% GTE resulted in 2 log₁₀ reduction of the viral titers. When supplemented with 2% citric acid, 0.1% sodium benzoate, and 0.2% ascorbic acid as anti-oxidant, the inactivating activity of GTE was temporarily compromised during earlier times of storage. However, the antiviral activity of the GTE was steadily recovered up to similar levels with those of the same concentrations of GTE without the supplements, effectively prolonging the duration of the virucidal function over extended period. Cryo-EM and DLS analyses showed a slight increase in the overall size of virus particles by GTE treatment. The results suggest that the virucidal activity of GTE is mediated by oxidative crosslinking of catechins to the viral proteins and the change of physical properties of viral membranes.

Conclusions

The durability of antiviral effects of GTE was examined as solution type and powder types over extended periods at various temperature conditions using human influenza A/H1N1 virus. GTE with supplements demonstrated potent viral inactivating activity, resulting in greater than 4 log₁₀ reduction of viral titers even after storage for up to two months at a wide range of temperatures. These data suggest that GTE-based antiviral agents could be formulated as a safe and environmentally friendly personal hygiene against viral infections.

The folding competence of HIV-1 Tat mediated by interaction with TAR RNA

The trans-activator Tat protein of HIV-1 belongs to the large family of intrinsically disordered proteins (IDPs), and is known to recruit various host proteins for the transactivation of viral RNA synthesis. Tat protein interacts with the transactivator response RNA (TAR RNA), exhibiting RNA chaperone activities for structural rearrangement of interacting RNAs. Here, considering that Tat-TAR RNA interaction is mutually cooperative, we examined the potential role of TAR RNA as Chaperna - RNA that provides chaperone function to proteins - for the folding of HIV-1 Tat. Using EGFP fusion as an indirect indicator for folding status, we monitored Tat-EGFP folding in HeLa cells via time-lapse fluorescence microscopy. The live cell imaging showed that the rate and the extent of folding of Tat-EGFP were stimulated by TAR RNA. The purified Tat-EGFP was denatured and the fluorescence was monitored in vitro under renaturation condition. The fluorescence was significantly increased by TAR RNA, and the mutations in TAR RNA that affected the interaction with Tat protein failed to promote Tat refolding. The results suggest that TAR RNA stabilizes Tat as unfolded, but prevents it from misfolding, and maintaining its folding competence for interaction with multiple host factors toward its transactivation. The Chaperna function of virally encoded RNA in establishing proteome link at the viral-host interface provides new insights to as yet largely unexplored RNA mediated protein folding in normal and dysregulated cellular metabolism.

Rifamycin B oxidase from Monocillium spp., a new type of diphenol oxidase

It was found that enzyme from a microbial strain, Monocillium spp. ATCC 20621, catalyzed the oxidative reaction of rifamycin B to form rifamycin O. The identification of the reaction products suggested that the reaction proceeded by the oxidative cyclization of rifamycin B to give rifamycin O, which spontaneously hydrolyzed to rifamycin S in neutral aqueous milieu. The characteristic of the enzyme was different as compared with that of other polyphenol oxidases such as laccase. It is proposed that this new type of enzyme be classified into a subgroup EC 1.10.3.6 with a trivial name rifamycin B oxidase.