Influenza B, C and D Viruses (Orthomyxoviridae)

Oxymatrine Modulation of TLR3 Signaling: A Dual-Action Mechanism for H9N2 Avian Influenza Virus Defense and Immune Regulation

In our research, we explored a natural substance called Oxymatrine, found in a traditional Chinese medicinal plant, to fight against a common bird flu virus known as H9N2. This virus not only affects birds but can also pose a threat to human health. We focused on how this natural compound can help in stopping the virus from spreading in cells that line the lungs of birds and potentially humans. Our findings show that Oxymatrine can both directly block the virus and boost the body's immune response against it. This dual-action mechanism is particularly interesting because it indicates that Oxymatrine might be a useful tool in developing new ways to prevent and treat this type of bird flu. Understanding how Oxymatrine works against the H9N2 virus could lead to safer and more natural ways to combat viral infections in animals and humans, contributing to the health and well-being of society. The H9N2 Avian Influenza Virus (AIV) is a persistent health threat because of its rapid mutation rate and the limited efficacy of vaccines, underscoring the urgent need for innovative therapies. This study investigated the H9N2 AIV antiviral properties of Oxymatrine (OMT), a compound derived from traditional Chinese medicine, particularly focusing on its interaction with pulmonary microvascular endothelial cells (PMVECs). Employing an array of in vitro assays, including 50% tissue culture infectious dose, Cell Counting Kit-8, reverse transcription-quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and Western blot, we systematically elucidated the multifaceted effects of OMT. OMT dose-dependently inhibited critical antiviral proteins (PKR and Mx1) and modulated the expression of type I interferons and key cytokines (IFN-α, IFN-β, IL-6, and TNF-α), thereby affecting TLR3 signaling and its downstream elements (NF-κB and IRF-3). OMT's antiviral efficacy extended beyond TLR3-mediated responses, suggesting its potential as a versatile antiviral agent. This study not only contributes to the growing body of research on the use of natural compounds as antiviral agents but also underscores the importance of further investigating the broader application of OMT for combating viral infections.

Tackling Influenza A virus by M2 ion channel blockers: Latest progress and limitations

Influenza outbreaks cause pandemics in millions of people. The treatment of influenza remains a challenge due to significant genetic polymorphism in the influenza virus. Also, developing vaccines to protect against seasonal and pandemic influenza infections is constantly impeded. Thus, antibiotics are the only first line of defense against antigenically distinct strains or new subtypes of influenza viruses. Among several anti-influenza targets, the M2 protein of the influenza virus performs several activities. M2 protein is an ion channel that permits proton conductance through the virion envelope and the deacidification of the Golgi apparatus. Both these functions are critical for viral replication. Thus, targeting the M2 protein of the influenza virus is an essential target. Rimantadine and amantadine are two well-known drugs that act on the M2 protein. However, these drugs acquired resistance to influenza and thus are not recommended to treat influenza infections. This review discusses an overview of anti-influenza therapy, M2 ion channel functions, and its working principle. It also discusses the M2 structure and its role, and the change in the structure leads to mutant variants of influenza A virus. We also shed light on the recently identified compounds acting against wild-type and mutated M2 proteins of influenza virus A. These scaffolds could be an alternative to M2 inhibitors and be developed as antibiotics for treating influenza infections.

Nucleic acid-based electrochemical biosensor for detection of influenza B by gold nanoparticles

The influenza virus is a pervasive pathogen that exhibits increased prevalence during colder seasons, resulting in a significant annual occurrence of infections. Notably, pharmaceutical interventions effective against influenza A strains often exhibit limited efficacy against influenza B variants. Against this backdrop, the need for innovative approaches to accurately and swiftly differentiate and detect influenza B becomes evident. Biosensors play a pivotal role in this detection process, offering rapid, specific, and sensitive identification of the virus, facilitating timely intervention and containment efforts. Oligonucleotide sequences targeting the conserved B/Victoria/2/87 influenza virus NP region were designed. Nasopharyngeal swabs were collected from patients suspected of influenza virus infection, and viral RNA was extracted. RNA quality was assessed through one-step PCR. cDNA synthesis was performed using random hexamers, and real-time PCR quantified the influenza genome. Gold nanoparticles were immobilized on a surface to immobilize the specific DNA probe, and electrochemical hybridization was electrochemically followed. The biosensor exhibited high selectivity and effective distinction of complementary sequences from mismatches and influenza virus cDNA genome. The biosensor successfully detected the influenza B virus genome in real samples. Non-influenza samples yielded no significant hybridization signals. The comparison between the results obtained from the biosensor and real-time PCR revealed full agreement of these methods. The biosensor utilized electrochemical detection of hybridization and proved effective in detecting the influenza B virus genome with high specificity, sensitivity, and selectivity. Comparative analysis with real-time PCR underscored the accuracy and potential applicability of the biosensor in rapid and specific virus detection. This innovative approach holds promise for future diagnostic and epidemiological applications in detecting influenza B virus and other pathogens.

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.

First influenza D virus full-genome sequence retrieved from livestock in Namibia, Africa

Influenza D virus (IDV) was first isolated in 2011 in the USA and has since been shown to circulate in cattle, pigs, sheep, wild boar, and camels. In Africa, there is limited data on the epidemiology of IDV and, so, we investigated the presence of IDV among domestic ruminants and wild animals in Namibia by screening nasal swabs using an IDV-specific molecular assay. IDV RNA was detected in bovines (n=2), giraffes (n=2) and wildebeest (n=1). The hemagglutinin-esterase-fusion (HEF) gene from one of the bovine and the wildebeest samples was successfully sequenced as well as the full genome for the second bovine sample. Phylogenetic analysis of the HEF gene positioned the African virus variants within the D/OK lineage but with a long branch. The African variant had an amino acid diversity of 2.41% and most likely represents a distinct genotype within the lineage. Notably, the polymerase acidic protein gene (PA) was more closely related to a different lineage (D/660), indicative of potential reassortment. This is the first genetic characterization of IDV in Africa and it adds important data to our understanding of the global IDV distribution.

Impact of the R292K Mutation on Influenza A (H7N9) Virus Resistance towards Peramivir: A Molecular Dynamics Perspective

In March 2013, a novel avian influenza A (H7N9) virus emerged in China. By March 2021, it had infected more than 1500 people, raising concerns regarding its epidemic potential. Similar to the highly pathogenic H5N1 virus, the H7N9 virus causes severe pneumonia and acute respiratory distress syndrome in most patients. Moreover, genetic analysis showed that this avian H7N9 virus carries human adaptation markers in the hemagglutinin and polymerase basic 2 (PB2) genes associated with cross-species transmissibility. Clinical studies showed that a single mutation, neuraminidase (NA) R292K (N2 numbering), induces resistance to peramivir in the highly pathogenic H7N9 influenza A viruses. Therefore, to evaluate the risk for human public health and understand the possible source of drug resistance, we assessed the impact of the NA-R292K mutation on avian H7N9 virus resistance towards peramivir using various molecular dynamics approaches. We observed that the single point mutation led to a distorted peramivir orientation in the enzyme active site which, in turn, perturbed the inhibitor's binding. The R292K mutation induced a decrease in the interaction among neighboring amino acid residues when compared to its wild-type counterpart, as shown by the high degree of fluctuations in the radius of gyration. MM/GBSA calculations revealed that the mutation caused a decrease in the drug binding affinity by 17.28 kcal/mol when compared to the that for the wild-type enzyme. The mutation caused a distortion of hydrogen bond-mediated interactions with peramivir and increased the accessibility of water molecules around the K292 mutated residue.

Structural and functional analysis of the roles of influenza C virus membrane proteins in assembly and budding

Assembly and budding of the influenza C virus is mediated by three membrane proteins: the hemagglutinin-esterase-fusion glycoprotein (HEF), the matrix protein (CM1), and the ion channel (CM2). Here we investigated whether the formation of the hexagonal HEF arrangement, a distinctive feature of influenza C virions is important for virus budding. We used super resolution microscopy and found 250-nm sized HEF clusters at the plasma membrane of transfected cells, which were insensitive to cholesterol extraction and cytochalasin treatment. Overexpression of either CM1, CM2, or HEF caused the release of membrane-enveloped particles. Cryo-electron microscopy of the latter revealed spherical vesicles exhibiting the hexagonal HEF clusters. We subsequently used reverse genetics to identify elements in HEF required for this clustering. We found that deletion of the short cytoplasmic tail of HEF reduced virus titer and hexagonal HEF arrays, suggesting that an interaction with CM1 stabilizes the HEF clusters. In addition, we substituted amino acids at the surface of the closed HEF conformation and identified specific mutations that prevented virus rescue, others reduced virus titers and the number of HEF clusters in virions. Finally, mutation of two regions that mediate contacts between trimers in the in-situ structure of HEF was shown to prevent rescue of infectious virus particles. Mutations at residues thought to mediate lateral interactions were revealed to promote intracellular trafficking defects. Taken together, we propose that lateral interactions between the ectodomains of HEF trimers are a driving force for virus budding, although CM2 and CM1 also play important roles in this process.

An Overview of Influenza Viruses and Vaccines

Influenza remains one of the major public health concerns because it causes annual epidemics and can potentially instigate a global pandemic. Numerous countermeasures, including vaccines and antiviral treatments, are in use against seasonal influenza infection; however, their effectiveness has always been discussed due to the ongoing resistance to antivirals and relatively low and unpredictable efficiency of influenza vaccines compared to other vaccines. The growing interest in vaccines as a promising approach to prevent and control influenza may provide alternative vaccine development options with potentially increased efficiency. In addition to currently available inactivated, live-attenuated, and recombinant influenza vaccines on the market, novel platforms such as virus-like particles (VLPs) and nanoparticles, and new vaccine formulations are presently being explored. These platforms provide the opportunity to design influenza vaccines with improved properties to maximize quality, efficacy, and safety. The influenza vaccine manufacturing process is also moving forward with advancements relating to egg- and cell-based production, purification processes, and studies into the physicochemical attributes and vaccine degradation pathways. These will contribute to the design of more stable, optimized vaccine formulations guided by contemporary analytical testing methods and via the implementation of the latest advances in the field.

Exploiting Pan Influenza A and Pan Influenza B Pseudotype Libraries for Efficient Vaccine Antigen Selection

We developed an influenza hemagglutinin (HA) pseudotype library encompassing Influenza A subtypes HA1-18 and Influenza B subtypes (both lineages) to be employed in influenza pseudotype microneutralization (pMN) assays. The pMN is highly sensitive and specific for detecting virus-specific neutralizing antibodies against influenza viruses and can be used to assess antibody functionality in vitro. Here we show the production of these viral HA pseudotypes and their employment as substitutes for wildtype viruses in influenza neutralization assays. We demonstrate their utility in detecting serum responses to vaccination with the ability to evaluate cross-subtype neutralizing responses elicited by specific vaccinating antigens. Our findings may inform further preclinical studies involving immunization dosing regimens in mice and may help in the creation and selection of better antigens for vaccine design. These HA pseudotypes can be harnessed to meet strategic objectives that contribute to the strengthening of global influenza surveillance, expansion of seasonal influenza prevention and control policies, and strengthening pandemic preparedness and response.

S-Acylation of Proteins of Coronavirus and Influenza Virus: Conservation of Acylation Sites in Animal Viruses and DHHC Acyltransferases in Their Animal Reservoirs

Recent pandemics of zoonotic origin were caused by members of coronavirus (CoV) and influenza A (Flu A) viruses. Their glycoproteins (S in CoV, HA in Flu A) and ion channels (E in CoV, M2 in Flu A) are S-acylated. We show that viruses of all genera and from all hosts contain clusters of acylated cysteines in HA, S and E, consistent with the essential function of the modification. In contrast, some Flu viruses lost the acylated cysteine in M2 during evolution, suggesting that it does not affect viral fitness. Members of the DHHC family catalyze palmitoylation. Twenty-three DHHCs exist in humans, but the number varies between vertebrates. SARS-CoV-2 and Flu A proteins are acylated by an overlapping set of DHHCs in human cells. We show that these DHHC genes also exist in other virus hosts. Localization of amino acid substitutions in the 3D structure of DHHCs provided no evidence that their activity or substrate specificity is disturbed. We speculate that newly emerged CoVs or Flu viruses also depend on S-acylation for replication and will use the human DHHCs for that purpose. This feature makes these DHHCs attractive targets for pan-antiviral drugs.