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: 9.67). 11/2011; 108(51):E1417-22. DOI: 10.1073/pnas.1108754108
Source: PubMed


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.

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    • "Glycan masking to avoid antibody neutralization by sterically blocking antibody-epitope interaction is a strategy used by viruses such as influenza and HIV [29], [30]. H5N1 viruses have evolved into distinct antigenic clades and subclades, and uncertainty regarding which strain will be involved in an expected pandemic outbreak increases the stakes for making the correct selection for vaccine development [18]. "
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    ABSTRACT: The highly pathogenic avian influenza (HPAI) H5N1 virus, a known trigger of diseases in poultry and humans, is perceived as a serious threat to public health. There is a clear need for a broadly protective H5N1 vaccine or vaccines for inducing neutralizing antibodies against multiple clades/subclades. We constructed single, double, and triple mutants of glycan-masked hemagglutiinin (HA) antigens at residues 83, 127 and 138 (i.e., g83, g127, g138, g83+g127, g127+g138, g83+g138 and g83+g127+g138), and then obtained their corresponding HA-expressing adenovirus vectors and recombinant HA proteins using a prime-boost immunization strategy. Our results indicate that the glycan-masked g127+g138 double mutant induced more potent HA-inhibition, virus neutralization antibodies, cross-clade protection against heterologous H5N1 clades, correlated with the enhanced bindings to the receptor binding sites and the highly conserved stem region of HA. The immune refocusing stem-specific antibodies elicited by the glycan-masked H5HA g127+g138 and g83+g127+g138 mutants overlapped with broadly neutralizing epitopes of the CR6261 monoclonal antibody that neutralizes most group 1 subtypes. These findings may provide useful information in the development of a broadly protective H5N1 influenza vaccine.
    PLoS ONE 03/2014; 9(3):e92822. DOI:10.1371/journal.pone.0092822 · 3.23 Impact Factor
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    • "The loss of the NLG site at residue 131 increased the binding affinity of the virus to 6' SA, but there appeared to be no effect on the specificity for 3' SA. When mapped in the HA crystal structure of A/Puerto Rico/8/34, glycosite 131 is located right next to the RBS.35,56 Due to the bulky side chains of oligosaccharides, NLG at this position might interfere heavily with the viral life cycle by blocking efficient access of HA to the SA receptor. "
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    ABSTRACT: Since the 1918 influenza A virus (IAV) pandemic, H1N1 viruses have circulated in human populations. The hemagglutinin (HA) of IAV determines viral antigenicity and often undergoes N-linked glycosylation (NLG) at several sites. Interestingly, structural analysis of the 1918 and 2009 H1N1 pandemic viruses revealed antigenic similarities attributable to the conserved epitopes and the NLG statuses of their HA proteins. NLG of the globular head of HA is known to modulate the antigenicity, fusion activity, virulence, receptor-binding specificity, and immune evasion of IAV. In addition, the HA of IAV often retains additional mutations. These supplemental mutations compensate for the attenuation of viral properties resulting from the introduced NLG. In human H1N1 viruses, the number and location of NLG sites has been regulated in accordance with the antigenic variability of the NLG-targeted antibody-binding site. The relationship between the NLG and the antigenic variance in HA appears to be stably controlled in the viral context.
    Yonsei medical journal 09/2012; 53(5):886-93. DOI:10.3349/ymj.2012.53.5.886 · 1.29 Impact Factor
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    • "Since the charge+ and charge− substitutions exert opposite effects to the gain and loss of NGS on virus infection and release [6], [24], and the net-charge can be changed more easily than the number of NGS, it is likely that the charge+ and charge− substitutions have occurred to compensate for the deleterious effect of the gain and loss of NGS. It has been reported that the virus that gained NGS in HA could escape from neutralization by Ab only after the occurrence of compensatory amino acid substitutions raising the avidity [24]. Although the loss of NGS in HA1 enhances the virus infectivity, it is also problematic because it impairs the release of progeny viruses from infected cells, inducing self-aggregation at the cell surface [23], [30], [31]. "
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    ABSTRACT: The propagation of influenza A virus depends on the balance between the activities of hemagglutinin (HA) for binding to host cells and neuraminidase (NA) for releasing from infected cells (HA-NA balance). Since the host cell membrane and the sialic acid receptor are negatively charged, the amino acid substitutions increasing (charge+) and decreasing (charge-) the positive charge of HA subunit 1 (HA1) enhance and reduce, respectively, the binding avidity and affinity. The positive charge of HA1 in human influenza A virus bearing subtype H3N2 (A/H3N2 virus) was observed to have increased during evolution, but the evolutionary mechanism for this observation was unclear because this may disrupt the HA-NA balance. Here we show, from the phylogenetic analysis of HA for human A/H3N2 and A/H1N1 viruses, that the relative frequencies of charge+ and charge- substitutions were elevated on the branches where the number of N-glycosylation sites (NGS) increased and decreased, respectively, compared to those where the number of NGS did not change. On the latter branches, the net-charge of HA1 appeared to have been largely maintained to preserve its structure and function. Since the charge+ and charge- substitutions in HA1 have opposite effects to the gain and loss of NGS on the binding and release of the virus, the net-charge of HA1 may have evolved to compensate for the effect of the gain and loss of NGS, probably through changing the avidity. Apparently, the relative frequency of charge- substitutions in HA1 of A/H3N2 virus was elevated after the introduction of oseltamivir, and that of charge+ substitutions in HA1 of A/H1N1 virus was elevated after the spread of oseltamivir resistance. These observations may also be explained by the compensatory effect of the net-charge in HA1 on the NA activity for keeping the HA-NA balance.
    PLoS ONE 07/2012; 7(7):e40422. DOI:10.1371/journal.pone.0040422 · 3.23 Impact Factor
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