Antigenic variants with amino acid deletions clarify a neutralizing epitope specific for influenza B virus Victoria group strains

To study the neutralizing epitopes of influenza B virus Victoria group stra ins, two monoclonal antibodies (MAbs) were used to select antigenic variant s of the virus. MAbs 10B8 and 8E6 were found to react with B/Victoria group strains in three tests, peroxidase-antiperoxidase staining, haemagglutinat ion inhibition and neutralization tests; no reactivity with B/Yamagata grou p strains was observed. Analysis of the deduced amino acid sequences of 10B 8-induced variants identified a single amino acid deletion at residue 165 o r 170, as well as a single amino acid substitution at residues 164(Asp --> Tyr), 165 (Asn --> Ser or Thr) or 203 (Lys --> Thr or Asn). A single amino acid substitution at residue 241 (Pro --> Ser) was observed in 8E6-induced variants. Three-dimensional analysis showed that the epitopes for both MAbs were situated in close proximity to each other. Since B/Yamagata group str ains are characterized by amino acid deletions at residues 164-166, the epi tope for MAb 10B8 is strictly specific for B/ Victoria group strains.