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Mimicry of viral epitopes with retro-inverso peptides of increased stability.

Two major limitations to the use of peptides as synthetic vaccines are their poor immunogenicity and low antigenic cross-reactivity with the epitopes of virus particles. Recently it has been shown that retro-inverso peptides corresponding to an immunodominant epitope of foot-and-mouth disease virus (FMDV) are able to mimic the structure and antigenic activity of natural L-peptides [1]. A series of L- and retro-inverso peptides of the loop 141-159 of the VP1 protein of FMDV has been synthesized. Antibodies to these peptides were produced by injecting rabbits with peptides covalently coupled to small unilamellar liposomes containing monophosphoryl lipid A as adjuvant. The retro-inverso peptides led to higher serum antibody titres which appeared earlier after the start of immunization and lasted longer than those found with L-peptides. Antibodies to retro-inverso peptides cross-reacted strongly with L-peptides and with virus particles, while guinea pig antisera to VP1 protein and virions cross-reacted strongly with the retro-inverso peptides. In view of their increased stability compared to natural L-peptides, retro-inverso peptidomimetics have considerable potential as synthetic viral vaccines.