Characterization of epitopes for neutralizing monoclonal antibodies to classical swine fever virus E2 and Erns using phage-displayed random peptide library.

Infection of cells with classical swine fever virus (CSFV) is mediated by the interaction of envelope glycoproteins E2 and Erns with receptor molecules on the cell surface. These proteins are also the major antigens for eliciting neutralizing antibodies and conferring protective immunity. Here we report the identification of multiple neutralizing epitopes on these proteins by screening a phage-displayed random peptide library with CSFV-specific neutralizing monoclonal antibodies. Two different E2-specific neutralizing mAbs (a18 and 24/10) were found to bind to a common motif SPTxL, which is similar to the sequence SPTTL of the E2 protein (aa 289-293), indicating that this is likely to be an immunodominant epitope. Similarly, an immunodominant epitope corresponding to the sequence DKN of Erns (aa 117-119) was identified for two independent Erns-specific neutralizing antibodies, b4-22 and 24/16, respectively. Another binding motif, CxNNxTC, was identified for mAb 24/16, but not for b4-22. Sequencing analysis of the genes coding for the light chain of these mAbs was conducted to ensure that all mAbs were derived from different hybridomas, rather than from different subclones of a common parent line. Inhibition studies using immunofluorescent antibody assay and virus neutralization test demonstrated that the mimotope peptides truly mimicked the antibody binding determinants on the viral proteins. The detailed mapping data for these neutralizing epitopes will be useful for development of improved diagnostic tests and perhaps a peptide-based vaccine for this important swine disease.