Effect of the Addition of Oligosaccharides on the Biological Activities and Antigenicity of Influenza A/H3N2 Virus Hemagglutinin

Abstract

The hemagglutinin (HA) of influenza A virus is a homotrimeric glycoprotein with an ectodomain composed of a globular head and stem region (26). Both regions carry N-linked oligosaccharide chains. The appearance or disappearance of oligosaccharides on the globular head has been reported to occur naturally during antigenic drift of influenza A/H3N2 viruses from 1968 to 1975 (15, 24, 25). The acquisition of new oligosaccharides is an important mechanism underlying the antigenic drift of HA. Antigenic drift occurs by accumulation of a series of point mutations resulting in amino acid substitutions in antigenic sites on the surface of the HA (1, 25). These substitutions prevent neutralization by antibodies directed against previous epidemic strains.Based on analysis of the HA sequences of A/H3N2 viruses isolated from 1968 to 2002, the oligosaccharide chains on the globular head show large variations in number among different A/H3N2 isolates, although five glycosylation sites at Asn residues 8, 22, 38, 285, and 483 on the stem region are strictly conserved. Most of the A/H3N2 viruses that circulated between 1968 and 1974 (represented by A/Aichi/2/68) had only two oligosaccharides at residues 81 and 165 on the globular head of the HA (Fig. 1A). However, viruses isolated in 1975 (represented by A/Victoria/3/75) had lost a glycosylation site at residue 81 and gained two new sites at residues 63 and 126. The 1986 isolates (represented by A/Memphis/6/86) had acquired a new carbohydrate attachment site at residue 246, and the 1997 isolates (represented by A/Sydney/5/97) had obtained two additional sites at residues 122 and 133. Some recent isolates (represented by A/Panama/2007/99) had often obtained a novel site at residue 144. Thus, the A/H3N2 viruses recently circulating have six or seven glycosylation sites on the globular head of the HA, although whether these are glycosylated is not known. Moreover, the HAs of influenza A/H1N1 viruses and influenza B viruses isolated recently also possess several oligosaccharide chains on their globular head. These observations suggest that the addition of new oligosaccharides to the globular head of the HA may provide influenza viruses with an increased ability to prevail among humans (14). Interestingly, however, examination of the available HA sequences of influenza A/H2N2 viruses showed that none of the HAs had obtained a new glycosylation site on the globular head, and they had only one carbohydrate chain at position 169 (21).We previously studied the antigenic structure of the HA of A/H2N2 virus and revealed that most of the escape mutants selected by monoclonal antibodies had acquired a new glycosylation site at position 131, 160, or 187 on the tip of the HA (21,22,23). The results indicated that A/H2N2 viruses have the potential to gain at least one additional oligosaccharide on the globular head of the HA, although this has never occurred during 11 years of its circulation in humans. We constructed HA glycosylation site mutants containing one to three oligosaccharides at posi...

A bivalent influenza VLP vaccine confers complete inhibition of virus replication in lungs

“…In addition, three additional Nglycosylation motifs (Asn 44, 109 and 127, Table 1) are predicted from these amino acid differences in A/Philippines compared to A/Aichi, which may also modulate antigenicity. Carbohydrate masking of antigenic sites has been observed for HAs [24,25].…”

Pandemic H1N1 Influenza A Viruses Are Resistant to the Antiviral Activities of Innate Immune Proteins of the Collectin and Pentraxin Superfamilies

“…Amino acid substitutions associated with the appearance of oligosaccharides on the globular head region of HA are believed to effectively mask or modify antigenic sites from neutralizing Ab, and therefore represent an important immune evasion mechanism. Since their appearance in the human population in 1968, H3N2 subtype viruses have shown a progressive increase in N-linked glycosylation (24,25) and recently circulating strains generally carry six to seven potential sites in the globular head region of HA. Recent seasonal H1N1 viruses carry four to five N-glycosylation sequons on the head of HA (25,26) compared with the prototypic 1918 H1N1 pandemic strain A/ South Carolina/1/18 (SC18), which carried a single site (27).…”

Isolation of novel triple‐reassortant swine H3N2 influenza viruses possessing the hemagglutinin and neuraminidase genes of a seasonal influenza virus in Vietnam in 2010

“…The Vietnamese isolates lost five potential glycosylation sites at positions 8, 122, 133, 144, and 165 that are conserved among human isolates (Table 3). 13 Among them, glycosylation sites at positions 122 and 133 are located in the vicinity of the receptor‐binding site that is conserved in humans but not in swine isolates 14 . The loss of the glycosylation sites at those positions could affect receptor recognition of the SIVs.…”