Abstract
Foot-and-mouth disease virus (FMDV) vaccines protect animals from infection by inducing antibodies. The level of neutralising antibody induced in response to vaccination (or infection), as measured by a virus neutralisation test, is an important parameter with regards to the level of protection afforded against subsequent challenge. However, in addition to overall titre, antibody avidity also represents a crucial metric when assessing the protective efficacy of antibodies. In this project we investigated the use of biolayer interferometry (BLI) to measure the avidity of FMDV antibodies to FMDV antigens. Antibodies targeting site I of the FMDV particle were detected using a commercially synthesised biotinylated peptide. In contrast, the entire antigenic landscape of the FMDV particle was represented by biotinylated FMDV capsids. The antigens were loaded onto Octet streptavidin biosensors at an optimal concentration prior to dipping into antibodies. The sera from different animals varied in avidity, reflecting the quantitative differences in avidity that exist between individual animals in response to FMDV vaccines. Interestingly, the Kdis values obtained for site I vs the entire capsid were different, supporting the importance of other sites beyond site I. Similarly, monoclonal antibodies targeting distinct, known antigenic sites on the capsid surface also resulted in different avidities. The BLI methodology reported here offers a useful approach by which to investigate the strength of antibody interactions at specific sites. In conjunction with recombinant technology, BLI will help aid in investigations into the relative importance of the different antigenic sites with regards to inducing a protective response.