Antigenic Epitopes in the Hemagglutinin of Qinghai-Type Influenza H5N1 Virus

Abstract

The highly pathogenic avian influenza H5N1 viruses have become widespread and evolved into several clades. In our previous studies, the antigenic sites of the H5 hemagglutinin (HA) were characterized by selection and sequencing of escape mutants. In the present studies we analyzed the antigenic epitopes recognized by monoclonal antibodies against avian influenza A/Duck/Novosibirsk/56/05 (H5N1) virus isolated in western Siberia and belonging to subclade 2.2 of the H5N1 viruses. The analysis revealed several antigenically relevant positions of amino acid residues in the globular head of the HA not encountered earlier in the escape mutants of the H5 subtype. The newly recognized positions (113, 117, 118, 120, and 123, mature H5 numbering) are concentrated in an area adjacent to the region described in earlier studies as corresponding to site B in H3 HA, but extending far beyond this area. The amino acid positions recognized by the monoclonal antibodies against A/Duck/Novosibirsk/56/05 (H5N1) virus differ from the positions recognized by the monoclonal antibodies against H5N2 influenza viruses. The data suggest that the evolution of the HA of H5 avian influenza viruses is associated not only with the changes of antigenic epitopes recognized by antibodies, but also with a change in the dominance of the immunogenicity of different sites in the HA.

Determination of H5N1 vaccine potency using reference antisera from heterologous strains of influenza

“…A fourth virus (A/Anhui/1/2005) for which limited quantities of reference antigen were available belongs to clade 2·3·4. Although of different clades, these four H5N1 virus HAs demonstrate substantial levels of antigenic homology, sharing more than a half of the antigenic sites discovered by mapping with H5 monoclonal antibodies 27 , 28 , 29 , 30 …”

Truncation and Sequence Shuffling of Segment 6 Generate Replication-Competent Neuraminidase-Negative Influenza H5N1 Viruses

“…During egg passages, immunogenic pressure results in the emergence of progeny viruses with mutations with an altered antigenic pattern (29). In vitro selection in the presence of monoclonal antibodies and polyclonal (rabbitor mouse-derived) antisera was utilized to identify several antigenic epitopes of the hemagglutinin (8,(30)(31)(32)(33) and the neuraminidase (34). Using polyclonal chicken sera in a cell culture system (10), we recently obtained escape variants whose variations reflect immunoescape beyond the major antigenic HA epitopes affecting several viral proteins.…”

“…The phenomenon of antigenic escape was classically investigated by the characterization of escape variants generated in vitro by virus passaging in the presence of monoclonal antibodies (7,8).…”

Highly Pathogenic Avian Influenza Virus Subtype H5N1 Escaping Neutralization: More than HA Variation

“…The importance of two of these residues is stressed by recent studies. Amino acid residues 157 and 178 were identified as relevant in the context of monoclonal immune characterization (37). More importantly, residue 157 was shown to be under positive selection in both avian and human hosts (7).…”

“…In different studies, antigenic epitopes in the hemagglutinin (HA) protein were identified by sequencing and structural mapping after generating escape variants in vitro using monoclonal antibodies (21,33,37) or polyclonal (rabbit-or mouse-derived) antiserum (3,23). However, polyclonal antisera from chickens were never used before to generate escape variants, although vaccine escape is a serious problem in influenza virus eradication programs for poultry, especially for HPAIV H5N1 (12).…”