Prediction and characterization of novel epitopes of serotype A foot-and-mouth disease viruses circulating in East Africa using site-directed mutagenesis

Abstract

Epitopes on the surface of the foot-and-mouth disease virus (FMDV) capsid have been identified by monoclonal antibody (mAb) escape mutant studies leading to the designation of four antigenic sites in serotype A FMDV. Previous work focused on viruses isolated mainly from Asia, Europe and Latin America. In this study we report on the prediction of epitopes in African serotype A FMDVs and testing of selected epitopes using reverse genetics. Twenty-four capsid amino acid residues were predicted to be of antigenic significance by analysing the capsid sequences (n = 56) using in silico methods, and six residues by correlating capsid sequence with serum–virus neutralization data. The predicted residues were distributed on the surface-exposed capsid regions, VP1–VP3. The significance of residue changes at eight of the predicted epitopes was tested by site-directed mutagenesis using a cDNA clone resulting in the generation of 12 mutant viruses involving seven sites. The effect of the amino acid substitutions on the antigenic nature of the virus was assessed by virus neutralization (VN) test. Mutations at four different positions, namely VP1-43, VP1-45, VP2-191 and VP3-132, led to significant reduction in VN titre (P value = 0.05, 0.05, 0.001 and 0.05, respectively). This is the first time, to our knowledge, that the antigenic regions encompassing amino acids VP1-43 to -45 (equivalent to antigenic site 3 in serotype O), VP2-191 and VP3-132 have been predicted as epitopes and evaluated serologically for serotype A FMDVs. This identifies novel capsid epitopes of recently circulating serotype A FMDVs in East Africa.

Emergence of antigenic variants within serotype A FMDV in the Middle East with antigenically critical amino acid substitutions

“…2 D) and could explain the inability of the antisera to cross-react with the field isolates, and are probably the sites prone to change to help the virus escape immune pressure. Out of these, VP2-191 has been reported to be part of a neutralising epitope (antigenic site-2) both in serotype O and A FMDV [9] , [10] . Further, epitopes involving antigenic site 2 have been reported to be dominant within polyclonal responses of vaccinated animals [11] .…”

Genetic and antigenic characterization of serotype O FMD viruses from East Africa for the selection of suitable vaccine strain

“…Of these, VP2 133 has never been reported to be of antigenically important, however it is located close to VP2 134 that has been reported to strongly influence the binding of neutralising antigenic site 2 mAbs in serotype O FMDV [13] . Similarly VP2 191 has been recently shown to be linked to serotype O and A antigenic site 2 using a reverse genetics approach [33] , [34] . VP1 45 involving antigenic site 3 and VP1 137–141, 197 involving antigenic site 1 have been reported to be critical in serotype O mar-mutant studies [27] , [35] .…”

Global Foot-and-Mouth Disease Research Update and Gap Analysis: 3 - Vaccines

“…Improved vaccines and vaccine strains are acutely needed in much of Africa, but their development has been hindered by a lack of definition of key parameters of circulating viruses. Recent work has investigated the relative antigenic significance of epitopes in African serotype A FMDVs (Bari et al., ). These data lead on from previous research by the same group that showed existing serotype A vaccine strains protected against only 5–46% of 56 East African field strains assessed and enabled identification of a candidate strain with broader vaccine match (Bari et al., ).…”