Immunodominance of Antigenic Site B over Site A of Hemagglutinin of Recent H3N2 Influenza Viruses

H3N2 influenza viruses have now circulated in the human population for 43 years since the pandemic of 1968, accumulating sequence changes in the hemagglutinin (HA) and neuraminidase (NA) that are believed to be predominantly due to selection for escape from antibodies. Examination of mutations that persist and accumulate led to identification of antigenically significant mutations that are contained in five antigenic sites (A–E) mapped on to the H3 HA. In early H3N2 isolates, antigenic site A appeared to be dominant while in the 1990s site B seemed more important. To obtain experimental evidence for dominance of antigenic sites on modern H3 HAs, we have measured antibodies in plasma of human subjects who received the 2006–07 trivalent subunit influenza vaccine (H3 component A/Wisconsin/67/05) or the 2008–09 formulation (H3 component A/Uruguay/716/07). Plasmas were tested against expressed HA of Wisconsin-like influenza A/Oklahoma/309/06 and site-directed mutants in antigenic site A (NNES121-124ITEG, N126T, N133D, TSSS135-138GSNA, K140I, RSNNS142-146PGSG), and antigenic site B (HL156-157KS, KFK158-160GST, NDQI189-192QEQT, A196V). “Native ELISA” analysis and escape mutant selection with two human monoclonal antibodies demonstrated that antibody E05 binds to antigenic site A and 1_C02 binds to site B. We find that most individuals, after vaccination in seasons 2006–07 and/or 2008–09, showed dominance of antigenic site B recognition over antigenic site A. A minority showed dominance of site A in 2006 but these were reduced in 2008 when the vaccine virus had a site A mutation. A better understanding of immunodominance may allow prediction of future antigenic drift and assist in vaccine strain selection.

自1968年大流行以来，H3N2型流感病毒（H3N2 influenza viruses）已在人群中传播了43年，其血凝素（hemagglutinin, HA）和神经氨酸酶（neuraminidase, NA）积累了序列变异，这类变异被认为主要源于针对抗体逃逸的选择压力。对持续存在并不断积累的突变进行分析后，研究人员鉴定出了抗原显著性突变，这些突变位于H3 HA上定位的5个抗原表位（A至E）中。在早期H3N2分离株中，抗原表位A似乎占据主导地位；而在20世纪90年代，表位B则更为关键。为获取现代H3 HA上抗原表位主导性的实验证据，我们检测了接种2006-2007年度三价亚单位流感疫苗（其H3成分为A/Wisconsin/67/05）或2008-2009年度疫苗（其H3成分为A/Uruguay/716/07）的人类受试者血浆中的抗体。我们以类Wisconsin甲型流感病毒A/Oklahoma/309/06的表达HA，以及抗原表位A的定点突变体（NNES121-124ITEG、N126T、N133D、TSSS135-138GSNA、K140I、RSNNS142-146PGSG）和抗原表位B的定点突变体（HL156-157KS、KFK158-160GST、NDQI189-192QEQT、A196V）为检测底物，开展抗体检测。天然酶联免疫吸附试验（Native ELISA）分析与两株人源单克隆抗体的逃逸突变株筛选实验证实，抗体E05结合抗原表位A，而1_C02结合表位B。我们发现，在2006-2007和/或2008-2009年度接种疫苗的多数个体中，其针对抗原表位B的抗体识别优势高于表位A。2006年有少数个体表现出表位A的识别优势，但当2008年的疫苗毒株携带表位A突变后，这类个体的占比有所降低。对免疫显性（immunodominance）的深入认知，有望为未来抗原漂移（antigenic drift）的预测提供依据，并辅助疫苗毒株的筛选工作。