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Title: PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME (PRRS): MECHANISMS OF DISEASE AND METHODS FOR THE DETECTION, PROTECTION AND ELIMINATION OF THE PRRS VIRUS.

Author
item Lunney, Joan
item ROYAEE, ATABAK - ARS BELTSVILLE MD

Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: 12/1/2003
Publication Date: 12/1/2003
Citation: Lunney, J.K., Royaee, A. 2003. Porcine Reproductive and Respiratory Syndrome (PRRS): Mechanisms of disease and methods for the detection, protection and elimination of the PRRS virus. Agricultural Experiment Station Publication.

Interpretive Summary:

Technical Abstract: Principal leaders at Illinois AES: Federico A. Zuckermann and Tony L. Goldberg, Department of Veterinary Pathobiology, University of Illinois, Urbana, IL Principal leaders at BARC: Joan K. Lunney and Atabak R. Royaee, APDL, ANRI, BARC, ARS, USDA, Beltsville, Maryland. Cooperating Agencies in the Research reported by the Illinois AES: Department of Veterinary Pathobiology, Illinois Veterinary Diagnostic Laboratory at Urbana and Illinois AES. Collaborating agencies and principal leaders outside Illinois: Dr. Fernando A. Osorio, Department of Veterinary and Biomedical Sciences, University of Nebraska-Lincoln (UNL) PROGRESS OF THE WORK AND PRINCIPAL ACCOMPLISHMENTS: Objective 3. Characterize the different components of the immune response during acute and persistent infection and the implications of this response in pathogenesis and diagnosis 1. Characteristics of the Immune Response of Pigs to PRRS virus a. Development of immunity to vaccination (IL AES). The immune response of pigs to infection with wild-type virus or vaccination with a conventional modified live virus (MLV) vaccine against the arterivirus Porcine Reproductive and Respiratory Syndrome virus (PRRSV) is characterized by an initial, weak interferon-gamma (IFN-g)response that increases gradually over a period of months (Meier et al., 2003). However a conflicting report has appeared (Batista et al., 2003, AASP) suggesting that the kinetics of the T-cell mediated IFN-' response to PRRS virus in not as we have described (i.e., gradual). In order to solve this discrepancy we conducted an additional experiment in which a group of 5 naïve pigs was immunized once at 10 weeks of age with the PRRS MLV produced by BI, instead of twice as we had done in our previous studies, in order to mimic the study done by Batista et al. Animals were maintained in isolation to prevent a subsequent exposure to PRRS virus. The kinetics of the IFN-g response was monitored for a period of 9 months. The result of this new study has confirmed that, as we showed previously, a weak IFN-g response to PRRS virus is initially detectable within a few weeks after vaccination by ELISPOT. Although, similar to the report by Batista, the response appeared to wane at 10 weeks after vaccination, the frequency of IFN-g-secreting cells (SC) then rebounded and, with fluctuation, the IFN-g SC increased gradually in intensity after a period of months without a booster immunization. The kinetics and fluctuation of the response as measured by the ELISPOT, was confirmed by ELISA determinations of the concentration of IFN-g in cell-free culture supernatants of parallel bulk cultures. These results suggest that the development of the IFN-' response is under complex regulation. The nature of plausible mechanisms that affect and determine the unusual kinetics of this response is being examined. b. Immune gene expression profile in response to PRRS virus (IL AES and BARC). To understand the mechanisms responsible for the regulation of the immune response to PRRS virus, we conducted studies aimed at establishing the expression of profile of genes known to play an important role in the development and regulation of immunity. Levels of several immune-regulatory genes (IFN-a, IFN-g, IL-1a, TNF-a, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-15, IL-18, IL-12 p35/p40, IL-23 and IL-25) were monitored by real time RT-PCR on cDNA prepared from PBMC isolated from pigs vaccinated with PRRS MLV. In one study blood was collected from 9pigs at week 0, 2, 5, 9, 11 and 13 following vaccination with PRRS MLV. Peripheral blood mononuclear cells (PBMC) were prepared, cultured with PRRSV, pelleted and stored in Trizol prior to RNA isolation. Gene expression was calculated relative to week 0. Our data indicated that, following vaccination, it takes up to 5 weeks for pigs to develop a statistically significant (p<0.05) I