The truncated GP3 fragments (A) and the pursue absence GP3-63-77aa fragments (B) were identified by Western blot with the anti-GST mAb, the mAb 1F10, and positive sera.

<p>(A) M: protein marker; 1: GST-GP3-1-171aa; 2: GST-GP3-41-100aa; 3: GST-GP3-41-55aa; 4: GST-GP3-56-70aa; 5: GST-GP3-48-62aa; 6: GST-GP3-63-77aa; 7: GST. (B) M: protein marker; 1: GST-GP3-63-76aa; 2: GST-GP3-63-75aa; 3: GST-GP3-63-74aa; 4: GST-GP3-63-73aa; 5: GST-GP3-63-72aa; 6: GST-GP3-63-71aa; 7: GST-GP3-64-77aa; 8: GST-GP3-65-77aa; 9: GST-GP3-66-77aa; 10: GST-GP3-67-77aa; 11: GST-GP3-68-77aa; 12: GST-GP3-69-77aa; 13: GST-GP3-70-77aa; 14: GST-GP3-68-76aa; 15: GST-GP3-69-76aa. The deduced epitope (69-76aa) was vertified not to be a true one, while the motif (68-76aa) was the epitope recognized by the mAb 1F10. But the epitope was not recognized by positive sera. The positive sera 4^# and 7^# were pig hyperimmune sera with high titer of neutralizing antibodies against HP-PRRSV, which were obtained from pigs immunized by HuN4-F112 once and then inoculated with HP-PRRSV HuN4 virulent strain (HuN4-F5) three times. The positive serum 28^# was collected from a pig inoculated with HP-PRRSV HuN4 virulent strain (HuN4-F5) at 14DPI. A pig was immunized with HuN4-F112 and then inoculated with HP-PRRSV HuN4 virulent strain (HuN4-F5) at 21DPI, the positive serum 71^# was collected from the pig after 3 weeks.