The H16-L10-4R5 monoclonal antibody reacts with influenza virus nucleoprotein (NP). All viruses with negative-sense RNA genomes encode a single-strand RNA-binding NP. The primary function of NP is to encapsidate the virus genome for the purposes of RNA transcription, replication and packaging.

InVivoMAb anti-Influenza A virus NP (Clone: H16-L10-4R5 (HB65))

 

Nigg, P. E. and J. Pavlovic (2015). “Oligomerization and GTP-binding requirements of MxA for viral target recognition and antiviral activity against influenza A virus.” J Biol Chem. pii: jbc.M115.681494. PubMed

The interferon (IFN)-induced human myxovirus resistance protein A (MxA) exhibits a broad antiviral activity against many viruses including influenza A virus (IAV). MxA belongs to the family of dynamin-like GTPases and assembles in vitro into dimers, tetramers and oligomeric ring-like structures. The molecular mechanism of action remains to be elucidated. Furthermore it is not clear whether MxA exerts its antiviral activity in a monomeric and/or multimeric form. Using a set of MxA mutants that form complexes with defined stoichiometry, we observed that in the presence of GTPgammaS, purified MxA disassembled into tetramers and dimers. Dimeric forms did not further disassemble into monomers. Infection experiments revealed that besides wild type MxA also dimeric and monomeric variants of MxA efficiently restricted IAV at a replication step after primary transcription. Moreover, only dimeric MxA was able to form stable complexes with the nucleoprotein (NP) of IAV. MxA interacted with NP independently of other viral components. Interestingly, the dimeric form of MxA was able to efficiently bind to NP from several MxA-sensitive strains but interacted much weaker with NP from the MxA-resistant PR8 strain derived from the H1N1 1918 lineage. Taken together, these data suggest that during infection a fraction of MxA disassembles into dimers that bind to NP synthesized following primary transcription in the cytoplasm, thereby preventing viral replication.

Leung, Y. H., et al. (2014). “Highly pathogenic avian influenza A H5N1 and pandemic H1N1 virus infections have different phenotypes in Toll-like receptor 3 knockout mice.” J Gen Virol 95(Pt 9): 1870-1879. PubMed

Toll-like receptors (TLRs) play an important role in innate immunity to virus infections. We investigated the role of TLR3 in the pathogenesis of H5N1 and pandemic H1N1 (pH1N1) influenza virus infections in mice. Wild-type mice and those defective in TLR3 were infected with influenza A/HK/486/97 (H5N1) or A/HK/415742/09 (pH1N1) virus. For comparison, mice defective in the gene for myeloid differential factor 88 (MyD88) were also infected with the viruses, because MyD88 signals through a TLR pathway different from TLR3. Survival and body weight loss were monitored for 14 days, and lung pathology, the lung immune-cell profile, viral load and cytokine responses were studied. H5N1-infected TLR3(-/-) mice had better survival than H5N1-infected WT mice, evident by significantly faster regain of body weight, lower viral titre in the lung and fewer pathological changes in the lung. However, this improved survival was not seen upon pH1N1 infection of TLR3(-/-) mice. In contrast, MyD88(-/-) mice had an increased viral titre and decreased leukocyte infiltration in the lungs after infection with H5N1 virus and poorer survival after pH1N1 infection. In conclusion, TLR3 worsens the pathogenesis of H5N1 infection but not of pH1N1 infection, highlighting the differences in the pathogenesis of these two viruses and the different roles of TLR3 in their pathogenesis.

van Baalen, C. A., et al. (2014). “Detection of nonhemagglutinating influenza a(h3) viruses by enzyme-linked immunosorbent assay in quantitative influenza virus culture.” J Clin Microbiol 52(5): 1672-1677. PubMed

To assess the efficacy of novel antiviral drugs against influenza virus in clinical trials, it is necessary to quantify infectious virus titers in respiratory tract samples from patients. Typically, this is achieved by inoculating virus-susceptible cells with serial dilutions of clinical specimens and detecting the production of progeny virus by hemagglutination, since influenza viruses generally have the capacity to bind and agglutinate erythrocytes of various species through their hemagglutinin (HA). This readout method is no longer adequate, since an increasing number of currently circulating influenza A virus H3 subtype (A) viruses display a reduced capacity to agglutinate erythrocytes. Here, we report the magnitude of this problem by analyzing the frequency of HA-deficient A(H3) viruses detected in The Netherlands from 1999 to 2012. Furthermore, we report the development and validation of an alternative method for monitoring the production of progeny influenza virus in quantitative virus cultures, which is independent of the capacity to agglutinate erythrocytes. This method is based on the detection of viral nucleoprotein (NP) in virus culture plates by enzyme-linked immunosorbent assay (ELISA), and it produced results similar to those of the hemagglutination assay using strains with good HA activity, including A/Brisbane/059/07 (H1N1), A/Victoria/210/09 (H3N2), other seasonal A(H1N1), A(H1N1)pdm09, and the majority of A(H3) virus strains isolated in 2009. In contrast, many A(H3) viruses that have circulated since 2010 failed to display HA activity, and infectious virus titers were determined only by detecting NP. The virus culture ELISA described here will enable efficacy testing of new antiviral compounds in clinical trials during seasons in which nonhemagglutinating influenza A viruses circulate.

Haynes, L., et al. (2012). “Immunity to the conserved influenza nucleoprotein reduces susceptibility to secondary bacterial infections.” J Immunol 189(10): 4921-4929. PubMed

Influenza causes >250,000 deaths annually in the industrialized world, and bacterial infections frequently cause secondary illnesses during influenza outbreaks, including pneumonia, bronchitis, sinusitis, and otitis media. In this study, we demonstrate that cross-reactive immunity to mismatched influenza strains can reduce susceptibility to secondary bacterial infections, even though this fails to prevent influenza infection. Specifically, infecting mice with H3N2 influenza before challenging with mismatched H1N1 influenza reduces susceptibility to either Gram-positive Streptococcus pneumoniae or Gram-negative Klebsiella pneumoniae. Vaccinating mice with the highly conserved nucleoprotein of influenza also reduces H1N1-induced susceptibility to lethal bacterial infections. Both T cells and Abs contribute to defense against influenza-induced bacterial diseases; influenza cross-reactive T cells reduce viral titers, whereas Abs to nucleoprotein suppress induction of inflammation in the lung. These findings suggest that nonneutralizing influenza vaccines that fail to prevent influenza infection may nevertheless protect the public from secondary bacterial diseases when neutralizing vaccines are not available.