Fig. 2. Decreased viremia and high levels of E2-specific antibodies were detected in pigs immunized with KNB-E2 containing 25 µg, 50 µg, or 75 µg E2 antigen. Classical swine fever virus (CSFV) RNA was detected in 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. KNB-E2-vaccinated pigs exhibited transient viremia only at 6 days post-challenge compared with the marked viremia in the phosphate-buffered saline–vaccinated CSFV-challenged (−/+) control pigs. E2-specific antibodies were determined in the serum during the vaccination phase (dilution 1/1,000) (C) and the challenge phase (dilution 1/10,000) (D) by enzyme-linked immunosorbent assay. KNB-E2-vaccinated pigs produced significantly high levels of E2-specific antibodies after CSFV challenge. Data are presented as mean ± SEM values for five pigs per group. ^*p < 0.05.