Antigenicity of a type A influenza virus through comparison of hemagglutination inhibition and mass spectrometry immunoassays.

The antigenicity of a type A (H1N1) influenza strain has been characterised through the application of mass spectrometry (MS) and hemagglutination-inhibition immunoassays performed in parallel. Two monoclonal antibodies were found to be highly and equally specific in HI assays against influenza strain A/New Caledonia/20/99 while the MS immunoassay demonstrated that both antibodies recognise the same epitopic peptide localised to residues 225-232 of the hemagglutinin HA1 subunit whose C-terminal residues reside in close proximity to the receptor binding site. Both immunoassays showed no binding of a monoclonal antibody that recognizes the hemagglutinin antigen of type B strains.