Identification of a conformational neutralizing epitope on the VP1 protein of type A foot-and-mouth disease virus

Foot-and-mouth disease (FMD) caused by foot-and-mouth disease virus (FMDV), is a highly contagious infectious disease that affects domestic and wild cloven-hoofed animals worldwide. In recent years, outbreaks of serotype A FMD have occurred in many countries. High-affinity neutralizing antibodies against a conserved epitope could provide protective immunity against diverse subtypes of FMDV serotype A and protect against future pandemics. In this study, we generated a serotype A FMDV-specific potent neutralizing monoclonal antibody (MAb), 6C9, which recognizes a conformation-dependent epitope. MAb 6C9 potently neutralized FMDV A/XJBC/CHA/2010 with a 50% neutralization titer (NT50) of 4096. Screening of a phage-displayed random 12-mer peptide library revealed that MAb 6C9 bound to phages displaying the consensus motif YxxPxGDLG, which is highly homologous to the 135YxxPxxxxxGDLG147 motif found in the serotype A FMDV virus-encoded structural protein VP1. To further verify the authentic epitope recognized by MAb 6C9, two FMDV A/XJBC/CHA/2010 mutant viruses, P138A and G144A, were generated using a reverse genetic system. Subsequent micro-neutralization assays and double-antibody sandwich (DAS) ELISA analyses revealed that the Pro138 and Gly144 residues of the conformational epitope that are recognized by 6C9 are important for MAb 6C9 binding. Importantly, the epitope 135YxxPxxxxxGDLG147 was highly conserved among different topotypes of serotype A FMDV strains in a sequence alignment analysis. Thus, the results of this study could have potential applications in the development of novel epitope-based vaccines and suitable a MAb-based diagnostic method for the detection of serotype A FMDV and the quantitation of antibodies against this serotype.