title: swIFN-β promotes genetic mutation of porcine reproductive and respiratory syndrome virus in Marc-145.
abstract: This result, for the first time, demonstrates that under swine interferon-β (swIFN-β) immune pressure molecular variation of porcine reproductive and respiratory syndrome virus (PRRSV) accelerates. PRRSV-A1 strain was continuously propagated in Marc-145 cells primed with swIFN-β for 20 passages to develop RRRSV-A1βf20 strains while PRRSV-A1f20 was control without swIFN-β respectively. NSP2, ORF3, ORF5 and ORF6 genes of these strains were amplified, cloned and sequenced. Sequencing analysis indicated that PRRSV-A1βf20 had 43 nucleotide mutations while PRRSV-A1f20 had only 14 in NSP2, ORF3, ORF5 and ORF6. The ratio of mutative nucleotides between them was 307%. Amino acid variations were 24 in RRRSV-A1βf20 and 5 in PRRSV-A1, so that mutation in RRRSV-A1βf20 appeared to be 4.8 times faster than that in PRRSV-A1. The ratio of non-synonymous (NS) mutations to synonymous (S) mutations, named NS/S, was 3 in RRRSV-A1βf20 and 0.625 in PRRSV-A1f20. The nucleotide mutation rate of NSP2 ORF3 ORF5 and ORF6 of PRRSV-A1βf20 were 3.8%, 2.3%, 4.5%, 0.57% and their NS/S were 5, 2, 6 and 1 respectively, which is much higher than those in PRRSV-A1f20. Thus the mutative frequency of PRRSV passaged under swIFN-β immune pressure was significantly faster than that without swIFN-β. The immuno-pressure of swIFN-β accelerated genetic variation on PRRSV ORF5, NSP2 and ORF3, but not on the ORF6 gene. PRRSV NSP2 and ORF5 genes may play a key role in escaping from inhibition of swIFN-β.
authors.affiliation: College of Veterinary Medicine, South China Agricultural University, Guangdong, Guangzhou 510642, China. dhe@scau.edu.cn
authors.forename: Dongsheng
authors.initials: D
authors.lastname: He
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Niu
authors.forename: Aixiang
authors.initials: A
authors.lastname: Jiang
authors.forename: Danping
authors.initials: D
authors.lastname: Su
authors.forename: Wang
authors.initials: W
authors.lastname: Zhong
authors.forename: Jing
authors.initials: J
authors.lastname: Hu
authors.forename: Yanli
authors.initials: Y
authors.lastname: Wang
authors.forename: Ruiai
authors.initials: R
authors.lastname: Chen
mesh_terms: D000818:Animals; D001483:Base Sequence; D014644:Genetic Variation; D016899:Interferon-beta / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009154:Mutation; D019316:Porcine respiratory and reproductive syndrome virus / Q000235:genetics* / Q000378:metabolism; D013552:Swine; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D014764:Viral Proteins; D016899:Interferon-beta
keywords: Immune pressure; Mutation; PRRSV; swIFN-β