A PROTECTIVE ANTIPEPTIDE ANTIBODY AGAINST THE IMMUNODOMINANT SITE OF THE A(24) CRUZEIRO STRAIN OF FOOT-AND-MOUTH-DISEASE VIRUS AND ITS REACTIVITY WITH OTHER SUBTYPE VIRUSES CONTAINING THE SAME MINIMUM BINDING SEQUENCE

A synthetic peptide vaccine of the general sequence 200-213)-Pro-Pro-S er-(141-158)-Pro-Cys-Gly(peptide A40), where the numbered residues ref er to the VP1. sequence of foot-and-mouth disease virus (FMDV) strain A(24) Cruzeiro, has previously been shown to elicit neutralizing and p rotective antibodies in guinea-pigs and cattle. To examine this immuno genic tract in more detail monoclonal antibodies (MAbs) were raised to this peptide. One such MAb, C1.1, which recognized the homologous pep tide, bound to native virus, neutralized infectivity in vitro and pass ively protected mice from challenge. Using overlapping dodecameric pep tides the minimum binding 'footprint' of this MAb, incorporated residu es 149-154 which were respectively Gly-Ser-Leu-Ala-Ala-Arg. Since this 'footprint' occurs in several other A subtype strains of FMDV, the ex tent to which MAb C1.1 could cross-react was also examined. Using a li quid-phase competition ELISA, only viruses with a sequence that encomp assed the same minimum binding 'footprint', namely A(27) Cundinamarca Colombia/76, A Argentina/79, and A Venceslau Brazil/76 reacted with si milar affinity against MAb C1.1. However, further serological examinat ion of C1.1 with these viruses by indirect ELISA, in vitro neutralizat ion and passive protection showed clear functional disparity. In contr ast to the liquid-phase ELISA, the ability of C1.1 to react with elect rostatically bound virus varied significantly depending on the subtype examined. Moreover, the capacity of this MAb to neutralize these subt ypes showed wide divergence which was mirrored by the protection data.