The invention relates to a polypeptide of a protective antigenic determinant(PAD polypeptide) of porcine reproductive and respiratory syndrome virus(PRRSV) and nucleic acids encoding a PAD polypeptide. The PAD is generated bya heterodimer consisting of the GP 5 protein and the M protein of PRRSVwherein the ectodomain of GP 5 has different N-glycosylated states. The PADpolypeptide and nucleic acids encoding a PAD polypeptide are useful in thedevelopment of antibodies directed to PAD, vaccines effective in providingprotection against PRRSV infection, and diagnostic assays detecting thepresence of PAD antibodies generated by a PAD-specific vaccine. The inventionalso discloses methods of generating antibodies to PAD, for vaccinating a pigto provide protection from PRRSV infections, a method of preparing thevaccine, a method of treating PRRSV infections in a pig, and a method ofdetecting antibodies to PAD of PRRSV.
