Characterization of porcine T lymphocytes and their immune response against viral antigens

Abstract

T lymphocytes play a central role in the antigen-specific immune response against various pathogens. To detect and to characterize porcine T lymphocytes, monoclonal antibodies (mAb) against leukocyte differentiation antigens had been raised and classified for their specificity. Analyses of porcine T lymphocytes with specific mAb against CD4 and CD8 differentiation antigens revealed differences in the composition of the porcine T-lymphocyte population compared to other species. In addition to the known subpopulations, CD4 +CD8 − T helper cells and CD4 −CD8 + cytolytic T lymphocytes, extra-thymic CD4 +CD8 + T lymphocytes and a substantial proportion of CD2 −CD4 −CD8 − T cell receptor (TcR)-γδ + T cells could be detected in swine. Functional analyses of porcine T-lymphocyte subpopulations revealed the existence of two T-helper cell fractions with the phenotype CD4 +CD8 − and CD4 +CD8 +. Both were reactive in primary immune responses in vitro, whereas only cells derived from the CD4 +CD8 + T-helper-cell subpopulation were able to respond to recall antigen in a secondary immune response. With regard to T lymphocytes with cytolytic activities, two subsets within the CD4 −CD8 + T-cell subpopulation could be defined by the expression of CD6 differentiation antigens: CD6 − cells which showed spontaneous cytolytic activity and CD6 + MHC I-restricted cytolytic T lymphocytes including virus-specific cytolytic T lymphocytes. These results enable now a detailed view into the porcine T-cell population and the reactivity of specific T cells involved in the porcine immune response against pathogens. Furthermore this knowledge offers the possibility to investigate specific interactions of porcine T lymphocytes with virus-specific epitopes during vaccination and viral infections.