Submitted to: International Pig Veterinary Society (IPVS)
Publication Type: Proceedings
Publication Acceptance Date: 6/3/2002
Publication Date: N/A
Technical Abstract: The study was designed to compare the cellular immune response induced by an attenuated porcine reproductive and respiratory syndrome virus (PRRSV) and its wild-type parent virus (strain NADC-8). Two experiments were conducted using 52, 4-5 week-old-pigs free of PRRSV and PRRSV-specific antibody. Each experiment had a similar design: a sham-inoculated control group, an attenuated virus-inoculated group and a wild-type parent virus inoculated group. Based on sequence of ORFs 2-7 (3,184 nucleotides) the attenuated virus was 99.4% homologous with its parent virus. In experiment 2 there was a 4th group inoculated with a different wild-type PRRSV (SDSU 73). Pigs were inoculated intramuscularly with their respective virus (about 2 x 105 TCID50 virus) on day 0. Blood samples were collected on days -7, -4, 0, 3, 6, 9, 13, and 21. A panel of monoclonal antibodies was used to analyze peripheral blood leukocytes by two-color flow cytometric analysis. Results represent the combined data from the two experiments. Th percentage of CD8+ T lymphocytes was significantly increased on day 6 to 13 in wild-type NADC-8 group and on days 9 to 13 in the SDSU group compared to control and attenuated virus groups. The percentage of CD 4+ T cells was increased on day 9 for SDSU virus group only. Percentages of CD3+ T cells were increased on day 9 in both wild type virus groups. After an initial decrease, the percentage of cells expressing Class II marker increased with time. Total white blood cell counts decreased shortly after infection then increased with time. No significant changes were found in peripheral blood leukocytes of pigs inoculated with attenuated PRRSV or sham inoculum. Results indicate that the peripheral blood leukocytes response to PRRSV infection mainly involves CD8+ T cells.