ANTIGENIC DIFFERENCES BETWEEN EUROPEAN AND AMERICAN ISOLATES OF PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS (PRRSV) ARE ENCODED BY THE CARBOXYTERMINAL PORTION OF VIRAL OPEN READING FRAME-3

Antigenic differences between European and American isolates of porcin e reproductive and respiratory syndrome virus (PRRSV) were revealed by serologic analysis of a recombinant protein derived from PRRSV open r eading frame 3 (ORF 3). The hydrophilic carboxyterminal 199 amino acid s encoded by the ORF 3 of a European (Lelystad) isolate of PRRSV were expressed as a recombinant fusion protein (BP03-P) in a baculovirus ge ne expression system. Sera from gnotobiotic swine exposed to prototypi c reference European and American isolates of PRRSV and sera from conv entionally reared European and American swine convalescing from natura lly acquired PRRSV infections were used to characterize the BP03-P pro tein. Sera from gnotobiotic and conventionally reared swine exposed to European isolates of PRRSV were significantly more reactive (P<0.01) with BP03-P than were the corresponding American PRRSV antisera using the indirect immunoperoxidase monolayer assay (IPMA). Prototypic Europ ean, but not American, PRRSV antisera also recognized BP03-P using wes tern immunoblotting and radioimmunoprecipitation assay (RIPA) procedur es. However, gnotobiotically derived antiserum to an atypical American -origin PRRSV was reactive with BP03-P by both IPMA and western immuno blot. Despite a predicted potential for N-linked glycosylation, studie s with tunicamycin and peptide-N-glycosidase F (PNGase F) indicated th at BP03-P was not N-glycosylated in either insect cell cultures or Tri choplusia ni larvae infected with the recombinant baculovirus, Sera fr om rabbits inoculated with BP03-P failed to neutralize both the Europe an (Lelystad) and American (ATCC VR-2332) reference isolates of PRRSV and did not react by IPMA with PRRSV-infected cell cultures. Taken tog ether, the data suggest that the carboxyterminal portion of PRRSV ORF 3 encodes a non-neutralizing viral peptide that is partially responsib le for the serologic differences noted between European and most Ameri can isolates of PRRSV.