Discrimination of different subsets of cytolytic cells in pseudorabies virus-immune and naive pigs

We previously observed that pseudorabies virus (PRV)-induced, cell-mediated cytolysis in pigs includes killing by natural killer (NK) cells. We also o bserved that IL-2 stimulation in vitro of naive PBMC expands porcine NK cel ls, The purpose of this study was to compare the phenotypes of the cytolyti c subsets stimulated in vitro by PRV and by IL-2. PBMC were isolated from b lood of PRV-immune and naive pigs and stimulated in vitro with PRV or IL-2, After 6 days, the frequency of various lymphocyte subsets in these culture d PBMC was determined by Row cytometry: the cells were separated with a mag net-activated cell sorter and the cytolytic activity of the separated popul ations was determined. When lymphocytes were separated and analysed with FA CScan, the following lymphocyte subsets were discriminated: CD6(+) CD8(brig ht+) CD4(-) (CTL phenotype), CD6(+) CD8(dull+) CD4(+) (the fraction contain ing memory T helper cells), CD6(+) CD8(-) CD4(+) (T helper cell phenotype), CD6(-) CD8(dull+) CD4(-) gamma delta-T+ (gamma delta-T cell phenotype), CD 6(-) CD8(dull+) CD4(-) gamma delta-T- (NK phenotype) and CD6(-) CD8(-) CD4( -) gamma delta-T- or gamma delta-T+. Flow cytometry analysis demonstrated t hat PRV stimulation of immune PBMC resulted in the occurrence of more CD6() CD8(+) and CD4(+) CD8(+) and fewer CD6(-) CD8(+) and gamma delta-T+ CD8() lymphocytes than IL-2 stimulation of naive PBMC (P < 0.05). It was demons trated further that killing by PRV-stimulated PBMC was mediated mainly by C D6(+) CD8(+) T lymphocytes. Killing by IL-2-stimulated PBMC was mediated ma inly by CD6(-) CD8(+) T lymphocytes, These results demonstrate that both na tural killing and killing by classical PRV-specific CTL were detected in PR V-immune pigs, whereas IL-2 stimulation of PBMC isolated from naive pigs ma inly induced natural killing.