Development of Serological Tools to Support the Control of Foot-and-mouth Disease in Egypt

Inter-serotype cross-reactivity in foot-and-mouth disease virus (FMDV) specific antibody ELISAs can exceed 50%, which can lead to incorrect serotyping. The hypothesis of this project is that the hypervariable G-H loop within the capsid protein VP1 of FMDV can serve as a serotype-specific target to develop novel peptide ELISAs. Results show that G-H loop peptides present FMDV epitopes, however, cross reactivity was seen between the tested serotypes. Further custom-designed peptides related to the O1K and A22 strains were tested against a set of experimental sera to understand the factors that underpin the inter-serotype cross-reactivity of G-H loop. Sensitivity and specificity were higher in serotype O than A; with the A peptide suffering from cross-reactivity against Asia1 sera. This led to the design of overlapping peptides, which highlighted the important role of amino acid residues surrounding the RGD motif with different patterns of reactivity for homologous (A) and heterologous (Asia 1) sera, indicating that type-specific and cross-reactive epitopes are in close proximity but are not identical. This conclusion was supported by testing peptides with mutated RGDL residues. To map the cross-reactive epitopes within the G-H loop, a set of monoclonal antibodies were tested against the peptides, showing that the cross-reactive epitope is located around the RGD motif which could explain the inter-serotypic cross-reactivity observed in diagnostic serological assays. The impact of the RGD motif was further studied using peptides based on non-FMD viruses that contain an RGD motif, where highly cross-reactive FMDV sera and monoclonal antibodies were able to bind to some of these peptides. The results from this thesis will help to engineer peptides which could be used to improve the sensitivity and specificity of FMDV serological assays.