title: Emerging antigenic variants at the antigenic site Sb in pandemic A(H1N1)2009 influenza virus in Japan detected by a human monoclonal antibody.
abstract: The swine-origin pandemic A(H1N1)2009 virus, A(H1N1)pdm09, is still circulating in parts of the human population. To monitor variants that may escape from vaccination specificity, antigenic characterization of circulating viruses is important. In this study, a hybridoma clone producing human monoclonal antibody against A(H1N1)pdm09, designated 5E4, was prepared using peripheral lymphocytes from a vaccinated volunteer. The 5E4 showed viral neutralization activity and inhibited hemagglutination. 5E4 escape mutants harbored amino acid substitutions (A189T and D190E) in the hemagglutinin (HA) protein, suggesting that 5E4 recognized the antigenic site Sb in the HA protein. To study the diversity of Sb in A(H1N1)pdm09, 58 viral isolates were obtained during the 2009/10 and 2010/11 winter seasons in Osaka, Japan. Hemagglutination-inhibition titers were significantly reduced against 5E4 in the 2010/11 compared with the 2009/10 samples. Viral neutralizing titers were also significantly decreased in the 2010/11 samples. By contrast, isolated samples reacted well to ferret anti-A(H1N1)pdm09 serum from both seasons. Nonsynonymous substitution rates revealed that the variant Sb and Ca2 sequences were being positively selected between 2009/10 and 2010/11. In 7,415 HA protein sequences derived from GenBank, variants in the antigenic sites Sa and Sb increased significantly worldwide from 2009 to 2013. These results indicate that the antigenic variants in Sb are likely to be in global circulation currently.
authors.affiliation: Department of Virology, Research Institute for Microbial Diseases (RIMD), Osaka University, Suita, Osaka, Japan ; Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Izumisano, Osaka, Japan ; The Japan Science and Technology Agency/Japan International Cooperation Agency, Science and Technology Research Partnership for Sustainable Development (JST/JICA, SATREPS), Tokyo, Japan.
authors.forename: Mayo
authors.initials: M
authors.lastname: Yasugi
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Kubota-Koketsu
authors.forename: Akifumi
authors.initials: A
authors.lastname: Yamashita
authors.forename: Norihito
authors.initials: N
authors.lastname: Kawashita
authors.forename: Anariwa
authors.initials: A
authors.lastname: Du
authors.forename: Ryo
authors.initials: R
authors.lastname: Misaki
authors.forename: Motoki
authors.initials: M
authors.lastname: Kuhara
authors.forename: Naphatsawan
authors.initials: N
authors.lastname: Boonsathorn
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Fujiyama
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Okuno
authors.forename: Takaaki
authors.initials: T
authors.lastname: Nakaya
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Ikuta
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D002417:Cattle; D005455:Fluorescent Antibody Technique; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal