Effect of amino acids residues 323–433 and 628–747 in Nsp2 of representative porcine reproductive and respiratory syndrome virus strains on inflammatory response in vitro

•Five recombinant PRRSV strains with different deletion region in Nsp2 were rescued.•The aa323–433 and 628–747 in Nsp2 could down-regulate the immune cytokines production.•The aa323–433 and 628–747 in Nsp2 could decrease the IκB phosphorylation levels.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that is responsible for large economic losses in the swine industry worldwide. In PRRSV strains, many genetic variations occur in the central hypervariable region (HV2) of the Nsp2 gene, which encodes non-structural protein 2. For example, PRRSV strains VR2332, Em2007, MN184C, and TJM-F92 contained variations in the Nsp2 sequences and exhibited differing levels of virulence in adult pigs. However, the role of HV2 with respect to PRRSV immunity is unclear. In this study, four recombinant PRRSV strains (rBB/+30aa, rBB/Δ68aa, rBB/Δ111aa, and rBB/Δ120aa) were rescued using a highly pathogenic type 2 PRRSV cDNA clone (pBB). All rescued strains displayed similar growth characteristics to the parental rBB virus in pulmonary alveolar macrophages (PAMs). Expression levels of inflammatory cytokines IL-β, IL-6, and TNF-α were significantly lower, at the mRNA and protein level, for groups infected with rBB/Δ111aa and rBB/Δ120aa than those in the rBB group. Levels of these inflammatory cytokines in the rBB/+30aa and rBB/Δ68aa groups were not significantly different with those in the rBB group. Phosphorylation levels of IκB were decreased to a greater extent in the rBB/Δ111aa and rBB/Δ120aa groups compared with those in the rBB/+30aa, rBB/Δ68aa, and rBB groups. Our results indicate that amino acids 323–433 and 628–747 of Nsp2 failed to exert significant effects on PRRSV replication in PAMs, but modulated the expression of inflammatory cytokines in vitro.