A chemically synthesized peptide consisting essentially of two separate regions (residues 141 to 158 and 200 to 213) of a virus coat protein (VP1) from the O1 Kaufbeuren strain of foot-and-mouth disease virus was prepared free of any carrier protein. It elicited high levels of neutralizing antibody and protected cattle against intradermolingual challenge by inoculation with infectious virus. Comparative evaluation of this peptide with a single-site peptide (residues 141 to 158) in guinea pigs suggests the importance of the VP1 carboxyl terminal residues in enhancing the protective response.

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SUMMARYFoot-and-mouth disease virus challenge experiments in guinea-pigs and immunoassays with a range of peptides equivalent to either or both of the sequences 141 to 158 and 200 to 213 of VP 1 showed the most effective structure, in terms of protection, to be one in which both 'sites' were present with a minimum of additional amino acids. An 80 residue peptide comprising amino acids 134 to 213 was considerably less effective than 40 or 45 residue peptides. The major site for the induction of protection was deduced to be in the region 141 to 158. Thus, protection with the 40 or 45 residue peptide did not appear to be due to the presence of antibody directed solely to the 200 to 213 sequence. Finally, induction of antibody to the latter site appeared to be dependent on both the size of the peptide and the disposition of 'sites' within it.In a previous communication, we demonstrated protection of cattle against challenge with foot-and-mouth-disease virus (FMDV) by immunization with a synthetic peptide (DiMarchi et al., 1986). The sequence used was based on the published data of Strohmaier et al. (1982) for the coat protein, VP1 of the O1 Kaufbeuren (O1K) strain of the virus and was Cys-Cys-200-213-ProPro-Ser-141-158-Pro-Cys-Gly (throughout this communication sequences unique to VP1 are shown numerically, whereas 'additional' amino acids used in the construction of the peptide are shown by their three-letter codes). The peptide differed from those described by Bittle et al. (1982) and Pfaff et al. (1982) in a number of important respects. First, it incorporated the 200 to 213 sequence of VP1 which had been recognized by Strohmaier et al. (1982) and Bittle et al. (1982) as capable of inducing low levels of neutralizing antibody. Second, the 200 to 213 and 141 to 158 sequences were linked via Pro-Pro-Ser and terminated with Cys-Cys (N terminus) and Pro-Cys-Gly (C terminus). The broad aim of this construction was the formation of a cyclic/polymerized peptide that would not require a carrier protein. Protection tests in guineapigs showed this carrier-free peptide (P40) to be considerably more effective than either 141-158-Pro-Cys-Gly (P21) or P21 linked to keyhole limpet haemocyanin. These results prompted questions on the role of the 200 to 213 sequences in the induction of a protective immune response.We have directed our attention to delineating the structural basis for the action of P40 and have prepared by solid-phase synthetic methods (Merrifield et al., 1982) a number of peptides which represent regions of VP 1 of the O IK strain of FMDV. Each peptide was purified to near homogeneity by preparative reverse-phase chromatography. The following peptides were synthesized and evaluated: P 14, 200 213; P27, 134-160; P40, Cys-Cys-200-213-Pro-Pro-Ser-141-158-Pro-Cys-Gly; P45, (134-160) (196-213); P53, 161-213; P80, 134-213. For a given peptide, a range of concentrations was prepared in 0.04 M-phosphate buffer pH 7.6 and emulsified with an equal volume of Freund's complete adjuvant. A guinea-pig dose of 0-2 ml contain...

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