Neutralizing Antibody Formation in Swine Infected with Seven Strains of Porcine Reproductive and Respiratory Syndrome Virus as Measured by Indirect ELISA with Peptides Containing the GP5 Neutralization Epitope

An indirect ELISA with peptides containing the GP5 neutralization epitope was used to measure the time courses of formation of neutralizing antibodies in sera of groups of 10 pigs infected with seven different strains of porcine reproductive and respiratory syndrome virus (PRRSV) generated in an earlier study (Johnson et al., Vet.Immunol. Immunopath. 102:233–247. 2004). The neutralizing antibody responses varied greatly between individual pigs infected with each PRRSV strain. Some pigs generated high titers of neutralizing antibodies between 7 and 28 days post infection (p.i), whereas other pigs had not generated a significant response by 42 days p.i. The heterogeneity in antibody formation in individual pigs also pertained to anti-N-protein antibody formation as measured by both HerdCheck and peptide ELISAs and there was no correlation between anti-N-protein and neutralizing antibody formation. Also, viremia was disconnected from neutralizing antibody formation. Viremia peaked 7–15 days p.i. and then precipitously declined to undetectable levels in most infected pigs by 21–28 day p.i. whether or not they had generated neutralizing antibodies. Furthermore, contrary to an earlier conclusion from this study the formation of neither neutralizing nor anti-N-protein antibodies was related to viral load as measured by infectious virus levels in serum.