Figure 2.

Serum neutralizing antibody titer is associated with PRRSV vaccination-induced protection against homologous and heterologous challenge. (a) PRRSV-specific antibodies were detected in the serum using IDEXX ELISA kit. The threshold for positive sera was set at a sample to positive (s/p) ratio of 0.4 according to the manufacturer's instructions. ((b)–(d)) Serum samples were titrated on MARC-145 cells and the levels of anti-PRRSV neutralizing Abs were determined as the reciprocal of the highest dilution that could inhibit CPE. Data were shown as mean ± SEM for 5 pigs per group. *P < 0.05.