γδ lymphocyte response to porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be one of the most important diseases facing swine industry today. Following PRRSV infection pigs develop both humoral and cell-mediated responses following PRRSV exposure; however, the relative importance in protection and clearance of the virus is not yet completely understood. Swine contain a large percentage of gamma delta T-lymphocytes in peripheral circulation capable of responding to various pathogens in both an innate and specific immune response. The objectives of this study were to determine whether gamma delta lymphocytes functionally respond to PRRSV upon initial exposure and re-exposure. Four month old PRRSV free gilts were intranasally inoculated with a field isolate MN-30100 then assessed at various time points post infection. On day 120, pigs were re-exposed with MN-30100 PRRSV strain and subsequently were bled on days 0, 7, and 14 post re-exposure. Lymphocyte subpopulations, antigen specific proliferation, and IFN-gamma production were evaluated throughout the study. Circulating gamma delta lymphocytes in PRRSV exposed animals expanded between days 14 to 70 (d14-d70, p = 0.016); following antigen stimulation, gamma delta lymphocyte proliferated by day 14 (d0-d14, p = 0.001) continuing through day 60. gamma delta lymphocytes produced IFN-gamma by day 14 pi continuing through day 50 (d0-d50, p = 0.004). Following re-exposure both gamma delta(+) and CD4(+) lymphocytes increased in IFN-gamma production. These results are not fully conclusive on the role of gamma delta lymphocytes against PRRSV; the data indicate that gamma delta lymphocytes specifically respond to PRRSV.