ANTIGENIC STRUCTURE OF INFLUENZA A VIRUS SUBTYPE H5 HEMAGGLUTININ: MECHANISM OF THE ACQUISITION OF RESISTANCE TO MONOCLONAL ANTIBODIES IN ESCAPE MUTANTS

摘要

An analysis of escape mutants of avian influenza virus of subtype H5 (strain A/Mlalard/Pennsylvania/10218/84) revealed the localization and structure of two antigenic sites in the hemagglutinin (HA) molecule. Certain escape mutants exhibited unusual properties in immunologic reactions with monoclonal antibodies. In the reaction of neutralization of infectiousness they were completely resistant to the monoclonal antibody (MAB) used for selection of this mutant, but they retained the ability to bind the MAB, detected in enzyme-linked immunosorbent assay (ELISA). In one of these mutants, binding of the MAB increased after the acquisition of an additional amino acid substitution (AAS) in a different site but disappeared entirely in the presence of a mutation selected for by successive passages in the presence of an MAB capable of binding to HA but not exhibiting a neutralizing effect. The observed effects were not due to changes in the affinity of the HA of escape mutants for the sialic receptor. The data obtained suggest that the same AAS in the antigenic site may prevent neutralization of the virus by different methods for different MABs that react with the same epitope, or binding of MABs is prevented, or the bound antibody molecule does not block the receptor-recognizing pocket of the HA molecule. Various mechanisms of acquisition of resistance to MABs during the selection of escape mutants with respect to the HA gene are discussed.