Abstract
Many cases of human infection with the H7N9 virus have been detected in China since 2013. H7N9 viruses are maintained in chickens and are transmitted to humans at live bird markets. During circulation in birds, H7N9 viruses have accumulated amino acid substitutions in their hemagglutinin (HA), which resulted in an antigenically change in the recent H7N9 viruses. Here, we characterized 46 mouse monoclonal antibodies against the HA of the prototype strain. 16 H7-HA-specific monoclonal antibodies (mAbs) possessed hemagglutination inhibition (HI) and neutralization activities by recognizing the major antigenic site A; four other H7-HA-specific clones also showed HI and neutralizing activities via recognition of the major antigenic sites A and D; seven mAbs that reacted with several HA subtypes and possibly recognized the HA stem partially protected mice from lethal infection with prototype H7N9 virus; and the remaining 19 mAbs had neither HI nor neutralization activity. All human H7N9 viruses tested showed a similar neutralization sensitivity to the first group of 16 mAbs, whereas human H7N9 viruses isolated in 2016–2017 were not neutralized by a second group of 4 mAbs. These results suggest that amino acid substitutions at the epitope of the second mAb group appear to be involved in the antigenic drift of the H7N9 viruses. Further analysis is required to fully understand the antigenic change in H7N9 viruses.
Highlights
The first severe human cases of influenza A(H7N9) virus infection were reported in the spring of2003 [1]
These results suggest that these amino acid substitutions and creation of a novel N-linked glycosylation site might be involved in the low susceptibility of recent human H7N9 viruses to monoclonal antibodies (mAbs) clones [13-9-19-7 (#24), 10-2-9 (#25), 10-3-17 (#26), and 19-9-13 (#27)]
Epitope mapping using escape mutants and reactivity to 15 human H7N9 viruses revealed 20 neutralizing mAbs that could be roughly divided into two groups
Summary
The first severe human cases of influenza A(H7N9) virus infection were reported in the spring of2003 [1]. The highly pathogenic H7N9 viruses that were isolated from these human cases possessed amino acid mutations in HA and NA that enhances binding to human-type receptors and are associated with resistance to NA inhibitors [8,9]. One of these isolates, A/Guangdong/17SF003/2016, possessed three amino acid changes, two in PB2 and one in PA, that enhanced virus polymerase activity, virus growth in cultured cells, and pathogenicity in mice [10]; this virus transmitted among ferrets via respiratory droplets [11]. The emergence of such highly pathogenic H7N9 viruses is a serious threat to public health
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