The kinetics of cytokine production and CD25 expression by porcine lymphocyte subpopulations following exposure to classical swine fever virus (CSFV)

Surface expression of IL-2R-alpha (CD25) is widely used to identify activated lymphocyte populations, while interferon-gamma (IFN-γ) levels have been shown to be a good indicator of cell-mediated immunity (CMI) in pigs. To investigate the relationship between these two parameters, we developed an intracellular cytokine-staining assay and studied the kinetics of cytokine (IFN-γ and interleukin-10, IL-10) production relative to CD25 expression in porcine lymphocyte subpopulations, following immunization with a classical swine fever (CSF) vaccine. The number of activated memory T cells (CD4+CD8+CD25+ cells) increased slightly in the peripheral blood mononuclear cell (PBMC) population soon after vaccination, then diminished within a few weeks. The number of activated cytotoxic T cells (CD4−CD8+CD25+ cells) peaked approximately 2 weeks after the memory population. Although the number of IFN-γ producing cells detected in this experiment was relatively low, the CD4+CD8+ T cells were major IFN-γ producers in the PBMCs throughout the experiment. In another experiment, CSF-vaccinated pigs were challenged with a virulent classical swine fever virus (CSFV), and the kinetics of CD25 expression and cytokine productions were monitored. Following exposure to the virus, the number of IFN-γ producing cells in the PBMCs increased markedly in both the vaccinated and unvaccinated groups. The CD4−CD8+ cells were major IFN-γ producing cells in vaccinated pigs, while both CD4+CD8+ and CD4−CD8+ populations contributed to the IFN-γ production in the control group. Interestingly, the enhanced IFN-γ production was not associated with the upregulation of CD25 expression following the CSFV challenge. In addition, exposure to the virulent CSFV significantly increased interleukin-10 production by the CD4−CD8+ populations in PBMCs of the unvaccinated pigs. Taken together, our results indicated that CD25 expression and IFN-γ production were not tightly associated in porcine lymphocytes. In addition, the CD4−CD8+ lymphocytes of the PBMCs played a major role in cytokine productions following the CSFV challenge.