Dissociation of porcine reproductive and respiratory syndrome virus neutralization from antibody production to major envelope protein peptides (49.22)

Abstract

Abstract Porcine reproductive and respiratory syndrome (PRRS) is the most severe infectious disease facing the swine industry worldwide. The etiologic agent is PRRSV, an enveloped arterivirus. GP5 and M, the major envelope proteins, form disulfide-bonded heterodimeric complexes that are involved in PRRSV entry into porcine alveolar macrophages (PAM). Previous studies identified several neutralization epitopes in GP5 polypeptide, containing amino acid residues (AA) 29-52, and potential unknown neutralization epitopes in M protein. To test whether PRRSV-neutralizing antibodies (NA) are directed to GP5 and M ectodomain polypeptides, we constructed three recombinant single-chain proteins: the two predicted ectodomains of GP5 (GP5-5’), the two ectodomains of M (M-5’), and all four ectodomains (GP5-M). In particular, GP5-5’ contains the reported neutralization epitopes. We found that the convalescent pig sera after PRRSV infection contained various levels of antibodies to those proteins, but the Ab titers did not correlate with the NA response. Immunization of pigs with these recombinant proteins did not induce detectable NA response. Finally, protein-specific Abs that were purified from PRRSV-neutralizing serum by affinity chromatography showed no neutralizing activity, whereas the protein-specific Ab-depleted sera retained similar neutralizing activity as the original sera. The results, therefore, do not support that PRRSV-NA are directed to the ectodomain polypeptides of GP5/M.