Topological mapping of antigenic sites on the influenza A/PR/8/34 virus hemagglutinin using monoclonal antibodies

It was found that several antibodies directed against the site Sa did not compete with the binding of a radiolabeled antibody to the site Cb and, vice versa, antibody directed against site C b did not competing with the Binding of a Radiolabeling antibody to site Sa, proving unequivocally that at least part of the “strain-specific” site Sa and of the“cross-reactive” sites Cb are topologically distinct.

Abstract

We have previously constructed an antigenic map of the PR8 virus hemagglutinin (HA) using monoclonal antibodies and PR8 virus antigenic variants. Four different antigenic sites were operationally defined: two predominantly "strain-specific" antigenic sites (designated Sa and Sb) and two predominantly "cross-reactive" antigenic sites (designated Ca and Cb). In the present study, we have conducted competitive binding assays using monoclonal antibodies to investigate the topologic relationship among these antigenic sites. It was found that several antibodies directed against the site Sa did not compete with the binding of a radiolabeled antibody to the site Cb and, vice versa, antibodies directed against site Cb did not compete with the binding of a radiolabeled antibody to site Sa. This proved unequivocally that at least part of the "strain-specific" site Sa and of the "cross-reactive" site Cb are topologically distinct. Various degrees of competition were observed, however, between other antibodies directed against operationally defined antigenic sites. This may indicate that parts of these sites are either structurally overlapping or in close proximity. Alternatively, it is possible that the binding of antibody to any of these sites allosterically affects the binding of antibody at topologically distant sites.