FIG. 6.

Reduction of replication of LV (A), 07V063 (B) and 08V204 (C) in PAM by antibodies against the neutralizing epitopes on GP4 of the respective heterologous virus strains. Single-replication virus-neutralization tests were performed with LV, 07V063, and 08V204, with a 1:2 dilution series (500–16 μg/mL) of serum antibodies against the neutralizing epitope of the two respective heterologous virus strains. Epitope-specific antibodies were purified from polyclonal serum by peptide affinity chromatography. Protein A purified immunoglobulins of a PRRSV-negative pig were included as mock antibodies (open symbols). The number of infected cells for each antibody dilution was set relative to the mean number of infected cells for all mock conditions within one experiment. The means and standard deviations of three experiments were calculated and are given in the graphs. Statistically significant differences (*p < 0.01) were observed with RTNTTQGKVPSQ-specific antibodies, compared to mock antibodies, for antibody concentrations of 500 and 250 μg/mL in the test with virus strain 07V063 (B). In the test with virus strain 08V204 (C), statistically significant differences (*p < 0.01) were observed with RVTAAQGRIYTR-specific antibodies, compared to mock antibodies, for an antibody concentration of 250 μg/mL.