Monoclonal antibody and porcine antisera recognized B-cell epitopes of Nsp2 protein of a Chinese strain of porcine reproductive and respiratory syndrome virus.

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important pathogens for swine industry. The non-structural protein 2 (Nsp2) is considered to be one of the immunogenic proteins of PRRSV. In this study, the B-cell epitopes of the Nsp2 protein of a North American type Chinese strain PRRSV BJ-4 were identified on a prokaryotic expressed Nsp2 fragment (73-567aa). A total of six monoclonal antibodies (mAbs) recognizing different epitopes on the expressed protein were prepared. All six mAbs exhibited immunoreactivity with the denatured Nsp2 protein in Western blotting and produced strong perinuclear staining in PRRSV infected MARC-145 cells in an immunofluorescence assay. Pepscan analysis revealed six distinct linear epitopes for the six mAbs, respectively, and of which four were identified to be novel linear Nsp2 B-cell epitopes: T(73)LPERVRPPDDWAT(86), D(385)ELKDQMEED(394), P(452)VPAPRRKVGSDCGS(466), and P(467)VSLGGDVPNS(477). All of the six mAb specific peptides could be recognized by porcine PRRSV antiserum, indicating that the epitopes involving these synthetic peptides were immunogenic and immunodominant during PRRSV infection in pigs. Our results provided valuable information for developing novel PRRSV vaccines using the Nsp2 epitopes as potential serological markers.