Detection of circulating Asian H5N1 viruses by a newly established monoclonal antibody

Antigenic diversity of H5 highly pathogenic avian influenza viruses of clade 2.3.4.4 isolated in Asia

H5 highly pathogenic avian influenza viruses (HPAIV) have spread in both poultry and wild birds since late 2003. Continued circulation of HPAIV in poultry in several regions of the world has led to antigenic drift. In the present study, we analyzed the antigenic properties of H5 HPAIV isolated in Asia using four neutralizing mAbs recognizing hemagglutinin, which were established using A/chicken/Kumamoto/1-7/2014 (H5N8), belonging to clade 2.3.4.4 and also using polyclonal antibodies. Viruses of clades 1.1, 2.3.2.1, 2.3.4, and 2.3.4.4 had different reactivity patterns to the panel of mAbs, thereby indicating that the antigenicity of the viruses of clade 2.3.4.4 were similar but differed from the other clades. In particular, the antigenicity of the viruses of clade 2.3.4.4 differed from those of the viruses of clades 2.3.4 and 2.3.2.1, which suggests that the recent H5 HPAIV have further evolved antigenically divergent. In addition, reactivity of antiserum suggests that the antigenicity of viruses of clade 2.3.4.4 differed slightly among groups A, B, and C. Vaccines are still used in poultry in endemic countries, so the antigenicity of H5 HPAIV should be monitored continually to facilitate control of avian influenza. The panel of mAbs established in the present study will be useful for detecting antigenic drift in the H5 viruses that emerge from the current strains.

Characterization of cross-clade monoclonal antibodies against H5N1 highly pathogenic avian influenza virus and their application to the antigenic analysis of diverse H5 subtype viruses

H5N1 highly pathogenic avian influenza viruses (HPAIVs) are a threat to both animal and public health and require specific and rapid detection for prompt disease control. We produced three neutralizing anti-hemagglutinin (HA) monoclonal antibodies (mAbs) using two clades (2.2 and 2.5) of the H5N1 HPAIV isolated in Japan. Blocking immunofluorescence tests showed that each mAb recognized different epitopes; 3B5.1 and 3B5.2 mAbs against the clade 2.5 virus showed cross-clade reactivity to all 26 strains from clades 1, 2.2, 2.3.2.1, 2.3.2.1a, b, c and 2.3.4, suggesting that the epitope(s) recognized are conserved. Conversely, the 1G5 mAb against the clade 2.2 virus showed reactivity to only clades 1, 2.3.4 and 2.5 strains. An analysis of escape mutants, and some clades of the H5N1 viruses recognized by 3B5.1 and 3B5.2 mAbs, suggested that the mAbs bind to an epitope, including amino acid residues at position 162 in the HA1 protein (R162 and K162). Unexpectedly, however, when five Eurasian-origin H5 low-pathogenic AIV (LPAIV) strains with R162 were examined (EA-nonGsGD clade) as well as two American-origin strains (Am-nonGsGD clade), the mAb recognized only EA-nonGsGD clade strains. The R162 and K162 residues in the HA1 protein were highly conserved among 36 of the 43 H5N1 clades reported, including clades 2.3.2.1a and 2.3.2.1c that are currently circulating in Asia, Africa and Europe. The amino acid residues (158-PTIKRSYNNTNQE-170) in the HA1 protein are probably an epitope responsible for the cross-clade reactivity of the mAbs, considering the epitopes reported elsewhere. The 3B5.1 and 3B5.2 mAbs may be useful for the specific detection of H5N1 HPAIVs circulating in the field.

Diagnostic Potential of Recombinant scFv Antibodies Generated Against Hemagglutinin Protein of Influenza A Virus

Human influenza A viruses have been the cause of enormous socio-economic losses worldwide. In order to combat such a notorious pathogen, hemagglutinin protein (HA) has been a preferred target for generation of neutralizing-antibodies as potent therapeutic/diagnostic agents. In the present study, recombinant anti-HA single chain variable fragment antibodies were constructed using the phage-display technology to aid in diagnosis and treatment of human influenza A virus infections. Spleen cells of mice hyper-immunized with A/New Caledonia/20/99 (H1N1) virus were used as the source for recombinant antibody (rAb) production. The antigen-binding phages were quantified after six rounds of bio-panning against A/New Caledonia/20/99 (H1N1), A/California/07/2009 (H1N1)-like, or A/Udorn/307/72(H3N2) viruses. The maximum phage yield was for the A/New Caledonia/20/99 (H1N1), however, considerable cross-reactivity was observed for the other virus strains as well. The HA-specific polyclonal rAb preparation was subjected to selection of single clones for identification of high reactive relatively conserved epitopes. The high-affinity rAbs were tested against certain known conserved HA epitopes by peptide ELISA. Three recombinant mAbs showed reactivity with both the H1N1 strains and one (C5) showed binding with all the three viral strains. The C5 antibody was thus used for development of an ELISA test for diagnosis of influenza virus infection. Based on the sample size in the current analysis, the ELISA test demonstrated 83.9% sensitivity and 100% specificity. Thus, the ELISA, developed in our study, may prove as a cheaper alternative to the presently used real time RT–PCR test for detection of human influenza A viruses in clinical specimens, which will be beneficial, especially in the developing countries.

Antibody-dependent SARS coronavirus infection is mediated by antibodies against spike proteins

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The SARS coronavirus exhibits antibody-dependent enhancement (ADE).

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SARS-CoV ADE is strongly mediated by anti-spike but not anti-nucleocapsid Abs.

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Formerly untested HL-CZ cells are susceptible to SARS-CoV infection.

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Highly diluted anti-sera against SARS-CoV enhances SARS-CoV infectivity.

The severe acute respiratory syndrome coronavirus (SARS-CoV) still carries the potential for reemergence, therefore efforts are being made to create a vaccine as a prophylactic strategy for control and prevention. Antibody-dependent enhancement (ADE) is a mechanism through which dengue viruses, feline coronaviruses, and HIV viruses take advantage of anti-viral humoral immune responses to infect host target cells. Here we describe our observations of SARS-CoV using ADE to enhance the infectivity of a HL-CZ human promonocyte cell line. Quantitative-PCR and immunofluorescence staining results indicate that SARS-CoV is capable of replication in HL-CZ cells, and of displaying virus-induced cytopathic effects and increased levels of TNF-α, IL-4 and IL-6 two days post-infection. According to flow cytometry data, the HL-CZ cells also expressed angiotensin converting enzyme 2 (ACE2, a SARS-CoV receptor) and higher levels of the FcγRII receptor. We found that higher concentrations of anti-sera against SARS-CoV neutralized SARS-CoV infection, while highly diluted anti-sera significantly increased SARS-CoV infection and induced higher levels of apoptosis. Results from infectivity assays indicate that SARS-CoV ADE is primarily mediated by diluted antibodies against envelope spike proteins rather than nucleocapsid proteins. We also generated monoclonal antibodies against SARS-CoV spike proteins and observed that most of them promoted SARS-CoV infection. Combined, our results suggest that antibodies against SARS-CoV spike proteins may trigger ADE effects. The data raise new questions regarding a potential SARS-CoV vaccine, while shedding light on mechanisms involved in SARS pathogenesis.

Broad cross-reactive epitopes of the H5N1 influenza virus identified by murine antibodies against the A/Vietnam/1194/2004 hemagglutinin

There is an urgent need for a rapid diagnostic system to detect the H5 subtype of the influenza A virus. We previously developed monoclonal antibodies (mAbs) against the H5 hemagglutinin (HA) for use in a rapid diagnostic kit. In this study, we determined the epitopes of the anti-H5 HA murine mAbs OM-b, AY-2C2, and YH-1A1. Binding assays of the mAbs to different strains of H5 HAs indicated that OM-b and AY-2C2 cross-reacted with HAs from clades 1, 2.1.3.2, 2.2, and 2.3.4, whereas YH-1A1 failed to bind to those of clades 2.1.3.2 and 2.3.4. HA chimeras revealed that the epitopes for each of the mAbs were in the HA1 region. Analysis of escape mutants revealed that OM-b and AY-2C2 mAbs interacted mainly with amino acid residues D43 and G46, and the YH-1A1 mAb interacted with G139 and K or R140 of H5 HA. Multiple alignments of H5 HA protein sequences showed that D43 and G46 were very conserved among H5N1 HAs, except those in clade 2.2.1 and clade 7 (88.7%). The epitope for YH-1A1 mAb was highly variable in the HAs of H5N1, although it was well conserved in those of H5N2-N9. The OM-b and AY-2C2 mAbs could bind to the HAs of clades 1.1 and 2.3.2.1 that are currently epidemic in Asia, and we conclude that these would be effective for the detection of H5N1 infections in this region.

Antigenic analyses of highly pathogenic avian influenza a viruses

In response to the ongoing threat to animal and human health posed by HPAI endemic in poultry, Asia (H5N1) and North America (H7N3) have revived efforts to reduce pandemic risk by disease control at the source and improved pandemic vaccines. Discovery of conserved neutralization epitopes in the HA, which mediate broad protection within and across HA subtypes have changed the paradigm of "broadly reactive" or "universal" vaccine design. Development of such vaccines would benefit from comparative antigenic analysis of viruses with increasing divergence within (and between) HA subtypes. A review of recent work to define the antigenic properties of HPAI viruses revealed data generated through an array of experimental approaches. This information has supported diagnostics and vaccine development for animal and human health. Further harmonization of analytical methods is needed to determine the antigenic relationships among multiple lineages of rapidly evolving HPAI viruses.

The antigenic architecture of the hemagglutinin of influenza H5N1 viruses

Human infection with the highly pathogenic avian influenza A virus H5N1 is associated with a high mortality and morbidity. H5N1 continues to transmit from poultry to the human population, raising serious concerns about its pandemic potential. Current influenza H5N1 vaccines are based upon the elicitation of a neutralizing antibody (Ab) response against the major epitope regions of the viral surface glycoprotein, hemagglutinin (HA). However, antigenic drift mutations in immune-dominant regions on the HA structure allow the virus to escape Ab neutralization. Epitope mapping using neutralizing monoclonal antibodies (mAb) helps define mechanisms of antigenic drift, neutralizing escape and can facilitate pre-pandemic vaccine design. This review explores the current knowledge base of the antigenic sites of the H5N1 HA molecule. The relationship between the epitope architecture of the H5N1 HA, antigenic evolution of the different H5N1 lineages and the antigenic complexity of the H5N1 virus lineages that constitute potential pandemic strains are discussed in detail.

Isolation of recombinant phage antibodies targeting the hemagglutinin cleavage site of highly pathogenic avian influenza virus

Highly pathogenic avian influenza (HPAI) H5N1 viruses, which have emerged in poultry and other wildlife worldwide, contain a characteristic multi-basic cleavage site (CS) in the hemagglutinin protein (HA). Because this arginine-rich CS is unique among influenza virus subtypes, antibodies against this site have the potential to specifically diagnose pathogenic H5N1. By immunizing mice with the CS peptide and screening a phage display library, we isolated four antibody Fab fragment clones that specifically bind the antigen peptide and several HPAI H5N1 HA proteins in different clades. The soluble Fab fragments expressed in Escherichia coli bound the CS peptide and the H5N1 HA protein with nanomolar affinity. In an immunofluorescence assay, these Fab fragments stained cells infected with HPAI H5N1 but not those infected with a less virulent strain. Lastly, all the Fab clones could detect the CS peptide and H5N1 HA protein by open sandwich ELISA. Thus, these recombinant Fab fragments will be useful novel reagents for the rapid and specific detection of HPAI H5N1 virus.

The lipid mediator protectin D1 inhibits influenza virus replication and improves severe influenza

Influenza A viruses are a major cause of mortality. Given the potential for future lethal pandemics, effective drugs are needed for the treatment of severe influenza such as that caused by H5N1 viruses. Using mediator lipidomics and bioactive lipid screen, we report that the omega-3 polyunsaturated fatty acid (PUFA)-derived lipid mediator protectin D1 (PD1) markedly attenuated influenza virus replication via RNA export machinery. Production of PD1 was suppressed during severe influenza and PD1 levels inversely correlated with the pathogenicity of H5N1 viruses. Suppression of PD1 was genetically mapped to 12/15-lipoxygenase activity. Importantly, PD1 treatment improved the survival and pathology of severe influenza in mice, even under conditions where known antiviral drugs fail to protect from death. These results identify the endogenous lipid mediator PD1 as an innate suppressor of influenza virus replication that protects against lethal influenza virus infection.

CXCL10-CXCR3 enhances the development of neutrophil-mediated fulminant lung injury of viral and nonviral origin

RATIONALE

Patients who developed acute respiratory distress syndrome (ARDS) after infection with severe respiratory viruses (e.g., severe acute respiratory syndrome-coronavirus, H5N1 avian influenza virus), exhibited unusually high levels of CXCL10, which belongs to the non-ELR (glutamic-leucine-arginine) CXC chemokine superfamily. CXCL10 may not be a bystander to the severe virus infection but may directly contribute to the pathogenesis of neutrophil-mediated, excessive pulmonary inflammation.

OBJECTIVES

We investigated the contribution of CXCL10 and its receptor CXCR3 axis to the pathogenesis of ARDS with nonviral and viral origins.

METHODS

We induced nonviral ARDS by acid aspiration and viral ARDS by intratracheal influenza virus infection in wild-type mice and mice deficient in CXCL10, CXCR3, IFNAR1 (IFN-α/β receptor 1), or TIR domain-containing adaptor inducing IFN-β (TRIF).

MEASUREMENTS AND MAIN RESULTS

We found that the mice lacking CXCL10 or CXCR3 demonstrated improved severity and survival of nonviral and viral ARDS, whereas mice that lack IFNAR1 did not control the severity of ARDS in vivo. The increased levels of CXCL10 in lungs with ARDS originate to a large extent from infiltrated pulmonary neutrophils, which express a unique CXCR3 receptor via TRIF. CXCL10-CXCR3 acts in an autocrine fashion on the oxidative burst and chemotaxis in the inflamed neutrophils, leading to fulminant pulmonary inflammation.

CONCLUSIONS

CXCL10-CXCR3 signaling appears to be a critical factor for the exacerbation of the pathology of ARDS. Thus, the CXCL10-CXCR3 axis could represent a prime therapeutic target in the treatment of the acute phase of ARDS of nonviral and viral origins.

Antigenic analysis of highly pathogenic avian influenza virus H5N1 sublineages co-circulating in Egypt

Highly pathogenic avian influenza virus H5N1 has spread across Eurasia and Africa, and outbreaks are now endemic in several countries, including Indonesia, Vietnam and Egypt. Continuous circulation of H5N1 virus in Egypt, from a single infected source, has led to significant genetic diversification with phylogenetically separable sublineages, providing an opportunity to study the impact of genetic evolution on viral phenotypic variation. In this study, we analysed the phylogeny of H5 haemagglutinin (HA) genes in influenza viruses isolated in Egypt from 2006 to 2011 and investigated the effect of conserved amino acid mutations in the HA genes in each of the sublineages on their antigenicity. The analysis showed that viruses in at least four sublineages still persisted in poultry in Egypt as of 2011. Using reverse genetics to generate HA-reassortment viruses with specific HA mutations, we found antigenic drift in the HA in two influenza virus sublineages, compared with the other currently co-circulating influenza virus sublineages in Egypt. Moreover, the two sublineages with significant antigenic drift were antigenically distinguishable. Our findings suggested that phylogenetically divergent H5N1 viruses, which were not antigenically cross-reactive, were co-circulating in Egypt, indicating that there was a problem in using a single influenza virus strain as seed virus to produce influenza virus vaccine in Egypt and providing data for designing more efficacious control strategies in H5N1-endemic areas.

Generation and characterisation of monoclonal antibodies against influenza virus A, subtype H5N1

The emergence of highly pathogenic avian influenza A virus (HPAIV) subtype H5N1 in 1997 has since resulted in large outbreaks in poultry and in transmission from poultry to humans, mostly in southeast Asia, but also in several European countries. Effective diagnosis and control measures are essential for the management of HPAIV infections. To develop a rapid diagnostic test, a panel of murine monoclonal antibodies (mAbs) against influenza virus A subtype H5 was generated. Eleven mAbs were produced and characterised according to their reactivity by indirect and sandwich ELISA and western blotting against different H5 subtypes representing past and viruses currently circulating. Ten out of 11 mAbs reacted strongly with the haemagglutinin (HA) protein of H5 viruses, whereas one mAb reacted with the M1 protein. Targeted HA protein epitopes seemed to be conformational. One hybridoma clone binds to a linear epitope of the M1 protein. One specific mAb reacts with HPAIV H5 in the immunofluorescence test, and two antibodies neutralised H5 viruses. On the basis of the results, the set of seven mAbs is appropriate for developing diagnostic tests. With the generated mAbs, a sandwich ELISA was developed recognising all H5N1 strains tested but no other influenza viruses. With this ELISA, as little as 0.005 HA units or 0.1 ng/ml H5N1 was detected, surpassing other ELISA tests. The novel reagents have the potential to improve significantly available rapid antigen detection systems.

Avian influenza A H5N1 virus

Although influenza A viruses of avian origin have long been responsible for influenza pandemics, including the "Spanish flu" pandemic of 1918, human infections caused by avian subtypes of influenza A virus, most notably H5N1, have emerged since the 1990s (H5N1 in 1997; H9N2 in 1999; and H7N7 in 2003). The wide geographic distribution of influenza A H5N1 in avian species, and the number and severity of human infections are unprecedented. Together with the ongoing genetic evolution of this virus, these features make influenza A H5N1 a likely candidate for a future influenza pandemic. This article discusses the epidemiology, pathogenesis, and diagnosis of human infections caused by influenza A H5N1 virus.

Fab MAbs specific to HA of influenza virus with H5N1 neutralizing activity selected from immunized chicken phage library

Hemagglutinin protein (HA) was considered to be the primary target for monoclonal antibody production. This protein not only plays an important role in viral infections, but can also be used to differentiate H5N1 virus from other influenza A viruses. Hence, for diagnostic and therapeutic applications, it is important to develop anti-HA monoclonal antibody (MAb) with high sensitivity, specificity, stability, and productivity. Nine unique Fab MAbs were generated from chimeric chicken/human Fab phage display library constructed from cDNA derived from chickens immunized with recombinant hemagglutinin protein constructed from H5N1 avian influenza virus (A/Vietnam/1203/04). The obtained Fab MAbs showed several characteristics for further optimization and development-three clones were highly specific to only H5N1 virus. This finding can be applied to the development of H5N1 diagnostic testing. Another clone showed neutralization activity that inhibited H5N1 influenza virus infection in Madin-Darby canine kidney (MDCK) cells. In addition, one clone showed strong reactivity with several of the influenza A virus subtypes tested. The conversion of this clone to whole IgG is a promising study for a cross-neutralization activity test.

Novel type II transmembrane serine proteases, MSPL and TMPRSS13, Proteolytically activate membrane fusion activity of the hemagglutinin of highly pathogenic avian influenza viruses and induce their multicycle replication

Host cellular proteases induce influenza virus entry into cells by cleaving the viral surface envelope glycoprotein hemagglutinin (HA). However, details on the cellular proteases involved in this event are not fully available. We report here that ubiquitous type II transmembrane serine proteases, MSPL and its splice variant TMPRSS13, are novel candidates for proteases processing HA proteins of highly pathogenic avian influenza (HPAI) viruses, apart from the previously identified furin and proprotein convertases 5 and 6. HAs from all HPAI virus H5 and H7 strains have one of two cleavage site motifs, the R-X-K/R-R motif with R at position P4 and the K-K/R-K/T-R motif with K at position P4. In studies of synthetic 14-residue HPAI virus HA peptides with these cleavage site motifs, furin preferentially cleaved only HA peptides with the R-K-K-R motif in the presence of calcium and not peptides with the other motif, whereas MSPL and TMPRSS13 cleaved both types of HA peptides (those with the R/K-K-K-R motif) efficiently in the absence of calcium. Full-length recombinant HPAI virus HA with the K-K-K-R cleavage motif exhibited poor susceptibility to cleavage in the absence of MSPL or TMPRSS13 and the presence of furin in infected cells, but it was converted to mature HA subunits in transfected cells expressing MSPL or TMPRSS13, with membrane-fused giant-cell formation. This conversion and membrane fusion were suppressed by inhibitors of MSPL and TMPRSS13. Furthermore, infection with and multiplication of genetically modified live HPAI virus A/Crow/Kyoto/53/2004 (H5N1) with the K-K-K-R cleavage site motif were detected only in MSPL- and TMPRSS13-expressing cells.

Research and development of universal influenza vaccines

The continuous threat of influenza pandemics determines the urgency and necessity to develop safe and effective vaccines against divergent influenza viruses. This review describes the advancements in the research and development of universal influenza vaccines based on the relatively conserved sequences of M2e, HA, and other proteins of influenza viruses.

Highly pathogenic H5N1 avian influenza virus induces extracellular Ca2+ influx, leading to apoptosis in avian cells

In this study, we show that the highly pathogenic H5N1 avian influenza virus (AIV) (A/crow/Kyoto/53/04 and A/chicken/Egypt/CL6/07) induced apoptosis in duck embryonic fibroblasts (DEF). In contrast, apoptosis was reduced among cells infected with low-pathogenic AIVs (A/duck/HK/342/78 [H5N2], A/duck/HK/820/80 [H5N3], A/wigeon/Osaka/1/01 [H7N7], and A/turkey/Wisconsin/1/66 [H9N2]). Thus, we investigated the molecular mechanisms of apoptosis induced by H5N1-AIV infection. Caspase-dependent and -independent pathways contributed to the cytopathic effects. We further showed that, in the induction of apoptosis, the hemagglutinin of H5N1-AIV played a major role and its cleavage sequence was not critical. We also observed outer membrane permeabilization and loss of the transmembrane potential of the mitochondria of infected DEF, indicating that mitochondrial dysfunction was caused by the H5N1-AIV infection. We then analyzed Ca(2+) dynamics in the infected cells and demonstrated an increase in the concentration of Ca(2+) in the cytosol ([Ca(2+)](i)) and mitochondria ([Ca(2+)](m)) after H5N1-AIV infection. Regardless, gene expression important for regulating Ca(2+) efflux from the endoplasmic reticulum did not significantly change after H5N1-AIV infection. These results suggest that extracellular Ca(2+) may enter H5N1-AIV-infected cells. Indeed, EGTA, which chelates extracellular free Ca(2+), significantly reduced the [Ca(2+)](i), [Ca(2+)](m), and apoptosis induced by H5N1-AIV infection. In conclusion, we identified a novel mechanism for influenza A virus-mediated cell death, which involved the acceleration of extracellular Ca(2+) influx, leading to mitochondrial dysfunction and apoptosis. These findings may be useful for understanding the pathogenesis of H5N1-AIV in avian species as well as the impact of Ca(2+) homeostasis on influenza A virus infection.

Characterization of conserved properties of hemagglutinin of H5N1 and human influenza viruses: possible consequences for therapy and infection control

Background

Epidemics caused by highly pathogenic avian influenza virus (HPAIV) are a continuing threat to human health and to the world's economy. The development of approaches, which help to understand the significance of structural changes resulting from the alarming mutational propensity for human-to-human transmission of HPAIV, is of particularly interest. Here we compare informational and structural properties of the hemagglutinin (HA) of H5N1 virus and human influenza virus subtypes, which are important for the receptor/virus interaction.

Results

Presented results revealed that HA proteins encode highly conserved information that differ between influenza virus subtypes H5N1, H1N1, H3N2, H7N7 and defined an HA domain which may modulate interaction with receptor. We also found that about one third of H5N1 viruses which are isolated during the 2006/07 influenza outbreak in Egypt possibly evolve towards receptor usage similar to that of seasonal H1N1.

Conclusion

The presented results may help to better understand the interaction of influenza virus with its receptor(s) and to identify new therapeutic targets for drug development.

Generating and characterizing monoclonal and polyclonal antibodies against avian H5N1 hemagglutinin protein

Accurate and timely diagnoses are central to H5N1 infection control. Here we describe the cloning and expression of the HA1 protein of the A/Vietnam/1203/04 strain in a bacterial system to generate mono-/polyclonal antibodies. All of the eight generated monoclonal antibodies recognized the same linear epitope on the top globular region of the HA structure -- a highly conserved epitope among all circulating H5N1 clades identified by amino acid alignment. Results from immunofluorescence staining and Western blotting indicate that all monoclonal antibodies interacted with a denatured form of HA proteins, while the resultant polyclonal antibodies recognized both denatured and native HA proteins on H5N1 reverse-genetics (RG) viruses. Results from flow cytometry and microneutralization assays indicate that the polyclonal antibodies blocked viral binding and neutralized H5N1-RG viruses. Our results may prove useful to establishing future H5N1 mono-and polyclonal antibodies, and perhaps contribute to the development of an alternative H5N1 vaccine.