Delineation of protective epitopes on the E 2-envelope glycoprotein of Semliki Forest virus

Abstract

Two short linear peptides, 17 and 14 amino acids long, on the Semliki Forest virus (SFV) E 2-envelope polypeptide are shown to be involved in the protection of mice against lethal challenge with SFV. Peptides corresponding to these two regions, designated H and L, were selected for study on the basis of our model for prediction of protective epitopes on E 2 polypeptide of alphaviruses. These peptides were produced in Escherichia coli as recombinant proteins fused to the amino terminus of β-galactosidase. Both the H epitope (amino acid positions 227–243 on E 2) and L epitope (amino acid positions 297–310) are recognized by antibodies raised against SFV, and both trigger antibodies that interact with native SFV-E 2. Vaccination of mice with the H-β-galactosidase polypeptide confers 64–87% protection against a lethal viral challenge (250 LD 50), and immunization with L-β-galactosidase leads to 23–66% protection of challenged mice. The efficacy of the L-based synthetic vaccine could be improved further (up to 100% protection) by presentation of this epitope as a dimer fused to β-galactosidase. These results provide evidence that the algorithm and the methodology proposed by us previously 1,2 are effective tools for identification of linear protective epitopes on E 2-envelope of SFV.