Functional characterization of a swine CD4+/CD8+ double positive lymphoblastoid T-cell line with a CD25+/CD45RA− phenotype generated in vitro with interleukin-2

A dual expressing (CD4+/CD8+) porcine lymphoblastoid T-cell line (pIL-2d) generated from peripheral blood mononuclear (MN) cells shown to be highly responsive to exogenous interleukin-2 (IL-2) was characterized. The swine MN cells were initially stimulated with concanavalin A (Con A), and sub-passaged using decreasing amounts of conditioned medium (CM), which was prepared from culture fluids of Con A activated porcine MN cells, until a steady growth was observed. The resulting pIL-2d cells require exogenous IL-2 from CM and are highly responsive to recombinant human IL-2 (rhIL-2). The pIL-2d cells exhibited a specific, dose-dependent proliferative response to stimulation with IL-2. The specificity of this proliferative response was confirmed to be IL-2 induced by its inhibition with an anti-swine IL-2 receptor (α-swIL-2R) monoclonal antibody (mAb). Furthermore, the pIL-2d cells are highly responsive to exogenous IL-2 contained in culture fluids derived from antigen-driven blastogenic tests performed with lymphocytes of vaccinated swine. This property makes the pIL-2d cells an ideal functional adjunct to immunochemical or molecular tests that are commonly used to measure total porcine IL-2. Interestingly, the phenotype of the pIL-2d cells after five or more passages was shown by flow cytometric analysis to be CD4+/CD8+/CD45RA−/CD25+ and to remain unchanged thereafter. Although, the mechanism of selection and maintenance of the CD4+/CD8+ DP cells developed here remains unclear, our data suggest that an oligoclonal or polyclonal expansion and maintenance of cells of this phenotype was mediated by exogenous IL-2.