Blood and serum samples were collected at days 7 and 14 after challenge in swine experiments. To assess the neutralizing antibody response in the swine, plaque reduction neutralization assays were performed as described previously [31] . Neutralizing titers were reported as the highest serum dilution causing a 50% reduction in the number of HKN/ 2002 plaques on BHK-21 cells. The presence of antibodies against viral NS protein 3ABC of FMDV in the sera was detected using a solid-phase blocking enzyme-linked immunosorbent assay (SPB-ELISA) according to the procedures described by Chenard et al. [7] . Briefly, ELISA microtiter test plates were coated overnight at 4°C with recombinant 3ABC antigen expressed in E. coli [45] . After five washes with PBS containing 0.05% Tween 80 (PBST), each well of the plates was filled with 100 lL of test or reference serum diluted 1:2 in PBST and incubated at 37°C for 60 min. The serum was then removed, and the wells of the plates were washed as described above. After rewashing, 100 lL of anti-3ABC immunoglobulin-horseradish peroxidase conjugate was added, and the incubation proceeded at 37°C for 30 min. The conjugate was then removed, the wells of the plates were washed again, and 100 lL of a commercially ready-to-use tetramethyl benzidine chromogen substrate was added to the plates. After incubation at 37°C for 10 min, the reaction was stopped by adding 50 lL of 2.0 M H 2 SO 4 per well, and the OD at 450 nm was measured by using an ELISA reader. The sera were considered positive if the OD was reduced by ! 30% compared to a standard negative serum corrected for background signal by subtracting the OD of the high positive reference serum. Statistical analysis was performed with the Microsoft Excel program.