Effects of repeated porcine reproductive and respiratory syndrome virus vaccinations on lymphocyte recall responses in sows

Bassaganya-Riera, J., B.J. Thacker, S. Yu, E. Strait, M.J. Wannemuehler, and E.L. Thacker (2001) Effects of repeated porcine reproductive and respiratory syndrome virus vaccinations on lymphocyte recall responses in sows. Proceedings of the 82^nd Annual Meeting of the Conference of Research Workers in Animal Diseases; Nov 11-13; St. Louis, MO; (Abstract #171).

It is a commonly utilized practice in porcine production to repeatedly immunize the reproductive stock against several pathogens, including porcine reproductive and respiratory syndrome virus (PRRSV). The goal of this study was to investigate the effects of a long-term exposure of sows to repeated PRRSV immunizations with a modified-live (MLV) or a killed (KV) PRRSV vaccines on recall responses to PRRSV antigens. Twelve sows were obtained from each of three herds with a history of receiving, either a MLV, KV or no PRRSV vaccine. In addition, the unimmunized group was procured from a PRRSV-negative herd. Within source of origin, sows were further inoculated on days 0 and 14 of the experiment with the KV vaccine while the MLV vaccine was administered on day 14 only. On days 0, 27, and 38 recall responses of peripheral blood mononuclear cells (PBMC) to the PRRSV strains used in the MLV or KV vaccines (i.e., 2332 or ISUP, respectively) were assessed using a proliferation assay coupled to a phenotypic evaluation of the lymphocyte subsets. Following the experimental immunization(s) with MLV or KV, the antigen-driven proliferation of CD8αβ+ and CD4CD8 double-positive (DP) lymphocytes in sows of the unimmunized source was greater than in sows of the other two sources. Upon ex vivo stimulation of PBMC from sows repeatedly immunized with the KV vaccine, a greater proliferative response of the CD4CD8 DP T cells was induced by vaccination with the MLV vaccine than by the KV vaccine. Similarly, the KV vaccine induced better CD8+ responses than MLV vaccine in sows repeatedly immunized with the MLV vaccine. These studies indicated that repeated, long-term immunization with the same PRRSV vaccine induced a state of vaccine-specific, immunologic unresponsiveness. However, use of a PRRSV vaccine containing a heterologous strain for immunization could induce detectable cellular responses (e.g., CD8+ cells) in apparently anergic sows.