Antigenic Surveillance of the Influenza Virus by Mass Spectrometry

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Abstract
The use of a mass spectrometric-based immunoassay to survey the antigenic identity of a type A influenza strain is described. Antigenic surveillance of the influenza virus remains a critical step in the identification of new viral strains and the subsequent use of such strains or synthetic constructs in vaccine preparations. The immunoassay is shown to be capable of detecting a determinant of a single hemagglutinin antigen, responsible for the initial stages of infection, in a mixture of viral proteins with high sensitivity and specificity. The determinant comprises residues 207−225 of the hemagglutinin HA1 chain of the type A strain which occupies a highly accessible region of β-sheet atop the antigen. Peptide determinants are identified without the need to immobilize antibody or isolate antibody−peptide complexes which are shown to be preserved during mass spectrometric analysis. This immunoassay achieves optimal sensitivity (femtomole level) with minimal sample handling and is amenable to high sample throughput and automation. Determinants are identified by a direct comparison of the matrix-assisted laser desorption ionization mass spectra obtained for an antibody reaction mixture and unreacted control. The sequence and antigenic identity of a component antigen can be rapidly identified by searching protein databases with the mass spectral data in conjunction with tandem mass spectrometric sequencing.