Porcine regulatory T cells: mechanisms and T-cell targets of suppression.

Tregs are known for their suppressive capacity on various immune reactions. In swine, existence as well as suppressive activity of Foxp3(+) Tregs could be demonstrated but detailed functional investigations are lacking. Therefore, we analysed the functional properties of porcine Tregs. We observed that besides TCR stimulation Tregs require IL-2 for activation. Furthermore, we investigated the following mechanisms of suppression: (i) cell-cell contact dependency, (ii) production of soluble suppressive factors and (iii) competition for growth factors. Our experiments revealed that suppression by porcine Tregs is abrogated by blocking cell-cell contact or by supplementing excessive amounts of IL-2. Additionally it could be shown that porcine Tregs produce immunosuppressive IL-10. Thereby, we demonstrated that porcine Tregs can use all main mechanisms of suppression mentioned above. Further investigations on the suppressive activity of Tregs using CFSE proliferation assays demonstrated that suppression affects T-helper cells as well as cytotoxic T lymphocytes and TCR-γδ T cells.