Immunogenic potential of the E protein of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)

摘要

The E protein, also known as 2b protein, is a non-glycosylated, minor structural protein of the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). As a highly conserved structural protein among all PRRSV strains, the E protein is a potential target for development of a broadly protective vaccine. In this study, we assessed the kinetics, and the domain specificity of E protein-specific antibodies produced during the early stages of PRRSV infection in pigs, and the role of these antibodies in in vitro neutralization of the virus. Using custom-synthesized peptides that correspond to the N-terminus and C-terminus of the E protein as antigens in ELISA, we showed that all experimentally infected pigs and 73% (46 out of 63) of naturally infected pigs produced antibodies to the C-terminus peptide. In contrast, only one out of 15 experimentally infected pigs, and 20% (13 out of 63) of field-infected pigs produced antibodies to the N-terminus peptides. Immunization of mice with the peptides mixed with alum adjuvant resulted in production of antibodies to the C-terminus, but not N-terminus, peptide. Conjugation of N-terminus peptide to heat-killed Brucella abortus RB51 surface also did not improve its immunogenicity in mice. Mouse antibodies specific to the C-terminus peptides did not show any virus neutralizing activity in in vitro assays. Swine serum samples containing antibodies to the N-terminus peptide were used in a peptide competition in vitro neutralization assay to determine the role of these antibodies in neutralization of the virus. This experimental approach was found to be unsuitable for this purpose, but these experiments revealed that N-terminus peptide alone had a neutralizing effect on PRRSV. These results suggest that, unlike the N-terminus peptide, the C-terminus peptide of the E protein is highly immunogenic and it may be useful for developing a broadly reactive serological test for detection of PRRSV infection in pigs.