Variability of NS1 proteins among H9N2 avian influenza viruses isolated in Israel during 2000–2009

Abstract

The main aims of the present study were to characterize NS1 protein from H9N2 avian influenza viruses (AIVs) isolated in Israel and to investigate the possibility to use NS1-based indirect ELISA. To achieve these purposes, the non-structural gene (NS1) of 79 AIVs of the H9N2 subtype isolated in Israel in 2000-2009 was sequenced and genetically analyzed. The phylogenetic analysis demonstrated that four distinct introductions of H9N2 occurred in Israel during this period. Analysis of the inferred amino acid sequences of the NS1 proteins showed high, about 10%, differences between viruses of the 3rd and 4th introductions. Antibodies against NS1 protein in immune sera were tested by means of indirect ELISA using recombinant NS1 as antigen. Immune sera were obtained from experimentally H9N2-infected chicken after infection on 4, 7, 10, 14, and 21 days. All sera from chickens experimentally infected with 3rd- or 4th-introduction AIV contained anti-NS1 antibodies that were detected by enzyme-linked immunosorbent assay (NS1-ELISA) even though the recombinant NS1 used as antigen for NS1-ELISA differed significantly in its amino acid sequences from the NS1 protein of AIV that caused infection in experimental birds. These findings indicate that the sites of the NS1 protein by which viruses belonging to 3rd and 4th introduction are out of antigenic epitope positions were responsible for the results of NS1-based iELISA.

Phylogenetic analysis of NS gene of avian influenza viruses (H9N2) isolated from chicken in Iran during 2007–2011

“…Two potential immunodominant antigenic regions (IARs) have been reported for the NS1 protein: the first located at positions 53-80 and the second at positions 94-101 (9). Three amino acid substitutions were observed in the first IAR in most recently studied isolates (A60E, K62R, and E72K).…”

“…Reverse transcription was done by using influenza universal primer Uni12: 5'-AGCAAAAGCAGG -3' (20). Amplification of the NS full-length gene was carried out by PCR with specific primers (9,21).…”

“…It is only expressed in influenza A virusinfected cells and is not present in mature virions (7). Because of the presence of the NS1 protein only in infected cells, antibody responses against this protein can be used as a marker of distinction between active infection and vaccination with killed vaccines in the chicken host (DIVA system) (8,9). The NS1 protein is multifunctional and plays an important role as a posttranscriptional regulator in the influenza virus life cycle.…”

Mouse-Adapted H9N2 Influenza A Virus PB2 Protein M147L and E627K Mutations Are Critical for High Virulence

“…H9N2 influenza viruses circulate worldwide and are endemic in multiple terrestrial avian species in Asia [1], [2], [3], [4]. It is noteworthy that H9N2 influenza viruses in poultry have occasionally been transmitted to mammalian species, including humans and pigs [5], [6], [7], [8], [9].…”

High genetic compatibility and increased pathogenicity of reassortants derived from avian H9N2 and pandemic H1N1/2009 influenza viruses

“…Our results indicate that some avian H9-pandemic reassortants could emerge with a potentially higher threat for humans and also highlight the importance of monitoring the H9-pandemic reassortant viruses that may arise, especially those that possess the PA gene of H1N1/2009 origin. H 9N2 influenza viruses circulate worldwide and are endemic in multiple terrestrial avian species in Asia (1)(2)(3)(4). It is noteworthy that H9N2 influenza viruses in poultry have occasionally been transmitted to mammalian species, including humans and pigs (5)(6)(7)(8)(9).…”