Cytolytic function for pseudorabies virus-stimulated porcine CD4(+)CD8(dull+) lymphocytes

We previously observed that pseudorabies (PRV) virus-specific killing in vi tro was mediated by CD6(+)CD8(+) lymphocytes. Also a high percentage of CD4 (+) lymphocytes, among these CD6(+)CD8(+) lymphocytes, was observed. The pu rpose of this study was, therefore, to further characterize the killing abi lity of PRV-stimulated CD4(+)CD8(+) lymphocytes. Peripheral blood mononucle ar cells (PBMC) were isolated from blood of PRV-immune pigs and were stimul ated in vitro with PRV. After 6 days, the frequency of CD4(+)CD8(+) lymphoc ytes in peripheral blood was determined by flow cytometry analyses. Lymphoc ytes were separated using a magnet-activated cell sorter or a FACSVantage S E, and the cytolytic activity of the isolated populations was determined. F low cytometry analyses demonstrated that PRV stimulation of immune PBMC res ulted in the occurrence of 26% +/- 4% CD4(+)CD8(dull+) lymphocytes. We furt her demonstrated that killing by PRV-stimulated PBMC was mediated by CD4(+) CD8(dull+) T lymphocytes and CD4(-)CD8(+) T lymphocytes (classic cytolytic T lymphocytes and natural killer cells). The CD4(+)CD8(dull+) T lymphocytes showed major histocompatibility complex (MHC) II-restricted PRV-specific k illing. The CD4(-)CD8(+) T lymphocytes showed both PRV-specific and natural killing. The CD4(+)CD8(dull+) lymphocytes, which are unique in the pig, se emed to have a more heterogeneous function than was earlier demonstrated. I n conclusion, we demonstrated that PRV-specific CD4(+)CD8(dull+) lymphocyte s are able to kill PRV-infected target cells in a MHC II-restricted manner.