The emergence of new antigen branches of H9N2 avian influenza virus in China due to antigenic drift on hemagglutinin through antibody escape at immunodominant sites

Vaccination is a crucial prevention and control measure against H9N2 avian influenza viruses (AIVs) that threaten poultry production and public health. However, H9N2 AIVs in China undergo continuous antigenic drift of hemagglutinin (HA) under antibody pressure, leading to the emergence of immune escape variants. In this study, we investigated the molecular basis of the current widespread antigenic drift of H9N2 AIVs. Specifically, the most prevalent h9.4.2.5-lineage in China was divided into two antigenic branches based on monoclonal antibody (mAb) hemagglutination inhibition (HI) profiling analysis, and 12 antibody escape residues were identified as molecular markers of these two branches. The 12 escape residues were mapped to antigenic sites A, B, and E (H3 was used as the reference). Among these, eight residues primarily increased 3`SLN preference and contributed to antigenicity drift, and four of the eight residues at sites A and B were positively selected. Moreover, the analysis of H9N2 strains over time and space has revealed the emergence of a new antigenic branch in China since 2015, which has replaced the previous branch. However, the old antigenic branch recirculated to several regions after 2018. Collectively, this study provides a theoretical basis for understanding the molecular mechanisms of antigenic drift and for developing vaccine candidates that contest with the current antigenicity of H9N2 AIVs.</p

Multiplex one-step Real-time PCR by Taqman-MGB method for rapid detection of pan and H5 subtype avian influenza viruses

<div><p>Avian influenza virus (AIV) can infect a variety of avian species and mammals, leading to severe economic losses in poultry industry and posing a substantial threat to public health. Currently, traditional virus isolation and identification is inadequate for the early diagnosis because of its labor-intensive and time-consuming features. Real-time RT-PCR (RRT-PCR) is an ideal method for the detection of AIV since it is highly specific, sensitive and rapid. In addition, as the new quencher MGB is used in RRT-PCR, it only needs shorter probe and helps the binding of target gene and probe. In this study, a pan-AIV RRT-PCR for the detection of all AIVs and H5-AIV RRT-PCR for detection of H5 AIV based on NP gene of AIV and HA gene of H5 AIV were successfully established using Taqman-MGB method. We tested 14 AIV strains in total and the results showed that the pan-AIV RRT-PCR can detect AIV of various HA subtypes and the H5-AIV RRT-PCR can detect H5 AIV circulating in poultry in China in recent three years, including H5 viruses of clade 7.2, clade 2.3.4.4 and clade 2.3.2.1. Furthermore, the multiplex detection limit for pan-AIV and H5-AIV RRT-PCR was 5 copies per reaction. When this multiplex method was applied in the detection of experimental and live poultry market samples, the detection rates of pan-AIV and H5 AIV in RRT-PCR were both higher than the routine virus isolation method with embryonated chicken eggs. The multiplex RRT-PCR method established in our study showed high sensitivity, reproducibility and specificity, suggesting the promising application of our method for surveillance of both pan AIV and prevalent H5 AIV in live poultry markets and clinical samples.</p></div

450th-L-NP mediates a higher translation efficiency of GFP mRNA from the minigenome.

(A) Cells were collected at 24h after transfection of minigenome or the control plasmid, and half of them were lysed to isolate ribosomes. Top: Total cytoplasmic ribosomes were separated by sucrose density gradient centrifugation, and the absorbance of each fraction was measured at 254nm. Cycloheximide was present in each sample. Lower panel: Protein in half of each fraction’s volume was subjected to TCA precipitation and subsequently utilized for immunoblotting with anti-His and anti-rpS6 antibodies. (B) The remaining half of the cells were extracted for total RNA to detect the mRNA of GFP by quantitative RT-PCR. The results represent the mean ± SD of a representative quantitative RT-PCR experiment conducted in triplicate. (C) Samples from the remaining half of each fraction after ribosome isolation were extracted for RNA and assayed for the distribution of mRNA of GFP in complex with ribosomes by quantitative RT-PCR. Results are the mean ± SD of a representative quantitative RT-PCR experiment performed in duplicate three times. Significance was analyzed by two-way ANOVA. (** means pp<0.001). (D) Schematic representation of NP protein deletion mutants. Boxes indicate the protein product of each truncated NP gene, with amino acid positions indicated above the boxes. Straight lines indicate the region of deletion. (E) Residues 122–366 and 366–489 of NP are sufficient for its localization to the ribosome. Multiple c- and n-terminal truncated NPs were expressed in HeLa cells. Cell extracts from transfected cells were subjected to 10–50% sucrose density gradient ultracentrifugation. RNase (100U/mL) was added to the cell lysate to eliminate the impact of varying RNA levels on polyribosome enrichment. Protein in each fraction was subjected to TCA precipitation and subsequently utilized for immunoblotting with anti-His and anti-rpS6 antibodies.</p

Deep sequencing of the mouse lung transcriptome reveals distinct long non-coding RNAs expression associated with the high virulence of H5N1 avian influenza virus in mice

<p>Long non-coding RNAs (lncRNAs) play multiple key regulatory roles in various biological processes. However, their function in influenza A virus (IAV) pathogenicity remains largely unexplored. Here, using next generation sequencing, we systemically compared the whole-transcriptome response of the mouse lung infected with either the highly pathogenic (A/Chicken/Jiangsu/k0402/2010, CK10) or the nonpathogenic (A/Goose/Jiangsu/k0403/2010, GS10) H5N1 virus. A total of 126 significantly differentially expressed (SDE) lncRNAs from three replicates were identified to be associated with the high virulence of CK10, whereas 94 SDE lncRNAs were related with GS10. Functional category analysis suggested that the SDE lncRNAs-coexpressed mRNAs regulated by CK10 were highly related with aberrant and uncontrolled inflammatory responses. Further canonical pathway analysis also confirmed that these targets were highly enriched for inflammatory-related pathways. Moreover, 9 lncRNAs and 17 lncRNAs-coexpressed mRNAs associated with a large number of targeted genes were successfully verified by qRT-PCR. One targeted lncRNA (NONMMUT011061) that was markedly activated and correlated with a great number of mRNAs was selected for further in-depth analysis, including predication of transcription factors, potential interacting proteins, genomic location, coding ability and construction of the secondary structure. More importantly, NONMMUT011061 was also distinctively stimulated during the highly pathogenic H5N8 virus infection in mice, suggesting a potential universal role of NONMMUT011061 in the pathogenesis of different H5 IAV. Altogether, these results provide a subset of lncRNAs that might play important roles in the pathogenesis of influenza virus and add the lncRNAs to the vast repertoire of host factors utilized by IAV for infection and persistence.</p

AIV strains used in this study and the detection limit of RRT-PCR method.

<p>AIV strains used in this study and the detection limit of RRT-PCR method.</p

NP is the main protein responsible for the phenotype.

(A) Schematic diagram of the cloning strategy for replacement of NP, P, and L genes between rHerts/33 and rI4. The construction strategy is described in the S1 Table. The virulence of the different recombinant viruses was determined by measuring the ICPI in 1-day-old chickens. (B and C) TCID50 value of the virulent strains after simultaneous replacement of NP, P, and L at 72hpi on tumor cell lines. (D) Expression of viral proteins on HeLa cells by recombinant viruses after simultaneous replacement of NP, P, and L. Western blot analysis was performed by anti-NP and anti-HN at 24h after infection with NDVs at 1MOI and 10MOI, respectively. (E and F) TCID50 value of the virulent strains after individual gene replacement of NP, P, or L at 72hpi on tumor cell lines. (G-H) Viral proteins expression on HeLa cells by recombinant viruses after individual gene replacement of NP, P, or L. Western blot analysis was performed by anti-NP and anti-HN at 24h after infection with NDVs at 1MOI and 10MOI, respectively. Representative data, shown as the means ± SDs (n = 3), were analyzed with two-way ANOVA. ****, P<0.0001.</p

Viruses containing phenylalanine residues at 450 of NP are primarily found in genotype VII.

(A) ML phylogenetic tree of 890 NDV strains based on full-length F-gene sequences. The evolutionary tree was constructed using PhyloSuite in a SYM model. Pie chart representing the number of various residues at position 450 of amino acids for 890 NDV strains. (B) The pie chart illustrates all possible amino acids at position 450 of the NP protein and their proportions. (C) The pie chart shows the distribution of 450aa-phe-NP strains in each genotype. (D) The pie chart displays all the possibilities and their frequencies of the 450th amino acid position of the genotype VII strains’ NP protein.</p

No synergistic effect was found among the homologous NP, P, and L proteins.

(A) The cloning strategy schematic for simultaneous replacement of NP and P, NP, and L, or P and L genes between rHerts/33 and rI4. The virulence of the different recombinant viruses was determined by measuring the Intracerebral Pathogenicity Index (ICPI) in 1-day-old chickens. (B and C) TCID50 value of the virulent strains after simultaneous replacement of NP and P, NP and L, or P and L genes. Representative data, shown as the means ± SDs (n = 3), were analyzed with two-way ANOVA. ****, P (TIF)</p

Variations in viral replicative capability occur during the translation of viral mRNA.

(A) HeLa cells and DF1 cells were infected with NDVs at 10MOI at 37°C for 1h and then incubated with anti-HN mouse monoclonal antibody and goat anti-mouse IgG/FITC at 4°C. After that, cells were washed and assessed by flow cytometry. (B, C, D) HeLa cells were infected with NDV (10MOI) at 37°C for 0.5h and then were collected at 0h, 1h, 2h, 4h, and 8h. Total RNA was extracted and reverse-transcribed using specific primers for gRNA (B), mRNA (C), and cRNA (D) of NDVs. Copy numbers were determined using quantitative RT-PCR. (E and F) Total cellular RNA was extracted at 12h and 24h after transfection of 1.5 μg minigenome into HeLa cells. Reverse transcription was performed using specific primers to detect genomic RNA (E) and mRNA (F) of GFP by quantitative RT-PCR. (G) Expression of GFP was detected at 24h in HeLa cells after transfecting 0.5μg or 1.5μg minigenome with anti-GFP, anti-NP, and anti-β-actin. (H) After transfection with different minigenome systems for 24h, cells were treated with 100μg/ml CHX, and then cells were harvested at 4, 8, and 12 hours. Expression of GFP and NP was detected with anti-GFP, anti-NP, and anti-β-actin. (I, J, K) HeLa cells were treated with 100μg/ml CHX for 30mins and then infected with NDV (10MOI) at 37°C for 0.5h. After that, cells were collected at 0h, 1h, 2h, 4h, and 8h. Total RNA was extracted and reverse-transcribed using specific primers for gRNA (I), mRNA (J), and cRNA (K) of NDVs. Copy numbers were determined using quantitative RT-PCR. Data are presented as means from three independent experiments. Significance is analyzed by two-way ANOVA (****, p<0.0001).</p

Primer and probe sequences used in the qRT-PCR experiments.

Primer and probe sequences used in the qRT-PCR experiments.</p