Identification of a conserved epitope cluster in the N protein of porcine reproductive and respiratory syndrome virus.

In this study, 4 overlapping fragments and 12 overlapping peptides of the nucleocapsid (N) protein from porcine reproductive and respiratory syndrome virus (PRRSV) were expressed as glutathione S-transferase (GST) fusion proteins and used to probe a panel of 16 anti-N protein monoclonal antibodies (mAbs) by ELISA. The minimal epitope sequence of the following seven mAbs was determined by sequential deletion of terminal amino acid residues from each peptide: N2H7 corresponded to H54FPLA58; N2F7 corresponded to K52PHFPLA58; and N1A2, N1E3, N1G4, and N2E5 were reactive against E51KPHFP56. Furthermore, a polypeptide containing this epitope cluster was recognized by PRRSV-immune pig serum by Western blot, suggesting that residues 51-58 represent an immunodominant region of the N protein. Sequence alignment revealed that these epitopes are well conserved among North American and European genotypes of PRRSV. These findings enhance our knowledge of the antigenic structure of N protein and may facilitate the development of better diagnostic methods for PRRSV.