Fig. 4. Decreased viremia and high levels of E2-specific antibodies were detected in pigs challenged with classical swine fever virus (CSFV) at 2-week, 3-week, and 4-week post KNB-E2 vaccination. CSFV RNA was detected in the serum (A) and nasal cavity (B) by real-time reverse transcriptase polymerase chain reaction analyses in which threshold cycle values equal to or less than 40 were considered CSFV positive. The KNB-E2-vaccinated pigs challenged at 3 weeks and 4 weeks post-vaccination had little or no CSFV RNA detected. CSFV RNA was detected in KNB-E2-vaccinated pigs challenged at 2 weeks post-vaccination but the level had recovered by 12 days post-challenge (DPC). E2-specific antibodies were determined in the serum during the challenge phase (dilution 1/10,000) (C) by enzyme-linked immunosorbent assay. KNB-E2-vaccinated pigs produced significantly high levels of E2-specific antibodies after CSFV challenge. At 3 weeks and 4 weeks post-vaccination, KNB-E2 pigs produced higher E2-specific antibodies than the pigs challenged at 2 weeks post-vaccination. Data are presented as mean ± SEM values for five pigs per group. ^*p < 0.05.