Cross-Protective Potential of a Novel Monoclonal Antibody Directed against Antigenic Site B of the Hemagglutinin of Influenza A Viruses

• DOI: 10.1371/journal.ppat.1000350
• Publication Date: 2009-03-19T22:29:10Z
• Authors: Reiko Yoshida; Manabu Igarashi; Hiroichi Ozaki; Noriko Kishida; Daisuke Tomabechi; Hiroshi Kida; Kimihito Ito; Ayato Takada
• Keywords: 493; QH301-705.5; Molecular Sequence Data; Enzyme-Linked Immunosorbent Assay; Hemagglutinin Glycoproteins, Influenza Virus; Cross Reactions; Antibodies, Viral; Epitopes; Mice; 03 medical and health sciences; 0302 clinical medicine; Orthomyxoviridae Infections; Antibody Specificity; Animals; Amino Acid Sequence; Biology (General); Mice, Inbred BALB C; Reverse Transcriptase Polymerase Chain Reaction; Immunization, Passive; Antibodies, Monoclonal; RC581-607; 3. Good health; Influenza A virus; Female; Immunologic diseases. Allergy; Research Article

The hemagglutinin (HA) of influenza A viruses has been classified into sixteen distinct subtypes (H1-H16) to date. The HA subtypes of influenza A viruses are principally defined as serotypes determined by neutralization or hemagglutination inhibition tests using polyclonal antisera to the respective HA subtypes, which have little cross-reactivity to the other HA subtypes. Thus, it is generally believed that the neutralizing antibodies are not broadly cross-reactive among HA subtypes. In this study, we generated a novel monoclonal antibody (MAb) specific to HA, designated MAb S139/1, which showed heterosubtypic cross-reactive neutralization and hemagglutination inhibition of influenza A viruses. This MAb was found to have broad reactivity to many other viruses (H1, H2, H3, H5, H9, and H13 subtypes) in enzyme-linked immunosorbent assays. We further found that MAb S139/1 showed neutralization and hemagglutination-inhibition activities against particular strains of H1, H2, H3, and H13 subtypes of influenza A viruses. Mutant viruses that escaped neutralization by MAb S139/1 were selected from the A/Aichi/2/68 (H3N2), A/Adachi/2/57 (H2N2), and A/WSN/33 (H1N1) strains, and sequence analysis of the HA genes of these escape mutants revealed amino acid substitutions at positions 156, 158, and 193 (H3 numbering). A molecular modeling study showed that these amino acids were located on the globular head of the HA and formed a novel conformational epitope adjacent to the receptor-binding domain of HA. Furthermore, passive immunization of mice with MAb S139/1 provided heterosubtypic protection. These results demonstrate that MAb S139/1 binds to a common antigenic site shared among a variety of HA subtypes and neutralizes viral infectivity in vitro and in vivo by affecting viral attachment to cells. The present study supports the notion that cross-reactive antibodies play some roles in heterosubtypic immunity against influenza A virus infection, and underscores the potential therapeutic utility of cross-reactive antibodies against influenza.