Phenotypic and functional characterisation of porcine CD4+CD25high regulatory T cells

Over the last years regulatory T cells (Tregs) were defined as CD4+CD25+ T lymphocytes expressing the transcription factor Foxp3 (Forkhead Box P3) with the ability to downregulate various immune responses. In swine the existence of CD4+CD25+ T lymphocytes was described before but nothing is known about the function of this minor cell population to date. Therefore, we studied porcine CD4+CD25+ T cells with regard to major attributes of murine and human Tregs: their phenotype concerning the expression of several T-cell specific antigens, including Foxp3, their IL-10 production and their suppressive capacity. Our results revealed that porcine CD4+CD25+ T cells with high CD25 expression count for about 2–9% of the CD4+ T-cell subset. They demonstrate a strong Foxp3 expression, a heterogeneous CD45RC-, CD8α- and MHC-II-defined phenotype and a moderate IL-10 production. Co-cultivation of increasing numbers of CD4+CD25high T cells with a constant number of CD4+CD25− responder-T cells caused a decrease in proliferation of the entire culture. This demonstrates the suppressive capacity of the CD4+CD25high T-cell subset and – together with their Foxp3 expression – the existence of porcine Tregs.