title: Influence of the amino acid residues at 70 in M protein of porcine reproductive and respiratory syndrome virus on viral neutralization susceptibility to the serum antibody.
abstract: BACKGROUND
  Porcine reproductive and respiratory syndrome virus (PRRSV) is mainly responsible for the significant economic losses in pig industry in the world. The adaptive immune responses of the host act as an important source of selective pressure in the evolutionary process of the virus. In the previous study, we confirmed that the amino acid (aa) residues at 102 and 104 sites in GP5 played an important role in escaping from the neutralizing antibodies (NAbs) against highly pathogenic PRRSV (HP-PRRSV). In this study, we further analyzed the aa mutants affecting neutralization susceptibility of NAbs in other structure proteins in NAbs resistant variants.
  
  
  METHODS
  Based on the different aa residues of the structural proteins between the resistant virus BB20s and the parent virus BB, 12 recombinant PRRSV strains containing these aa residue substitutions were constructed using reverse genetic techniques. The neutralizing antibody (NA) titers of the recombinant strains were tested on MARC-145 and porcine alveolar macrophages (PAMs). And the NAbs binding abilities of parent and rescued viruses were tested by using ELISA method.
  
  
  RESULTS
  By using the neutralization assay, it was revealed that the NA titer of N4 serum with rBB/Ms was significantly lower than that with rBB. Meanwhile, NA titer of the serum with rBB20s/M was significantly higher than that with rBB20s. The ELISA binding results showed that rBB/Ms had higher binding inability to N4 than did rBB. And alignment of M protein revealed that the variant aa residue lysine (K) at 70 was also existed in field type 2 and vaccine PRRSV strains.
  
  
  CONCLUSIONS
  The aa residue at 70 in M protein of PRRSV played an important role in regulating neutralization susceptibility to the porcine serum NAbs. It may be helpful for monitoring the antigen variant strains in the field and developing new vaccine against PRRSV in the future.
authors.affiliation: Key Laboratory of Animal Diseases Diagnostic and Immunology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, P.R. China.
authors.forename: Baochao
authors.initials: B
authors.lastname: Fan
authors.affiliation: Key Laboratory of Animal Diseases Diagnostic and Immunology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, P.R. China.
authors.forename: Xing
authors.initials: X
authors.lastname: Liu
authors.affiliation: Key Laboratory of Animal Diseases Diagnostic and Immunology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, P.R. China.
authors.forename: Juan
authors.initials: J
authors.lastname: Bai
authors.affiliation: Key Laboratory of Animal Diseases Diagnostic and Immunology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, P.R. China.
authors.forename: Tingjie
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Animal Diseases Diagnostic and Immunology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, P.R. China.
authors.forename: Qiaoya
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Animal Diseases Diagnostic and Immunology, Ministry of Agriculture, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, P.R. China. jiangp@njau.edu.cn.|Jiangsu Co-innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou, China. jiangp@njau.edu.cn.
authors.forename: Ping
authors.initials: P
authors.lastname: Jiang
mesh_terms: D000596:Amino Acids / Q000235:genetics*; D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood*; D000914:Antibodies, Viral / Q000097:blood*; D002478:Cells, Cultured; D004252:DNA Mutational Analysis; D050505:Mutant Proteins / Q000235:genetics / Q000276:immunology; D009500:Neutralization Tests; D019316:Porcine respiratory and reproductive syndrome virus / Q000235:genetics / Q000276:immunology*; D059386:Reverse Genetics; D044967:Serum / Q000276:immunology*; D014763:Viral Matrix Proteins / Q000235:genetics / Q000276:immunology*
chemical_list: D000596:Amino Acids; D057134:Antibodies, Neutralizing; D000914:Antibodies, Viral; C525999:M protein, porcine reproductive and respiratory syndrome virus; D050505:Mutant Proteins; D014763:Viral Matrix Proteins
keywords: 70; M protein; Neutralizing antibody; PRRSV