Identification and characterization of linear B cell epitopes on the nucleocapsid protein of porcine epidemic diarrhea virus using monoclonal antibodies.

The nucleocapsid (N) protein of porcine epidemic diarrhea virus (PEDV), the most important pathogen causing severe diarrhea in piglets, is a highly conserved structural protein. In this study, 5 monoclonal antibodies (McAbs) against the PEDV N-protein were prepared and identified. Three new epitopes, (56)QIRWRMRRGERI(67), (318)GYAQIASLAPNVAALLFGGNVA VRE(342) and (398)HEEAIYDDV(406), were firstly identified in the viral N-protein, by using McAbs 3F10, 6A11, and 1C9. The epitope (398)HEEAIYDDV(406) was deleted in SH strain (isolated by our lab) and different between CV777 and YZ strain (isolated by our lab). To study the characters of this epitope, four peptides were synthesized according to the sequence of SH and CV777 and used in the study. The result showed that the 398(th) amino acid maybe an important amino acid of the epitope. Biological information analysis showed that the three B cell linear epitopes are highly conserved among different PEDV isolates. In addition, McAb 1C9, which attached to the epitope (398)HEEAIYDDV(406), showed variant reactivity with PEDV CV777, SH, YZ and MS strains. McAb 1C9 reacted with PEDV strains CV777 and YZ, but not with SH which had a deletion from 399 to 410 amino acids in N-protein (No. MK841494). Among the three McAbs, 6A11, 3F10 and 1C9, only 6A11 reacted with porcine transmissible gastroenteritis virus (TGEV) in immunofluorescence assay, therefore the other two could be used to distinguish TGEV and PEDV. These mAbs and their defined epitopes may provide useful tool for the study of the PEDV N-protein structure and function, and facilitate the development of diagnostic methods for PEDV.