Screening and identification of B cell antigenic Epitopes of porcine epidemic diarrhea virus spike glycoprotein by phage display

S1 gene targeted libraries containing the major immunodominant region (1 similar to 2367 bp) of PEDV spike glycoprotein were constructed by phage-display vectors based on filamentous phage strain fd-tet, in which the exogenous polypeptides were expressed in the N-terminal of gene III coat protein. The S I libraries were panned three times using the purified rabbit sera against PEDV. Three peptides, displayed on recombinant phages, showed strong binding affinity with the PEDV antisera, and were designated as SIM (248 similar to 280aa), SIP2 (442 similar to 499aa) and SIP3 (697 similar to 742aa) respectively. In ELISA and Western blot, the three peptides were all recognized by the PEDV antisera, but SIP3 showed strong binding activity. To further determine antigenicity of the three peptides, the antisera of S1P1-GST, S1P2-GST, S1P3-GST and their ligations GST fusion protein were prepared. In ELISA, S1P1-GST, S1P2-GST, S1P3-GST and S1P123-GST fusion proteins were able to induce the SI-specific antisera. The result of indirect immunofluorescence assay (IFA) demonstrated that the antisera induced by S1P2-GST, S1P3-GST and S1P123-GST fusion proteins possessed binding ability to the native S protein of PEDV cultured in Vero cells.