Abstract
Four antigenic sites (designated Sa, Sb, Ca, and Cb) have been previously delineated on the hemagglutinin (HA) molecule of influenza A/PR/8/34 virus by means of anti-HA hybridoma antibodies. In the present study we show by radioimmunoassay that the binding of some radiolabeled antibodies to the antigenic site Sa is enhanced by the simultaneous binding of an antibody to the site Ca and, vice versa, the same anti-Sa antibodies enhance the binding of the anti-Ca antibody. The enhancement is maximal if the enhancing antibody saturates the available antigenic sites on the viral immunoadsorbent. One Sa antibody exhibits, under these conditions, a roughly 10-fold higher avidity for the corresponding antigenic site in the presence of enhancing antibody. The synergistic binding of these antibodies is not due to direct antibody-antibody interactions. We conclude, therefore, that the binding of these antibodies induces conformational changes in the HA molecule which result in the increased avidity of the given antibody-HA interactions.
Published Version
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