In this study, a panel of monoclonal antibodies （mAbs） against Porcine reproductive and respiratory syndrome virus（PRRSV）, named as 8C9 and4B4, were produced by fusing SP2/0 myeloma cells and spleen cells of BALB/c mice immunized with the PRRSV （TCID50=5.5）, screened by the indirect ELISA and subjected to several limiting dilutions, mAbs were then identified by biological characterization. Among the two fusion cell strains, 8C9 belonged to the IgG1 subclass and 4B4 belonged to the IgG2a subclass. The titers in cell culture supematant and abdomen liquor reached to 1：104and 1：105, respectively. The specificity test indicated that the two cells had specific reactions for the PRRSV and GP5 protein respectively, and no reaction with Classical swine fever virus （CSFV） or Swine vesicular disease virus （SVDV）. The molecular weights of the heavy chain and light chain were about 45.0 kDa and 25.0 kDa, respectively. In neutralization activity tests, the results showed that the prepared mAb 4B4 can protect 50% of cells with no CPE in dilution up to 1：512, but mAB 8C9 has no neutralization activities to PRRSV.
Hong Tian Yan Cheng Jin-yang Wu Jian-hui He You-jun Shang Xiang-tao Liu
The attenuated vaccine strains of CSFV have a 12-nucleotides （nt） insertion in the 3＇-UTR of genome as compared to that of CSFV virulent strains. In this study, we found a distinct heterogeneity in the 3＇-UTR of attenuated Thiverval and HCLV strains. The longest 3＇-UTR of Thiverval strain was 259 base pairs （bp） with a 32-nt insertion, the shortest 3＇-UTR had only 233 bp with a 6-nt insertion. The longest 3＇-UTR of HCLV strain was 244 bp with a 17-nt insertion and the shortest 3＇ UTR was 235 bp with a 8-nt insertion. Compared with the published sequences of 3＇-UTR of vaccine and virulent strains, the 3＇-UTR of CSFV vaccine strains have two variable regions where insertion among the different vaccine strains were frequently found. The first is located between the second conservative TALk codon and the start of T-rich region where we found the variable length insertion in the same vaccine strain Thiveral or HCLV and the second is located between the end of T-rich region and the front of GAA eodon, however, a 4-nt deletion was found in this region in the virulent Shimen strain. These two regions may represent the ＂hot spot＂ for mutation. Modeling the secondary structures of the 3＇-UTR suggests that the T-rich insertion could result in the change of structure and free energy, thus affecting the stability of the 3＇-UTR structure. These findings will help to understand the mechanism of attenuated vaccines and improve vaccine safety, stability, and efficacy.
FAN Yun-fengZHAO Qi-zuZHAO YunZOU Xing-qiZHANG Zhong-qiuWANG QinNING Yi-bao
