Delineation of a neutralizing subregion within the immunodominant epitope (GH loop) of foot-and-mouth disease virus VP1 which does not contain the RGD motif

The major immunogenic site of fool-and-mouth disease virus (FMDV) is contai ned in a disordered loop comprising residues 134-158 of capsid protein VP1, located on the surface of the viral particle. Peptides corresponding to th is sequence generally elicit protective levels of neutralizing antibodies i n guinea pigs. In some instances, however, the level of neutralizing antibo dies is low although the level of antibodies against the peptide, determine d by ELISA, is as high as that in the sera with high neutralizing antibody titres. In an attempt to ascertain the reason for this difference, we have synthesized on a cellulose membrane 10 overlapping decapeptides, offset by one residue, covering the segment 141-159 of VP1 of two viruses belonging t o serotypes A12 and O1, and tested them with guinea pig antisera raised aga inst peptide 141-159, VP1 and FMDV particles (SPOTscan method). With type A , some peptides which were strongly positive with highly neutralizing antis era did not include the RGD triplet located at residues 145-147. In contras t, antisera with low neutralization titres reacted only with decapeptides w hich included the RGD motif. Moreover, peptide 147-156 coupled to keyhole l impet haemocyanin, but not peptide 141-149 coupled to the same carrier, eli cited high levels of neutralizing antibodies in guinea pigs. In the case of serotype O, highly neutralizing antisera to virus reacted in ELISA with pe ptides 141-150 (containing the RGD motif) and 135-144 (located upstream fro m the RGD motif). The results suggest that the RGD tripler is not an indisp ensable constituent of peptides able to elicit a neutralizing antibody resp onse against the virus. (C) 1999 Elsevier Science Ltd. All rights reserved.