To investigate the conservation of the SVQYHPL epitope, we aligned the epitope identified in this study with REVs gp90 coding regions available in GenBank. The alignment results showed that all amino acids in the motif were identical among all REV strains ( Figure 5 ), indicating that the motif represented a conserved epitope on the gp90 protein of REVs. Figure 2 . Detection of the selected phages for antibody binding by Phage ELISA. Eight phage clones selected after three rounds of biopanning were added to the microplate wells (10 10 pfu/100 mL/well) coated with the mAb A9E8 or anti-porcine IFN-c mAb (negative control) (100 ng/well ), and incubated for 1 h at room temperature. Bound phages were subjected to reaction with horseradish peroxidase (HRP)-conjugated anti-M13 antibody, followed by color development with substrate solution containing o-phenylenediamine (OPD). Three independent assays were performed for each selected phage. doi:10.1371/journal.pone.0049842.g002 Table 2 . Sequence comparison of random peptide inserts displayed on the positive phages.