A Novel Peptide ELISA for Universal Detection of Antibodies to Human H5N1 Influenza Viruses

BACKGROUND: Active serologic surveillance of H5N1 highly pathogenic avian influenza (HPAI) virus in humans and poultry is critical to control this disease. However, the need for a robust, sensitive and specific serologic test for the rapid detection of antibodies to H5N1 viruses has not been met. METHODOLOGY/PRINCIPAL FINDINGS: Previously, we reported a universal epitope (CNTKCQTP) in H5 hemagglutinin (HA) that is 100% conserved in H5N1 human isolates and 96.9% in avian isolates. Here, we describe a peptide ELISA to detect antibodies to H5N1 virus by using synthetic peptide that comprises the amino acid sequence of this highly conserved and antigenic epitope as the capture antigen. The sensitivity and specificity of the peptide ELISA were evaluated using experimental chicken antisera to H5N1 viruses from divergent clades and other subtype influenza viruses, as well as human serum samples from patients infected with H5N1 or seasonal influenza viruses. The peptide ELISA results were compared with hemagglutinin inhibition (HI), and immunofluorescence assay and immunodot blot that utilize recombinant HA1 as the capture antigen. The peptide ELISA detected antibodies to H5N1 in immunized animals or convalescent human sera whereas some degree of cross-reactivity was observed in HI, immunofluorescence assay and immunodot blot. Antibodies to other influenza subtypes tested negative in the peptide-ELISA. CONCLUSION/SIGNIFICANCE: The peptide-ELISA based on the highly conserved and antigenic H5 epitope (CNTKCQTP) provides sensitive and highly specific detection of antibodies to H5N1 influenza viruses. This study highlighted the use of synthetic peptide as a capture antigen in rapid detection of antibodies to H5N1 in human and animal sera that is robust, simple and cost effective and is particularly beneficial for developing countries and rural areas

Development of Epitope-Blocking ELISA for Universal Detection of Antibodies to Human H5N1 Influenza Viruses

10.1371/journal.pone.0004566PLoS ONE4

Monoclonal Antibodies against the Fusion Peptide of Hemagglutinin Protect Mice from Lethal Influenza A Virus H5N1 Infection ▿

The HA2 glycopolypeptide (gp) is highly conserved in all influenza A virus strains, and it is known to play a major role in the fusion of the virus with the endosomal membrane in host cells during the course of viral infection. Vaccines and therapeutics targeting this HA2 gp could induce efficient broad-spectrum immunity against influenza A virus infections. So far, there have been no studies on the possible therapeutic effects of monoclonal antibodies (MAbs), specifically against the fusion peptide of hemagglutinin (HA), upon lethal infections with highly pathogenic avian influenza (HPAI) H5N1 virus. We have identified MAb 1C9, which binds to GLFGAIAGF, a part of the fusion peptide of the HA2 gp. We evaluated the efficacy of MAb 1C9 as a therapy for influenza A virus infections. This MAb, which inhibited cell fusion in vitro when administered passively, protected 100% of mice from challenge with five 50% mouse lethal doses of HPAI H5N1 influenza A viruses from two different clades. Furthermore, it caused earlier clearance of the virus from the lung. The influenza virus load was assessed in lung samples from mice challenged after pretreatment with MAb 1C9 (24 h prior to challenge) and from mice receiving early treatment (24 h after challenge). The study shows that MAb 1C9, which is specific to the antigenically conserved fusion peptide of HA2, can contribute to the cross-clade protection of mice infected with H5N1 virus and mediate more effective recovery from infection

Detection of H5 Avian Influenza Viruses by Antigen-Capture Enzyme-Linked Immunosorbent Assay Using H5-Specific Monoclonal Antibody

The unprecedented spread of highly pathogenic avian influenza virus subtype H5N1 in Asia and Europe is threatening animals and public health systems. Effective diagnosis and control management are needed to control the disease. To this end, we developed a panel of monoclonal antibodies (MAbs) against the H5N1 avian influenza virus (AIV) and implemented an antigen-capture enzyme-linked immunosorbent assay (AC-ELISA) to detect the H5 viral antigen. Mice immunized with denatured hemagglutinin (HA) from A/goose/Guangdong/97 (H5N1) expressed in bacteria or immunized with concentrated H5N2 virus yielded a panel of hybridomas secreting MAbs specific for influenza virus HA. The reactivity of each MAb with several subtypes of influenza virus revealed that hybridomas 3D4 and 8B6 specifically recognized H5 HA. Therefore, purified antibodies from hybridomas 3D4 and 8B6, which secrete immunoglobulin G (IgG) and IgM, respectively, were used as the capture antibodies and pooled hyperimmune guinea pig serum IgG served as the detector antibody. The specificity of the optimized AC-ELISA was evaluated by using AIV subtypes H5 H3, H4, H7, H9, and H10. Specimens containing AIV subtype H5 subtype yielded a specific and strong signal above the background, whereas specimens containing all other subtypes yielded background signals. The detection limits of the AC-ELISA were 62.5 ng of bacterium-expressed H5N1 HA1 protein and 124, 62, and 31 50% tissue culture infective doses of influenza virus subtypes H5N1/PR8, H5N2, and H5N3, respectively. Reconstituted clinical samples consisting of H5 AIVs mixed with pharyngeal-tracheal mucus from healthy chickens also yielded positive signals in the AC-ELISA, and the results were confirmed by reverse transcription-PCR. The tracheal swab samples from H9N2-infected chickens did not give positive signals. Taken together, the newly developed MAb-based AC-ELISA offers an attractive alternative to other diagnostic approaches for the specific detection of H5 AIV

Separation of purified recombinant HA1 proteins of H1–H13 and H16 [<b>14</b>] subtypes (38 kDa) in SDS-PAGE.

<p>Separation of purified recombinant HA1 proteins of H1–H13 and H16 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020737#pone.0020737-Yang2" target="_blank">[<b>14</b>]</a> subtypes (38 kDa) in SDS-PAGE.</p

Influenza A viruses H1–H13 and H16 subtypes used in this study for specificity evaluation.

<p>*Reassortant viruses generated from reverse genetics.</p

Analysis of human serum samples in H5 epitope-ELISA.

≠<p>Inhibition above the cut-off value of ≥30% blocking was considered positive (P).</p><p>*mean ± standard deviation of duplicate values of 2 independent experiments.</p>∧<p>Serum collected 2 days after the onset of infection.</p><p>P: positive, N: negative.</p

H5N1 subtype influenza A viruses used in this study.

<p>*Reassortant viruses generated from reverse genetics.</p

Recognition of H1–H13 and H16 rHA1 proteins by anti-H5N1 (A/Indonesia/CDC669/06-a representative for H5N1) chicken sera in immunodot blot.

<p>The membrane was blotted with column purified HA1 proteins of different subtypes, followed by incubation with anti-H5N1 chicken sera (A) or control chicken sera (B), and binding was evaluated with HRP-conjugated anti-chicken IgG.</p