Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/25/2008
Publication Date: 12/5/2008
Citation: Faaberg, K.S., Han, J., Guo, B., Lager, K.M., Kehrli, Jr., M.E. 2008. PRRSV Strain VR-2332 NSP2 Deletion Mutants Attenuate Clinical Symptoms in Swine [abstract]. International PRRS Symposium. p. 55. Interpretive Summary:
Technical Abstract: PRRSV nonstructural protein 2 (nsp2) contains a N-terminal cysteine proteinase (PL2) domain, a middle hypervariable region and C-terminal putative transmembrane domain. Prior studies had shown that as much as 403 amino acids could be removed from the hypervariable region without losing virus viability in vitro (Han et al., J. Virol, 2007). We utilized selected nsp2 deletion mutants to compare in vitro and in vivo growth. Young swine (4 pigs/group; 5 control swine) were inoculated intramuscularly with one of 4 nsp2 deletion mutants (delta727-813, delta543-726, delta324-523, delta324-726) and full-length recombinant virus (rVR-2332). Serum samples were collected on various days post-inoculation. Samples were analyzed by HerdChek ELISA, RT-PCR, interferon gamma ELISA, and nsp2 nucleotide sequence analysis. Lymph node weight compared to body weight was recorded for each animal and used as a clinical measurement of viral pathogenesis. Results showed that all deletion mutants grew less robustly than full-length recombinant virus, yet all but the large deletion virus (delta324-726) recovered to parental virus levels by study end. Swine receiving mutants delta727-813 and delta324-726 had a significant decrease in lymph node involvement compared to rVR-2332. Three of the 4 deletion mutants had significant reductions in serum IFN-gamma levels; only the delta543-726 nsp2 mutant mimicked rVR-2332 in inducing a host serum IFN-gamma response but exhibited a two-week delay. Sequencing results showed that all nsp2 deletions were stable. The data suggested that selected nsp2 deletion mutants may indicate regions responsible for inducing high levels of serum IFN-gamma, an innate cytokine of unknown function in PRRSV clearance, and domains that cause lymph node enlargement, and thus represents a significant advancement in our understanding of PRRSV pathogenesis.