Hemagglutinin stalk antibodies elicited by the 2009 pandemic influenza virus as a mechanism for the extinction of seasonal H1N1 viruses

Department of Microbiology, Emerging Pathogens Institute, Mount Sinai School of Medicine, New York, NY 10029, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 02/2012; 109(7):2573-8. DOI: 10.1073/pnas.1200039109
Source: PubMed


After the emergence of pandemic influenza viruses in 1957, 1968, and 2009, existing seasonal viruses were observed to be replaced in the human population by the novel pandemic strains. We have previously hypothesized that the replacement of seasonal strains was mediated, in part, by a population-scale boost in antibodies specific for conserved regions of the hemagglutinin stalk and the viral neuraminidase. Numerous recent studies have shown the role of stalk-specific antibodies in neutralization of influenza viruses; the finding that stalk antibodies can effectively neutralize virus alters the existing dogma that influenza virus neutralization is mediated solely by antibodies that react with the globular head of the viral hemagglutinin. The present study explores the possibility that stalk-specific antibodies were boosted by infection with the 2009 H1N1 pandemic virus and that those antibodies could have contributed to the disappearance of existing seasonal H1N1 influenza virus strains. To study stalk-specific antibodies, we have developed chimeric hemagglutinin constructs that enable the measurement of antibodies that bind the hemagglutinin protein and neutralize virus but do not have hemagglutination inhibition activity. Using these chimeric hemagglutinin reagents, we show that infection with the 2009 pandemic H1N1 virus elicited a boost in titer of virus-neutralizing antibodies directed against the hemagglutinin stalk. In addition, we describe assays that can be used to measure influenza virus-neutralizing antibodies that are not detected in the traditional hemagglutination inhibition assay.

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    • "Here we investigate the prevalence of anti-HA stalk antibodies in different age groups. Using reagents based on chimeric HAs (cHAs) (26,27), we determined titers for the group 1, group 2, and influenza B virus HA stalk domains in children (6 to 59 months), adults (18 to 49 years), and elderly individuals (65 years). Immunity was measured pre-and postvaccination with a licensed recombinant-protein-based influenza virus vaccine (28, 29). "
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    ABSTRACT: Influenza remains a major global health burden. Seasonal vaccines offer protection but can be rendered less effective when the virus undergoes extensive antigenic drift. Antibodies that target the highly conserved hemagglutinin stalk can protect against drifted viruses, and vaccine constructs designed to induce such antibodies form the basis for a universal influenza virus vaccine approach. In this study, we analyzed baseline and postvaccination serum samples of children (6 to 59 months), adults (18 to 49 years), and elderly individuals (≥65 years) who participated in clinical trials with a recombinant hemagglutinin-based vaccine. We found that baseline IgG and IgA antibodies against the H1 stalk domain correlated with the ages of patients. Children generally had very low baseline titers and did not respond well to the vaccine in terms of making stalk-specific antibodies. Adults showed the highest induction of stalk-specific antibodies, but the elderly had the highest absolute antibody titers against the stalk. Importantly, the stalk antibodies measured by enzyme-linked immunosorbent assay (ELISA) showed neutralizing activity in neutralization assays and protected mice in a passive-transfer model in a stalk titer-dependent manner. Finally, we found similar patterns of stalk-specific antibodies directed against the H3 and influenza B virus hemagglutinins, albeit at lower levels than those measured against the H1 stalk. The relatively high levels of stalk-specific antibodies in the elderly patients may explain the previously reported low influenza virus infection rates in this age group. (This study has been registered at under registration no. NCT00336453, NCT00539981, and NCT00395174.) IMPORTANCE The present study provides evidence that titers of broadly neutralizing hemagglutinin stalk-reactive antibodies increase with age, possibly due to repeated exposure to divergent influenza viruses. These relatively high levels of antistalk titers may be responsible for lower circulation rates of influenza viruses in older individuals. Our findings suggest that the level of antistalk antibodies is a good surrogate marker for protection against influenza virus infection. In addition, the levels of antistalk antibodies might determine the breadth of protection against different drifted strains.
    Full-text · Article · Mar 2016 · mBio
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    • "The HA mutations could change the epitope to escape the host immune response (Caton et al., 1982; Wiley et al., 1981). Thus, how to elicit the immune response against highly conserved region on HA with broad neutralizing activity is important for vaccine development (Ekiert et al., 2012; Lee et al., 2012; Pica et al., 2012). HA is activated by the proteolytic cleavage of the intact HA (HA0) into HA1 and HA2. "
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    ABSTRACT: Neutralizing antibodies on the globular head of the hemagglutinin (HA) of avian influenza virus (AIV) are crucial for controlling this disease. However, most neutralizing antibodies lack cross reaction. This report describes the identification of a hemagglutinin epitope on the globular head near the receptor binding site of the H6N1 AIV. A monoclonal antibody named EB2 was prepared against the H6N1 AIV HA. Flow cytometry of AIV-infected chicken embryo fibroblast, DF-1 cells and specific-pathogen-free embryonated eggs were used to verify the neutralizing activity of this mAb. To narrow down the binding region, partially overlapping HA fragments and synthetic peptides were used to map the epitope by immune-blotting. The linear motif RYVRMGTESMN, located on the surface on the globular head of the HA protein, was identified as the epitope bound by EB2 mAb. Alignment of the EB2-defined epitope with other H6 AIVs showed that this epitope was conserved and specific to H6. We propose that this motif is a linear B-cell epitope of the HA protein and is near the receptor binding site. The identified epitope might be useful for clinical applications and as a tool for further study of the structure and function of the AIV HA protein.
    Full-text · Article · Dec 2014 · Veterinary Microbiology
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    • "542 2014 K. Uranowska and others that they act by preventing the fusion step of viral entry. It was also confirmed that anti-stalk antibodies elicited by infection with the 2009 pH1N1 have contributed to the disappearance of normally circulating H1N1 influenza virus strains in the following season (Pica et al., 2012; Sangster et al., 2013). Antigenically conserved HA stalk domain is thus a promising candidate for preparation of a broadly protective universal influenza vaccine; a potential immunogen that would focus the immune response on the conserved epitopes and would elicit anti-stalk neutralizing antibodies , and may probably give higher protection against different strains of the virus. "
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    ABSTRACT: Influenza A virus infections are the major public health concern and cause significant morbidity and mortality each year worldwide. Vaccination is the main strategy of influenza epidemic prevention. However, seasonal vaccines induce strain-specific immunity and must be reformulated annually based on prediction of the strains that will circulate in the next season. Thus, it is essential to develop vaccines that would induce broad and persistent immunity to influenza viruses. Hemagglutinin is the major surface antigen of the influenza virus. Recent studies revealed the importance of HA stalk-specific antibodies in neutralization of different influenza virus strains. Therefore, it is important to design an immunogen that would focus the immune response on the HA stalk domain in order to elicit neutralizing antibodies. In the present study, we report characterization of a conserved truncated protein, potentially a universal influenza virus antigen from the H5N1 Highly Pathogenic Avian Influenza A virus strain. Our results indicate that exposure of the HA stalk domain containing conserved epitopes results in cross reactivity with different antibodies (against group 1 and 2 HAs). Additionally, we conclude that HA stalk domain contains not only conformational epitopes recognized by universal FI6 antibody, but also linear epitopes recognized by other antibodies.
    Full-text · Article · Sep 2014 · Acta biochimica Polonica
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