Inhibition of fusion activity of influenza A haemagglutinin mediated by HA2-specific monoclonal antibodies

Abstract

The effect of seven monoclonal antibodies (MAbs) specific to the light chain (HA2) of influenza A haemagglutinin (HA) on its fusion activity was investigated. These MAbs, which are non-virus neutralizing, defined four distinct antigenic sites on HA2 glycopolypeptide and the corresponding epitopes were attributed to the sequence stretches on HA2. The accessibility of all seven HA2 epitopes significantly increased after trypsin cleavage and pH 5 treatment of the HA (X-31). The influence of anti-HA2 MAbs on the fusion process was followed by cell-cell fusion of CHO cells expressing precursor HA, virus-liposome fusion assay, and haemolysis mediated by virus. MAb CF2, which bound directly to the fusion peptide 1-35 of HA2, was positive in all three fusion-inhibition assays and was the only one inhibiting the polykaryon formation of CHO-X-31 cells. Two other MAbs belonging to the same antigenic site but not binding directly to the fusion peptide inhibited virus to liposome fusion (EB12) or inhibited haemolysis (BB8). Moreover, MAb IIF4 binding to distinct antigenic site within 125-175 HA2 inhibited haemolysis, too. Thus, fusion activity of HA may be inhibited by anti-HA2 MAbs, mainly those binding to or near the fusion peptide. These antibodies represent useful probes for studies of influenza virus to cell membrane fusion.

Characterization of the Infectious Salmon Anemia Virus Fusion Protein

“…Type I fusion proteins contain a hydrophobic sequence, known as the fusion peptide (FP), at or near the new amino-terminal region created by the cleavage event (57,62,76), and their final (postfusion) state contains a characteristic ␣-helical coiled-coil core structure corresponding to a heptad repeat motif (12,57). In recent years, these structures have been targets for the development of new antiviral drugs, including fusion-inhibiting peptides and antibodies (20,50,82), suggesting that fusion proteins might be important candidates both for vaccination and as therapeutic targets.…”

Hemagglutinin stalk antibodies elicited by the 2009 pandemic influenza virus as a mechanism for the extinction of seasonal H1N1 viruses

“…An immune response can also be directed against the stalk of the influenza virus HA, but antibodies of this type are typically less abundant and less potent than are antibodies specific for the globular head. Nonetheless, antistalk antibodies can provide protection through passive transfer in animal models (7)(8)(9)(10)(11)(12)(13)(14). Whereas globular head antibodies can neutralize virus by preventing binding to the host cell, antistalk antibodies have been shown to act by preventing the fusion step of virus entry (13)(14)(15).…”

Two distinct regions of HA2 glycopolypeptide of influenza virus hemagglutinin elicit cross-protective immunity against influenza

“…Moreover, there are some regions of hA2 gp, which are conserved also among various subtypes (varečková et al, 2002, 2008). As we have shown previously, hA2 gp is immunogenic and able to induce a protective antibody response in mice (varečková et al, 2003a;Gocník et al, 2008). The most conserved part of hA2 gp is its n-terminus, FP.…”

“…In our previous studies we have shown that MAbs specific to hA2 gp, which are cross-reactive with different virus subtypes, inhibit the fusion activity of hA and reduce virus replication in vitro (varečková et al, 2002, 2003aStropkovská et al, 2009). these MAbs, when passively applied, protected mice against lethal infection with IAvs of homologous or heterologous hA subtype (Gocník et al, 2007;Janulíková, unpublished data).…”