Neutralizing monoclonal antibodies against porcinophilic foot-and-mouth disease virus mapped to antigenic site 2 by utilizing novel mutagenic virus-like particles to detect the antigenic change

In the case of serotype O foot-and-mouth disease virus (FMDV), antibodies against five neutralizing sites play a pivotal role in protection of animals, with site 1 being considered the most crucial. However, recent studies indicated that the antibodies of vaccinated farm animals are mainly against site 2 rather than site 1. In Taiwan, blanket vaccination had been implemented for more than fifteen years, in which the porcinophilic isolate O/Penghu/2012 showed significant amino acid alterations in site 2 compared to the early isolate O/TW/97. To study the antigenicity of site 2, MAbs against site 2 are required. In this study, we generated site 2 mutated virus-like particles (mVLPs) with only VP2-S72 N mutation, and successfully identified five site 2 MAbs from a previously prepared O/TW/97 MAb panel by immunofluorescence assay (IFA) and ELISA based on the different reactivity to wild-type VLP and mVLP. In conclusion, the established model was proved as an effective method to reveal the epitope that a MAb recognizes. By applying this MAb panel and sequence alignment, we demonstrated that the O/Penghu/2012 isolate not only showed significant genetic difference in site 2 but also significant antigenic difference from the ancestral O/TW/97.