The non-structural protein 1 (nsp1) of porcine reproductive and respiratory syndrome virus is partly responsible for inhibition of type I interferon (IFN) response by the infected host. By performing alanine-scanning mutagenesis, we have identified amino acid residues in nsp1α and nsp1Β (the proteolytic products of nsp1) that when substituted with alanine(s) exhibited significant relief of IFN-suppression. A mutant virus (16-5A, in which residues 16-20 of nsp1Β were substituted with alanines) encoding mutant nsp1Β recovered from infectious cDNA clone was shown to be attenuated for growth in vitro and induced significantly higher amount of type I IFN transcripts in infected macrophages. In infected pigs, the 16-5A virus exhibited reduced growth at early times after infection but quickly regained wild type growth properties as a result of substitutions within the mutated sequences. The results indicate a strong selection pressure towards maintaining the IFN-inhibitory property of the virus for successful propagation in pigs.
Bibliographical noteFunding Information:
This research has been supported by grants from USDA NRICGP project No. 2008-00903 (to FAO) and 2009-01654 & 2012-67015-30191 (to AKP). The help of animal care staff in the animal research facility is highly appreciated. We are indebted to Dr. Eric Snijder (LUMC, The Netherlands) for providing necessary reagent. We are also grateful to Dr. Saumendra N. Sarkar (Univ. of Pittsburg) for his suggestions and reagents.
- Innate immunity
- Non-structural protein 1α and 1Β
- Type-1 interferon inhibition