Fitness costs limit influenza A virus hemagglutinin glycosylation as an immune evasion strategy.

Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 11/2011; 108(51):E1417-22. DOI: 10.1073/pnas.1108754108
Source: PubMed

ABSTRACT Here, we address the question of why the influenza A virus hemagglutinin (HA) does not escape immunity by hyperglycosylation. Uniquely among dozens of monoclonal antibodies specific for A/Puerto Rico/8/34, escape from H28-A2 neutralization requires substitutions introducing N-linked glycosylation at residue 131 or 144 in the globular domain. This escape decreases viral binding to cellular receptors, which must be compensated for by additional substitutions in HA or neuraminidase that enable viral replication. Sequence analysis of circulating H1 influenza viruses confirms the in vivo relevance of our findings: natural occurrence of glycosylation at residue 131 is always accompanied by a compensatory mutation known to increase HA receptor avidity. In vaccinated mice challenged with WT vs. H28-A2 escape mutants, the selective advantage conferred by glycan-mediated global reduction in antigenicity is trumped by the costs of diminished receptor avidity. These findings show that, although N-linked glycosylation can broadly diminish HA antigenicity, fitness costs restrict its deployment in immune evasion.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A(H3N2) influenza viruses have circulated in humans since 1968, and antigenic drift of the hemagglutinin (HA) protein continues to be a driving force that allows the virus to escape the human immune response. Since the major antigenic sites of the HA overlap into the receptor binding site (RBS) of the molecule, the virus constantly struggles to effectively adapt to host immune responses, without compromising its functionality. Here, we have structurally assessed the evolution of the A(H3N2) virus HA RBS, using an established recombinant expression system. Glycan binding specificities of nineteen A(H3N2) influenza virus HAs, each a component of the seasonal influenza vaccine between 1968 and 2012, were analyzed. Results suggest that while its receptor-binding site has evolved from one that can bind a broad range of human receptor analogs to one with a more restricted binding profile for longer glycans, the virus continues to circulate and transmit efficiently among humans.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: H6N6 viruses are commonly isolated from domestic ducks and avian-to-swine transmissions of H6N6 viruses have been detected in China. Whether subsequent adaptation of H6N6 viruses in mammals would increase their pathogenicity towards humans is not known. To address this, we generated a mouse-adapted swine influenza H6N6 virus (GDK6-MA) which exhibited greater virulence than the wild-type virus (GDK6). Amino acid substitutions in PB2 (E627K), PA (I38M) and HA (L111F, H156N and S263R) occurred in GDK6-MA. HA H156N resulted in enlarged plaque sizes on MDCK cells and enhanced early stage viral replication in mammalian cells. PA I38M raised polymerase activity in vitro but did not change virus replication in either mammalian cells or mice. These single substitutions had only limited effects on virulence, however, a combination of HA H156N, S263R and PA I38M in the GDK6 backbone led to a significantly more virulent variant. This suggests these substitutions can compensate for the lack of PB2-627K and modulate virulence, revealing a new determinant of pathogenicity for H6N6 viruses in mice, which might also pose a threat to human health.
    Journal of Virology 10/2014; DOI:10.1128/JVI.01736-14 · 4.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The extent of the role of N-linked glycans (N-glycans) in shielding influenza A hemagglutinin against host antibodies has proved controversial, with different authors making widely different assumptions. One common assumption is that N-glycans physically shield surface residues that are near to glycosylation sites, thereby preventing antibodies from binding to them. However, it is unclear, from existing experimental evidence, whether antibodies that bind close to N-glycans are a rare or commonplace feature of human herd immune responses to influenza A hemagglutinin. The aim of this paper is to present a computational analysis of mutations in the vicinity of N-glycans that will facilitate a better understanding of their protective role. We identify, from an analysis of over 6,000 influenza A H3N2 sequences, a set of residues adjacent to N-glycosylation sites that are highly likely to be involved in antigenic escape from host antibodies. Fifteen of these residues occur within 10Å of an N-glycosylation site. Hence we conclude that it is relatively common for antibodies to bind in close proximity to N-glycans on the surface of hemagglutinin, with any shielding effect largely attributable to the inability of host antibodies to bind across an N-glycan attachment site, rather than to the physical masking of neighbouring residues.
    Glycobiology 09/2014; 25(1). DOI:10.1093/glycob/cwu097 · 3.75 Impact Factor

Full-text (2 Sources)

Available from
May 28, 2014