Abstract
We mapped the hemagglutinin-esterase (HE) antigenic epitopes of the influenza C virus on the three-dimensional (3D) structure of the HE glycoprotein using 246 escape mutants that were selected by a panel of nine anti-HE monoclonal antibodies (MAbs), including seven of the C/Ann Arbor/1/50 virus and two of the C/Yamagata/15/2004 virus. The frequency of variant selection in the presence of anti-HE MAbs was very low, with frequencies ranging from 10−4.62 to 10−7.58 for the C/Ann Arbor/1/50 virus and from 10−7.11 to 10−9.25 for the C/Yamagata/15/2004 virus. Sequencing of mutant HE genes revealed 25 amino acid substitutions at 16 positions in three antigenic sites: A-1, A-2, and A-3, and a newly designated Y-1 site. In the 3D structure, the A-1 site was widely located around the receptor-binding site, the A-2 site was near the receptor-destroying enzyme site, and the Y-1 site was located in the loop on the topside of HE. The hemagglutination inhibition reactions of the MAbs with influenza C viruses, circulating between 1947 and 2016, were consistent with the antigenic-site amino acid changes. We also found some amino acid variations in the antigenic site of recently circulating strains with antigenic changes, suggesting that viruses that have the potential to alter antigenicity continue to circulate in humans.
Highlights
The influenza C virus is a member of the Orthomyxoviridae family of enveloped and segmented negative-sense RNA viruses, together with the influenza A virus and influenza B virus
We recently revealed that influenza C viruses can be divided, based on the HE gene, into six genetic and antigenic lineages, designated C/Taylor, C/Mississippi, C/Aichi, C/Yamagata, C/Kanagawa, and C/Sao Paulo [9]
The monoclonal antibodies (MAbs) used for the selection of escape mutants were generated against the HE glycoprotein of the C/Ann Arbor/1/50 strain [15,16,17] or the
Summary
The influenza C virus is a member of the Orthomyxoviridae family of enveloped and segmented negative-sense RNA viruses, together with the influenza A virus and influenza B virus. The fourth segment of the influenza C viral genome encodes the hemagglutinin-esterase (HE) glycoprotein, which is present in virions as a homotrimer. (432 amino acids) is the globular region of the HE protein, and HE2 (209 amino acids) is the stalk region [1]. This protein possesses three biological activities: receptor-binding activity for. 9-O-acetyl-N-acetylneuraminic acid, fusion with the host cell membrane, and receptor-destroying. HE glycoprotein is the counterpart of both hemagglutinin (HA) and neuraminidase (NA) in influenza A and B viruses. Whereas influenza A virus infects a variety of hosts, influenza C viruses are predominantly found in humans [5]. Influenza C virus usually causes mild upper respiratory tract illness in children but can cause lower respiratory tract illness, such as bronchitis and pneumonia, in children less than two years old [6,7,8]
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