2011 Annual Report 1a.Objectives (from AD-416) Identify the underlying viral-specific elements of porcine reproductive and respiratory syndrome virus (PRRSV) disease pathogenesis. The goal of the study is to gain knowledge on the critical domains of PRRSV nonstructural protein 2, to assess the growth characteristics of constructed deletion mutants, to understand if the immune response of swine to the deletion mutants is altered, and to localize the protein in infected cells. 1b.Approach (from AD-416) Identify the underlying viral-specific elements of porcine reproductive and respiratory syndrome virus (PRRSV) disease pathogenesis. 1. Test the hypothesis that nsp2 harbors dispensable domains for nsp2 function. 2. Test the hypothesis that the porcine immune response will be improved by modification of nsp2 in recombinant porcine reproductive and respiratory virus (PRRSV). 3. Test the hypothesis that PRRSV nsp2 is targeted to the endosome-lysosome system. 3.Progress Report The aim was to inoculate swine with recombinant viruses that had engineered deletions in an area of the porcine reproductive and respiratory syndrome virus (PRRSV) genome known as nonstructural protein 2 (nsp2). The ARS completed a test growth experiment and amplified the viruses to a quantity needed. The large animal study was completed, including an additional nsp2 deletion mutant and increased animal numbers; the samples will be fully analyzed. The methods used for monitoring progress included yearly reports to USDA-NIFA.